- Email: [email protected]
Optimal control of turbulent premixed combustion instability with annular micropore air jets
JID:AESCTE AID:105650 /FLA
[m5G; v1.261; Prn:19/12/2019; 14:25] P.1 (1-11)
Aerospace Science and Technology ••• (••••) ••••••
1
Contents lists available at ScienceDirect
67 68
2 3
Aerospace Science and Technology
4
69 70 71
5
72
6
www.elsevier.com/locate/aescte
7
73
8
74
9
75
10
76
11 12 13
Optimal control of turbulent premixed combustion instability with annular micropore air jets
16 17
81
Zhejiang University, Institute for Thermal Power Engineering, State Key Laboratory of Clean Energy Utilization, Hangzhou, 310027, PR China
83 85
a r t i c l e
i n f o
a b s t r a c t
86 87
21 23 24 25
Article history: Received 30 June 2019 Received in revised form 12 December 2019 Accepted 16 December 2019 Available online xxxx
26 27 28 29 30 31
82 84
19
22
79
Hao Zhou ∗ , Chengfei Tao, Zihua Liu, Sheng Meng, Kefa Cen
18 20
78 80
14 15
77
Keywords: Combustion instability Micropore jets Optimal control CH* chemiluminescence Sound pressure
32 33 34 35
This article experimentally investigates the suppressing of combustion instability in a model gas turbine combustor with annular air jets. Three parameters were optimized to find the control effectiveness— variations of the air injection flow rate, number, and diameter of jet nozzles. Results indicate that the suppression ratio of the self-excited oscillations can reach 95% with optimal control, the transition and saturation region of control effectiveness are identified, and the four jet nozzles design case can lead to the best effect of damping. Besides, mode shifting of flame heat release rate is observed, the amplitude of heat release rate increases to 2 ∼ 4 times than that of the uncontrolled flame, the main resonance frequency at 264.5 Hz was eliminated and triggered to a new oscillation frequency near 110 Hz. Moreover, after air injection control, the flame length and temperature changes inversely proportional to the air injection flow rate, as the air injection transforms the flow field and improves the turbulent combustion velocity. This study not only explored the mechanism behind combustion instability control under annular micropore air jets but also proposed the application of air injection as a practical tool for damping of combustion instability, which could contribute to the prevention of potential thermoacoustic instabilities in gas turbines. © 2019 Published by Elsevier Masson SAS.
88 89 90 91 92 93 94 95 96 97 98 99 100 101
36
102
37
103
38
104
39 40
1. Introduction
41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59
Gas turbine engines are extensively used in the land-based power generation and aviation or astronautics industries [1–4]. As the premixing is improved and the local flame temperature is decreased, NOx formation is reduced exponentially [5]. However, the lean-premixed combustion technique is susceptible to combustion induced thermoacoustic instabilities, or self-excited oscillations [6–8]. In much combustion-based thermal propulsion systems, thermoacoustic instability is an undesired phenomenon that can cause serious pressure fluctuations and serve damages to the combustor components [9–12]. To eliminate thermoacoustic instabilities and develop effective approaches for their control, the transient mechanisms responsible for their occurrence must be understood [13–17]. Several factors appear to present in a combustor that triggers the unsteady thermoacoustic instability, including flame-acoustic wave interactions, flame-vortex interactions, equivalence ratio oscillations [18,19], burner design and swirlers geometry [20–22], all of which may be present individually or simultaneously, and hence promoting thermoacoustic instability.
60 61 62 63 64 65 66
*
Corresponding author. E-mail address: [email protected] (H. Zhou).
https://doi.org/10.1016/j.ast.2019.105650 1270-9638/© 2019 Published by Elsevier Masson SAS.
Active control techniques utilize external excitations (such as acoustic forcing and fuel modulation) to attenuate combustion oscillations. Generally, the purpose is to minimize the difference between the instantaneous desired and actual behavior of a dynamic system [2–4]. While effective in suppressing the instabilities, active control requires high-speed actuators and adds significant complexity to the design of the combustors [3,4]. For this reason, developing simple, passive and open loop control strategies that directly impact the flame anchoring zone with minimal complexity is desirable [13–24]. The method for suppressing thermoacoustic instability by injecting air or fuel near the flame anchoring zone has been extensively explored in the past. H. Murat Altay [25,26] employed steady air injection near the flame anchoring zone to mitigate the thermoacoustic instability of a backward-facing step combustor. Jong Ho Uhm [27–29] studied the effects and mechanisms of low-bandwidth open-loop control of combustion instability using a high-momentum air jet. Ahmed F. Ghoniem [30–33] examined thermoacoustic instability and NOx emissions suppression with microjet air injection and H2 addition in premixed combustion. Hao Zhou [34,35] proposed a novel control method for thermoacoustic instabilities with a jet in cross-flow (JICF) in a swirling combustor by CO2 and N2 injection which could transform the precessing vortex core near the flame anchoring zone. Nilaj N. Desh-
105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
JID:AESCTE
AID:105650 /FLA
1 2
Φ
8
FFT S Z PMT
9
5 6 7
10 11 12 13
67
Nomenclature
3 4
[m5G; v1.261; Prn:19/12/2019; 14:25] P.2 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
2
kW Hz T f
equivalence ratio fast Fourier Transform swirl number flame length photomultiplier tube inner diameter thermal power frequency flame temperature cutoff frequency
68 69
ϕ
swirler vane angle dh inner tube diameter dn vane cross-section diameter CH4 methane CH* chemiluminescence Pa sound pressure ◦C centigrade L/min air flow rate CCD High-speed camera arb. units CH* chemiluminescence
70 71 72 73 74 75 76 77 78 79 80
14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56
mukh [36,37] investigated thermoacoustic instability suppression with eight microjet holes in a horizontal Rijke tube and using air as an injection medium. Sébastien Ducruix [38] took methods of local H2 injection to eliminate combustion instabilities and recorded the pollutant emissions before and after hydrogen injection. Shigeru Tachibana [39] eliminated combustion oscillations in a lean premixed combustor by secondary fuel injection with five different types of injectors. Based on local flame structure, Gyung-Min Choi [40] studied the impacts of secondary fuel injection on thermoacoustic instabilities. Unlike steady air injection, Garrett M. Strickland [41] implemented resonant enhanced pulsed micro-actuators for the control of supersonic impinging jets. Jae Jeen Choi [42] used a quasi-closed loop steady and pulsed microjets to control of supersonic impingement tones. The secondary flow is thought to change the velocity field and disrupt the flame-vortex interaction, then break the coupling of flame-acoustic instability. Although there are many types of research on thermoacoustic control with air injection, to date, there is no research on the combined effects of air injection intensity, nozzle inner diameter and number of injection holes on thermoacoustic control, which need to be further explored and optimized. Besides, the mode shifting characteristics of flame CH* chemiluminescence during the process of air injection has never been investigated before. At the same time, flame length shortened and temperature distribution varied after air injection control, this phenomenon has not been specifically explained in terms of mechanism [36,37]. The purpose of the present work is to verify the damping effectiveness and plug the knowledge gap of mechanism of thermoacoustic instability air injection control in a laboratory-scale lean-premixed combustor. Systematic experimental study of thermoacoustic instability optimal control is proposed to evaluate the impact of each variable, which involves injection air flow rates, the diameter of jet nozzles and the number of injection holes. During the optimal control experiments, the sound pressure fluctuation, heat release rate intermittency, uniformity of the flame temperature field and flame morphology phenomena of the combustor before or after the air injection were investigated simultaneously. This study can promote a better understanding of thermoacoustic instability passive control. As a result, providing a useful tool for better combustion instability suppression of lean-premixed burners and improve operation safety of industrial gas turbines.
57 58
2. Experimental setup
59 60
2.1. Model combustor
61 62 63 64 65 66
Experiments were performed on a laboratory-scale, swirlstabilized premixed combustor, Fig. 1 shows a schematic of the lean premixed model gas turbine combustor. It consists of an airfuel mixture chamber, which is called the gas mixing section, a swirl burner nozzle, an optically accessible quartz combustion
81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103
Fig. 1. Schematic figure of the model combustor.
104
chamber, and an exhaust gas duct. Fuel and air are mixed in the upstream of the combustor, the length of the mixing chamber is 400 mm, and the downside of the mixing section is connected to a loudspeaker interface, which is 202 mm and designed for sound excitation of flames. The inner diameter of the whole combustor is fixed at 114 mm for the quartz combustion chamber, exhaust gas outlet section and the mixing chamber. The axial type swirler has 16 vanes with 60◦ vane angle, the height of the burner nozzle section is 100 mm, a bluff body with an external diameter of 6 mm is inserted in the middle of the swirler, the corresponding swirl number can be written as equation (1).
S=
2 3
3
1 − (dh /dn )
1 − (dh /dn )2
tan ϕ ≈
2 3
105 106 107 108 109 110 111 112 113 114 115 116 117
tan ϕ
(1)
Where ϕ is the swirler vane angle, dh and dn are the diameters of the inner tube and the vane cross-section [3]. With equation (1), the swirl numbers of the swirler are estimated to resemble the value of 1.153. The length of the optically accessible quartz combustion chamber is 300 mm, with two holes symmetrically placed at the downside of quartz for the application of pressure measuring, the inner diameter of the holes is 10 mm. The downstream of the quartz combustor is connected to a stainless exhaust outlet with a height of 315 mm, temperature measuring holes are reserved. With the above geometry parameters, the cutoff frequency of the lean-premixed combustor was calculated as f = 1504 Hz, this value was bigger than the excitation frequency of flame-acoustic resonance in this study.
118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
JID:AESCTE AID:105650 /FLA
[m5G; v1.261; Prn:19/12/2019; 14:25] P.3 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
1
3
67
Table 1 Experimental condition.
2 3 4 5 6 7 8 9
68
Parameters
Values
Fuel type Thermal power (kW) Equivalence ratio (Φ ) Swirl number (S) Injection tubes diameter (mm) Air injection flow rate (L/min) Jet nozzle numbers
CH4 , gas purity: 99.995% 2.5 0.90 1.153 0.8, 1.0, 1.5, 2.0 1, 2, 3, 4, 5, 6, 7 2, 4, 6, 8
69 70 71 72 73 74 75
10
76
11
77
12
78 79
13 14
Fig. 2. The geometry of the annular stainless tube with eight air injection holes.
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
Fig. 3. The layout of related measuring instruments for the thermoacoustic suppressing experiments.
41 42
2.2. Air injection section design
43 44 45 46 47 48 49 50 51 52 53 54 55
In Fig. 1 and Fig. 2, an annular stainless air injection section with eight annular holes is installed between the outlet of the burner nozzle and the quartz combustion chamber, the height of the air injection section is 50 mm and four types of copper nozzles were used for micropore jets, with inner diameter of 0.8 mm, 1.0 mm, 1.5 mm, and 2.0 mm respectively. The external diameter of the air injection section is 120 mm, eight air injection holes with an inner diameter of 4 mm were evenly weld around the section surface, the height of these weld holes is 25 mm. Air is transported from the thin copper pipes and injected at the root of the flames, the outer of the annular stainless tube is connected with Teflon tubes.
56 57
2.3. Experimental setup
58 59 60 61 62 63 64 65 66
Fig. 3 shows the layout of the measuring instruments of the experiment. Sound pressure oscillations of the combustion chamber are collected with dynamic pressure transducers (Sensitivity: 1 mV/Pa, bandwidth: 0–20 kHz, rise time: 5 μs). In Fig. 3, the dynamic pressure transducer is inserted in the holes of the quartz combustion chamber at the position. Flame CH* (430 ± 10 nm) chemiluminescence signal implies the fluctuation of the heat release rate of premixed flames during thermoacoustic instability.
