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Experimental investigation on the performance of a multi-strut mixing-enhancement ejector
Applied Thermal Engineering 154 (2019) 650–656
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Research Paper
Experimental investigation on the performance of a multi-strut mixingenhancement ejector
T
Wei Ye, Wanwu Xu , Ping Li, Fuqiang Zhang, Jiaqi Zhang ⁎
Science and Technology on Scramjet Laboratory, National University of Defense Technology, Changsha 410073, China
HIGHLIGHTS
2D ejector with multi-strut is developed for high operational performance. • AThenovel divide the flows into multiple jets, and the mixing area increases notably. • The struts region is P /P ≥ 36.96, the hysteresis region is P /P ∈ [31.07, 36.96]. • The self-starting minimum suction pressure P /P is 0.016. • A typical point is ER = 0.096, whilst CR = 7.5 in sub-critical mode. • 01
a
01
s
a
a
ARTICLE INFO
ABSTRACT
Keywords: 2D supersonic ejector Multiple nozzles Mixing enhancement Starting characteristics Operational performance
A novel design for multi-strut mixing-enhancement ejector (MSE) focuses on the improvement of entrainment ratio (ER) and compression ratio (CR). MSE is a 2D geometric ejector, which has multiple 2D struts and divides the primary and secondary flows into multiple sub-jets. The number of mixing layer and the mixing area increase to achieve mixing enhancement. A series of cold flow tests is conducted to explore the starting characteristics and operational mode performance of the ejector. An auxiliary method is developed. In this method, the P01 increase to the self-starting region in initial stage and then decreases to the hysteresis region. For this ejector, the o / Pa is 36.96. The self-starting region is P01/Pa ≥ 36.96, whilst the hysteresis region optimum starting pressure P01 of P01/Pa is at the range of 31.07–36.96. The ejector has excellent suction and ejection abilities. That is, the maximum suction pressure Ps/Pa = 0.016, whilst a typical point is ER = 0.096, CR = 7.5 in sub-critical mode.
1. Introduction Supersonic ejectors are simple gas-dynamic devices that utilise the augmentation of momentum and energy from a supersonic primary jet to entrain and pump a secondary flow [1]. To date, supersonic ejectors are extensively used in refrigerant systems [2], high altitude simulation facilities [3], rocket-based combined cycles [4] and pressure recovery systems of supersonic chemical lasers [5]. In recent years, a few studies were put forward to investigate the mixing-enhancement technologies on increasing the secondary flow entrainment and the total pressure recovery. The turbulence transport in the mixing layer between the primary and secondary flows is the main mechanism of the momentum and energy augmentations in the secondary flow. Therefore, mixing enhancement in the mixing layer between the primary and secondary flows is an effective method to improve the performance of supersonic ejectors.
⁎
Mixing enhancement technologies could be categorised as active control, passive control and shock wave induced mixing [6]. Active control techniques need some flow control facilities to add disturbance in the position of upstream, which can promote the flow unsteadiness and the rolling up of large scale K-H vortices. Passive flow control means the installation of some stationary devices to change the shear layer stability characteristics. So far, there are few engineering applications of active control techniques on ejector performance argument [7]. The existing studies on passive control technologies have concentrated on the method of utilising different nozzle geometries to promote flow instabilities, thereby maximising the pressure recovery in supersonic ejectors. Srisha Rao et al. [8,9] compared the mixing abilities between elliptic sharp tipped shallow lobed, bevelled and chevron nozzles. Results showed that both different geometry nozzles could achieve the effect of mixing enhancement, and a loss of compression ratio (CR) also occurred simultaneously. Matthew J. Opgenorth et al.
Corresponding author. E-mail address: [email protected] (W. Xu).
https://doi.org/10.1016/j.applthermaleng.2019.03.133 Received 15 October 2018; Received in revised form 27 February 2019; Accepted 27 March 2019 Available online 28 March 2019 1359-4311/ © 2019 Elsevier Ltd. All rights reserved.
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Nomenclature m P Ma T W H N X L A
D ER CR SPR
Subscripts
mass flow rate, kg·s−1 pressure, Pa Mach number temperature, K width, mm height, mm strut number axis distance, mm length, mm cross-section area, mm2 contraction semi-angle, ° expansion semi-angle, ° struts chocking ratio hydraulic diameter, mm entrainment ratio, m2/m1 compression ratio, Pa/P02 Stagnation pressure ratio, P01/P02
0 1 2 s a c m i t o v
stagnation condition primary flow secondary flow suction chamber atmospheric state secondary flow sub-channel constant area mixer diffuser inlet second throat diffuser outlet Venturi tube inlet
Superscripts h o
minimum hysteresis pressure optimum starting pressure
the performance. Although the studies on the 2D geometric multiplenozzle supersonic ejector are limited, the ejection principle has been validated in supersonic chemical laser facilities [17–20]. The 2D slitnozzle banks were used to increase gas mixing and accelerate lowmomentum gas flows to reach the goal of high chemical efficiency. Moreover, T. S. Lund et al. [21] developed a viscous − inviscid interaction methodology to evaluate the performance of the 2D incompressible dual-jet ejectors. To date, the potential better performance of the 2D multi-jet supersonic ejector has not been explored. The present research focuses on a novel design for 2D multi-strut mixing-enhancement ejector (MSE), and the cold experimental studies are conducted to explore the starting characteristics and operational mode performance. The MSE contains multiple 2D struts. These struts divide the primary and secondary flows into multiple small jets, thereby the mixing layer number and mixing areas amongst multiple small jets are increased. Hence, mixing enhancement is achieved to improve the ejection performance. The starting behaviours of MSE are analysed in detail in the self-starting and hysteresis regions. Finally, the parameters of primary and secondary flows and ejection performance are conducted to evaluate the engineering value.
[10] compared the maximum pressure recovery abilities of supersonic ejectors, which had circular nozzles, by adding different numbers of lobes. The study suggested that the optimum perimeter value of the lobe would be approximately 30 mm, which was determined using the designed profiles of the constant rate of momentum change method (CRMC) The maximum pressure recovery (or CR) for these lobed nozzle ejectors was the value of 6.4, whilst the corresponding entrainment ratio (ER) was the value of 0.05. The different geometries are applied to the single-nozzle ejector and are optimised on the basis of the axisymmetric nozzle. This method enhances the mixing between the primary and secondary flows. Additionally, the increase in the simultaneous shock wave losses causes flow instabilities, thereby inevitably decreasing the ability of pressure recovery. The other method for mixing enhancement would be to increase the mixing areas between the primary and secondary flows by applying multiple nozzles. Several numerical and experimental studies have been conducted to compare the incompressible jet pump efficiency for single nozzle with that for five nozzles of Tadashi Narabayashi et al. [11]. These studies showed that the five-nozzle jet pump did not show any advantages compared to the single-nozzle pump. A series of studies were conducted to evaluate the performance of ejectors that contain a 2D strut with rectangular shrouds, which imbed single or dual asymmetric nozzles in the strut. The results showed that the increasing number of nozzles can decrease the mixing length between the primary and secondary flows [12–14]. Jiping Wu [15] studied the unstarting problems in the ejectors with multiple axisymmetric nozzle and proposed to add a certain mass rate of secondary flow to decrease the optimum starting pressure [16]. The operational mode performance was studied in the ejectors with multiple axisymmetric and notched nozzles placed in several layers along the peripheral direction [15]. The results showed that an appropriate number of nozzles could improve the ejection performance and decrease the scale of ejectors. However, intensity disturbance amongst jets from too many nozzles, and would decrease the ejection performance. The majority of the studies had concentrated on the ejectors with multiple axisymmetric nozzles with axisymmetric shrouds. However, this sort of ejector could not obtain uniform jet distribution because of interactions among jets from multiple nozzles, which restricts the further improvement of the operational performance. This problem could be solved by a novel geometric structure, which is the multiple-nozzle supersonic ejector with rectangular profile shrouds. This type of ejector can achieve the uniform distribution of jets and increase the mixing areas and decrease shock wave losses simultaneously. Therefore, it is supported that the 2D multiple-nozzle supersonic ejector has a few potential advantages on
2. Experimental setup 2.1. Experimental system The schematic MSE experimental system can be shown in Fig. 1. High-pressure air and nitrogen tanks are used as gas sources of the primary and secondary flows respectively, to maintain the primary and secondary flow supplies independently. The air supply subsystem comprises a ball valve, a pressure regulator with a rated mass flow of 20 kg/s, the DN100 main pipeline, a orifice plate flow meter, two DN40 globe valves and DN20 throttle orifice installed in the back of globe valve 2 to control the total pressure of the primary flow. The nitrogen supply subsystem comprises a ball valve, pressure regulator with a rated mass flow of 10 kg/s, DN20 main pipeline, DN20 globe valve, venturi tube with throat diameter of 10 mm, transition section and suction chamber. The mass rate range of the primary flow is 0–10 kg/s, whilst the mass rate range of the secondary flow is 0–1.2 kg/s. In the starting processes of the experiments, both globe valves in the air supply subsystem are opened to ensure that the total pressure of the primary flow is above the optimum starting pressure of the ejector, and then the ejector achieves steady starting. In order to maintain the ejector starting at low pressure conditions, of which pressures are lower 651
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Primary-flow inlets
Secondary-flow sub-channels
2D nozzles
Primary-flow inlet chamber Secondary-flow inlet H
W Nozzle-surge chambers
Fig. 3. Sketch of MSE.
