- Email: [email protected]
Orthogonal experimental research on the structural parameters of a self-excited pulsed cavitation nozzle
European Journal of Mechanics B/Fluids 65 (2017) 179–183
Contents lists available at ScienceDirect
European Journal of Mechanics B/Fluids journal homepage: www.elsevier.com/locate/ejmflu
Orthogonal experimental research on the structural parameters of a self-excited pulsed cavitation nozzle Yanpeng Qu, Songying Chen ∗ Key Laboratory of High-efficiency and Clean Mechanical Manufacture, School of Mechanical Engineering, Shandong University, Jinan, Shandong 250062, PR China
article
info
Article history: Received 7 December 2016 Available online 31 March 2017 Keywords: Self-excited pulsed jet Cavitation nozzle Orthogonal experiment Strike force
abstract A variety of geometric sizes of a self-excited pulsed jet such as the diameter of the suction and discharge nozzle, jet chamber length and diameter, and the collision angle are the main structural parameters. Under certain operating conditions at a given fluid flow rate, target space, and dynamic head, the jet strike force amplitude and frequency were significantly influenced by these structural sizes. Twenty five group orthogonal experiments were designed to explore the jet dynamic performance with structural sizes to find which group was the best combination. The experiment employed five levels of the diameter of the suction and discharge nozzles, three levels of the chamber diameter, and five levels of the length of the chamber and collision angles. Experimental results showed that the suction nozzle diameter was the most important parameter influencing the jet performance. The next was discharge nozzle diameter. The other three sizes of chamber diameter and length, and collision angle had the similar effect on the selfexcited pulsed jet. The results can have guiding significance for the design of self-excited pulsed cavitation nozzles. © 2017 Elsevier Masson SAS. All rights reserved.
0. Introduction The self-excited pulsed cavitation jet is a kind of developed high efficiency novel jet which was created in the early 1980s based on the principle of self-excited oscillation [1]. Through reasonable nozzle design, a fluid will produce a self-excited oscillation in the cavity and intermittent big vortex rings appear which causes a huge pressure oscillation. Also, strong cavitation can be produced under confining pressure that gives the selfexcited pulsed cavitation jet the advantages of both a free jet and a pulsed jet [2,3]. In addition, the self-excited oscillation cavitation jet can be produced with changes of the nozzle structure without an additional source and it also has advantages of simple structure, small volume, without an additional external drive mechanism, and a dynamic seal [4]. Therefore, the self-excited pulsed cavitation jet has broad application prospects in the fields of coal mining, oil drilling, rock cutting, equipment cleaning, and derusting [5]. According to the principle of underwater acoustics, Vijay [6] put forward the concept of the natural cavitation water jet. Two kinds of typical structures of an acoustic harmonic vibration cavitating water jet were the result of a lot of research. This included the
∗
Corresponding author. E-mail address: [email protected] (S. Chen).
http://dx.doi.org/10.1016/j.euromechflu.2017.03.010 0997-7546/© 2017 Elsevier Masson SAS. All rights reserved.
organ pipe nozzle and the Helmholtz nozzle. Based on the research on the mechanism of the cavitation water jet, Zhonghou [7] established the theory design method of the cavitation nozzle. Ruliang [8] and Jiangyun [9,10] studied the mechanism of the jet through numerical analysis and experimental verification. They thought that the cavitation merged with periodical convergence and scattered with time. Structural and operational parameters of the self-excited pulsed cavitation jet device have a significant effect on the pulse performance. There have been many numerical simulations and experiments on high pressure and low flow rate jets [11]. Songying [12] and Yanpeng [13,14] studied the evolutionary process on the oscillation cavity under low pressure and high flow rate. Fenghua [15] made a further study on the effects of the cavitating nozzle with a converging–diverging exit on the cavitation effect through theoretical analysis and tests. Jiansheng [16] researched relations of the jet force and frequency with the nozzle structure and operation parameters, and many scholars did a lot of work in this field. Yang [17] studied the relationship between structural parameters and the natural frequency characteristics on the basis of the fluid network similarity theorem. Ziguang [18] obtained a force diagram through the force analysis generated by the self-excited oscillation cavitation jet. Geometric sizes such as diameter of suction d1 and discharge nozzle d2 , jet chamber length Lc and diameter Dc, and collision
180
Y. Qu, S. Chen / European Journal of Mechanics B/Fluids 65 (2017) 179–183 Table 1 The orthogonal experimental scheme and strike force.