CH* chemiluminescence signal is measured with a photomultiplier tube (PMT, Hamamatsu H10722 series), the sound pressure and CH* chemiluminescence signal is recorded simultaneously using a multi-channel signal recorder (National Instruments, USB-6210) at a 4k Hz sampling rate. The above experimental data is transmitted and processed by using Labview 2012 and Matlab 2019a commercial software. In Fig. 3, along with the PMT, the lean-premixed flame images during experiments are recorded synchronously using a high-speed CCD camera (AOS S-PRI plus) through a signal synchronizer (MODEL DG535). Flame temperature is recorded by a K-type thermocouple (TM-902C, −50–1300 ◦ C). In the present study, the combustor is operated at atmospheric pressure and ambient temperature. In Fig. 1 and Fig. 3, air as an oxidizer is conveyed through two radially opposed apertures at the upstream of the burner. The air is supplied with an industrial fan (YASHIBA-HG-1100, Output: 1.1 kW, Pressure-max: 24 kPa) and the flow rate is controlled by a glass rotameter (2% FS). Research level methane (CH4 , gas purity: 99.995%) is delivered through Teflon pipes to the mixing chamber and then mixed with air completely. In Fig. 3, the volume flow rate of the fuel (methane) is adjusted with a mass flow controller (Alicat MC-series, 0.2% FS) and the thermal power of the combustor is fixed at 2.5 kW, with the methane flow rate set as 4.6 L/min. The methane is provided with fuel storage tanks (10 MPa, 40 L). During the experiments, the global equivalence ratio of the lean-premixed flame is selected as 0.90. Two honeycombs are placed in the upstream of the combustor for better mixing. The visible length of the flame was calculated with the “Canny edge detection algorithm”. To identify the edge of the flame and extract the edge of the flame picture for calculation of flame length, the Canny edge detection method is not susceptible to noise and can detect true weak edges of flame, the strong and weak flame edges are detected separately using two different thresholds, and the weak edges are included in the output image when the weak and strong edges are connected. The Canny edge detection algorithm contains four steps. Step 1: smoothing the image with a Gaussian filter. Step 2: Calculate the magnitude and direction of the gradient using the finite-difference of the first-order partial derivative. Step 3: Non-maximum suppression of gradient amplitude. Step 4: Detect and join edges with a double threshold algorithm. The following figures are examples of the Canny edge detection algorithm to extract the edge of the flame. Experimental conditions of the combustion instability optimal control explored are summarized in Table 1. To explore the optimal conditions of thermoacoustic suppression, four types of air injection copper tubes (Type-A: 0.8 mm, Type-B: 1.0 mm, Type-C: 1.5 mm, Type-D: 2.0 mm) are employed to find the optimal inner diameter of copper tubes. The numbers of air injectors are essential in mitigating combustion instability, based on injection velocity, the number of injectors varied from two to eight. An air storage tanks (15 MPa, 40 L) is used as the air source of injection, and the air flow rate varies from 0 to 7 L/min.
80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
JID:AESCTE
AID:105650 /FLA
4
[m5G; v1.261; Prn:19/12/2019; 14:25] P.4 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
1
67
2
68
3
69
4
70
5
71
6
72
7
73
8
74
9
75
10
76
11
77
12
78
13
79
14
80
15
81
16
82
17
83
18
84
19
85
20
86
21
87
22
88
23
89
24
90
25
91
26
92
27
93
28
94
29
95
30
96 97
31 32 33
Fig. 4. (a) Resonance frequency of sound pressure in present combustor without air injection control, (b) Resonance frequency of heat release rate in present combustor without air injection control.
3. Results and discussion
3.1. Optimal control of thermoacoustic instability
In our experiments, the fuel flow rate is fixed at 4.6 L/min, as the air flow rate varies, the maximum pressure emerges at the equivalence ratio of 0.90, and the maximum pressure recorded was 50.15 Pa. Please see the following figure, the sound pressure level of the burner changes along with the equivalence ratio. The maximum pressure of 50.15 Pa at the equivalence ratio of 0.90 was selected to test the suppression results of annular air jets. Under these conditions, the combustor exhibits self-excited combustion instability at an oscillation frequency of 264.5 Hz without control. Fig. 4(a) and Fig. 4(b) shows the resonance frequency of sound pressure and flame heat release rate at conditions set in Table 1, the maximum pressure recorded was 50.15 Pa before micropore air injection. In Fig. 5(a), the coupling of thermoacoustic instability was recorded in a 0.1 s duration, time series of sound pressure and heat release rate is shown periodic oscillations in the combustion chamber. Fig. 5(b) shows the phase lag between CH* chemiluminescence signal and sound pressure tested in the combustor before air injection, to a great extent, it can be seen that the absolute value of phase difference less than 90◦ . With different types of copper tubes used for air injection, the suppression effects of combustion instability are experimentally demonstrated in the paper. Injector numbers and air flow rates are investigated simultaneously. Since annular air injection not only eliminates sound pressure, but also triggers frequency and amplitude shifting of flame heat release rate, the dynamic characteristics of the heat release rate before or after control is studied. Furthermore, temperature distribution and flame length are analyzed and compared before or after thermoacoustic control.
Fig. 6 shows the damping effects of thermoacoustic instability with different conditions of micropore jets. At the same fuel flow rate and equivalence ratio, sound pressure in combustion chamber oscillates at the dominant frequency of 264.5 Hz and amplitude of 50.15 Pa. Four types of copper tubes were used as jet nozzles at the air injection section, the inner diameter of jet nozzles was 0.8 mm, 1.0 mm, 1.5 mm, and 2.0 mm respectively. The air injection flow rate increases gradually from 0 to 7 L/min in Fig. 6, the corresponding sound pressure is recorded with the dynamic pressure transducer and then transmitted to the Labview USB-2010 signal acquisition card. From the control effects demonstrated in Fig. 6(a), Fig. 6(b), Fig. 6(c) and Fig. 6(d), the suppression tendency shows that the sound pressure amplitude decreases as the air injection flow rate increase. At the initial stage, when the air injection flow rate is relatively small (0–2 L/min) compared to the main output of the air fan (46 L/min), the pressure amplitude declines slowly. As the air injection flow rate increases from 2 to 5 L/min, in this transitional period, the pressure amplitude declines proportionally to the air injection rate. Damping effects of the annular micropore jets reaches a saturation region when the air injection rate greater than 5 L/min, in all four cases, the sound pressure vibration intensity after control was reduced to 5% compared to uncontrolled conditions. After this point of saturation, the sound pressure amplitude almost no longer decreases as the air injection flow rates until ultimately extinction. Fig. 4 shows the thermoacoustic damping effectiveness of jet nozzles with different inner diameter and number. The main performance of these jet nozzles are similar, but the four jet nozzles layout one is especially remarkable than other designs.
37 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
101 102
36 38
99 100
34 35
98
103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
JID:AESCTE AID:105650 /FLA
[m5G; v1.261; Prn:19/12/2019; 14:25] P.5 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
5
3.2. Amplitude and frequency shifting of heat release rate
1 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43
Fig. 5. Coupling characteristics of heat release rate and pressure coupling during 0.1 s and phase lag during 1 s under the condition of self-excited thermoacoustic instability. (For interpretation of the colors in the figure(s), the reader is referred to the web version of this article.)
44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
67 68
2
The amplitude-damped ratio of four micropore jet nozzles case is investigated in Fig. 7, it shows that the amplitude-damped ratio exceeds 80% after the air injection flow rate greater than 5 L/min, the thermoacoustic suppression effectiveness of the 4 ∗ 0.8 mm, 4 ∗ 1.0 mm, and 4 ∗ 1.5 mm cases are similar to each other. However, for the 4 ∗ 2.0 mm case, suppression effectiveness during the transitional region (2–5 L/min) grows slowly from 60 to 80%, this phenomenon maybe attribute to the output velocity of jet nozzles. As the inner diameter of the nozzles increases, the velocity of airflow decreases, causes the jet momentum to decline further then reduces the damping effectiveness of combustion instability. To test this further, Fig. 8 shows FFT (Fast Fourier Transform) of the pressure oscillations before and after control with four jet nozzles of different inner diameters, the selected air injection flow rate is 5 L/min. On the whole, the main peak of thermoacoustic instability at 264.5 Hz was eliminated after control, this is consistent with experimental results presented in Fig. 7. From the results demonstrated in Fig. 6, Fig. 7 and Fig. 8, with methods of annular micropore jets, self-excited thermoacoustic oscillation in the model gas turbine combustor can be largely suppressed.
Fig. 9 shows the CH* chemiluminescence intensity recorded during air injection for four types of jet nozzles. It can be inferred from Fig. 9 that the CH* chemiluminescence intensity maintains at a stable level when the air injection flow rates below 4 L/min, which denotes the heat release rate of lean-premixed flames in limit cycles states and the coupling of self-excited oscillations unperturbed. However, when the air injection flow rate reaches 4 L/min, the amplitude of CH* chemiluminescence intensity increases gradually and finally arrives at a saturation point, the CH* chemiluminescence intensity of flames under control are 2 to 4 times than that of the uncontrolled condition. Dynamic characteristics of the CH* chemiluminescence intensity in Fig. 9 stems from more oxidizer added decreases the equivalence ratio of combustion, and the cross injection makes reactant mixing evenly, thus significantly improves the reaction rate and of lean-premixed flames. At the same time, when the thermoacoustic coupling is broken by annular micropore jets, the process of thermoacoustic instability suppressing reduces or eliminates the kinetic energy of sound pressure oscillation in the combustion chamber, this part of kinetic energy converts into chemical energy and emitted with the form of heat release rate. The variation trend of CH* chemiluminescence intensity under different number of nozzles shows the mode migration trends of jet, but there was no clear trend in the effect of using different number of jets, the mechanism behind the transition of CH* chemiluminescence intensity may be fostered by different density gradient and precessing vortex core across the reaction zone. In addition, annular jets penetrated into the flame not only changes the local equivalence ratio but also alters the flame structure, the outer recirculation zone (ORZ) and the inner recirculation zone (IRZ), annular air injection may lead to different flame-vortex interaction mechanism thus changes the CH* chemiluminescence intensity. Fig. 10 shows the frequency shifting of CH* chemiluminescence intensity during the process of thermoacoustic suppressing. For all types of jet nozzles, the oscillation frequency shifted from 264.5 Hz to approximately 110 Hz as the air injection flow rate increases. When the thermoacoustic instability was fully damped, the mode of CH* chemiluminescence intensity was altered at the same time (In Fig. 9). The shifting frequency varies among different types of jet nozzles, both numbers and inner diameters of jet nozzles affect the initial shifting point of CH* chemiluminescence intensity. In Fig. 10, because the frequency shifting is connected with the process of thermoacoustic damping, mechanisms behind this phenomenon may attribute to the micropore injection that changes the flow field and vortex shedding of the flame, which triggered a new heat release rate oscillation near 110 Hz. Combined variation trend Fig. 9 with Fig. 10, the amplitude of heat release rate increases while the resonance frequency decreases, this strange dynamic characteristic signifies that although thermoacoustic coupling was broken by air injection, the variation tendency of flame heat release rate was different compared with that of sound pressure in the combustion chamber. Heat release rate experienced a more complicated evolution during the process of micropore jets control.