Fig. 1. Schematic of the MSE experimental system.
than the optimum starting pressure. The globe valve 2 is closed to decrease the total pressure of the primary flow in the starting processes, and a valve having a DN20 throttle orifice is installed behind valve 2. The secondary flow path comprises venturi tube, several multi-stage rectifiers, transition section and suction chamber. The section view can be seen in Fig. 2. The multi-stage rectifiers contain 2-layer tiny-hole arrays and a grill array. The holes with the diameters are 5 and 10 mm respectively, and the grill with the thickness is 8 mm. They are used to make the secondary flow evenly distributed in the suction chamber.
Fig. 4. MSE facility.
the constant area mixer (Lm/W) is 1.875. Two sides of the convergent section contract symmetrically along the width direction. The contraction semi-angle θ is 2.5°, whilst the contraction ratio (At/Ai) is 0.7. The ratio of the second throat length Lt to the hydraulic diameter Dt is 6.3. The divergent section is a four-sided expansion geometry. The expansion semi-angle is 2°, whilst the expansion ratio (Ao/At) is 2. In this study, x, y and z stand for the streamwise, transverse and vertical coordinates.
2.2. Ejector structure description The sketch of MSE is shown in Fig. 3. The ejector contains two primary flow inlets, one primary flow inlet chamber, four struts, one secondary flow inlet and five secondary flow sub-channels. Each strut contains a wedge in the leading end, nozzle surge chamber and 2D supersonic nozzle. The primary flow crosses the primary flow inlets into the primary inlet chamber and passes through the nozzle surge chambers. Thereafter, 2D nozzles come into four supersonic jets. The secondary flow crosses the secondary flow inlet into the ejector and enters the secondary flow sub-channels divided into five subsonic jets. Multiple supersonic and subsonic jets are mixing and pressure recovery in supersonic diffuser. The MSE facility is shown in Fig. 4. The supersonic diffuser is a rectangular cross-section diffuser (see Fig. 5 for the schematic), which comprises a constant area mixer, convergent section, second throat and divergent section. The ejector and diffuser geometric parameters are shown in Table 1, in which the secondary flow inlet width W is 280 mm, height H is 120 mm, the struts number N is 4 and the struts chocking ratio ψ (i.e., ratio of the struts’ total thickness to the secondary flow inlet width) is 0.314. The length of
Secondary-flow inlet
Venturi tube
2.3. Measurement methods and uncertain analysis The pressure, mass flow rate and temperature of MSE were measured in the experiments. The test equipment, test positions, measurement methods and uncertain analysis would be described as follows. (1) Pressure measurements: The absolute pressures of the MSE experimental system are measured using a few test facilities. The total pressures of the primary flow and secondary flow in the venturi tube inlet are higher than the ambient pressure, so the PT301 was used to measure these values. The range of the used transducer is 0–10 MPa, whilst the accuracy is 0.5% FS. The static pressures of the suction
Rectifiers
Transition section
Primary-flow inlet
Suction chamber
Fig. 2. Section view of the secondary flowpath. 652
Ejector
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Fig. 5. Schematic of the rectangular cross-section supersonic diffuser.
total pressure of secondary flow in the venturi tube inlet; At is the throat area; TOV is the total temperature of secondary flow in the venturi tube inlet, which is equal to the ambient temperature; is the specific heat ratio of the secondary flow; R is the gas constant of the secondary flow. It is assumed that the secondary flow is uniformity before entering into the MSE secondary-flow inlet. The Mach number of the flow in the MSE secondary-flow inlet can be obtained from the equation:
Table 1 Parameters of the geometric ejector and diffuser. Parameter
Value
Parameter
Value
W H N
280 mm 120 mm 4 0.314 1.875
At/Ai
0.7 2.5° 6.3 2° 2
Lm/W
Lt/Dt Ao/At
Ma2 =
P02 = P2 1 +
R
1) Ma22
/(
1)
3.1. Starting characteristics The total pressures of the primary and secondary flows were controlled by the pressure regulators in the gas supply subsystem, whereas the primary flow is the only gas applied to obtain the starting characteristics of MSE. The starting processes of MSE have three levels similar to a traditional ejector: A (nozzles and diffuser are unstarted); B (nozzles are started, whilst diffuser is unstarted) and C (nozzles are started, whilst diffuser is started). However, the ejector in the processes of A and B are unstarted, whilst that in the process of C is started [22]. Fig. 7 shows the starting characteristics of the ejector, in which the total temperature of the primary flow is 266.4 K. In the figure, the total pressure P01/Pa in primary flow designates the average value of the bottom wall parameters at the locations of the four-nozzle inlets, and the evacuation performance Ps/Pa denotes the suction chamber pressure. The experiment results in the unstarted and started processes of the ejector can be correlated well by linear fit curves. The optimum o / Pa of MSE was evaluated to be 36.96, which is starting pressure P01 corresponding to the suction chamber pressure of 0.029. The minimum h /Pa in the hysteresis region is 31.07, whilst the starting pressure P01
The inlet parameters of primary and secondary flows are significant arguments to evaluate the operational mode performance of MSE. The inlet parameters (P01, T01, m1) of primary flow are measured by a few test facilities, such as absolute pressure and temperature transducers, and so on. Some of the inlet parameters of secondary flow are calculated by some measured pressure values. The functions were shown as follows: The mass rate of the secondary flow is obtained from the equation:
2 +1
1 ( 2
3. Results and discussions
2.4. Inlet parameters of the MSE
Cd P0V At T0V
RT0V
where m2 is the mass rate of the secondary flow; A is the flow-path areas of the secondary flow inlet cross-section; P2 is the static pressure of the secondary flow inlet, and it is equal to the top wall pressure of the secondary-flow inlet. The total pressure of the secondary flow in the secondary-flow inlet is obtained from the equation:
chamber and supersonic diffuser are lower than ambient pressure, so the test devices are electronic pressure scanners (Pressure System Inc 9116). The range is 103 KPa, whilst the accuracy is 0.5% FS. The initial value of the scanners should be manually entered by atmosphere pressure. The atmosphere pressure gauge is used to measure such pressure, which ranges from 0.3 KPa to 110 KPa, whilst the accuracy is 0.5% FS. The small range absolute pressure transducer and scanner channel are used to measure the suction chamber pressure at the same point to calibrate the scanner accuracy. The type of the small range absolute pressure transducer used is PT301, which ranges from 0 to 20 KPa, whilst the accuracy is 0.5% FS. The calibration results are shown in Table 2. The errors are the value differences between the transducer and scanner measurements. These errors range from −2.25% to 3.6%. (2) Mass flow rate measurements: The mass rate of the primary flow m1 is measured using an orifice plate flow meter, with an uncertainty of ± 5.5%. The mass rate of the secondary flow is measured using a venturi tube, with an uncertainty of ± 3%. The venturi tube has an axisymmetric structure, with throat diameter of 10 mm, and with both inlet and outlet diameters of 20 mm. The schematic of the venturi tube can be seen in Fig. 6. (3) Temperature measurements: the temperatures of the primary flow inlet, suction and venturi tube inlet chambers are measured using Pt100 temperature transducers, which range from 223 K to 323 K, whilst the accuracy is 0.2% FS.