Fig. 1. Schematic diagram of the self-excited pulse nozzle device.
angle a are the main structural parameters of the self-excited pulsed jet that have a significantly influence on the target space, dynamic head, and the jet strike force amplitude and frequency. The present study used five levels of diameter size of the suction and discharge nozzle, three levels of the chamber diameter, and five levels of the length of the chamber and collision angles to study the effect of structural parameters on the effect of pulsation by L25 (56 ) orthogonal experiments. 1. Experiment 1.1. Experimental setup The self-excited pulsed cavitation jet nozzle is mainly composed of a suction nozzle, discharge nozzle, chamber, oscillation chamber, and collision angle, as shown in Fig. 1. Fig. 2 shows the self-excited pulsed jet device test system in which the inverter can regulate the supply pressure of the circulation pump and the water flow rate of the nozzle can be controlled by the control valve and diverter. Water flow will form a pulse jet through the nozzle and directly spray towards the target. The pressure, temperature, rate of flow, and the force in the suction nozzle or chamber are measured by the pressure sensor, thermal sensor, electromagnetic flowmeter, and weighing sensor, respectively. The transmitter transmits the signal to the data acquisition system and it is analyzed by the computer. Photos of the pulse nozzle and test system are shown in Figs. 3 and 4, respectively. 1.2. The orthogonal experimental scheme and results The orthogonal experiment was designed by the orthogonal table L25 (56 ) as shown in Table 1. The strike force was chosen as the test index since it is a key factor of actual job quality. The average of pressure and the peak value of the strike force were chosen as the test results without the effect of pulse and the pulsing condition. A total of 25 group tests were given the same input pressure of 1.0 MPa and the value of the strike force was measured by a weighing sensor at the target distance of 300 mm. The experimental results showed that the suction nozzle diameter was the most influential parameter for the jet performance. The next was the discharge nozzle diameter. The other three sizes of the chamber diameter and length, and collision angle had an almost similar effect on the self-excited pulsed jet. It can be concluded that three geometric sizes are in charge of the kinetic values within the jet device. The first is the upstream nozzle which provides the inlet pressure and velocity. In order to reach the vaporized pressure, the local pressure at the center of vortex ring should be lower than the jet fluid saturated vapor pressure, and enough turbulent kinetic energy should be produced under the operating conditions. The second is the discharge nozzle which can provide smooth flow conditions for pulsed fluid to produce a strong and periodical jet in the downstream flow. The third is chamber diameter, chamber length, and collision angle which should be able to cause the axisymmetric vortex ring.
Number
d1 (mm)
d2 (mm)
a (°)
Lc (mm)
Dc (mm)
F (N)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 k1 k2 k3 k4 k5 R R′
8.7 8.7 8.7 8.7 8.7 3 3 3 3 3 4 4 4 4 4 6 6 6 6 6 8 8 8 8 8 7.628 2.632 4.508 6.016 7.860 5.228 4.676
8 10 12 14 16 8 10 12 14 16 8 10 12 14 16 8 10 12 14 16 8 10 12 14 16 4.708 4.884 5.352 6.684 7.016 2.308 2.064
90 120 150 180 240 120 150 180 240 90 150 180 240 90 120 180 240 90 120 150 240 90 180 150 120 5.264 6.146 5.562 6.058 5.614 0.882 0.789
20 30 50 65 80 50 65 80 20 30 80 20 30 50 65 30 50 65 80 20 50 80 20 30 65 5.834 5.854 5.018 6.046 5.892 1.028 0.919
80 95 110 80 95 80 95 80 95 110 95 110 80 95 80 95 80 95 110 80 110 80 95 80 95 5.729 5.957 5.272 – – 0.685 0.796
66.22 70.14 51.40 87.80 98.59 26.49 27.96 17.85 32.37 24.43 31.88 45.82 52.48 36.99 53.95 47.38 32.96 67.88 77.99 68.87 58.96 62.69 72.89 93.01 110.06 – – – – – – –
1.3. Analysis of the best working condition The experimental strike force value in Table 1 shows that when the suction nozzle diameter was 8 mm, the discharge nozzle diameter was 16 mm, the chamber diameter was 95 mm, the chamber length was 65 mm, and the collision angle was 120°, the strike force F reached the maximum value of 110.06 N which is the best working condition. The phenomenon of scattering and convergent is formed by the pulse jet. Convergent is the stage of energy storage as shown in Fig. 5(a). Scattering is the stage of energy release as shown in Fig. 5(b). The relation between force and time is shown in Fig. 6 which shows that the strike force causes cyclical changes. Fig. 7 shows that the cavity pressure periodical changes with time, the same as the strike force because the cavitation area expands with the reduced pressure which hinders the center jet resulting in a decrease of the strike force, and when the cavity pressure increases, the cavitation area narrows and the strike force increases. The whole process is a low-pressure self-excited pulsed cavitation water jet formation. 1.4. Comparison of the strike force between the pulsed and usual cylinder jet The self-excited pulsed cavitation jet nozzle can convert the continuous energy into pulse energy through the stage of energy storage and release which makes the instantaneous peak force of a pulse jet bigger than the continuous jet force. Fig. 8 shows that the maximum strike force of the self-excited pulsed cavitation jet can be 1.6–1.7 times that of the continuous cylinder jet. 2. Analysis of the influence of structural parameters on the pulse effect The structure parameters which can offer the best working condition were determined in Section 2. On this basis, the influence of
Y. Qu, S. Chen / European Journal of Mechanics B/Fluids 65 (2017) 179–183
181
Fig. 2. Schematic diagram of the self-excited pulsed jet device test system.
bigger discharge nozzle diameter will decrease the energy loss. The inflection point of the force change was not found in the experiment due to the selection of discharge nozzle diameters. 2.3. Influence of the chamber length on the jet
Fig. 3. Self-excited pulse nozzle.