69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123
3.3. Variation of flame length and temperature distribution
124 125
The main purpose of this section is to investigate the variation of flame length and the distribution of temperature under air injection control. In Fig. 6, Fig. 7 and Fig. 8, the parameters of jet nozzles that can achieve the best combustion instability suppression were tested, four types of diameters (Type-A: 0.8 mm, Type-B: 1.0 mm, Type-C: 1.5 mm, Type-D: 2.0 mm) were taken. The number of jet nozzles varied from two, four, six and eight, all the noz-
126 127 128 129 130 131 132
JID:AESCTE
6
AID:105650 /FLA
[m5G; v1.261; Prn:19/12/2019; 14:25] P.6 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
1
67
2
68
3
69
4
70
5
71
6
72
7
73
8
74
9
75
10
76
11
77
12
78
13
79
14
80
15
81
16
82
17
83
18
84
19
85
20
86
21
87
22
88
23
89
24
90
25
91
26
92
27
93
28
94
29
95
30
96
31
97
32
98
33
99
34
100
35
101
36
102
37
103
38
104
39
105
40
106
41
107
42
108
43
109
44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
Fig. 6. Sound pressure amplitude after optimal air injection control (a) 0.8 mm jet nozzles, (b) 1.0 mm jet nozzles, (c) 1.5 mm jet nozzles, (d) 2.0 mm jet nozzles.
zles inserted in the injection section spaced evenly around the circumference. Through the test, as the air injection flow rate grows from 0 to 7 L/min, the combination of four jet nozzles with 1.0 mm inner diameter can achieve a better damping effects than other nozzles. With air injection flow rate adjusted during 0–7 L/min, the corresponding appearance and length of the flame were recorded at a specific point of 0, 1, 2, 3, 4, 5, 6, and 7 L/min, the inner diameter of these jet nozzles are 0.8 mm, 1.0 mm, 1.5 mm, and 2.0 mm. In Fig. 11, lean-premixed flame images during experiments are recorded synchronously using a high-speed CCD camera through a signal synchronizer. The length of the flame shortens as the air injection flow rate increases. At the initial stage, the tails of the flame changes slightly with air injection. When reaches the critical point of 5 L/min in Fig. 6, the length of flame was almost cut in half at an injection rate of 5 L/min, then the length of the flame continues to decrease and reaches a stable saturation level. At the 7 L/min cases, flame tails almost invisible, the appearance of the flame becomes flattened and blue, this was different from the no air injection condition, where the flame is stretched and bright. As the air injection flow rate increases, thermoacoustic in-
stability was suppressed and the flame becomes more stable. For all types of jet nozzles used in Fig. 11, appearance changing process of flame was similar to each other, the combustion noise was eliminated and the flame became stable, which proves the effectiveness of thermoacoustic damping through methods of micropore jets. When annular air jets injected into the core of flame, it alters the local equivalence ratio and hence the heat release dynamics simultaneously. In Fig. 11, the luminosity of uncontrolled flame is intense than that of controlled cases. As luminous flame contains more carbon particles that result in higher radiation heat loss, whereas in a non-luminous flame with less triatomic gas, combustion is spread out uniformly resulting in a lower heat loss [37], the control technique studied promises not only a safety combustion process but also a lower pollutant emission. Fig. 12 shows the flame length before and after control recorded in Fig. 11. With the experimental condition presented in Table 1, the original length of flame without air injection is 105 mm. Fig. 12 compared the length of flame and the air injection flow rate, and the result was a strong negative relationship
110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
JID:AESCTE AID:105650 /FLA
[m5G; v1.261; Prn:19/12/2019; 14:25] P.7 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
7
1
67
2
68
3
69
4
70
5
71
6
72
7
73
8
74
9
75
10
76
11
77
12
78
13
79
14
80
15
81
16
82
17
83 84
18 19 20 21
Fig. 7. Amplitude-damped ratio of sound pressure after control with air injection flow rate range from 0 ∼ 7 L/min, = 0.8 mm, 1.0 mm, 1.5 mm and 2.0 mm.
Fig. 8. Pressure oscillations frequency after air injection control, = 0.8 mm, 1.0 mm, 1.5 mm and 2.0 mm, air flow rate = 5 L/min.
85 86 87
22
88
23
89
24
90
25
91
26
92
27
93
28
94
29
95
30
96
31
97
32
98
33
99
34
100
35
101
36
102
37
103
38
104
39
105
40
106
41
107
42
108
43
109
44
110
45
111
46
112
47
113
48
114
49
115
50
116
51
117
52
118
53
119
54
120
55
121
56
122
57
123
58
124
59
125
60
126
61
127
62
128
63
129
64
130 131
65 66
Fig. 9. CH* chemiluminescence intensity fluctuation after air injection control (a) 0.8 mm jet nozzles, (b) 1.0 mm jet nozzles, (c) 1.5 mm jet nozzles, (d) 2.0 mm jet nozzles.
132
JID:AESCTE
8
AID:105650 /FLA
[m5G; v1.261; Prn:19/12/2019; 14:25] P.8 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
1
67
2
68
3
69
4
70
5
71
6
72
7
73
8
74
9
75
10
76
11
77
12
78
13
79
14
80
15
81
16
82
17
83
18
84
19
85
20
86
21
87
22
88
23
89
24
90
25
91
26
92
27
93
28
94
29
95
30
96
31
97
32
98
33
99
34
100
35
101
36
102
37
103
38
104
39
105
40
106
41
107
42
108 109
43 44
Fig. 10. Frequency shifting of flame CH* chemiluminescence (a) 0.8 mm jet nozzles, (b) 1.0 mm jet nozzles, (c) 1.5 mm jet nozzles, (d) 2.0 mm jet nozzles.
46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
110 111
45
between both variables. For all types of jet nozzles in Fig. 12, the flame length is inversely proportional to air injection flow rate, variation tendency of flame length was similar to each other. According to Fig. 1 and Fig. 2, the air injection holes were drilled at the height of 25 mm, when the air injection flow rate arrives at 7 L/min, flame length nears 25 mm. The temperature distribution changes simultaneously with the flame shortening process. To make an in-depth investigation of this associated relation, the temperature distribution along the radial direction is measured at three axial positions of Z1 = 21 mm, Z2 = 48 mm and Z3 = 94 mm, as indicated by the arrows at the bottom of Fig. 13. With the same experimental conditions in Table 1, the flame temperature is recorded with a thermocouple before and after control, in Fig. 13, there are three gauging points in the combustion chamber. The geometrical benchmark of temperature measuring set at Z = 0 is parallel to the airflow direction, root temperature of flame recorded at Z1 = 21 mm, the core temperature of flame recorded at Z2 = 48 mm, the tail temperature of flame recorded at Z3 = 94 mm. There are 13 gauging points in the radius direction within the combustion chamber, for reconstruction of temperature distribution before or after thermoacoustic control.
The optimal cases of four jet nozzles with inner diameter equals 1.0 mm were chosen to study temperature distribution during thermoacoustic suppressing, air injection flow rate fixed at 5 L/min. In each measurement, the temperature is tested at least five times for error reduction, and the average temperature value is plotted in Fig. 14. The temperature distribution of flame before or after control is presented in the form of adiabatic temperature. Fig. 14 signifies that before air injection control, the temperature distribution shows a typical reversed V shape for each axial position. At Z1 = 21 mm, close to the inner wall of the quartz combustion chamber (radius = 57 mm), the gas temperature is relatively lower; the temperature gradually increases to its peak around the flame front; by approaching the center (radius = 0 mm), the temperature reaches the highest value of 1290 K, the peak temperature of uncontrolled flames at Z2 = 48 mm or Z3 = 94 mm is 1328 K and 1319 K respectively. At Z1 = 21 mm, the temperature is relatively low in the zone of the flame root, they increase significantly at Z2 = 48 mm in the zone of the flame core, by increasing the axial position, the temperature decreases at Z3 = 94 mm owning to heat loss. After air injection control, the temperature distribution at Z1 = 21 mm shows an M shape and
112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
JID:AESCTE AID:105650 /FLA
[m5G; v1.261; Prn:19/12/2019; 14:25] P.9 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
9
1
67
2
68
3
69
4
70
5
71
6
72
7
73
8
74
9
75
10
76
11
77
12
78
13
79
14
80
15
81
16
82
17
83
18
84
19
85
20 21 22
86
Fig. 11. The appearance of flame before and after air injection control with four kinds of jet nozzles, = 0.8 mm, 1.0 mm, 1.5 mm and 2.0 mm, air injection flow rate varies from 0 to 7 L/min, equivalence ratio = 0.90.
87 88
23
89
24
90
25
91
26
92
27
93
28
94
29
95
30
96
31
97
32
98
33
99
34
100
35
101
36
102
37
103
38
104
39
105
40
106 107
41 42 43 44
Fig. 12. Variation tendency of flame length before and after air injection with four jet nozzles, = 0.8 mm, 1.0 mm, 1.5 mm and 2.0 mm, air injection flow rate varies from 0 to 7 L/min, equivalence ratio = 0.90.
108 109 110
45
111
46
112
47
113
48
114
49
115
50
116
51
117
52
118
53
119 120
54 55
Fig. 14. Temperature distribution at the height of Z1 = 21 mm, Z2 = 48 mm, and Z3 = 94 mm. Equivalence ratio = 0.90, number of jet nozzles = 4, = 1.0 mm.
56
124
58 59 60 61 62 63 65 66
122 123
57
64
121
Fig. 13. Temperature measurement points at the height of Z1 = 21 mm, Z2 = 48 mm, and Z3 = 94 mm. Equivalence ratio = 0.90, number of jet nozzles = 4, = 1.0 mm.
the overall temperature increased compared to the uncontrolled one in Fig. 14(a). But at Z2 = 48 mm in Fig. 14(b), the overall temperature declines compared to the uncontrolled one. In Fig. 14(c), the overall temperature at Z3 = 94 mm declines significantly than the uncontrolled one, the reversed V shape was altered to a W shape under conditions of air injection. Dynamic characteristics of temperature distribution in Fig. 14 conforms to the flame length variation in Fig. 12. The mechanism
125 126 127 128 129 130 131 132
JID:AESCTE
AID:105650 /FLA
1 2 3 4 5 6 7 8 9 10 11 12
[m5G; v1.261; Prn:19/12/2019; 14:25] P.10 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
10
behind these characteristics pertains to the flame structure variation and better air-fuel mixing. In Fig. 11, the internal and external recirculation zone of the flame was changed by the annular micropore jets, which improves combustion efficiency and reaction rate with more oxidizer added. In Fig. 14, the strain rate of flame was reduced when air injection flow rose up, the shorter flame length may attribute to the increased reaction rate of turbulent combustion. Then the turbulent swirling combustion velocity of the gaseous mixture significantly increased and finally shortens the tail of flame. At the same time, cross injection of airflow enhances the swirling intensity of the flame and brings fresh air which could reduce the temperature in combustion chamber.
[6]
[7]
[8]
[9]
13 14
4. Conclusion [10]
15 16 17 18
The feasibility of optimal controlling combustion instability by annular micropore jets is demonstrated and the mechanism is investigated.
[11]
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
(1) The results obtained demonstrate that the method can suppress the self-excited thermoacoustic oscillations effectively. Thermoacoustic instability was suppressed and the sound pressure level was reduced to 5% compared to the original uncontrolled cases. The saturation region and transition region of air injection control were also identified for effective control. (2) Frequency shifting of flame heat release rate was observed. During the process of air injection, peak oscillation of heat release rate at 264.5 Hz was eliminated and triggered to a new frequency near 110 Hz. Flame heat release rate was enhanced after air injection, the annular air injection has the potential to improve the combustion efficiency, reduce exhaust emission and attenuate the overheating of the combustor. (3) The shape and temperature distribution of the flame were transformed after annular micropore injection, and the increasing of turbulent combustion velocity is essential behind the mechanism that causes the flame more compact and stable. Future developments will be focused on testing the damping effectiveness with different gas medium and combustor design optimization, the shifting mechanism of flame heat release rate and flame length also needs further study.
[14]
[15]
[16]
[17]
[18]
[19]
Declaration of competing interest
43 44
[13]
[20]
41 42
[12]
[21]
The authors declare that they have no conflicts of interest.