m2 =
m2 RT0V · / A P2
Table 2 Comparison of the electronic pressure scanner and transducer.
+1 1
where Cd is the flow coefficient, and it is a constant value; P0V is the 653
No
Scanner (kPa)
Transducer (kPa)
Error (kPa)
1 2 3 4
1.73 1.59 8.67 8.95
1.67 1.56 8.87 8.87
+0.06 +0.03 −0.2 −0.04
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P0V, T0V
the condition of total pressure of primary flow in hysteresis region, the starting location of shock train in the secondary throat is further than the other condition. The influence of the starting characteristics in various primary flow total temperatures (T01) is observed in the experiments. Table 3 compares the different starting characteristics in T01. As T01 increases, the optimum starting pressure decreases. When T01 in cases 1 and 2 increases by 30 K, the optimum starting pressure P01/Pa decreases by 2.3. The evacuation performance augments with the increase of T01. When T01 is 266.4 K, the primary flow pressure P01/Pa is 31.07 in the hysteresis region, whilst the suction pressure Ps/Pa is 0.023. When T01 is 291.4 K, the primary flow temperature P01/Pa is 32.24 in the hysteresis region, whilst the minimum suction pressure is 0.016.
Fig. 6. Schematic of the venturi tube.
3.2. Operational mode performance analysis The same method as the starting characteristics experiments was used to maintain the ejector starting in the hysteresis region. After that, the globe valve in the nitrogen supply subsystem would be opened to feed the secondary flow. In the present study, the mass rate of the secondary flow m2, was controlled by Pov in the sub-critical mode of the ejector. Table 4 shows the parameters describing the operational mode performance in various experimental conditions. Amongst the experiments, the ambient temperature is about 286 K, and the parameters of the primary flow remain in a same state (m1 = 4.98 kg/s, P01/ Pa = 31.59). As shown in the table, in the sub-critical mode, as the secondary flow mass rate m2 increases, the P2/Pa, Ma2 and ER increase, however, SPR and CR decrease correspondingly. The static pressures of the secondary flow (P2/Pa) are at the range of 0.044–0.162, and the inlet Mach number of the secondary flow (Ma2) are at the range of 0–0.4. The ejector has a high CR (CR ≥ 7.5) when ER ≤ 0.10. The operational mode performance parameters of the MSE are compared with the referenced ejector (REF) in [10] as illustrated in Fig. 10. REF is a three-lobed constant pressure method-designed supersonic ejector which has considerable maximum pressure recovery abilities compared with other geometric ejectors. Although REF has a higher performance in the sub-critical mode (see Fig. 10), MSE has better entrainment and pressure recovery abilities than the former at the conditions of CR > 6. Although the geometry of MSE is a standard 2D structure, the internal flow field is a quasi-2D structure. Fig. 11 shows pressure distributions on the different side-walls in the supersonic diffuser when ER = 0.124. All the sensors were set in the middle of each wall. Pressure gradient along the width-wise direction generates the internal main-flow expansion in the middle of the constant area mixer. Therefore, the pressures on both top and bottom walls of the constant area mixer decrease along the x-axis direction. The interaction of the shock
Fig. 7. Starting characteristics of the MSE (T01 = 266.4 K).
corresponding suction chamber pressure is 0.023, which is the maximum evacuation performance. The minimum starting pressure in the o h o P01 )/ P01 hysteresis region (P01 is 15.9% lower than the optimum starting pressure. At this temperature condition, the self-starting region is P01/Pa ≥ 36.96, whilst the hysteresis region of P01/Pa is at the range of 31.07–36.96. The process of C can be divided into self-starting and hysteresis regions. The dividing point of these two regions is the optimum starting o pressure P01 . In the self-starting region, the ejector can be started ino dependently when P01 would be higher than P01 . On contrary, the ejector cannot be started independently in the hysteresis region when o P01 would be lower than P01 . In order of realize the MSE starting in the hysteresis region, some auxiliary methods are needed to help the MSE achieves starting. An effective method is that increasing the value of P01/Pa in the self-starting region, then the MSE achieves steady selfstarting, and reducing the P01/Pa to the hysteresis region in the next step, and then the ejector keeps a smooth starting status. A typical starting case by utilizing this method can be shown in Fig. 8. In the starting case, both globe value 1 and 2 in the primary supply subsystem are opened simultaneously to allow the P01/Pa to reach the self-starting region (P01/Pa = 39.5) to start the ejector. When the 4.3 s later, the glove value 2 is closed to reduce the P01/Pa to the hysteresis region (P01/Pa = 33). In this region, the ejector remains a smooth starting status. Furthermore, the evacuation performance in hysteresis region is better than in self-starting region. The pressure distributions on the bottom wall of the supersonic diffuser in self-starting and hysteresis regions can be seen in Fig. 9. Comparison shows that the wall pressure distributions in the constant area mixer and convergent section, it can be seen that the values are similar and have the same variation regularity in the two regions. Whereas, the comparison of the wall pressure distributions in the secondary throat and divergent section, shows that the values are higher in self-starting region than those in hysteresis region. This indicates that at
Fig. 8. Pressure history of the MSE during a typical starting case. 654
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Static pressure, P/P a
0.9 0.8 0.7
top wall bottom wall front wall back wall
0.6 0.5 0.4 0.3 0.2 0.1 0.0
0
1
23
4
56
7
8
9
10
11
12
X-axis distance, X/W Fig. 9. Wall pressure comparison of the supersonic diffuser in self-starting and hysteresis regions.
Fig. 11. Different side wall pressure distributions of the supersonic diffuser in ER = 0.124.