Fig. 11 shows the relationship between the strike force and chamber length. The strike force did not have a regular change with the chamber length and the force showed a tendency of increasing at Lc = 30 mm which may be related to the moving of the cavitation balloon and the feedback of the pressure wave in the cavity. The pulse jet appeared when the chamber length was 50, 65, and 80 mm. The optimization range of these two structural parameters was Lc /Dc = 0.53–0.84 and it reached the maximum when the ratio was 0.68. 2.4. Influence of the chamber diameter on the jet
Fig. 4. Self-excited pulsed jet device test system.
various parameters on the pulse jet was studied by the controlling variable method. 2.1. Influence of the suction nozzle diameter on the jet Fig. 9 shows the changes of values of the strike force with suction nozzle diameters of 3, 4, 6, 8, and 8.7 mm under an inlet total pressure of 1.0 MPa. The strike force had a tendency of increasing with an increase of the suction nozzle diameter because the upstream nozzle determines the inlet pressure and velocity. The strike force declined when the suction nozzle diameter was 8.7 mm because there is no pulsed jet under this condition. If the flow energy from the suction nozzle can be better accepted by the discharge nozzle, energy loss decreases and strike force increases, which indicates the combination of the suction nozzle and discharge nozzle is also very important. The pulse jet appeared when suction nozzle diameters were 6, 8, and 8.7 mm, and was most obvious at a suction nozzle diameter of 8 mm. So the optimum range of these two structural parameters was d2/d1 = 1.84–2.67 and it reached the best when the ratio was 2. 2.2. Influence of the discharge nozzle diameter on the jet The relationship between the strike force and the discharge nozzle diameter is shown in Fig. 10. The strike force increased with an increase of the discharge nozzle diameter because a
The relationship between the strike force and the chamber diameter is shown in Fig. 12. The strike force first increased and then decreased with an increase of chamber diameter. The change phenomenon of the chamber indicated that the range of low pressure increased with an increase of the chamber diameter and the chamber diameter plays a decisive role in producing a periodical change of the cavitation balloon and the effective kinetic energy output. The energy output of the discharge nozzle can be influenced by the discharge diameter d2 and the chamber diameter Dc. This relationship can be expressed by the dimensionless parameter. The optimization range of these two structural parameters was Dc/d2 = 5–6.88 and the maximum was when the ratio was 5.94. 2.5. Influence of the collision angle on the jet Fig. 13 shows the relationship between the strike force and the collision angle. The pulse jet always appeared no matter what the value of the collision angle and the pulse phenomenon was most obvious when the collision angle was 120°. 3. Conclusions Twenty five group orthogonal experiments were designed to explore the influence of the five nozzle structural sizes on the jet dynamic performance under the best working condition. Conclusions are as follows. (1) The suction nozzle diameter is the first parameter influencing the jet performance. The next is the discharge nozzle diameter. The other three sizes of chamber diameter and length, collision angle almost have a similar effect on the self-excited pulsed jet. (2) Three geometric sizes are responsible for the kinetic values within the jet device. The first is the upstream nozzle which offers
182
Y. Qu, S. Chen / European Journal of Mechanics B/Fluids 65 (2017) 179–183
(a) Jet convergent form.
(b) Jet scattering form. Fig. 5. Jet energy store and release.
120 Strike force (N)
100 80 60 40 20 0
1
28
55
82 109 136 163 190 217 244 271 298 325 352 379 Sampling point
Cavity pressure (MPa)
Fig. 6. Relationship between strike force and time. 1 0 -0.01 -0.02 -0.03 -0.04 -0.05 -0.06 -0.07 -0.08 -0.09 -0.1
15
29
43
57
71
85
Fig. 10. Relationship between the strike force and the discharge nozzle diameter.
99 113 127 141 155 169 183 197
Sampling point
Fig. 7. Relationship between cavity pressure and time. Fig. 11. Relationship between the strike force and the chamber length.
Fig. 8. The comparison of force between the pulsed and usual cylinder jet.
Fig. 12. Relationship between the strike force and the chamber diameter.