45 46
Acknowledgement
47 48 49
This work was supported by National Science Fund for Distinguished Young Scholars (51825605). [23]
50 51
[22]
References
52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
[1] Can Ruan, Feier Chen, Weiwei Cai, Yong Qian, Liang Yu, Xingcai Lu, Principles of non-intrusive diagnostic techniques and their applications for fundamental studies of combustion instabilities in gas turbine combustors: a brief review, Aerosp. Sci. Technol. 84 (2019) 585–603, https://doi.org/10.1016/j.ast.2018.10. 002. [2] Dan Zhao, X.Y. Li, A review of acoustic dampers applied to combustion chambers in aerospace industry, Prog. Aerosp. Sci. 74 (2015) 114–130, https:// doi.org/10.1016/j.paerosci.2014.12.003. [3] Dan Zhao, Zhengli Lu, He Zhao, X.Y. Li, Bing Wang, Peijin Liu, A review of active control approaches in stabilizing combustion systems in aerospace industry, Prog. Aerosp. Sci. 97 (2018) 35–60, https://doi.org/10.1016/j.paerosci.2018.01. 002. [4] Ying Huang, Vigor Yang, Dynamics and stability of lean-premixed swirlstabilized combustion, Prog. Energy Combust. Sci. 35 (2009) 293–364, https:// doi.org/10.1016/j.pecs.2009.01.002. [5] Feier Chen, Can Ruan, Tao Yu, Weiwei Cai, Yebing Mao, Xingcai Lu, Effects of fuel variation and inlet air temperature on combustion stability in a gas turbine
[24]
[25]
[26]
[27]
[28]
model combustor, Aerosp. Sci. Technol. 92 (2019) 126–138, https://doi.org/10. 1016/j.ast.2019.05.052. M. Stöhr, R. Sadanandan, W. Meier, Experimental study of unsteady flame structures of an oscillating swirl flame in a gas turbine model combustor, Proc. Combust. Inst. 32 (2009) 2925–2932, https://doi.org/10.1016/j.proci.2008. 05.086. Oliver Schulz, Nicolas Noiray, Autoignition flame dynamics in sequential combustors, Combust. Flame 192 (2018) 86–100, https://doi.org/10.1016/j. combustflame.2018.01.046. Oliver Schulz, Nicolas Noiray, Combustion regimes in sequential combustors: flame propagation and autoignition at elevated temperature and pressure, Combust. Flame 205 (2019) 253–268, https://doi.org/10.1016/j.combustflame. 2019.03.014. Hao Zan, Weixing Zhou, Xuefeng Xiao, Long Lin, Junlong Zhang, Haowei Li, Recurrence network analysis for uncovering dynamic transition of thermoacoustic instability of supercritical hydrocarbon fuel flow, Aerosp. Sci. Technol. 85 (2019) 1–12, https://doi.org/10.1016/j.ast.2018.11.040. Jaime Rubio-Hervas, Dan Zhao, Mahmut Reyhanoglu, Nonlinear feedback control of self-sustained thermoacoustic oscillations, Aerosp. Sci. Technol. 41 (2015) 209–215, https://doi.org/10.1016/j.ast.2014.12.026. Li Lei, Dan Zhao, Prediction of stability behaviors of longitudinal and circumferential eigenmodes in a choked thermoacoustic combustor, Aerosp. Sci. Technol. 46 (2015) 12–21, https://doi.org/10.1016/j.ast.2015.06.024. Li Lei, Dan Zhao, Xiaofeng Sun, Nonorthogonality analysis of acoustics and vorticity modes: should thermoacoustic energy norm be time-invariant?, Aerosp. Sci. Technol. 77 (2018) 149–155, https://doi.org/10.1016/j.ast.2018.02.036. Xinyan Li, Dan Zhao, Xinglin Yang, Huabing Wen, Xiao Jin, Shen Li, He Zhao, Changqing Xie, Haili Liu, Transient growth of acoustical energy associated with mitigating thermoacoustic oscillations, Appl. Energy 169 (2016) 481–490, https://doi.org/10.1016/j.apenergy.2016.01.060. Dan Zhao, Transient growth of flow disturbances in triggering a Rijke tube combustion instability, Combust. Flame 159 (2012) 2126–2137, https://doi.org/ 10.1016/j.combustflame.2012.02.002. Xinyan Li, Dan Zhao, Xinglin Yang, Shuhui Wang, Unity maximum transient energy growth of heat-driven acoustic oscillations, Energy Convers. Manag. 116 (2016) 1–10, https://doi.org/10.1016/j.enconman.2016.02.062. Dan Zhao, Mahmut Reyhanoglu, Feedback control of acoustic disturbance transient growth in triggering thermoacoustic instability, J. Sound Vib. 333 (2014) 3639–3656, https://doi.org/10.1016/j.jsv.2014.04.015. Dan Zhao, X.Y. Li, Minimizing transient energy growth of nonlinear thermoacoustic oscillations, Int. J. Heat Mass Transf. 81 (2015) 188–197, https:// doi.org/10.1016/j.ijheatmasstransfer.2014.10.023. Maria L. Frezzotti, Francesco Nasuti, Cheng Huang, Charles L. Merkle, William E. Anderson, Quasi-1D modeling of heat release for the study of longitudinal combustion instability, Aerosp. Sci. Technol. 75 (2018) 261–270, https://doi.org/ 10.1016/j.ast.2018.02.001. Dan Zhao, C. Ji, X. Li, S. Li, Mitigation of premixed flame-sustained thermoacoustic oscillations using an electrical heater, Int. J. Heat Mass Transf. 86 (2015) 309–318, https://doi.org/10.1016/j.ijheatmasstransfer.2015.03.012. Zhiguo Zhang, Dan Zhao, Nuomin Han, Shuhui Wang, Junwei Li, Control of combustion instability with a tunable Helmholtz resonator, Aerosp. Sci. Technol. 41 (2015) 55–62, https://doi.org/10.1016/j.ast.2014.12.011. Seonghwi Jo, Yunho Choi, Hong Jip Kim, Evaluation of the damping capacity according to the geometric and the number of resonator with thermal environment using a Rijke tube, Aerosp. Sci. Technol. 88 (2019) 1–8, https:// doi.org/10.1016/j.ast.2019.02.040. Seungtaek Oh, Hyunggeun Ji, Yongmo Kim, FDF-based combustion instability analysis for stabilization effects of a slotted plate in a multiple flame combustor, Aerosp. Sci. Technol. 70 (2017) 95–107, https://doi.org/10.1016/j.ast.2017. 07.045. Yu Guan, Vikrant Gupta, Karthik Kashinath, Larry K.B. Li, Open-loop control of periodic thermoacoustic oscillations: experiments and low-order modelling in a synchronization framework, Proc. Combust. Inst. 37 (2019) 5315–5323, https://doi.org/10.1016/j.proci.2018.07.077. Yu Guan, Wei He, Meenatchidevi Murugesan, Qiang Li, Peijin Liu, Larry K.B. Li, Control of self-excited thermoacoustic oscillations using transient forcing, hysteresis and mode switching, Combust. Flame 202 (2019) 262–275, https:// doi.org/10.1016/j.combustflame.2019.01.013. H. Murat Altay, Duane E. Hudgins, Raymond L. Speth, Anuradha M. Annaswamy, Ahmed F. Ghoniem, Mitigation of thermoacoustic instability utilizing steady air injection near the flame anchoring zone, Combust. Flame 157 (2010) 686–700, https://doi.org/10.1016/j.combustflame.2010.01.012. M. Altay, R. Speth, D. Snarheim, D. Hudgins, A. Ghoniem, A. Annaswamy, Impact on microjet actuation on stability of a backward-facing step combustor, in: AIAA Aerospace Sciences Meeting & Exhibit, vol. 563, 2007, pp. 1–7. Jong Ho Uhm, Sumanta Acharya, Control of combustion instability with a highmomentum air-jet, Combust. Flame 139 (2004) 106–125, https://doi.org/10. 1016/j.combustflame.2004.07.007. Jong Ho Uhm, Sumanta Acharya, Low-bandwidth open-loop control of combustion instability, Combust. Flame 142 (2005) 348–363, https://doi.org/10.1016/j. combustflame.2005.03.015.
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
JID:AESCTE AID:105650 /FLA
[m5G; v1.261; Prn:19/12/2019; 14:25] P.11 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
[29] Jong Ho Uhm, Sumanta Acharya, Role of low-bandwidth open-loop control of combustion instability using a high-momentum air jet—mechanistic details, Combust. Flame 147 (2006) 22–31, https://doi.org/10.1016/j.combustflame. 2006.08.002. [30] Ahmed F. Ghoniem, Anuradha Annaswamy, Sungbae Park, Ziaieh C. Sobhani, Stability and emissions control using air injection and H2 addition in premixed combustion, Proc. Combust. Inst. 30 (2005) 1765–1773, https://doi.org/10.1016/ j.proci.2004.08.175. [31] Z. Labry, S. Shanbhogue, R. Speth, A. Ghoniem, Instability suppression in a swirl-stabilized combustor using microjet air injection, in: AIAA Aerospace Sciences Meeting Including the New Horizons Forum & Aerospace Exposition, vol. 1524, 2010, pp. 1–10. [32] Zachary A. Labry, Santosh J. Shanbhogue, Raymond L. Speth, Ahmed F. Ghoniem, Flow structures in a lean-premixed swirl-stabilized combustor with microjet air injection, Proc. Combust. Inst. 33 (2011) 1575–1581, https://doi. org/10.1016/j.proci.2010.06.092. [33] Z. Labry, S. Shanbhogue, A. Ghoniem, Microjet injection strategies for mitigating dynamics in a lean premixed swirl-stabilized combustor, in: 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, vol. 515, 2011, pp. 1–14. [34] Hao Zhou, Qi Tang, Tao Ren, Guoneng Li, Kefa Cen, Control of thermoacoustic instabilities by CO2 and N2 jet in cross-flow, Appl. Therm. Eng. 36 (2012) 353–359, https://doi.org/10.1016/j.applthermaleng.2011.10.048. [35] H. Zhou, Y. Huang, S. Meng, Response of non-premixed swirl-stabilized flames to acoustic excitation and jet in cross-flow perturbations, Exp. Therm. Fluid Sci. 82 (2017) 124–135, https://doi.org/10.1016/j.expthermflusci.2016.11.007.
11
[36] N.N. Deshmukh, S. Sharma, Experiments on heat content inside a Rijke tube with suppression of thermo-acoustics instability, Int. J. Spray Combust. Dyn. 9 (2016) 85–101, https://doi.org/10.1177/1756827716655007. [37] Nilaj N. Deshmukh, S.D. Sharma, Suppression of thermo-acoustic instability using air injection in horizontal Rijke tube, J. Energy Inst. 90 (2017) 485–495, https://doi.org/10.1016/j.joei.2016.03.001. [38] Séverine Barbosa, Marta de La Cruz Garcia, Sébastien Ducruix, Bernard Labegorre, François Lacas, Control of combustion instabilities by local injection of hydrogen, Proc. Combust. Inst. 31 (2007) 3207–3214, https://doi.org/ 10.1016/j.proci.2006.07.085. [39] Shigeru Tachibana, Laurent Zimmer, Yoji Kurosawa, Kazuo Suzuki, Active control of combustion oscillations in a lean premixed combustor by secondary fuel injection coupling with chemiluminescence imaging technique, Proc. Combust. Inst. 31 (2007) 3225–3233, https://doi.org/10.1016/j.proci.2006.08.037. [40] Gyung-Min Choi, Mamoru Tanahashi, Toshio Miyauchi, Control of oscillating combustion and noise based on local flame structure, Proc. Combust. Inst. 30 (2005) 1807–1814, https://doi.org/10.1016/j.proci.2004.08.249. [41] G. Strickland, J. Gustavsson, J. Solomon, F. Alvi, Implementing resonant enhanced pulsed micro-actuators for the control of supersonic impinging jets, in: AIAA Aerospace Sciences Meeting Including the New Horizons Forum & Aerospace Exposition, vol. 65, 2012, pp. 1–15. [42] J. Choi, A.M. Annaswamy, H. Lou, F.S. Alvi, Active control of supersonic impingement tones using steady and pulsed microjets, Exp. Fluids 41 (2006) 841–855, https://doi.org/10.1007/s00348-006-0189-7.