Table 3 Comparison of the starting characteristics in T01. Cases
T01 (K)
P01/Pa
Ps/Pa
Remarks
1 2
266.4 295.9
36.96 34.66
0.029 0.025
Optimum starting pressure
3 4
266.4 291.4
31.07 32.24
0.023 0.016
Minimum suction pressure
pressure curves depicting the top and bottom walls almost coincide with each other precisely. On the other hand, the pressure curves of the front and back walls coincide well in both the constant area mixer and convergent section. The pressure curve of the back wall is substantially higher than that of the other side walls in the back end of the second throat and divergent section, which is caused by unevenness of the flow field structure. Leaded from the instability of the pseudo-shock. 4. Conclusion
Table 4 Operational mode performance parameters in various experimental conditions. Cases
P01/Pa
m1
m2
P2/Pa
P02/Pa
Ma2
SPR
ER
CR
5 6 7 8 9 10
31.59 31.59 31.59 31.59 31.59 31.59
4.98 4.98 4.98 4.98 4.98 4.98
0.041 0.183 0.332 0.478 0.616 0.768
0.044 0.086 0.109 0.127 0.144 0.162
0.044 0.087 0.112 0.134 0.154 0.175
0.07 0.15 0.22 0.27 0.31 0.34
717.95 363.10 282.05 235.75 205.13 180.51
0.008 0.037 0.067 0.096 0.124 0.154
22.8 11.5 8.9 7.5 6.5 5.7
This research focuses on the development of a novel 2D geometric mixing-enhancement ejector and the validation of its operational performance in sub-critical mode. The ejector has a typical 2D geometry and covers four 2D struts in a rectangular cross-section. Each strut contains a wedge at the leading end, nozzle-surge chamber and 2D nozzle. The multiple 2D struts divide the primary and secondary flows into multiple sub-jets and increase the mixing area to achieve the mixing enhancement. A rectangular cross-section supersonic diffuser is installed at the ejector outlet. This diffuser comprises a constant area mixer, convergent section, second throat and divergent section. The starting characteristics and operational mode performance of the mixing-enhancement ejector are explored by a series of cold experiments. The main results and conclusions are summarised as follows.
• The starting mode can be divided into self-starting and hysteresis
• •
Fig. 10. Comparison of MSE’s operational mode performance with REF in [10]
•
and expansion waves in the mixer and convergent section causes the wall pressures to fluctuate along the x-axis direction. The pseudo-shock structure in the back end of the second throat and divergent section pressures and increases the pressure oscillation in the throat, which causes the uneven of the pressure along the x-axis direction. The
• 655
regions. When the P01 is in the self-starting region, the MSE can start independently. Whereas, when the P01 is in the hysteresis region, the MSE cannot start independently. Thus, some auxiliary methods are needed to help the MSE achieves starting. In this paper, increasing the P01 to the self-starting region in initial stage and then reducing the P01 to the hysteresis region is an effective method. The dividing point of the two regions is the optimum starting pressure o P01 . At the temperature condition of T01 = 266.4 K, The optimum o / Pa is 36.96. Moreover, at this temperature starting pressure P01 condition, the self-starting region is P01/Pa ≥ 36.96, whilst the hysteresis region of P01/Pa is at the range of 31.07–36.96. The ejector has strong suction capacity. The minimum suction pressure Ps/Pa is 0.025 when the P01 is in the self-starting region, and is 0.016 when the P01 is in the self-starting region. The ejector has excellent ejection performance. In the operational mode, when the Ta is 286 K, ER is 0.096 and CR is 7.5. Therefore, MSE has considerable potential values in engineering. The flow field of MSE is a quasi-2D structure. The wall pressure
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curves nearly coincide precisely in the interaction region of the weak shock and expansion waves. However, a few differences occur in the intense oscillate region of pseudo-shock.
nozzles of complex geometry, Appl. Therm. Eng. 99 (2016) 599–612. [9] S.M.V. Rao, G. Jagadeesh, Novel supersonic nozzles for mixing enhancement in supersonic ejectors, Appl. Therm. Eng. 71 (2014) 62–71. [10] M.J. Opgenorth, D. Sederstrom, W. Mcdermott, C.S. Lengsfeld, Maximizing pressure recovery using lobed nozzles in a supersonic ejector, Appl. Therm. Eng. 37 (2012) 396–402. [11] T. Narabayashi, Y. Yamazaki, H. Kobayashi, T. Shakouchi, Flow analysis for single and multi-nozzle jet pump, JSME Int. J. Ser. B Fluids Therm. Eng. 49 (2006) 933–940. [12] N.S.D. Lineberry, D.B. Landrum, Characterization of cold flow non-axisymmetric ejectors, AIAA vol. 5231, (2003). [13] D. Lineberry, B. Landrum, Effects of multiple nozzles on asymmetric ejector performance, Aiaa J. (2005). [14] M. Balasubramanya, D.B. Landrum, C.P. Chen, D. Lineberry, Numerical investigation of cold flow non-axisymmetric ejectors, AIAA vol. 1209, (2005). [15] H. Liu, Development of numerical mehtod and investigation on performances of supersonic ejectors, China Aerodynamics Research and Development Center Graduate School, vol. PHD, 2009, pp. 113–177. [16] J. Wu, Design theory, method and experimental investigation of high compression ratio multi-nozzle supersonic ejector, National University of Defense Technology, vol. PHD, 2007, pp. 102–146. [17] G.D. Hager, V.D. Nikolaev, M.I. Svistun, M.V. Zagidullin, Lasing performance of a chemical oxygen iodine laser (COIL) with advanced ejector-nozzle banks, Appl. Phys. A 77 (2003) 325–329. [18] V.D. Nikolaev, M.V. Zagidullin, M.I. Svistun, B.T. Anderson, R.F. Tate, G.D. Hager, Results of small-signal gain measurements on a supersonic chemical oxygen iodine laser with an advanced nozzle bank, IEEE J. Quantum Electron. 38 (2002) 421–428. [19] K. Tei, D. Sugimoto, T. Fujioka, Cold flow test of a new high-pressure nozzle bank for chemical oxygen iodine laser, 35th AIAA Plasmadynamics and Lasers Conference, American Institute of Aeronautics and Astronautics, 2004. [20] M.V. Zagidullin, V.D. Nikolaev, M.I. Svistun, N.A. Khvatov, G.D. Heiger, T.J. Madden, Efficient chemical oxygen — iodine laser with a high total pressure of the active medium, Quantum Electron. 31 (2001) 30. [21] T.S. Lund, Viscous-inviscid analysis of dual-jet ejectors, J. Propul. Power 7 (1991) 99–107. [22] B.H. Park, H.L. Ji, W. Yoon, Fluid dynamics in starting and terminating transients of zero-secondary flow ejector, Int. J. Heat Fluid Flow 29 (2008) 327–339.