Fig. 9. Relationship between the strike force and the suction nozzle diameter.
the inlet pressure and velocity. In order to reach the vaporized pressure, the local pressure at the center of vortex ring should be lower than the jet fluid saturated vapor pressure, and enough turbulent kinetic energy should be produced under the operational condition. The second is the discharge nozzle which can provide smooth flow conditions for pulsed fluid to produce a strong
Fig. 13. Relationship between the strike force and the collision angle.
and periodical jet in the downstream flow. The third comprises chamber diameter, chamber length, and collision angle which should be able to produce the axisymmetric vortex ring.
Y. Qu, S. Chen / European Journal of Mechanics B/Fluids 65 (2017) 179–183
(3) The best size combination of the nozzle structural parameters is a suction nozzle diameter of 8 mm, a discharge nozzle diameter of 16 mm, a chamber diameter of 95 mm, a chamber length of 65 mm, and a collision angle of 120° in which case a low frequency pulsed cavitation jet appears and the strike force reaches 1.6–1.7 times that of a continuous jet force. (4) The optimization range of cavity structural parameters is that the diameter ratio of the chamber and the discharge nozzle is Dc/d = 5–6.88, the ratio of the discharge nozzle diameter and the 2 suction nozzle diameter is d2/d1 = 1.84–2.67, and the ratio of the chamber length and the chamber diameter is Lc/Dc = 0.53–0.84. Acknowledgments The authors acknowledge the National Natural Science Foundation of China (51176102) and Science and Technology Development Planning of Shandong Province, China (2014GGX108001 and 2016GGX104018). Thanks to Dr. Edward C. Mignot, Shandong University, for linguistic advice. References [1] Zhiming Wang, Zhonghou Shen, Mathematical model of jet–driven oscillator and experimental study, J. Univ. Pet. 13 (1989) 22–30. [2] Zhenfang Liao, Chuanlin Tang, Theoretical analysis of self-excited pulsed jet nozzle, J. Chongqing Univ. 25 (2002) 24–27. [3] Xunming Wang, Lei Jiao, Leqin Wang, Self-excited pulse generating mechanism numerical simulation and parameters impact analysis, J. Zhejiang Univ. 39 (2005) 1450–1454. [4] Chuanlin Tang, Zhenfang Liao, Theoretical analysis and experimental study a self-excited oscillation pulsed jet device, J. China Coal Soc. (1989) 90–100.
183
[5] Gensheng Li, Zhonghou Shen, Design principle of organ-pipe cavitation jet nozzles, J. Univ. Pet. 16 (1992) 35–39. [6] M.M. Vijay, et al. A study of the practicality of cavitating water jets. On jet cutting technology, St. Andrews, Scotland, 1992. [7] Zhonghou Shen, Experimental study on rock erosion by self-resonating cavitating jets, in: Proceeding of International Water Jet Symposium, Beijing 1987. [8] Ruliang Xu, Studies on the technologies of jet cleaning, sludge forming and resourceful treatment for the industrial oil tank (Ph. D. Dissertation), Zhejiang University, 2004. [9] Jiangyun Li, Leqin Wang, Ruliang Xu, Cavition model for the low-pressure large-diameter self-excited pulse nozzle, J. Eng. Thermo-Phys. 26 (2005) 438–440. [10] Jiangyun Li, Ruliang Xu, Leqin Wang, Numerical simulation of mechanism of the self-excited pulse nozzle, J. Eng. Thermo-Phys. 25 (2004) 241–243. [11] Chuanchang Gao, Hao Chen, Ting Lei, Research and progress of the self-excited oscillation pulsed jet, J. N. China Univ. Water Conserv. Electr. Power 30 (2009) 41–44. [12] Songying Chen, Chunfeng Li, Yanpeng Qu, Research on the effect factors of the novel self-excited oscillation pulse jet, J. Shandong Univ. 36 (2006) 12–15. [13] Yanpeng Qu, Chunfeng Li, Rongjuan Sui, The numerical analysis on structural parameters of self-excited pulsed jet to the eddy ring, J. Shandong Univ. 36 (2006) 17–21. [14] Yanpeng Qu, Songying Chen, Chunfeng Li, The numerical simulation of liquidvapor two phase flow in low pressure-high flow rate self-excited pulsed jet nozzle, J. Shandong Univ. 36 (2006) 16–20. 25. [15] Fenghua Zhang, Chuanlin Tang, Lin Yang, Zhenfang Liao, Investigation of cavitating nozzle with converging-diverging exit, Fluid Mach. 32 (2004) 25–28. [16] Jiansheng Wang, Effects of the oscillating frequency on the penetration capability of an oscillation pulsed water jet in submerged condition, J. Exp. Mech. 7 (2002) 106–110. [17] Yang Lin, Xiaohong Li, Jiansheng Wang, Effects of structure parameters on the inherent frequency characteristics of self-excited oscillation pulsed jet, Fluid Mach. 29 (2001) 26–28. [18] Liu Ziguang, Experimental Study on Cavitation Water Jet Nozzle for Cleaning, Tianjin University of Science and Technology, 2009.