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88
23
89
24
90
25
91
26
92
27
93
28
94
29
95
30
96
31
97
32
98
33
99
34
100
35
101
36
102
37
103
38
104
39
105
40
106
41
107
42
108
43
109
44
110
45
111
46
112
47
113
48
114
49
115
50
116
51
117
52
118
53
119
54
120
55
121
56
122
57
123
58
124
59
125
60
126
61
127
62
128
63
129
64
130
65
131
66
132
[m5G; v1.261; Prn:19/12/2019; 14:25] P.1 (1-11)
Aerospace Science and Technology ••• (••••) ••••••
1
Contents lists available at ScienceDirect
67 68
2 3
Aerospace Science and Technology
4
69 70 71
5
72
6
www.elsevier.com/locate/aescte
7
73
8
74
9
75
10
76
11 12 13
Optimal control of turbulent premixed combustion instability with annular micropore air jets
16 17
81
Zhejiang University, Institute for Thermal Power Engineering, State Key Laboratory of Clean Energy Utilization, Hangzhou, 310027, PR China
83 85
a r t i c l e
i n f o
a b s t r a c t
86 87
21 23 24 25
Article history: Received 30 June 2019 Received in revised form 12 December 2019 Accepted 16 December 2019 Available online xxxx
26 27 28 29 30 31
82 84
19
22
79
Hao Zhou ∗ , Chengfei Tao, Zihua Liu, Sheng Meng, Kefa Cen
18 20
78 80
14 15
77
Keywords: Combustion instability Micropore jets Optimal control CH* chemiluminescence Sound pressure
32 33 34 35
This article experimentally investigates the suppressing of combustion instability in a model gas turbine combustor with annular air jets. Three parameters were optimized to find the control effectiveness— variations of the air injection flow rate, number, and diameter of jet nozzles. Results indicate that the suppression ratio of the self-excited oscillations can reach 95% with optimal control, the transition and saturation region of control effectiveness are identified, and the four jet nozzles design case can lead to the best effect of damping. Besides, mode shifting of flame heat release rate is observed, the amplitude of heat release rate increases to 2 ∼ 4 times than that of the uncontrolled flame, the main resonance frequency at 264.5 Hz was eliminated and triggered to a new oscillation frequency near 110 Hz. Moreover, after air injection control, the flame length and temperature changes inversely proportional to the air injection flow rate, as the air injection transforms the flow field and improves the turbulent combustion velocity. This study not only explored the mechanism behind combustion instability control under annular micropore air jets but also proposed the application of air injection as a practical tool for damping of combustion instability, which could contribute to the prevention of potential thermoacoustic instabilities in gas turbines. © 2019 Published by Elsevier Masson SAS.
88 89 90 91 92 93 94 95 96 97 98 99 100 101
36
102
37
103
38
104
39 40
1. Introduction
41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59
Gas turbine engines are extensively used in the land-based power generation and aviation or astronautics industries [1–4]. As the premixing is improved and the local flame temperature is decreased, NOx formation is reduced exponentially [5]. However, the lean-premixed combustion technique is susceptible to combustion induced thermoacoustic instabilities, or self-excited oscillations [6–8]. In much combustion-based thermal propulsion systems, thermoacoustic instability is an undesired phenomenon that can cause serious pressure fluctuations and serve damages to the combustor components [9–12]. To eliminate thermoacoustic instabilities and develop effective approaches for their control, the transient mechanisms responsible for their occurrence must be understood [13–17]. Several factors appear to present in a combustor that triggers the unsteady thermoacoustic instability, including flame-acoustic wave interactions, flame-vortex interactions, equivalence ratio oscillations [18,19], burner design and swirlers geometry [20–22], all of which may be present individually or simultaneously, and hence promoting thermoacoustic instability.
60 61 62 63 64 65 66
*
Corresponding author. E-mail address: [email protected] (H. Zhou).
https://doi.org/10.1016/j.ast.2019.105650 1270-9638/© 2019 Published by Elsevier Masson SAS.
Active control techniques utilize external excitations (such as acoustic forcing and fuel modulation) to attenuate combustion oscillations. Generally, the purpose is to minimize the difference between the instantaneous desired and actual behavior of a dynamic system [2–4]. While effective in suppressing the instabilities, active control requires high-speed actuators and adds significant complexity to the design of the combustors [3,4]. For this reason, developing simple, passive and open loop control strategies that directly impact the flame anchoring zone with minimal complexity is desirable [13–24]. The method for suppressing thermoacoustic instability by injecting air or fuel near the flame anchoring zone has been extensively explored in the past. H. Murat Altay [25,26] employed steady air injection near the flame anchoring zone to mitigate the thermoacoustic instability of a backward-facing step combustor. Jong Ho Uhm [27–29] studied the effects and mechanisms of low-bandwidth open-loop control of combustion instability using a high-momentum air jet. Ahmed F. Ghoniem [30–33] examined thermoacoustic instability and NOx emissions suppression with microjet air injection and H2 addition in premixed combustion. Hao Zhou [34,35] proposed a novel control method for thermoacoustic instabilities with a jet in cross-flow (JICF) in a swirling combustor by CO2 and N2 injection which could transform the precessing vortex core near the flame anchoring zone. Nilaj N. Desh-
105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
JID:AESCTE
AID:105650 /FLA
1 2
Φ
8
FFT S Z PMT
9
5 6 7
10 11 12 13
67
Nomenclature
3 4
[m5G; v1.261; Prn:19/12/2019; 14:25] P.2 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
2
kW Hz T f
equivalence ratio fast Fourier Transform swirl number flame length photomultiplier tube inner diameter thermal power frequency flame temperature cutoff frequency
68 69
ϕ
swirler vane angle dh inner tube diameter dn vane cross-section diameter CH4 methane CH* chemiluminescence Pa sound pressure ◦C centigrade L/min air flow rate CCD High-speed camera arb. units CH* chemiluminescence
70 71 72 73 74 75 76 77 78 79 80
14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56
mukh [36,37] investigated thermoacoustic instability suppression with eight microjet holes in a horizontal Rijke tube and using air as an injection medium. Sébastien Ducruix [38] took methods of local H2 injection to eliminate combustion instabilities and recorded the pollutant emissions before and after hydrogen injection. Shigeru Tachibana [39] eliminated combustion oscillations in a lean premixed combustor by secondary fuel injection with five different types of injectors. Based on local flame structure, Gyung-Min Choi [40] studied the impacts of secondary fuel injection on thermoacoustic instabilities. Unlike steady air injection, Garrett M. Strickland [41] implemented resonant enhanced pulsed micro-actuators for the control of supersonic impinging jets. Jae Jeen Choi [42] used a quasi-closed loop steady and pulsed microjets to control of supersonic impingement tones. The secondary flow is thought to change the velocity field and disrupt the flame-vortex interaction, then break the coupling of flame-acoustic instability. Although there are many types of research on thermoacoustic control with air injection, to date, there is no research on the combined effects of air injection intensity, nozzle inner diameter and number of injection holes on thermoacoustic control, which need to be further explored and optimized. Besides, the mode shifting characteristics of flame CH* chemiluminescence during the process of air injection has never been investigated before. At the same time, flame length shortened and temperature distribution varied after air injection control, this phenomenon has not been specifically explained in terms of mechanism [36,37]. The purpose of the present work is to verify the damping effectiveness and plug the knowledge gap of mechanism of thermoacoustic instability air injection control in a laboratory-scale lean-premixed combustor. Systematic experimental study of thermoacoustic instability optimal control is proposed to evaluate the impact of each variable, which involves injection air flow rates, the diameter of jet nozzles and the number of injection holes. During the optimal control experiments, the sound pressure fluctuation, heat release rate intermittency, uniformity of the flame temperature field and flame morphology phenomena of the combustor before or after the air injection were investigated simultaneously. This study can promote a better understanding of thermoacoustic instability passive control. As a result, providing a useful tool for better combustion instability suppression of lean-premixed burners and improve operation safety of industrial gas turbines.
57 58
2. Experimental setup
59 60
2.1. Model combustor
61 62 63 64 65 66
Experiments were performed on a laboratory-scale, swirlstabilized premixed combustor, Fig. 1 shows a schematic of the lean premixed model gas turbine combustor. It consists of an airfuel mixture chamber, which is called the gas mixing section, a swirl burner nozzle, an optically accessible quartz combustion
81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103
Fig. 1. Schematic figure of the model combustor.
104
chamber, and an exhaust gas duct. Fuel and air are mixed in the upstream of the combustor, the length of the mixing chamber is 400 mm, and the downside of the mixing section is connected to a loudspeaker interface, which is 202 mm and designed for sound excitation of flames. The inner diameter of the whole combustor is fixed at 114 mm for the quartz combustion chamber, exhaust gas outlet section and the mixing chamber. The axial type swirler has 16 vanes with 60◦ vane angle, the height of the burner nozzle section is 100 mm, a bluff body with an external diameter of 6 mm is inserted in the middle of the swirler, the corresponding swirl number can be written as equation (1).
S=
2 3
3
1 − (dh /dn )
1 − (dh /dn )2
tan ϕ ≈
2 3
105 106 107 108 109 110 111 112 113 114 115 116 117
tan ϕ
(1)
Where ϕ is the swirler vane angle, dh and dn are the diameters of the inner tube and the vane cross-section [3]. With equation (1), the swirl numbers of the swirler are estimated to resemble the value of 1.153. The length of the optically accessible quartz combustion chamber is 300 mm, with two holes symmetrically placed at the downside of quartz for the application of pressure measuring, the inner diameter of the holes is 10 mm. The downstream of the quartz combustor is connected to a stainless exhaust outlet with a height of 315 mm, temperature measuring holes are reserved. With the above geometry parameters, the cutoff frequency of the lean-premixed combustor was calculated as f = 1504 Hz, this value was bigger than the excitation frequency of flame-acoustic resonance in this study.
118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
JID:AESCTE AID:105650 /FLA
[m5G; v1.261; Prn:19/12/2019; 14:25] P.3 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
1
3
67
Table 1 Experimental condition.
2 3 4 5 6 7 8 9
68
Parameters
Values
Fuel type Thermal power (kW) Equivalence ratio (Φ ) Swirl number (S) Injection tubes diameter (mm) Air injection flow rate (L/min) Jet nozzle numbers
CH4 , gas purity: 99.995% 2.5 0.90 1.153 0.8, 1.0, 1.5, 2.0 1, 2, 3, 4, 5, 6, 7 2, 4, 6, 8
69 70 71 72 73 74 75
10
76
11
77
12
78 79
13 14
Fig. 2. The geometry of the annular stainless tube with eight air injection holes.
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
Fig. 3. The layout of related measuring instruments for the thermoacoustic suppressing experiments.
41 42
2.2. Air injection section design
43 44 45 46 47 48 49 50 51 52 53 54 55
In Fig. 1 and Fig. 2, an annular stainless air injection section with eight annular holes is installed between the outlet of the burner nozzle and the quartz combustion chamber, the height of the air injection section is 50 mm and four types of copper nozzles were used for micropore jets, with inner diameter of 0.8 mm, 1.0 mm, 1.5 mm, and 2.0 mm respectively. The external diameter of the air injection section is 120 mm, eight air injection holes with an inner diameter of 4 mm were evenly weld around the section surface, the height of these weld holes is 25 mm. Air is transported from the thin copper pipes and injected at the root of the flames, the outer of the annular stainless tube is connected with Teflon tubes.
56 57
2.3. Experimental setup
58 59 60 61 62 63 64 65 66
Fig. 3 shows the layout of the measuring instruments of the experiment. Sound pressure oscillations of the combustion chamber are collected with dynamic pressure transducers (Sensitivity: 1 mV/Pa, bandwidth: 0–20 kHz, rise time: 5 μs). In Fig. 3, the dynamic pressure transducer is inserted in the holes of the quartz combustion chamber at the position. Flame CH* (430 ± 10 nm) chemiluminescence signal implies the fluctuation of the heat release rate of premixed flames during thermoacoustic instability.