Acknowledgement Wei Ye is grateful to his wife, Yao Shu, for her invaluable support and encouragement over the years. I love you forever. Appendix A. Supplementary material Supplementary data to this article can be found online at https:// doi.org/10.1016/j.applthermaleng.2019.03.133. References [1] A. Addy, J. Dutton, C. Mikkelensen, Supersonic Ejector-Diffuser Theory and Experiment, University of Illinois, Urbana, 1981. [2] I.W. Eames, A.E. Ablwaifa, V. Petrenko, Results of an experimental study of an advanced jet-pump refrigerator operating with R245fa, Appl. Therm. Eng. 27 (2007) 2833–2840. [3] R.L.P. David, E. Reubush, Modification to the Langley 8-foot high temperature tunnel for hypersonic propulsion testing, AIAA vol. 1887, (1987). [4] A.S. Mel Bulman, The strutjet engine: exploding the mythssurrounding high speed airbreathing propulsion, AIAA vol. 2475, (1995). [5] A.S. Boreisho, V.M. Khailov, V.M. Malkov, A.V. Savin, Pressure recovery systems for high-power gas flow chemical lasers, XIII International Symposium on Gas Flow and Chemical Lasers and High-Power Laser Conference, vol. 4184, SPIE, 2001, p. 5. [6] J. Tan, D. Zhang, L. Lv, A review on enhanced mixing methods in supersonic mixing layer flows, Acta Astronautica 152 (2018) 310–324. [7] D. Zhang, J. Tan, L. Lv, Investigation on flow and mixing characteristics of supersonic mixing layer induced by forced vibration of cantilever, Acta Astronautica 117 (2015) 440–449. [8] S.M.V. Rao, S. Asano, T. Saito, Comparative studies on supersonic free jets from
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Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng
Research Paper
Experimental investigation on the performance of a multi-strut mixingenhancement ejector
T
Wei Ye, Wanwu Xu , Ping Li, Fuqiang Zhang, Jiaqi Zhang ⁎
Science and Technology on Scramjet Laboratory, National University of Defense Technology, Changsha 410073, China
HIGHLIGHTS
2D ejector with multi-strut is developed for high operational performance. • AThenovel divide the flows into multiple jets, and the mixing area increases notably. • The struts region is P /P ≥ 36.96, the hysteresis region is P /P ∈ [31.07, 36.96]. • The self-starting minimum suction pressure P /P is 0.016. • A typical point is ER = 0.096, whilst CR = 7.5 in sub-critical mode. • 01
a
01
s
a
a
ARTICLE INFO
ABSTRACT
Keywords: 2D supersonic ejector Multiple nozzles Mixing enhancement Starting characteristics Operational performance
A novel design for multi-strut mixing-enhancement ejector (MSE) focuses on the improvement of entrainment ratio (ER) and compression ratio (CR). MSE is a 2D geometric ejector, which has multiple 2D struts and divides the primary and secondary flows into multiple sub-jets. The number of mixing layer and the mixing area increase to achieve mixing enhancement. A series of cold flow tests is conducted to explore the starting characteristics and operational mode performance of the ejector. An auxiliary method is developed. In this method, the P01 increase to the self-starting region in initial stage and then decreases to the hysteresis region. For this ejector, the o / Pa is 36.96. The self-starting region is P01/Pa ≥ 36.96, whilst the hysteresis region optimum starting pressure P01 of P01/Pa is at the range of 31.07–36.96. The ejector has excellent suction and ejection abilities. That is, the maximum suction pressure Ps/Pa = 0.016, whilst a typical point is ER = 0.096, CR = 7.5 in sub-critical mode.
1. Introduction Supersonic ejectors are simple gas-dynamic devices that utilise the augmentation of momentum and energy from a supersonic primary jet to entrain and pump a secondary flow [1]. To date, supersonic ejectors are extensively used in refrigerant systems [2], high altitude simulation facilities [3], rocket-based combined cycles [4] and pressure recovery systems of supersonic chemical lasers [5]. In recent years, a few studies were put forward to investigate the mixing-enhancement technologies on increasing the secondary flow entrainment and the total pressure recovery. The turbulence transport in the mixing layer between the primary and secondary flows is the main mechanism of the momentum and energy augmentations in the secondary flow. Therefore, mixing enhancement in the mixing layer between the primary and secondary flows is an effective method to improve the performance of supersonic ejectors.
⁎
Mixing enhancement technologies could be categorised as active control, passive control and shock wave induced mixing [6]. Active control techniques need some flow control facilities to add disturbance in the position of upstream, which can promote the flow unsteadiness and the rolling up of large scale K-H vortices. Passive flow control means the installation of some stationary devices to change the shear layer stability characteristics. So far, there are few engineering applications of active control techniques on ejector performance argument [7]. The existing studies on passive control technologies have concentrated on the method of utilising different nozzle geometries to promote flow instabilities, thereby maximising the pressure recovery in supersonic ejectors. Srisha Rao et al. [8,9] compared the mixing abilities between elliptic sharp tipped shallow lobed, bevelled and chevron nozzles. Results showed that both different geometry nozzles could achieve the effect of mixing enhancement, and a loss of compression ratio (CR) also occurred simultaneously. Matthew J. Opgenorth et al.
Corresponding author. E-mail address: [email protected] (W. Xu).
https://doi.org/10.1016/j.applthermaleng.2019.03.133 Received 15 October 2018; Received in revised form 27 February 2019; Accepted 27 March 2019 Available online 28 March 2019 1359-4311/ © 2019 Elsevier Ltd. All rights reserved.
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Nomenclature m P Ma T W H N X L A
D ER CR SPR
Subscripts
mass flow rate, kg·s−1 pressure, Pa Mach number temperature, K width, mm height, mm strut number axis distance, mm length, mm cross-section area, mm2 contraction semi-angle, ° expansion semi-angle, ° struts chocking ratio hydraulic diameter, mm entrainment ratio, m2/m1 compression ratio, Pa/P02 Stagnation pressure ratio, P01/P02
0 1 2 s a c m i t o v
stagnation condition primary flow secondary flow suction chamber atmospheric state secondary flow sub-channel constant area mixer diffuser inlet second throat diffuser outlet Venturi tube inlet
Superscripts h o
minimum hysteresis pressure optimum starting pressure
the performance. Although the studies on the 2D geometric multiplenozzle supersonic ejector are limited, the ejection principle has been validated in supersonic chemical laser facilities [17–20]. The 2D slitnozzle banks were used to increase gas mixing and accelerate lowmomentum gas flows to reach the goal of high chemical efficiency. Moreover, T. S. Lund et al. [21] developed a viscous − inviscid interaction methodology to evaluate the performance of the 2D incompressible dual-jet ejectors. To date, the potential better performance of the 2D multi-jet supersonic ejector has not been explored. The present research focuses on a novel design for 2D multi-strut mixing-enhancement ejector (MSE), and the cold experimental studies are conducted to explore the starting characteristics and operational mode performance. The MSE contains multiple 2D struts. These struts divide the primary and secondary flows into multiple small jets, thereby the mixing layer number and mixing areas amongst multiple small jets are increased. Hence, mixing enhancement is achieved to improve the ejection performance. The starting behaviours of MSE are analysed in detail in the self-starting and hysteresis regions. Finally, the parameters of primary and secondary flows and ejection performance are conducted to evaluate the engineering value.
[10] compared the maximum pressure recovery abilities of supersonic ejectors, which had circular nozzles, by adding different numbers of lobes. The study suggested that the optimum perimeter value of the lobe would be approximately 30 mm, which was determined using the designed profiles of the constant rate of momentum change method (CRMC) The maximum pressure recovery (or CR) for these lobed nozzle ejectors was the value of 6.4, whilst the corresponding entrainment ratio (ER) was the value of 0.05. The different geometries are applied to the single-nozzle ejector and are optimised on the basis of the axisymmetric nozzle. This method enhances the mixing between the primary and secondary flows. Additionally, the increase in the simultaneous shock wave losses causes flow instabilities, thereby inevitably decreasing the ability of pressure recovery. The other method for mixing enhancement would be to increase the mixing areas between the primary and secondary flows by applying multiple nozzles. Several numerical and experimental studies have been conducted to compare the incompressible jet pump efficiency for single nozzle with that for five nozzles of Tadashi Narabayashi et al. [11]. These studies showed that the five-nozzle jet pump did not show any advantages compared to the single-nozzle pump. A series of studies were conducted to evaluate the performance of ejectors that contain a 2D strut with rectangular shrouds, which imbed single or dual asymmetric nozzles in the strut. The results showed that the increasing number of nozzles can decrease the mixing length between the primary and secondary flows [12–14]. Jiping Wu [15] studied the unstarting problems in the ejectors with multiple axisymmetric nozzle and proposed to add a certain mass rate of secondary flow to decrease the optimum starting pressure [16]. The operational mode performance was studied in the ejectors with multiple axisymmetric and notched nozzles placed in several layers along the peripheral direction [15]. The results showed that an appropriate number of nozzles could improve the ejection performance and decrease the scale of ejectors. However, intensity disturbance amongst jets from too many nozzles, and would decrease the ejection performance. The majority of the studies had concentrated on the ejectors with multiple axisymmetric nozzles with axisymmetric shrouds. However, this sort of ejector could not obtain uniform jet distribution because of interactions among jets from multiple nozzles, which restricts the further improvement of the operational performance. This problem could be solved by a novel geometric structure, which is the multiple-nozzle supersonic ejector with rectangular profile shrouds. This type of ejector can achieve the uniform distribution of jets and increase the mixing areas and decrease shock wave losses simultaneously. Therefore, it is supported that the 2D multiple-nozzle supersonic ejector has a few potential advantages on
2. Experimental setup 2.1. Experimental system The schematic MSE experimental system can be shown in Fig. 1. High-pressure air and nitrogen tanks are used as gas sources of the primary and secondary flows respectively, to maintain the primary and secondary flow supplies independently. The air supply subsystem comprises a ball valve, a pressure regulator with a rated mass flow of 20 kg/s, the DN100 main pipeline, a orifice plate flow meter, two DN40 globe valves and DN20 throttle orifice installed in the back of globe valve 2 to control the total pressure of the primary flow. The nitrogen supply subsystem comprises a ball valve, pressure regulator with a rated mass flow of 10 kg/s, DN20 main pipeline, DN20 globe valve, venturi tube with throat diameter of 10 mm, transition section and suction chamber. The mass rate range of the primary flow is 0–10 kg/s, whilst the mass rate range of the secondary flow is 0–1.2 kg/s. In the starting processes of the experiments, both globe valves in the air supply subsystem are opened to ensure that the total pressure of the primary flow is above the optimum starting pressure of the ejector, and then the ejector achieves steady starting. In order to maintain the ejector starting at low pressure conditions, of which pressures are lower 651
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Primary-flow inlets
Secondary-flow sub-channels
2D nozzles
Primary-flow inlet chamber Secondary-flow inlet H
W Nozzle-surge chambers
Fig. 3. Sketch of MSE.