Contents lists available at ScienceDirect
European Journal of Mechanics B/Fluids journal homepage: www.elsevier.com/locate/ejmflu
Orthogonal experimental research on the structural parameters of a self-excited pulsed cavitation nozzle Yanpeng Qu, Songying Chen ∗ Key Laboratory of High-efficiency and Clean Mechanical Manufacture, School of Mechanical Engineering, Shandong University, Jinan, Shandong 250062, PR China
article
info
Article history: Received 7 December 2016 Available online 31 March 2017 Keywords: Self-excited pulsed jet Cavitation nozzle Orthogonal experiment Strike force
abstract A variety of geometric sizes of a self-excited pulsed jet such as the diameter of the suction and discharge nozzle, jet chamber length and diameter, and the collision angle are the main structural parameters. Under certain operating conditions at a given fluid flow rate, target space, and dynamic head, the jet strike force amplitude and frequency were significantly influenced by these structural sizes. Twenty five group orthogonal experiments were designed to explore the jet dynamic performance with structural sizes to find which group was the best combination. The experiment employed five levels of the diameter of the suction and discharge nozzles, three levels of the chamber diameter, and five levels of the length of the chamber and collision angles. Experimental results showed that the suction nozzle diameter was the most important parameter influencing the jet performance. The next was discharge nozzle diameter. The other three sizes of chamber diameter and length, and collision angle had the similar effect on the selfexcited pulsed jet. The results can have guiding significance for the design of self-excited pulsed cavitation nozzles. © 2017 Elsevier Masson SAS. All rights reserved.
0. Introduction The self-excited pulsed cavitation jet is a kind of developed high efficiency novel jet which was created in the early 1980s based on the principle of self-excited oscillation [1]. Through reasonable nozzle design, a fluid will produce a self-excited oscillation in the cavity and intermittent big vortex rings appear which causes a huge pressure oscillation. Also, strong cavitation can be produced under confining pressure that gives the selfexcited pulsed cavitation jet the advantages of both a free jet and a pulsed jet [2,3]. In addition, the self-excited oscillation cavitation jet can be produced with changes of the nozzle structure without an additional source and it also has advantages of simple structure, small volume, without an additional external drive mechanism, and a dynamic seal [4]. Therefore, the self-excited pulsed cavitation jet has broad application prospects in the fields of coal mining, oil drilling, rock cutting, equipment cleaning, and derusting [5]. According to the principle of underwater acoustics, Vijay [6] put forward the concept of the natural cavitation water jet. Two kinds of typical structures of an acoustic harmonic vibration cavitating water jet were the result of a lot of research. This included the
∗
Corresponding author. E-mail address: [email protected] (S. Chen).
http://dx.doi.org/10.1016/j.euromechflu.2017.03.010 0997-7546/© 2017 Elsevier Masson SAS. All rights reserved.
organ pipe nozzle and the Helmholtz nozzle. Based on the research on the mechanism of the cavitation water jet, Zhonghou [7] established the theory design method of the cavitation nozzle. Ruliang [8] and Jiangyun [9,10] studied the mechanism of the jet through numerical analysis and experimental verification. They thought that the cavitation merged with periodical convergence and scattered with time. Structural and operational parameters of the self-excited pulsed cavitation jet device have a significant effect on the pulse performance. There have been many numerical simulations and experiments on high pressure and low flow rate jets [11]. Songying [12] and Yanpeng [13,14] studied the evolutionary process on the oscillation cavity under low pressure and high flow rate. Fenghua [15] made a further study on the effects of the cavitating nozzle with a converging–diverging exit on the cavitation effect through theoretical analysis and tests. Jiansheng [16] researched relations of the jet force and frequency with the nozzle structure and operation parameters, and many scholars did a lot of work in this field. Yang [17] studied the relationship between structural parameters and the natural frequency characteristics on the basis of the fluid network similarity theorem. Ziguang [18] obtained a force diagram through the force analysis generated by the self-excited oscillation cavitation jet. Geometric sizes such as diameter of suction d1 and discharge nozzle d2 , jet chamber length Lc and diameter Dc, and collision
180
Y. Qu, S. Chen / European Journal of Mechanics B/Fluids 65 (2017) 179–183 Table 1 The orthogonal experimental scheme and strike force.