CH* chemiluminescence signal is measured with a photomultiplier tube (PMT, Hamamatsu H10722 series), the sound pressure and CH* chemiluminescence signal is recorded simultaneously using a multi-channel signal recorder (National Instruments, USB-6210) at a 4k Hz sampling rate. The above experimental data is transmitted and processed by using Labview 2012 and Matlab 2019a commercial software. In Fig. 3, along with the PMT, the lean-premixed flame images during experiments are recorded synchronously using a high-speed CCD camera (AOS S-PRI plus) through a signal synchronizer (MODEL DG535). Flame temperature is recorded by a K-type thermocouple (TM-902C, −50–1300 ◦ C). In the present study, the combustor is operated at atmospheric pressure and ambient temperature. In Fig. 1 and Fig. 3, air as an oxidizer is conveyed through two radially opposed apertures at the upstream of the burner. The air is supplied with an industrial fan (YASHIBA-HG-1100, Output: 1.1 kW, Pressure-max: 24 kPa) and the flow rate is controlled by a glass rotameter (2% FS). Research level methane (CH4 , gas purity: 99.995%) is delivered through Teflon pipes to the mixing chamber and then mixed with air completely. In Fig. 3, the volume flow rate of the fuel (methane) is adjusted with a mass flow controller (Alicat MC-series, 0.2% FS) and the thermal power of the combustor is fixed at 2.5 kW, with the methane flow rate set as 4.6 L/min. The methane is provided with fuel storage tanks (10 MPa, 40 L). During the experiments, the global equivalence ratio of the lean-premixed flame is selected as 0.90. Two honeycombs are placed in the upstream of the combustor for better mixing. The visible length of the flame was calculated with the “Canny edge detection algorithm”. To identify the edge of the flame and extract the edge of the flame picture for calculation of flame length, the Canny edge detection method is not susceptible to noise and can detect true weak edges of flame, the strong and weak flame edges are detected separately using two different thresholds, and the weak edges are included in the output image when the weak and strong edges are connected. The Canny edge detection algorithm contains four steps. Step 1: smoothing the image with a Gaussian filter. Step 2: Calculate the magnitude and direction of the gradient using the finite-difference of the first-order partial derivative. Step 3: Non-maximum suppression of gradient amplitude. Step 4: Detect and join edges with a double threshold algorithm. The following figures are examples of the Canny edge detection algorithm to extract the edge of the flame. Experimental conditions of the combustion instability optimal control explored are summarized in Table 1. To explore the optimal conditions of thermoacoustic suppression, four types of air injection copper tubes (Type-A: 0.8 mm, Type-B: 1.0 mm, Type-C: 1.5 mm, Type-D: 2.0 mm) are employed to find the optimal inner diameter of copper tubes. The numbers of air injectors are essential in mitigating combustion instability, based on injection velocity, the number of injectors varied from two to eight. An air storage tanks (15 MPa, 40 L) is used as the air source of injection, and the air flow rate varies from 0 to 7 L/min.
80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
JID:AESCTE
AID:105650 /FLA
4
[m5G; v1.261; Prn:19/12/2019; 14:25] P.4 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
1
67
2
68
3
69
4
70
5
71
6
72
7
73
8
74
9
75
10
76
11
77
12
78
13
79
14
80
15
81
16
82
17
83
18
84
19
85
20
86
21
87
22
88
23
89
24
90
25
91
26
92
27
93
28
94
29
95
30
96 97
31 32 33
Fig. 4. (a) Resonance frequency of sound pressure in present combustor without air injection control, (b) Resonance frequency of heat release rate in present combustor without air injection control.
3. Results and discussion
3.1. Optimal control of thermoacoustic instability
In our experiments, the fuel flow rate is fixed at 4.6 L/min, as the air flow rate varies, the maximum pressure emerges at the equivalence ratio of 0.90, and the maximum pressure recorded was 50.15 Pa. Please see the following figure, the sound pressure level of the burner changes along with the equivalence ratio. The maximum pressure of 50.15 Pa at the equivalence ratio of 0.90 was selected to test the suppression results of annular air jets. Under these conditions, the combustor exhibits self-excited combustion instability at an oscillation frequency of 264.5 Hz without control. Fig. 4(a) and Fig. 4(b) shows the resonance frequency of sound pressure and flame heat release rate at conditions set in Table 1, the maximum pressure recorded was 50.15 Pa before micropore air injection. In Fig. 5(a), the coupling of thermoacoustic instability was recorded in a 0.1 s duration, time series of sound pressure and heat release rate is shown periodic oscillations in the combustion chamber. Fig. 5(b) shows the phase lag between CH* chemiluminescence signal and sound pressure tested in the combustor before air injection, to a great extent, it can be seen that the absolute value of phase difference less than 90◦ . With different types of copper tubes used for air injection, the suppression effects of combustion instability are experimentally demonstrated in the paper. Injector numbers and air flow rates are investigated simultaneously. Since annular air injection not only eliminates sound pressure, but also triggers frequency and amplitude shifting of flame heat release rate, the dynamic characteristics of the heat release rate before or after control is studied. Furthermore, temperature distribution and flame length are analyzed and compared before or after thermoacoustic control.
Fig. 6 shows the damping effects of thermoacoustic instability with different conditions of micropore jets. At the same fuel flow rate and equivalence ratio, sound pressure in combustion chamber oscillates at the dominant frequency of 264.5 Hz and amplitude of 50.15 Pa. Four types of copper tubes were used as jet nozzles at the air injection section, the inner diameter of jet nozzles was 0.8 mm, 1.0 mm, 1.5 mm, and 2.0 mm respectively. The air injection flow rate increases gradually from 0 to 7 L/min in Fig. 6, the corresponding sound pressure is recorded with the dynamic pressure transducer and then transmitted to the Labview USB-2010 signal acquisition card. From the control effects demonstrated in Fig. 6(a), Fig. 6(b), Fig. 6(c) and Fig. 6(d), the suppression tendency shows that the sound pressure amplitude decreases as the air injection flow rate increase. At the initial stage, when the air injection flow rate is relatively small (0–2 L/min) compared to the main output of the air fan (46 L/min), the pressure amplitude declines slowly. As the air injection flow rate increases from 2 to 5 L/min, in this transitional period, the pressure amplitude declines proportionally to the air injection rate. Damping effects of the annular micropore jets reaches a saturation region when the air injection rate greater than 5 L/min, in all four cases, the sound pressure vibration intensity after control was reduced to 5% compared to uncontrolled conditions. After this point of saturation, the sound pressure amplitude almost no longer decreases as the air injection flow rates until ultimately extinction. Fig. 4 shows the thermoacoustic damping effectiveness of jet nozzles with different inner diameter and number. The main performance of these jet nozzles are similar, but the four jet nozzles layout one is especially remarkable than other designs.
37 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
101 102
36 38
99 100
34 35
98
103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
JID:AESCTE AID:105650 /FLA
[m5G; v1.261; Prn:19/12/2019; 14:25] P.5 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
5
3.2. Amplitude and frequency shifting of heat release rate
1 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43
Fig. 5. Coupling characteristics of heat release rate and pressure coupling during 0.1 s and phase lag during 1 s under the condition of self-excited thermoacoustic instability. (For interpretation of the colors in the figure(s), the reader is referred to the web version of this article.)
44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
67 68
2
The amplitude-damped ratio of four micropore jet nozzles case is investigated in Fig. 7, it shows that the amplitude-damped ratio exceeds 80% after the air injection flow rate greater than 5 L/min, the thermoacoustic suppression effectiveness of the 4 ∗ 0.8 mm, 4 ∗ 1.0 mm, and 4 ∗ 1.5 mm cases are similar to each other. However, for the 4 ∗ 2.0 mm case, suppression effectiveness during the transitional region (2–5 L/min) grows slowly from 60 to 80%, this phenomenon maybe attribute to the output velocity of jet nozzles. As the inner diameter of the nozzles increases, the velocity of airflow decreases, causes the jet momentum to decline further then reduces the damping effectiveness of combustion instability. To test this further, Fig. 8 shows FFT (Fast Fourier Transform) of the pressure oscillations before and after control with four jet nozzles of different inner diameters, the selected air injection flow rate is 5 L/min. On the whole, the main peak of thermoacoustic instability at 264.5 Hz was eliminated after control, this is consistent with experimental results presented in Fig. 7. From the results demonstrated in Fig. 6, Fig. 7 and Fig. 8, with methods of annular micropore jets, self-excited thermoacoustic oscillation in the model gas turbine combustor can be largely suppressed.
Fig. 9 shows the CH* chemiluminescence intensity recorded during air injection for four types of jet nozzles. It can be inferred from Fig. 9 that the CH* chemiluminescence intensity maintains at a stable level when the air injection flow rates below 4 L/min, which denotes the heat release rate of lean-premixed flames in limit cycles states and the coupling of self-excited oscillations unperturbed. However, when the air injection flow rate reaches 4 L/min, the amplitude of CH* chemiluminescence intensity increases gradually and finally arrives at a saturation point, the CH* chemiluminescence intensity of flames under control are 2 to 4 times than that of the uncontrolled condition. Dynamic characteristics of the CH* chemiluminescence intensity in Fig. 9 stems from more oxidizer added decreases the equivalence ratio of combustion, and the cross injection makes reactant mixing evenly, thus significantly improves the reaction rate and of lean-premixed flames. At the same time, when the thermoacoustic coupling is broken by annular micropore jets, the process of thermoacoustic instability suppressing reduces or eliminates the kinetic energy of sound pressure oscillation in the combustion chamber, this part of kinetic energy converts into chemical energy and emitted with the form of heat release rate. The variation trend of CH* chemiluminescence intensity under different number of nozzles shows the mode migration trends of jet, but there was no clear trend in the effect of using different number of jets, the mechanism behind the transition of CH* chemiluminescence intensity may be fostered by different density gradient and precessing vortex core across the reaction zone. In addition, annular jets penetrated into the flame not only changes the local equivalence ratio but also alters the flame structure, the outer recirculation zone (ORZ) and the inner recirculation zone (IRZ), annular air injection may lead to different flame-vortex interaction mechanism thus changes the CH* chemiluminescence intensity. Fig. 10 shows the frequency shifting of CH* chemiluminescence intensity during the process of thermoacoustic suppressing. For all types of jet nozzles, the oscillation frequency shifted from 264.5 Hz to approximately 110 Hz as the air injection flow rate increases. When the thermoacoustic instability was fully damped, the mode of CH* chemiluminescence intensity was altered at the same time (In Fig. 9). The shifting frequency varies among different types of jet nozzles, both numbers and inner diameters of jet nozzles affect the initial shifting point of CH* chemiluminescence intensity. In Fig. 10, because the frequency shifting is connected with the process of thermoacoustic damping, mechanisms behind this phenomenon may attribute to the micropore injection that changes the flow field and vortex shedding of the flame, which triggered a new heat release rate oscillation near 110 Hz. Combined variation trend Fig. 9 with Fig. 10, the amplitude of heat release rate increases while the resonance frequency decreases, this strange dynamic characteristic signifies that although thermoacoustic coupling was broken by air injection, the variation tendency of flame heat release rate was different compared with that of sound pressure in the combustion chamber. Heat release rate experienced a more complicated evolution during the process of micropore jets control.