Fig. 1. Schematic of the MSE experimental system.
than the optimum starting pressure. The globe valve 2 is closed to decrease the total pressure of the primary flow in the starting processes, and a valve having a DN20 throttle orifice is installed behind valve 2. The secondary flow path comprises venturi tube, several multi-stage rectifiers, transition section and suction chamber. The section view can be seen in Fig. 2. The multi-stage rectifiers contain 2-layer tiny-hole arrays and a grill array. The holes with the diameters are 5 and 10 mm respectively, and the grill with the thickness is 8 mm. They are used to make the secondary flow evenly distributed in the suction chamber.
Fig. 4. MSE facility.
the constant area mixer (Lm/W) is 1.875. Two sides of the convergent section contract symmetrically along the width direction. The contraction semi-angle θ is 2.5°, whilst the contraction ratio (At/Ai) is 0.7. The ratio of the second throat length Lt to the hydraulic diameter Dt is 6.3. The divergent section is a four-sided expansion geometry. The expansion semi-angle is 2°, whilst the expansion ratio (Ao/At) is 2. In this study, x, y and z stand for the streamwise, transverse and vertical coordinates.
2.2. Ejector structure description The sketch of MSE is shown in Fig. 3. The ejector contains two primary flow inlets, one primary flow inlet chamber, four struts, one secondary flow inlet and five secondary flow sub-channels. Each strut contains a wedge in the leading end, nozzle surge chamber and 2D supersonic nozzle. The primary flow crosses the primary flow inlets into the primary inlet chamber and passes through the nozzle surge chambers. Thereafter, 2D nozzles come into four supersonic jets. The secondary flow crosses the secondary flow inlet into the ejector and enters the secondary flow sub-channels divided into five subsonic jets. Multiple supersonic and subsonic jets are mixing and pressure recovery in supersonic diffuser. The MSE facility is shown in Fig. 4. The supersonic diffuser is a rectangular cross-section diffuser (see Fig. 5 for the schematic), which comprises a constant area mixer, convergent section, second throat and divergent section. The ejector and diffuser geometric parameters are shown in Table 1, in which the secondary flow inlet width W is 280 mm, height H is 120 mm, the struts number N is 4 and the struts chocking ratio ψ (i.e., ratio of the struts’ total thickness to the secondary flow inlet width) is 0.314. The length of
Secondary-flow inlet
Venturi tube
2.3. Measurement methods and uncertain analysis The pressure, mass flow rate and temperature of MSE were measured in the experiments. The test equipment, test positions, measurement methods and uncertain analysis would be described as follows. (1) Pressure measurements: The absolute pressures of the MSE experimental system are measured using a few test facilities. The total pressures of the primary flow and secondary flow in the venturi tube inlet are higher than the ambient pressure, so the PT301 was used to measure these values. The range of the used transducer is 0–10 MPa, whilst the accuracy is 0.5% FS. The static pressures of the suction
Rectifiers
Transition section
Primary-flow inlet
Suction chamber
Fig. 2. Section view of the secondary flowpath. 652
Ejector
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Fig. 5. Schematic of the rectangular cross-section supersonic diffuser.
total pressure of secondary flow in the venturi tube inlet; At is the throat area; TOV is the total temperature of secondary flow in the venturi tube inlet, which is equal to the ambient temperature; is the specific heat ratio of the secondary flow; R is the gas constant of the secondary flow. It is assumed that the secondary flow is uniformity before entering into the MSE secondary-flow inlet. The Mach number of the flow in the MSE secondary-flow inlet can be obtained from the equation:
Table 1 Parameters of the geometric ejector and diffuser. Parameter
Value
Parameter
Value
W H N
280 mm 120 mm 4 0.314 1.875
At/Ai
0.7 2.5° 6.3 2° 2
Lm/W
Lt/Dt Ao/At
Ma2 =
P02 = P2 1 +
R
1) Ma22
/(
1)
3.1. Starting characteristics The total pressures of the primary and secondary flows were controlled by the pressure regulators in the gas supply subsystem, whereas the primary flow is the only gas applied to obtain the starting characteristics of MSE. The starting processes of MSE have three levels similar to a traditional ejector: A (nozzles and diffuser are unstarted); B (nozzles are started, whilst diffuser is unstarted) and C (nozzles are started, whilst diffuser is started). However, the ejector in the processes of A and B are unstarted, whilst that in the process of C is started [22]. Fig. 7 shows the starting characteristics of the ejector, in which the total temperature of the primary flow is 266.4 K. In the figure, the total pressure P01/Pa in primary flow designates the average value of the bottom wall parameters at the locations of the four-nozzle inlets, and the evacuation performance Ps/Pa denotes the suction chamber pressure. The experiment results in the unstarted and started processes of the ejector can be correlated well by linear fit curves. The optimum o / Pa of MSE was evaluated to be 36.96, which is starting pressure P01 corresponding to the suction chamber pressure of 0.029. The minimum h /Pa in the hysteresis region is 31.07, whilst the starting pressure P01
The inlet parameters of primary and secondary flows are significant arguments to evaluate the operational mode performance of MSE. The inlet parameters (P01, T01, m1) of primary flow are measured by a few test facilities, such as absolute pressure and temperature transducers, and so on. Some of the inlet parameters of secondary flow are calculated by some measured pressure values. The functions were shown as follows: The mass rate of the secondary flow is obtained from the equation:
2 +1
1 ( 2
3. Results and discussions
2.4. Inlet parameters of the MSE
Cd P0V At T0V
RT0V
where m2 is the mass rate of the secondary flow; A is the flow-path areas of the secondary flow inlet cross-section; P2 is the static pressure of the secondary flow inlet, and it is equal to the top wall pressure of the secondary-flow inlet. The total pressure of the secondary flow in the secondary-flow inlet is obtained from the equation:
chamber and supersonic diffuser are lower than ambient pressure, so the test devices are electronic pressure scanners (Pressure System Inc 9116). The range is 103 KPa, whilst the accuracy is 0.5% FS. The initial value of the scanners should be manually entered by atmosphere pressure. The atmosphere pressure gauge is used to measure such pressure, which ranges from 0.3 KPa to 110 KPa, whilst the accuracy is 0.5% FS. The small range absolute pressure transducer and scanner channel are used to measure the suction chamber pressure at the same point to calibrate the scanner accuracy. The type of the small range absolute pressure transducer used is PT301, which ranges from 0 to 20 KPa, whilst the accuracy is 0.5% FS. The calibration results are shown in Table 2. The errors are the value differences between the transducer and scanner measurements. These errors range from −2.25% to 3.6%. (2) Mass flow rate measurements: The mass rate of the primary flow m1 is measured using an orifice plate flow meter, with an uncertainty of ± 5.5%. The mass rate of the secondary flow is measured using a venturi tube, with an uncertainty of ± 3%. The venturi tube has an axisymmetric structure, with throat diameter of 10 mm, and with both inlet and outlet diameters of 20 mm. The schematic of the venturi tube can be seen in Fig. 6. (3) Temperature measurements: the temperatures of the primary flow inlet, suction and venturi tube inlet chambers are measured using Pt100 temperature transducers, which range from 223 K to 323 K, whilst the accuracy is 0.2% FS.