Fig. 1. Schematic diagram of the self-excited pulse nozzle device.
angle a are the main structural parameters of the self-excited pulsed jet that have a significantly influence on the target space, dynamic head, and the jet strike force amplitude and frequency. The present study used five levels of diameter size of the suction and discharge nozzle, three levels of the chamber diameter, and five levels of the length of the chamber and collision angles to study the effect of structural parameters on the effect of pulsation by L25 (56 ) orthogonal experiments. 1. Experiment 1.1. Experimental setup The self-excited pulsed cavitation jet nozzle is mainly composed of a suction nozzle, discharge nozzle, chamber, oscillation chamber, and collision angle, as shown in Fig. 1. Fig. 2 shows the self-excited pulsed jet device test system in which the inverter can regulate the supply pressure of the circulation pump and the water flow rate of the nozzle can be controlled by the control valve and diverter. Water flow will form a pulse jet through the nozzle and directly spray towards the target. The pressure, temperature, rate of flow, and the force in the suction nozzle or chamber are measured by the pressure sensor, thermal sensor, electromagnetic flowmeter, and weighing sensor, respectively. The transmitter transmits the signal to the data acquisition system and it is analyzed by the computer. Photos of the pulse nozzle and test system are shown in Figs. 3 and 4, respectively. 1.2. The orthogonal experimental scheme and results The orthogonal experiment was designed by the orthogonal table L25 (56 ) as shown in Table 1. The strike force was chosen as the test index since it is a key factor of actual job quality. The average of pressure and the peak value of the strike force were chosen as the test results without the effect of pulse and the pulsing condition. A total of 25 group tests were given the same input pressure of 1.0 MPa and the value of the strike force was measured by a weighing sensor at the target distance of 300 mm. The experimental results showed that the suction nozzle diameter was the most influential parameter for the jet performance. The next was the discharge nozzle diameter. The other three sizes of the chamber diameter and length, and collision angle had an almost similar effect on the self-excited pulsed jet. It can be concluded that three geometric sizes are in charge of the kinetic values within the jet device. The first is the upstream nozzle which provides the inlet pressure and velocity. In order to reach the vaporized pressure, the local pressure at the center of vortex ring should be lower than the jet fluid saturated vapor pressure, and enough turbulent kinetic energy should be produced under the operating conditions. The second is the discharge nozzle which can provide smooth flow conditions for pulsed fluid to produce a strong and periodical jet in the downstream flow. The third is chamber diameter, chamber length, and collision angle which should be able to cause the axisymmetric vortex ring.
Number
d1 (mm)
d2 (mm)
a (°)
Lc (mm)
Dc (mm)
F (N)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 k1 k2 k3 k4 k5 R R′
8.7 8.7 8.7 8.7 8.7 3 3 3 3 3 4 4 4 4 4 6 6 6 6 6 8 8 8 8 8 7.628 2.632 4.508 6.016 7.860 5.228 4.676
8 10 12 14 16 8 10 12 14 16 8 10 12 14 16 8 10 12 14 16 8 10 12 14 16 4.708 4.884 5.352 6.684 7.016 2.308 2.064
90 120 150 180 240 120 150 180 240 90 150 180 240 90 120 180 240 90 120 150 240 90 180 150 120 5.264 6.146 5.562 6.058 5.614 0.882 0.789
20 30 50 65 80 50 65 80 20 30 80 20 30 50 65 30 50 65 80 20 50 80 20 30 65 5.834 5.854 5.018 6.046 5.892 1.028 0.919
80 95 110 80 95 80 95 80 95 110 95 110 80 95 80 95 80 95 110 80 110 80 95 80 95 5.729 5.957 5.272 – – 0.685 0.796
66.22 70.14 51.40 87.80 98.59 26.49 27.96 17.85 32.37 24.43 31.88 45.82 52.48 36.99 53.95 47.38 32.96 67.88 77.99 68.87 58.96 62.69 72.89 93.01 110.06 – – – – – – –
1.3. Analysis of the best working condition The experimental strike force value in Table 1 shows that when the suction nozzle diameter was 8 mm, the discharge nozzle diameter was 16 mm, the chamber diameter was 95 mm, the chamber length was 65 mm, and the collision angle was 120°, the strike force F reached the maximum value of 110.06 N which is the best working condition. The phenomenon of scattering and convergent is formed by the pulse jet. Convergent is the stage of energy storage as shown in Fig. 5(a). Scattering is the stage of energy release as shown in Fig. 5(b). The relation between force and time is shown in Fig. 6 which shows that the strike force causes cyclical changes. Fig. 7 shows that the cavity pressure periodical changes with time, the same as the strike force because the cavitation area expands with the reduced pressure which hinders the center jet resulting in a decrease of the strike force, and when the cavity pressure increases, the cavitation area narrows and the strike force increases. The whole process is a low-pressure self-excited pulsed cavitation water jet formation. 1.4. Comparison of the strike force between the pulsed and usual cylinder jet The self-excited pulsed cavitation jet nozzle can convert the continuous energy into pulse energy through the stage of energy storage and release which makes the instantaneous peak force of a pulse jet bigger than the continuous jet force. Fig. 8 shows that the maximum strike force of the self-excited pulsed cavitation jet can be 1.6–1.7 times that of the continuous cylinder jet. 2. Analysis of the influence of structural parameters on the pulse effect The structure parameters which can offer the best working condition were determined in Section 2. On this basis, the influence of
Y. Qu, S. Chen / European Journal of Mechanics B/Fluids 65 (2017) 179–183
181
Fig. 2. Schematic diagram of the self-excited pulsed jet device test system.
bigger discharge nozzle diameter will decrease the energy loss. The inflection point of the force change was not found in the experiment due to the selection of discharge nozzle diameters. 2.3. Influence of the chamber length on the jet
Fig. 3. Self-excited pulse nozzle.