69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123
3.3. Variation of flame length and temperature distribution
124 125
The main purpose of this section is to investigate the variation of flame length and the distribution of temperature under air injection control. In Fig. 6, Fig. 7 and Fig. 8, the parameters of jet nozzles that can achieve the best combustion instability suppression were tested, four types of diameters (Type-A: 0.8 mm, Type-B: 1.0 mm, Type-C: 1.5 mm, Type-D: 2.0 mm) were taken. The number of jet nozzles varied from two, four, six and eight, all the noz-
126 127 128 129 130 131 132
JID:AESCTE
6
AID:105650 /FLA
[m5G; v1.261; Prn:19/12/2019; 14:25] P.6 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
1
67
2
68
3
69
4
70
5
71
6
72
7
73
8
74
9
75
10
76
11
77
12
78
13
79
14
80
15
81
16
82
17
83
18
84
19
85
20
86
21
87
22
88
23
89
24
90
25
91
26
92
27
93
28
94
29
95
30
96
31
97
32
98
33
99
34
100
35
101
36
102
37
103
38
104
39
105
40
106
41
107
42
108
43
109
44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
Fig. 6. Sound pressure amplitude after optimal air injection control (a) 0.8 mm jet nozzles, (b) 1.0 mm jet nozzles, (c) 1.5 mm jet nozzles, (d) 2.0 mm jet nozzles.
zles inserted in the injection section spaced evenly around the circumference. Through the test, as the air injection flow rate grows from 0 to 7 L/min, the combination of four jet nozzles with 1.0 mm inner diameter can achieve a better damping effects than other nozzles. With air injection flow rate adjusted during 0–7 L/min, the corresponding appearance and length of the flame were recorded at a specific point of 0, 1, 2, 3, 4, 5, 6, and 7 L/min, the inner diameter of these jet nozzles are 0.8 mm, 1.0 mm, 1.5 mm, and 2.0 mm. In Fig. 11, lean-premixed flame images during experiments are recorded synchronously using a high-speed CCD camera through a signal synchronizer. The length of the flame shortens as the air injection flow rate increases. At the initial stage, the tails of the flame changes slightly with air injection. When reaches the critical point of 5 L/min in Fig. 6, the length of flame was almost cut in half at an injection rate of 5 L/min, then the length of the flame continues to decrease and reaches a stable saturation level. At the 7 L/min cases, flame tails almost invisible, the appearance of the flame becomes flattened and blue, this was different from the no air injection condition, where the flame is stretched and bright. As the air injection flow rate increases, thermoacoustic in-
stability was suppressed and the flame becomes more stable. For all types of jet nozzles used in Fig. 11, appearance changing process of flame was similar to each other, the combustion noise was eliminated and the flame became stable, which proves the effectiveness of thermoacoustic damping through methods of micropore jets. When annular air jets injected into the core of flame, it alters the local equivalence ratio and hence the heat release dynamics simultaneously. In Fig. 11, the luminosity of uncontrolled flame is intense than that of controlled cases. As luminous flame contains more carbon particles that result in higher radiation heat loss, whereas in a non-luminous flame with less triatomic gas, combustion is spread out uniformly resulting in a lower heat loss [37], the control technique studied promises not only a safety combustion process but also a lower pollutant emission. Fig. 12 shows the flame length before and after control recorded in Fig. 11. With the experimental condition presented in Table 1, the original length of flame without air injection is 105 mm. Fig. 12 compared the length of flame and the air injection flow rate, and the result was a strong negative relationship
110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
JID:AESCTE AID:105650 /FLA
[m5G; v1.261; Prn:19/12/2019; 14:25] P.7 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
7
1
67
2
68
3
69
4
70
5
71
6
72
7
73
8
74
9
75
10
76
11
77
12
78
13
79
14
80
15
81
16
82
17
83 84
18 19 20 21
Fig. 7. Amplitude-damped ratio of sound pressure after control with air injection flow rate range from 0 ∼ 7 L/min, = 0.8 mm, 1.0 mm, 1.5 mm and 2.0 mm.
Fig. 8. Pressure oscillations frequency after air injection control, = 0.8 mm, 1.0 mm, 1.5 mm and 2.0 mm, air flow rate = 5 L/min.
85 86 87
22
88
23
89
24
90
25
91
26
92
27
93
28
94
29
95
30
96
31
97
32
98
33
99
34
100
35
101
36
102
37
103
38
104
39
105
40
106
41
107
42
108
43
109
44
110
45
111
46
112
47
113
48
114
49
115
50
116
51
117
52
118
53
119
54
120
55
121
56
122
57
123
58
124
59
125
60
126
61
127
62
128
63
129
64
130 131
65 66
Fig. 9. CH* chemiluminescence intensity fluctuation after air injection control (a) 0.8 mm jet nozzles, (b) 1.0 mm jet nozzles, (c) 1.5 mm jet nozzles, (d) 2.0 mm jet nozzles.
132
JID:AESCTE
8
AID:105650 /FLA
[m5G; v1.261; Prn:19/12/2019; 14:25] P.8 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
1
67
2
68
3
69
4
70
5
71
6
72
7
73
8
74
9
75
10
76
11
77
12
78
13
79
14
80
15
81
16
82
17
83
18
84
19
85
20
86
21
87
22
88
23
89
24
90
25
91
26
92
27
93
28
94
29
95
30
96
31
97
32
98
33
99
34
100
35
101
36
102
37
103
38
104
39
105
40
106
41
107
42
108 109
43 44
Fig. 10. Frequency shifting of flame CH* chemiluminescence (a) 0.8 mm jet nozzles, (b) 1.0 mm jet nozzles, (c) 1.5 mm jet nozzles, (d) 2.0 mm jet nozzles.
46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
110 111
45
between both variables. For all types of jet nozzles in Fig. 12, the flame length is inversely proportional to air injection flow rate, variation tendency of flame length was similar to each other. According to Fig. 1 and Fig. 2, the air injection holes were drilled at the height of 25 mm, when the air injection flow rate arrives at 7 L/min, flame length nears 25 mm. The temperature distribution changes simultaneously with the flame shortening process. To make an in-depth investigation of this associated relation, the temperature distribution along the radial direction is measured at three axial positions of Z1 = 21 mm, Z2 = 48 mm and Z3 = 94 mm, as indicated by the arrows at the bottom of Fig. 13. With the same experimental conditions in Table 1, the flame temperature is recorded with a thermocouple before and after control, in Fig. 13, there are three gauging points in the combustion chamber. The geometrical benchmark of temperature measuring set at Z = 0 is parallel to the airflow direction, root temperature of flame recorded at Z1 = 21 mm, the core temperature of flame recorded at Z2 = 48 mm, the tail temperature of flame recorded at Z3 = 94 mm. There are 13 gauging points in the radius direction within the combustion chamber, for reconstruction of temperature distribution before or after thermoacoustic control.
The optimal cases of four jet nozzles with inner diameter equals 1.0 mm were chosen to study temperature distribution during thermoacoustic suppressing, air injection flow rate fixed at 5 L/min. In each measurement, the temperature is tested at least five times for error reduction, and the average temperature value is plotted in Fig. 14. The temperature distribution of flame before or after control is presented in the form of adiabatic temperature. Fig. 14 signifies that before air injection control, the temperature distribution shows a typical reversed V shape for each axial position. At Z1 = 21 mm, close to the inner wall of the quartz combustion chamber (radius = 57 mm), the gas temperature is relatively lower; the temperature gradually increases to its peak around the flame front; by approaching the center (radius = 0 mm), the temperature reaches the highest value of 1290 K, the peak temperature of uncontrolled flames at Z2 = 48 mm or Z3 = 94 mm is 1328 K and 1319 K respectively. At Z1 = 21 mm, the temperature is relatively low in the zone of the flame root, they increase significantly at Z2 = 48 mm in the zone of the flame core, by increasing the axial position, the temperature decreases at Z3 = 94 mm owning to heat loss. After air injection control, the temperature distribution at Z1 = 21 mm shows an M shape and
112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
JID:AESCTE AID:105650 /FLA
[m5G; v1.261; Prn:19/12/2019; 14:25] P.9 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
9
1
67
2
68
3
69
4
70
5
71
6
72
7
73
8
74
9
75
10
76
11
77
12
78
13
79
14
80
15
81
16
82
17
83
18
84
19
85
20 21 22
86
Fig. 11. The appearance of flame before and after air injection control with four kinds of jet nozzles, = 0.8 mm, 1.0 mm, 1.5 mm and 2.0 mm, air injection flow rate varies from 0 to 7 L/min, equivalence ratio = 0.90.
87 88
23
89
24
90
25
91
26
92
27
93
28
94
29
95
30
96
31
97
32
98
33
99
34
100
35
101
36
102
37
103
38
104
39
105
40
106 107
41 42 43 44
Fig. 12. Variation tendency of flame length before and after air injection with four jet nozzles, = 0.8 mm, 1.0 mm, 1.5 mm and 2.0 mm, air injection flow rate varies from 0 to 7 L/min, equivalence ratio = 0.90.
108 109 110
45
111
46
112
47
113
48
114
49
115
50
116
51
117
52
118
53
119 120
54 55
Fig. 14. Temperature distribution at the height of Z1 = 21 mm, Z2 = 48 mm, and Z3 = 94 mm. Equivalence ratio = 0.90, number of jet nozzles = 4, = 1.0 mm.
56
124
58 59 60 61 62 63 65 66
122 123
57
64
121
Fig. 13. Temperature measurement points at the height of Z1 = 21 mm, Z2 = 48 mm, and Z3 = 94 mm. Equivalence ratio = 0.90, number of jet nozzles = 4, = 1.0 mm.
the overall temperature increased compared to the uncontrolled one in Fig. 14(a). But at Z2 = 48 mm in Fig. 14(b), the overall temperature declines compared to the uncontrolled one. In Fig. 14(c), the overall temperature at Z3 = 94 mm declines significantly than the uncontrolled one, the reversed V shape was altered to a W shape under conditions of air injection. Dynamic characteristics of temperature distribution in Fig. 14 conforms to the flame length variation in Fig. 12. The mechanism
125 126 127 128 129 130 131 132
JID:AESCTE
AID:105650 /FLA
1 2 3 4 5 6 7 8 9 10 11 12
[m5G; v1.261; Prn:19/12/2019; 14:25] P.10 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
10
behind these characteristics pertains to the flame structure variation and better air-fuel mixing. In Fig. 11, the internal and external recirculation zone of the flame was changed by the annular micropore jets, which improves combustion efficiency and reaction rate with more oxidizer added. In Fig. 14, the strain rate of flame was reduced when air injection flow rose up, the shorter flame length may attribute to the increased reaction rate of turbulent combustion. Then the turbulent swirling combustion velocity of the gaseous mixture significantly increased and finally shortens the tail of flame. At the same time, cross injection of airflow enhances the swirling intensity of the flame and brings fresh air which could reduce the temperature in combustion chamber.
[6]
[7]
[8]
[9]
13 14
4. Conclusion [10]
15 16 17 18
The feasibility of optimal controlling combustion instability by annular micropore jets is demonstrated and the mechanism is investigated.
[11]
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
(1) The results obtained demonstrate that the method can suppress the self-excited thermoacoustic oscillations effectively. Thermoacoustic instability was suppressed and the sound pressure level was reduced to 5% compared to the original uncontrolled cases. The saturation region and transition region of air injection control were also identified for effective control. (2) Frequency shifting of flame heat release rate was observed. During the process of air injection, peak oscillation of heat release rate at 264.5 Hz was eliminated and triggered to a new frequency near 110 Hz. Flame heat release rate was enhanced after air injection, the annular air injection has the potential to improve the combustion efficiency, reduce exhaust emission and attenuate the overheating of the combustor. (3) The shape and temperature distribution of the flame were transformed after annular micropore injection, and the increasing of turbulent combustion velocity is essential behind the mechanism that causes the flame more compact and stable. Future developments will be focused on testing the damping effectiveness with different gas medium and combustor design optimization, the shifting mechanism of flame heat release rate and flame length also needs further study.
[14]
[15]
[16]
[17]
[18]
[19]
Declaration of competing interest
43 44
[13]
[20]
41 42
[12]
[21]
The authors declare that they have no conflicts of interest.