m2 =
m2 RT0V · / A P2
Table 2 Comparison of the electronic pressure scanner and transducer.
+1 1
where Cd is the flow coefficient, and it is a constant value; P0V is the 653
No
Scanner (kPa)
Transducer (kPa)
Error (kPa)
1 2 3 4
1.73 1.59 8.67 8.95
1.67 1.56 8.87 8.87
+0.06 +0.03 −0.2 −0.04
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P0V, T0V
the condition of total pressure of primary flow in hysteresis region, the starting location of shock train in the secondary throat is further than the other condition. The influence of the starting characteristics in various primary flow total temperatures (T01) is observed in the experiments. Table 3 compares the different starting characteristics in T01. As T01 increases, the optimum starting pressure decreases. When T01 in cases 1 and 2 increases by 30 K, the optimum starting pressure P01/Pa decreases by 2.3. The evacuation performance augments with the increase of T01. When T01 is 266.4 K, the primary flow pressure P01/Pa is 31.07 in the hysteresis region, whilst the suction pressure Ps/Pa is 0.023. When T01 is 291.4 K, the primary flow temperature P01/Pa is 32.24 in the hysteresis region, whilst the minimum suction pressure is 0.016.
Fig. 6. Schematic of the venturi tube.
3.2. Operational mode performance analysis The same method as the starting characteristics experiments was used to maintain the ejector starting in the hysteresis region. After that, the globe valve in the nitrogen supply subsystem would be opened to feed the secondary flow. In the present study, the mass rate of the secondary flow m2, was controlled by Pov in the sub-critical mode of the ejector. Table 4 shows the parameters describing the operational mode performance in various experimental conditions. Amongst the experiments, the ambient temperature is about 286 K, and the parameters of the primary flow remain in a same state (m1 = 4.98 kg/s, P01/ Pa = 31.59). As shown in the table, in the sub-critical mode, as the secondary flow mass rate m2 increases, the P2/Pa, Ma2 and ER increase, however, SPR and CR decrease correspondingly. The static pressures of the secondary flow (P2/Pa) are at the range of 0.044–0.162, and the inlet Mach number of the secondary flow (Ma2) are at the range of 0–0.4. The ejector has a high CR (CR ≥ 7.5) when ER ≤ 0.10. The operational mode performance parameters of the MSE are compared with the referenced ejector (REF) in [10] as illustrated in Fig. 10. REF is a three-lobed constant pressure method-designed supersonic ejector which has considerable maximum pressure recovery abilities compared with other geometric ejectors. Although REF has a higher performance in the sub-critical mode (see Fig. 10), MSE has better entrainment and pressure recovery abilities than the former at the conditions of CR > 6. Although the geometry of MSE is a standard 2D structure, the internal flow field is a quasi-2D structure. Fig. 11 shows pressure distributions on the different side-walls in the supersonic diffuser when ER = 0.124. All the sensors were set in the middle of each wall. Pressure gradient along the width-wise direction generates the internal main-flow expansion in the middle of the constant area mixer. Therefore, the pressures on both top and bottom walls of the constant area mixer decrease along the x-axis direction. The interaction of the shock
Fig. 7. Starting characteristics of the MSE (T01 = 266.4 K).
corresponding suction chamber pressure is 0.023, which is the maximum evacuation performance. The minimum starting pressure in the o h o P01 )/ P01 hysteresis region (P01 is 15.9% lower than the optimum starting pressure. At this temperature condition, the self-starting region is P01/Pa ≥ 36.96, whilst the hysteresis region of P01/Pa is at the range of 31.07–36.96. The process of C can be divided into self-starting and hysteresis regions. The dividing point of these two regions is the optimum starting o pressure P01 . In the self-starting region, the ejector can be started ino dependently when P01 would be higher than P01 . On contrary, the ejector cannot be started independently in the hysteresis region when o P01 would be lower than P01 . In order of realize the MSE starting in the hysteresis region, some auxiliary methods are needed to help the MSE achieves starting. An effective method is that increasing the value of P01/Pa in the self-starting region, then the MSE achieves steady selfstarting, and reducing the P01/Pa to the hysteresis region in the next step, and then the ejector keeps a smooth starting status. A typical starting case by utilizing this method can be shown in Fig. 8. In the starting case, both globe value 1 and 2 in the primary supply subsystem are opened simultaneously to allow the P01/Pa to reach the self-starting region (P01/Pa = 39.5) to start the ejector. When the 4.3 s later, the glove value 2 is closed to reduce the P01/Pa to the hysteresis region (P01/Pa = 33). In this region, the ejector remains a smooth starting status. Furthermore, the evacuation performance in hysteresis region is better than in self-starting region. The pressure distributions on the bottom wall of the supersonic diffuser in self-starting and hysteresis regions can be seen in Fig. 9. Comparison shows that the wall pressure distributions in the constant area mixer and convergent section, it can be seen that the values are similar and have the same variation regularity in the two regions. Whereas, the comparison of the wall pressure distributions in the secondary throat and divergent section, shows that the values are higher in self-starting region than those in hysteresis region. This indicates that at
Fig. 8. Pressure history of the MSE during a typical starting case. 654
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Static pressure, P/P a
0.9 0.8 0.7
top wall bottom wall front wall back wall
0.6 0.5 0.4 0.3 0.2 0.1 0.0
0
1
23
4
56
7
8
9
10
11
12
X-axis distance, X/W Fig. 9. Wall pressure comparison of the supersonic diffuser in self-starting and hysteresis regions.
Fig. 11. Different side wall pressure distributions of the supersonic diffuser in ER = 0.124.