Fig. 11 shows the relationship between the strike force and chamber length. The strike force did not have a regular change with the chamber length and the force showed a tendency of increasing at Lc = 30 mm which may be related to the moving of the cavitation balloon and the feedback of the pressure wave in the cavity. The pulse jet appeared when the chamber length was 50, 65, and 80 mm. The optimization range of these two structural parameters was Lc /Dc = 0.53–0.84 and it reached the maximum when the ratio was 0.68. 2.4. Influence of the chamber diameter on the jet
Fig. 4. Self-excited pulsed jet device test system.
various parameters on the pulse jet was studied by the controlling variable method. 2.1. Influence of the suction nozzle diameter on the jet Fig. 9 shows the changes of values of the strike force with suction nozzle diameters of 3, 4, 6, 8, and 8.7 mm under an inlet total pressure of 1.0 MPa. The strike force had a tendency of increasing with an increase of the suction nozzle diameter because the upstream nozzle determines the inlet pressure and velocity. The strike force declined when the suction nozzle diameter was 8.7 mm because there is no pulsed jet under this condition. If the flow energy from the suction nozzle can be better accepted by the discharge nozzle, energy loss decreases and strike force increases, which indicates the combination of the suction nozzle and discharge nozzle is also very important. The pulse jet appeared when suction nozzle diameters were 6, 8, and 8.7 mm, and was most obvious at a suction nozzle diameter of 8 mm. So the optimum range of these two structural parameters was d2/d1 = 1.84–2.67 and it reached the best when the ratio was 2. 2.2. Influence of the discharge nozzle diameter on the jet The relationship between the strike force and the discharge nozzle diameter is shown in Fig. 10. The strike force increased with an increase of the discharge nozzle diameter because a
The relationship between the strike force and the chamber diameter is shown in Fig. 12. The strike force first increased and then decreased with an increase of chamber diameter. The change phenomenon of the chamber indicated that the range of low pressure increased with an increase of the chamber diameter and the chamber diameter plays a decisive role in producing a periodical change of the cavitation balloon and the effective kinetic energy output. The energy output of the discharge nozzle can be influenced by the discharge diameter d2 and the chamber diameter Dc. This relationship can be expressed by the dimensionless parameter. The optimization range of these two structural parameters was Dc/d2 = 5–6.88 and the maximum was when the ratio was 5.94. 2.5. Influence of the collision angle on the jet Fig. 13 shows the relationship between the strike force and the collision angle. The pulse jet always appeared no matter what the value of the collision angle and the pulse phenomenon was most obvious when the collision angle was 120°. 3. Conclusions Twenty five group orthogonal experiments were designed to explore the influence of the five nozzle structural sizes on the jet dynamic performance under the best working condition. Conclusions are as follows. (1) The suction nozzle diameter is the first parameter influencing the jet performance. The next is the discharge nozzle diameter. The other three sizes of chamber diameter and length, collision angle almost have a similar effect on the self-excited pulsed jet. (2) Three geometric sizes are responsible for the kinetic values within the jet device. The first is the upstream nozzle which offers
182
Y. Qu, S. Chen / European Journal of Mechanics B/Fluids 65 (2017) 179–183
(a) Jet convergent form.
(b) Jet scattering form. Fig. 5. Jet energy store and release.
120 Strike force (N)
100 80 60 40 20 0
1
28
55
82 109 136 163 190 217 244 271 298 325 352 379 Sampling point
Cavity pressure (MPa)
Fig. 6. Relationship between strike force and time. 1 0 -0.01 -0.02 -0.03 -0.04 -0.05 -0.06 -0.07 -0.08 -0.09 -0.1
15
29
43
57
71
85
Fig. 10. Relationship between the strike force and the discharge nozzle diameter.
99 113 127 141 155 169 183 197
Sampling point
Fig. 7. Relationship between cavity pressure and time. Fig. 11. Relationship between the strike force and the chamber length.
Fig. 8. The comparison of force between the pulsed and usual cylinder jet.
Fig. 12. Relationship between the strike force and the chamber diameter.
