Comparison of Velocities Driven by Repetitive Nanosecond Pulses to AC Result

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1 AIAA SciTech January 214, National Harbor, Maryland 52nd Aerospace Sciences Meeting AIAA Comparison of Velocities Driven by Repetitive Nanosecond Pulses to AC Result Jie Li 1, Jianlei Wang 2, Xuanshi Meng 3,Huaxing Li 4 (1. Northwestern Polytechnical University, Xi an 7172, China) Feng Liu 5 and Shijun Luo 6 (2.University of California, Irvine, CA , America) Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / The character of the plasma actuator induce the quiescent air is studied. The plasma actuator is powered by two different kinds of power sources. One is Alternative Current (AC) plasma power source, the other is Nanosecond Pulse (NS) plasma power source. The experiment conducted in an optical glass box which dimension is 6mm 5mm 5mm. A Particle Image Velocimetry (PIV) system is used in this study to measure the flow filed induced by the plasma actuator, the average velocity distribution shown as the results. The average results of effects to quiescent air by two different kinds of power sources are similar. Both of them are present in the form of flow jet along the wall. The highest velocity and jet flow filed area is increased by the power source voltage. The induced jet flow which is powered by AC power source is pointed from the exposed electrode to the encapsulated electrode, however, the induced jet flow which is powered by NS power source is pointed to both side and the main jet flow filed is from the encapsulated electrode to the exposed electrode. The highest jet flow velocity is 4m/s for the AC power source and.3m/s for the NS power source. The jet velocity induced by the NS power source is ignorable from the point of view of induce velocity to the quiescent air. Nomenclature V = voltage of the sources, kv V p-p = peak-to-peak voltage of AC voltage source, kv F = control frequency of the sources, khz t = time, s U = resultant velocity, m/s u, v = x-, y-component of velocity, m/s 1 Graduate Student, Department of Fluid Mechanics. 2 PHD Student, Department of Fluid Mechanics. 3 Associate Professor, Department of Fluid Mechanics. 4 Professor, Department of Fluid Mechanics.. 5 Professor, Department of Mechanical and Aerospace Engineering. Fellow AIAA. 6 Researcher, Department of Mechanical and Aerospace Engineering. 1 Copyright 214 by the, Inc. All rights reserved.

2 Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / A I. Introduction ctive flow control in the form of localized periodic excitation has been used to impart global changes to separated flow fields. Flow control with plasma actuation is attractive because these devices are entirely surface mounted, lack mechanical parts and possess high bandwidth while requiring relatively low power. Dielectric Barrier Discharge (DBD) plasma actuators driven by AC waveforms (AC-DBD) are the most popular of these devices. They have been widely used for controlling flow separation 1-2, turbulent drag reduction 3, noise reduction 4, boundary layer control 5-7 and transition delay 8, particularly on the leading edge of airfoils in relatively low velocity freestreams (~3 m/s) 9. The control mechanism for AC-DBD plasma actuators arises from an electro hydro dynamic (EHD) effect 1. Interaction between the charged species in the plasma and neutral particles near the surface generates a low speed (<1 m/s) near wall jet in quiescent air, thus limiting its application in practical flight environments. For NS-DBD plasma, Keisuke Takashima et al. 11 in Ohio university used Phase-locked schlieren images to visualize compression waves generated by the NS-DBD plasma. The results suggest that the compression wave may be a superposition of individual waves generated by discharge filaments, some of which remain fairly reproducible pulse-to-pulse. Little et al. 12 obtained the ns-dbd transfers substantially less momentum to the neutral air molecules than the more widely studied ac-dbd plasma actuator. The momentum transfer is quite weak and is not expected to have a significant effect in the flow in the conditions tested. Instead, the control authority generated by ns-dbd plasma is believed to stem from rapid localized heating of the near-surface gas layer by the plasma. This gives rise to a complex pattern of quasi-planar and spherical compression waves in still air. Patel et al 13 Li et al. 14 found that when the inflow velocity is.2 Ma, Microsecond pulse plasma aerodynamic actuation can effectively suppress flow separation on the suction side of the NACA 15 airfoil.. Roupassov et al. 15 used ns-dbd to study airfoil flow separation, results showed that the flow rate increases to.74ma, ns-dbd can still effectively inhibit the airfoil surface flow separation. The present work promotes the spatial resolution of PIV system and obtains a fine velocity field induced by NS-DBD plasma actuators. The experimental results show that the velocity induced by NS-DBD is far less than that induced by AC-DBD, and the direction of the main induced velocity is opposite. II. Experimental Setup A. Dielectric-Barrier-Discharge Plasma Actuator and Test Chamber Dielectric Barrier Discharge (DBD) actuators as shown in Fig. 1 are used in the present research. The plasma actuator consists of two asymmetric copper electrodes each of.3 mm thickness. Seven Kapton tape layers (.56 mm thick per layer) separate the encapsulated electrode from the exposed electrode. The effective span wise length (along which plasma is generated) is 2 mm. The width of the exposed and encapsulated electrode is 5 mm and 1mm, respectively. The two electrodes are separated by a gap of mm, where the plasma is created and emits a blue glow in darkness. 2