45 46
Acknowledgement
47 48 49
This work was supported by National Science Fund for Distinguished Young Scholars (51825605). [23]
50 51
[22]
References
52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
[1] Can Ruan, Feier Chen, Weiwei Cai, Yong Qian, Liang Yu, Xingcai Lu, Principles of non-intrusive diagnostic techniques and their applications for fundamental studies of combustion instabilities in gas turbine combustors: a brief review, Aerosp. Sci. Technol. 84 (2019) 585–603, https://doi.org/10.1016/j.ast.2018.10. 002. [2] Dan Zhao, X.Y. Li, A review of acoustic dampers applied to combustion chambers in aerospace industry, Prog. Aerosp. Sci. 74 (2015) 114–130, https:// doi.org/10.1016/j.paerosci.2014.12.003. [3] Dan Zhao, Zhengli Lu, He Zhao, X.Y. Li, Bing Wang, Peijin Liu, A review of active control approaches in stabilizing combustion systems in aerospace industry, Prog. Aerosp. Sci. 97 (2018) 35–60, https://doi.org/10.1016/j.paerosci.2018.01. 002. [4] Ying Huang, Vigor Yang, Dynamics and stability of lean-premixed swirlstabilized combustion, Prog. Energy Combust. Sci. 35 (2009) 293–364, https:// doi.org/10.1016/j.pecs.2009.01.002. [5] Feier Chen, Can Ruan, Tao Yu, Weiwei Cai, Yebing Mao, Xingcai Lu, Effects of fuel variation and inlet air temperature on combustion stability in a gas turbine
[24]
[25]
[26]
[27]
[28]
model combustor, Aerosp. Sci. Technol. 92 (2019) 126–138, https://doi.org/10. 1016/j.ast.2019.05.052. M. Stöhr, R. Sadanandan, W. Meier, Experimental study of unsteady flame structures of an oscillating swirl flame in a gas turbine model combustor, Proc. Combust. Inst. 32 (2009) 2925–2932, https://doi.org/10.1016/j.proci.2008. 05.086. Oliver Schulz, Nicolas Noiray, Autoignition flame dynamics in sequential combustors, Combust. Flame 192 (2018) 86–100, https://doi.org/10.1016/j. combustflame.2018.01.046. Oliver Schulz, Nicolas Noiray, Combustion regimes in sequential combustors: flame propagation and autoignition at elevated temperature and pressure, Combust. Flame 205 (2019) 253–268, https://doi.org/10.1016/j.combustflame. 2019.03.014. Hao Zan, Weixing Zhou, Xuefeng Xiao, Long Lin, Junlong Zhang, Haowei Li, Recurrence network analysis for uncovering dynamic transition of thermoacoustic instability of supercritical hydrocarbon fuel flow, Aerosp. Sci. Technol. 85 (2019) 1–12, https://doi.org/10.1016/j.ast.2018.11.040. Jaime Rubio-Hervas, Dan Zhao, Mahmut Reyhanoglu, Nonlinear feedback control of self-sustained thermoacoustic oscillations, Aerosp. Sci. Technol. 41 (2015) 209–215, https://doi.org/10.1016/j.ast.2014.12.026. Li Lei, Dan Zhao, Prediction of stability behaviors of longitudinal and circumferential eigenmodes in a choked thermoacoustic combustor, Aerosp. Sci. Technol. 46 (2015) 12–21, https://doi.org/10.1016/j.ast.2015.06.024. Li Lei, Dan Zhao, Xiaofeng Sun, Nonorthogonality analysis of acoustics and vorticity modes: should thermoacoustic energy norm be time-invariant?, Aerosp. Sci. Technol. 77 (2018) 149–155, https://doi.org/10.1016/j.ast.2018.02.036. Xinyan Li, Dan Zhao, Xinglin Yang, Huabing Wen, Xiao Jin, Shen Li, He Zhao, Changqing Xie, Haili Liu, Transient growth of acoustical energy associated with mitigating thermoacoustic oscillations, Appl. Energy 169 (2016) 481–490, https://doi.org/10.1016/j.apenergy.2016.01.060. Dan Zhao, Transient growth of flow disturbances in triggering a Rijke tube combustion instability, Combust. Flame 159 (2012) 2126–2137, https://doi.org/ 10.1016/j.combustflame.2012.02.002. Xinyan Li, Dan Zhao, Xinglin Yang, Shuhui Wang, Unity maximum transient energy growth of heat-driven acoustic oscillations, Energy Convers. Manag. 116 (2016) 1–10, https://doi.org/10.1016/j.enconman.2016.02.062. Dan Zhao, Mahmut Reyhanoglu, Feedback control of acoustic disturbance transient growth in triggering thermoacoustic instability, J. Sound Vib. 333 (2014) 3639–3656, https://doi.org/10.1016/j.jsv.2014.04.015. Dan Zhao, X.Y. Li, Minimizing transient energy growth of nonlinear thermoacoustic oscillations, Int. J. Heat Mass Transf. 81 (2015) 188–197, https:// doi.org/10.1016/j.ijheatmasstransfer.2014.10.023. Maria L. Frezzotti, Francesco Nasuti, Cheng Huang, Charles L. Merkle, William E. Anderson, Quasi-1D modeling of heat release for the study of longitudinal combustion instability, Aerosp. Sci. Technol. 75 (2018) 261–270, https://doi.org/ 10.1016/j.ast.2018.02.001. Dan Zhao, C. Ji, X. Li, S. Li, Mitigation of premixed flame-sustained thermoacoustic oscillations using an electrical heater, Int. J. Heat Mass Transf. 86 (2015) 309–318, https://doi.org/10.1016/j.ijheatmasstransfer.2015.03.012. Zhiguo Zhang, Dan Zhao, Nuomin Han, Shuhui Wang, Junwei Li, Control of combustion instability with a tunable Helmholtz resonator, Aerosp. Sci. Technol. 41 (2015) 55–62, https://doi.org/10.1016/j.ast.2014.12.011. Seonghwi Jo, Yunho Choi, Hong Jip Kim, Evaluation of the damping capacity according to the geometric and the number of resonator with thermal environment using a Rijke tube, Aerosp. Sci. Technol. 88 (2019) 1–8, https:// doi.org/10.1016/j.ast.2019.02.040. Seungtaek Oh, Hyunggeun Ji, Yongmo Kim, FDF-based combustion instability analysis for stabilization effects of a slotted plate in a multiple flame combustor, Aerosp. Sci. Technol. 70 (2017) 95–107, https://doi.org/10.1016/j.ast.2017. 07.045. Yu Guan, Vikrant Gupta, Karthik Kashinath, Larry K.B. Li, Open-loop control of periodic thermoacoustic oscillations: experiments and low-order modelling in a synchronization framework, Proc. Combust. Inst. 37 (2019) 5315–5323, https://doi.org/10.1016/j.proci.2018.07.077. Yu Guan, Wei He, Meenatchidevi Murugesan, Qiang Li, Peijin Liu, Larry K.B. Li, Control of self-excited thermoacoustic oscillations using transient forcing, hysteresis and mode switching, Combust. Flame 202 (2019) 262–275, https:// doi.org/10.1016/j.combustflame.2019.01.013. H. Murat Altay, Duane E. Hudgins, Raymond L. Speth, Anuradha M. Annaswamy, Ahmed F. Ghoniem, Mitigation of thermoacoustic instability utilizing steady air injection near the flame anchoring zone, Combust. Flame 157 (2010) 686–700, https://doi.org/10.1016/j.combustflame.2010.01.012. M. Altay, R. Speth, D. Snarheim, D. Hudgins, A. Ghoniem, A. Annaswamy, Impact on microjet actuation on stability of a backward-facing step combustor, in: AIAA Aerospace Sciences Meeting & Exhibit, vol. 563, 2007, pp. 1–7. Jong Ho Uhm, Sumanta Acharya, Control of combustion instability with a highmomentum air-jet, Combust. Flame 139 (2004) 106–125, https://doi.org/10. 1016/j.combustflame.2004.07.007. Jong Ho Uhm, Sumanta Acharya, Low-bandwidth open-loop control of combustion instability, Combust. Flame 142 (2005) 348–363, https://doi.org/10.1016/j. combustflame.2005.03.015.
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
JID:AESCTE AID:105650 /FLA
[m5G; v1.261; Prn:19/12/2019; 14:25] P.11 (1-11)
H. Zhou et al. / Aerospace Science and Technology ••• (••••) ••••••
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
[29] Jong Ho Uhm, Sumanta Acharya, Role of low-bandwidth open-loop control of combustion instability using a high-momentum air jet—mechanistic details, Combust. Flame 147 (2006) 22–31, https://doi.org/10.1016/j.combustflame. 2006.08.002. [30] Ahmed F. Ghoniem, Anuradha Annaswamy, Sungbae Park, Ziaieh C. Sobhani, Stability and emissions control using air injection and H2 addition in premixed combustion, Proc. Combust. Inst. 30 (2005) 1765–1773, https://doi.org/10.1016/ j.proci.2004.08.175. [31] Z. Labry, S. Shanbhogue, R. Speth, A. Ghoniem, Instability suppression in a swirl-stabilized combustor using microjet air injection, in: AIAA Aerospace Sciences Meeting Including the New Horizons Forum & Aerospace Exposition, vol. 1524, 2010, pp. 1–10. [32] Zachary A. Labry, Santosh J. Shanbhogue, Raymond L. Speth, Ahmed F. Ghoniem, Flow structures in a lean-premixed swirl-stabilized combustor with microjet air injection, Proc. Combust. Inst. 33 (2011) 1575–1581, https://doi. org/10.1016/j.proci.2010.06.092. [33] Z. Labry, S. Shanbhogue, A. Ghoniem, Microjet injection strategies for mitigating dynamics in a lean premixed swirl-stabilized combustor, in: 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, vol. 515, 2011, pp. 1–14. [34] Hao Zhou, Qi Tang, Tao Ren, Guoneng Li, Kefa Cen, Control of thermoacoustic instabilities by CO2 and N2 jet in cross-flow, Appl. Therm. Eng. 36 (2012) 353–359, https://doi.org/10.1016/j.applthermaleng.2011.10.048. [35] H. Zhou, Y. Huang, S. Meng, Response of non-premixed swirl-stabilized flames to acoustic excitation and jet in cross-flow perturbations, Exp. Therm. Fluid Sci. 82 (2017) 124–135, https://doi.org/10.1016/j.expthermflusci.2016.11.007.
11
[36] N.N. Deshmukh, S. Sharma, Experiments on heat content inside a Rijke tube with suppression of thermo-acoustics instability, Int. J. Spray Combust. Dyn. 9 (2016) 85–101, https://doi.org/10.1177/1756827716655007. [37] Nilaj N. Deshmukh, S.D. Sharma, Suppression of thermo-acoustic instability using air injection in horizontal Rijke tube, J. Energy Inst. 90 (2017) 485–495, https://doi.org/10.1016/j.joei.2016.03.001. [38] Séverine Barbosa, Marta de La Cruz Garcia, Sébastien Ducruix, Bernard Labegorre, François Lacas, Control of combustion instabilities by local injection of hydrogen, Proc. Combust. Inst. 31 (2007) 3207–3214, https://doi.org/ 10.1016/j.proci.2006.07.085. [39] Shigeru Tachibana, Laurent Zimmer, Yoji Kurosawa, Kazuo Suzuki, Active control of combustion oscillations in a lean premixed combustor by secondary fuel injection coupling with chemiluminescence imaging technique, Proc. Combust. Inst. 31 (2007) 3225–3233, https://doi.org/10.1016/j.proci.2006.08.037. [40] Gyung-Min Choi, Mamoru Tanahashi, Toshio Miyauchi, Control of oscillating combustion and noise based on local flame structure, Proc. Combust. Inst. 30 (2005) 1807–1814, https://doi.org/10.1016/j.proci.2004.08.249. [41] G. Strickland, J. Gustavsson, J. Solomon, F. Alvi, Implementing resonant enhanced pulsed micro-actuators for the control of supersonic impinging jets, in: AIAA Aerospace Sciences Meeting Including the New Horizons Forum & Aerospace Exposition, vol. 65, 2012, pp. 1–15. [42] J. Choi, A.M. Annaswamy, H. Lou, F.S. Alvi, Active control of supersonic impingement tones using steady and pulsed microjets, Exp. Fluids 41 (2006) 841–855, https://doi.org/10.1007/s00348-006-0189-7.
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88
23
89
24
90
25
91
26
92
27
93
28
94
29
95
30
96
31
97
32
98
33
99
34
100
35
101
36
102
37
103
38
104
39
105
40
106
41
107
42
108
43
109
44
110
45
111
46
112
47
113
48
114
49
115
50
116
51
117
52
118
53
119
54
120
55
121
56
122
57
123
58
124
59
125
60
126
61
127
62
128
63
129
64
130
65
131
66
132