Table 3 Comparison of the starting characteristics in T01. Cases
T01 (K)
P01/Pa
Ps/Pa
Remarks
1 2
266.4 295.9
36.96 34.66
0.029 0.025
Optimum starting pressure
3 4
266.4 291.4
31.07 32.24
0.023 0.016
Minimum suction pressure
pressure curves depicting the top and bottom walls almost coincide with each other precisely. On the other hand, the pressure curves of the front and back walls coincide well in both the constant area mixer and convergent section. The pressure curve of the back wall is substantially higher than that of the other side walls in the back end of the second throat and divergent section, which is caused by unevenness of the flow field structure. Leaded from the instability of the pseudo-shock. 4. Conclusion
Table 4 Operational mode performance parameters in various experimental conditions. Cases
P01/Pa
m1
m2
P2/Pa
P02/Pa
Ma2
SPR
ER
CR
5 6 7 8 9 10
31.59 31.59 31.59 31.59 31.59 31.59
4.98 4.98 4.98 4.98 4.98 4.98
0.041 0.183 0.332 0.478 0.616 0.768
0.044 0.086 0.109 0.127 0.144 0.162
0.044 0.087 0.112 0.134 0.154 0.175
0.07 0.15 0.22 0.27 0.31 0.34
717.95 363.10 282.05 235.75 205.13 180.51
0.008 0.037 0.067 0.096 0.124 0.154
22.8 11.5 8.9 7.5 6.5 5.7
This research focuses on the development of a novel 2D geometric mixing-enhancement ejector and the validation of its operational performance in sub-critical mode. The ejector has a typical 2D geometry and covers four 2D struts in a rectangular cross-section. Each strut contains a wedge at the leading end, nozzle-surge chamber and 2D nozzle. The multiple 2D struts divide the primary and secondary flows into multiple sub-jets and increase the mixing area to achieve the mixing enhancement. A rectangular cross-section supersonic diffuser is installed at the ejector outlet. This diffuser comprises a constant area mixer, convergent section, second throat and divergent section. The starting characteristics and operational mode performance of the mixing-enhancement ejector are explored by a series of cold experiments. The main results and conclusions are summarised as follows.
• The starting mode can be divided into self-starting and hysteresis
• •
Fig. 10. Comparison of MSE’s operational mode performance with REF in [10]
•
and expansion waves in the mixer and convergent section causes the wall pressures to fluctuate along the x-axis direction. The pseudo-shock structure in the back end of the second throat and divergent section pressures and increases the pressure oscillation in the throat, which causes the uneven of the pressure along the x-axis direction. The
• 655
regions. When the P01 is in the self-starting region, the MSE can start independently. Whereas, when the P01 is in the hysteresis region, the MSE cannot start independently. Thus, some auxiliary methods are needed to help the MSE achieves starting. In this paper, increasing the P01 to the self-starting region in initial stage and then reducing the P01 to the hysteresis region is an effective method. The dividing point of the two regions is the optimum starting pressure o P01 . At the temperature condition of T01 = 266.4 K, The optimum o / Pa is 36.96. Moreover, at this temperature starting pressure P01 condition, the self-starting region is P01/Pa ≥ 36.96, whilst the hysteresis region of P01/Pa is at the range of 31.07–36.96. The ejector has strong suction capacity. The minimum suction pressure Ps/Pa is 0.025 when the P01 is in the self-starting region, and is 0.016 when the P01 is in the self-starting region. The ejector has excellent ejection performance. In the operational mode, when the Ta is 286 K, ER is 0.096 and CR is 7.5. Therefore, MSE has considerable potential values in engineering. The flow field of MSE is a quasi-2D structure. The wall pressure
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curves nearly coincide precisely in the interaction region of the weak shock and expansion waves. However, a few differences occur in the intense oscillate region of pseudo-shock.
nozzles of complex geometry, Appl. Therm. Eng. 99 (2016) 599–612. [9] S.M.V. Rao, G. Jagadeesh, Novel supersonic nozzles for mixing enhancement in supersonic ejectors, Appl. Therm. Eng. 71 (2014) 62–71. [10] M.J. Opgenorth, D. Sederstrom, W. Mcdermott, C.S. Lengsfeld, Maximizing pressure recovery using lobed nozzles in a supersonic ejector, Appl. Therm. Eng. 37 (2012) 396–402. [11] T. Narabayashi, Y. Yamazaki, H. Kobayashi, T. Shakouchi, Flow analysis for single and multi-nozzle jet pump, JSME Int. J. Ser. B Fluids Therm. Eng. 49 (2006) 933–940. [12] N.S.D. Lineberry, D.B. Landrum, Characterization of cold flow non-axisymmetric ejectors, AIAA vol. 5231, (2003). [13] D. Lineberry, B. Landrum, Effects of multiple nozzles on asymmetric ejector performance, Aiaa J. (2005). [14] M. Balasubramanya, D.B. Landrum, C.P. Chen, D. Lineberry, Numerical investigation of cold flow non-axisymmetric ejectors, AIAA vol. 1209, (2005). [15] H. Liu, Development of numerical mehtod and investigation on performances of supersonic ejectors, China Aerodynamics Research and Development Center Graduate School, vol. PHD, 2009, pp. 113–177. [16] J. Wu, Design theory, method and experimental investigation of high compression ratio multi-nozzle supersonic ejector, National University of Defense Technology, vol. PHD, 2007, pp. 102–146. [17] G.D. Hager, V.D. Nikolaev, M.I. Svistun, M.V. Zagidullin, Lasing performance of a chemical oxygen iodine laser (COIL) with advanced ejector-nozzle banks, Appl. Phys. A 77 (2003) 325–329. [18] V.D. Nikolaev, M.V. Zagidullin, M.I. Svistun, B.T. Anderson, R.F. Tate, G.D. Hager, Results of small-signal gain measurements on a supersonic chemical oxygen iodine laser with an advanced nozzle bank, IEEE J. Quantum Electron. 38 (2002) 421–428. [19] K. Tei, D. Sugimoto, T. Fujioka, Cold flow test of a new high-pressure nozzle bank for chemical oxygen iodine laser, 35th AIAA Plasmadynamics and Lasers Conference, American Institute of Aeronautics and Astronautics, 2004. [20] M.V. Zagidullin, V.D. Nikolaev, M.I. Svistun, N.A. Khvatov, G.D. Heiger, T.J. Madden, Efficient chemical oxygen — iodine laser with a high total pressure of the active medium, Quantum Electron. 31 (2001) 30. [21] T.S. Lund, Viscous-inviscid analysis of dual-jet ejectors, J. Propul. Power 7 (1991) 99–107. [22] B.H. Park, H.L. Ji, W. Yoon, Fluid dynamics in starting and terminating transients of zero-secondary flow ejector, Int. J. Heat Fluid Flow 29 (2008) 327–339.
Acknowledgement Wei Ye is grateful to his wife, Yao Shu, for her invaluable support and encouragement over the years. I love you forever. Appendix A. Supplementary material Supplementary data to this article can be found online at https:// doi.org/10.1016/j.applthermaleng.2019.03.133. References [1] A. Addy, J. Dutton, C. Mikkelensen, Supersonic Ejector-Diffuser Theory and Experiment, University of Illinois, Urbana, 1981. [2] I.W. Eames, A.E. Ablwaifa, V. Petrenko, Results of an experimental study of an advanced jet-pump refrigerator operating with R245fa, Appl. Therm. Eng. 27 (2007) 2833–2840. [3] R.L.P. David, E. Reubush, Modification to the Langley 8-foot high temperature tunnel for hypersonic propulsion testing, AIAA vol. 1887, (1987). [4] A.S. Mel Bulman, The strutjet engine: exploding the mythssurrounding high speed airbreathing propulsion, AIAA vol. 2475, (1995). [5] A.S. Boreisho, V.M. Khailov, V.M. Malkov, A.V. Savin, Pressure recovery systems for high-power gas flow chemical lasers, XIII International Symposium on Gas Flow and Chemical Lasers and High-Power Laser Conference, vol. 4184, SPIE, 2001, p. 5. [6] J. Tan, D. Zhang, L. Lv, A review on enhanced mixing methods in supersonic mixing layer flows, Acta Astronautica 152 (2018) 310–324. [7] D. Zhang, J. Tan, L. Lv, Investigation on flow and mixing characteristics of supersonic mixing layer induced by forced vibration of cantilever, Acta Astronautica 117 (2015) 440–449. [8] S.M.V. Rao, S. Asano, T. Saito, Comparative studies on supersonic free jets from
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