Fig. 9. Relationship between the strike force and the suction nozzle diameter.
the inlet pressure and velocity. In order to reach the vaporized pressure, the local pressure at the center of vortex ring should be lower than the jet fluid saturated vapor pressure, and enough turbulent kinetic energy should be produced under the operational condition. The second is the discharge nozzle which can provide smooth flow conditions for pulsed fluid to produce a strong
Fig. 13. Relationship between the strike force and the collision angle.
and periodical jet in the downstream flow. The third comprises chamber diameter, chamber length, and collision angle which should be able to produce the axisymmetric vortex ring.
Y. Qu, S. Chen / European Journal of Mechanics B/Fluids 65 (2017) 179–183
(3) The best size combination of the nozzle structural parameters is a suction nozzle diameter of 8 mm, a discharge nozzle diameter of 16 mm, a chamber diameter of 95 mm, a chamber length of 65 mm, and a collision angle of 120° in which case a low frequency pulsed cavitation jet appears and the strike force reaches 1.6–1.7 times that of a continuous jet force. (4) The optimization range of cavity structural parameters is that the diameter ratio of the chamber and the discharge nozzle is Dc/d = 5–6.88, the ratio of the discharge nozzle diameter and the 2 suction nozzle diameter is d2/d1 = 1.84–2.67, and the ratio of the chamber length and the chamber diameter is Lc/Dc = 0.53–0.84. Acknowledgments The authors acknowledge the National Natural Science Foundation of China (51176102) and Science and Technology Development Planning of Shandong Province, China (2014GGX108001 and 2016GGX104018). Thanks to Dr. Edward C. Mignot, Shandong University, for linguistic advice. References [1] Zhiming Wang, Zhonghou Shen, Mathematical model of jet–driven oscillator and experimental study, J. Univ. Pet. 13 (1989) 22–30. [2] Zhenfang Liao, Chuanlin Tang, Theoretical analysis of self-excited pulsed jet nozzle, J. Chongqing Univ. 25 (2002) 24–27. [3] Xunming Wang, Lei Jiao, Leqin Wang, Self-excited pulse generating mechanism numerical simulation and parameters impact analysis, J. Zhejiang Univ. 39 (2005) 1450–1454. [4] Chuanlin Tang, Zhenfang Liao, Theoretical analysis and experimental study a self-excited oscillation pulsed jet device, J. China Coal Soc. (1989) 90–100.
183
[5] Gensheng Li, Zhonghou Shen, Design principle of organ-pipe cavitation jet nozzles, J. Univ. Pet. 16 (1992) 35–39. [6] M.M. Vijay, et al. A study of the practicality of cavitating water jets. On jet cutting technology, St. Andrews, Scotland, 1992. [7] Zhonghou Shen, Experimental study on rock erosion by self-resonating cavitating jets, in: Proceeding of International Water Jet Symposium, Beijing 1987. [8] Ruliang Xu, Studies on the technologies of jet cleaning, sludge forming and resourceful treatment for the industrial oil tank (Ph. D. Dissertation), Zhejiang University, 2004. [9] Jiangyun Li, Leqin Wang, Ruliang Xu, Cavition model for the low-pressure large-diameter self-excited pulse nozzle, J. Eng. Thermo-Phys. 26 (2005) 438–440. [10] Jiangyun Li, Ruliang Xu, Leqin Wang, Numerical simulation of mechanism of the self-excited pulse nozzle, J. Eng. Thermo-Phys. 25 (2004) 241–243. [11] Chuanchang Gao, Hao Chen, Ting Lei, Research and progress of the self-excited oscillation pulsed jet, J. N. China Univ. Water Conserv. Electr. Power 30 (2009) 41–44. [12] Songying Chen, Chunfeng Li, Yanpeng Qu, Research on the effect factors of the novel self-excited oscillation pulse jet, J. Shandong Univ. 36 (2006) 12–15. [13] Yanpeng Qu, Chunfeng Li, Rongjuan Sui, The numerical analysis on structural parameters of self-excited pulsed jet to the eddy ring, J. Shandong Univ. 36 (2006) 17–21. [14] Yanpeng Qu, Songying Chen, Chunfeng Li, The numerical simulation of liquidvapor two phase flow in low pressure-high flow rate self-excited pulsed jet nozzle, J. Shandong Univ. 36 (2006) 16–20. 25. [15] Fenghua Zhang, Chuanlin Tang, Lin Yang, Zhenfang Liao, Investigation of cavitating nozzle with converging-diverging exit, Fluid Mach. 32 (2004) 25–28. [16] Jiansheng Wang, Effects of the oscillating frequency on the penetration capability of an oscillation pulsed water jet in submerged condition, J. Exp. Mech. 7 (2002) 106–110. [17] Yang Lin, Xiaohong Li, Jiansheng Wang, Effects of structure parameters on the inherent frequency characteristics of self-excited oscillation pulsed jet, Fluid Mach. 29 (2001) 26–28. [18] Liu Ziguang, Experimental Study on Cavitation Water Jet Nozzle for Cleaning, Tianjin University of Science and Technology, 2009.