3 Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / Figure1. The plasma actuator In order to reduce the effect of any external disturbances on the measurement, all tests are conducted in still air which is achieved by a closed cuboids chamber with a length of 6 mm, a width of 5 mm and a height of 5 mm. The bottom is the surface of a test table, and the other five faces of the chamber are made from plexiglas of 5 mm thick to allow for optical viewing and access of the laser sheet. The air inside the chamber under one atmospheric pressure is shielded from the air in the laboratory room. The seeds are smoke particles of approximately 1μm in diameter commonly used in cinema industry. The seeds would stay suspended for many hours and were only replenished when needed. In our test, wo use two kinds of sources: one is AC source and another is NS source. (1)The waveform of the AC source is sine wave. The peak-to-peak voltage is set at V p-p = 12 kv/13kv and carrier frequency varies is khz. (2)The waveform of the NS source is impulse wave. The peak voltage is set at V p-p = 6.88 kv/9.2kv /9.8kV and carrier frequency varies is khz. All the tests in this paper are continuous discharge actuation. An overview of the actuator parameters for all measurements is shown in table 1. Table 1. dimensions of actuator and measured parameters Parameter Value Source AC(V p p ) NS(V) Operating voltage(kv) Operating frequency(f, khz) Upper electrode width(copper, mm) 5 Lower electrode width(copper, mm) 1 Gap distance(mm) Dielectric thickness(kapton, mm).392 Plasma actuator length (mm) 2 B. Voltage and Glow of Repetitive Nanosecond Pulses and AC Voltage Source Simultaneous measurements of voltage for NS-DBD plasma are shown in Fig. 2 a) and b). An example of the same measurement for a typical AC-DBD plasma actuator is also provided for reference in Fig. 2 c). The NS-DBD pulse width is ~4ns and reaches peak voltage of ~14.5kV. The AC-DBD voltage trace is sinusoidal with a peak to peak voltage of ~15 kv and frequency of khz. 3

4 Voltae[kV] 5 Voltae[kV] Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / Time[ns] F=1.712kHz Time[ns] F=1.712kHz a) b) Voltae[kV] Time[μs] F=11.75kHz c) Figure 2. voltage traces for NS-DBD (a, b) and AC-DBD (c) plasma actuators on a ~2cm long DBD load. Figure 2. a) and b) is the same voltage trace, but different time range.the NS-DBD pulse width is ~5 ns and reaches peak voltage of ~14.5 kv. The AC-DBD voltage trace produced by Suman plasma actuator is sinusoidal with a peak to peak voltage of ~12.4 kv and frequency of khz. 4

5 Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / a). Photograph of AC-DBD F=11.75kHz Exposure time is.4s. b). Photograph of NS-DBD F=11.75kHz There is about 68 pulses in exposure time (.4s). Figure 3. Photograph of DBD Figure 3. shown the higher the voltage is, the stronger the glow and the range are. For the same voltage and frequency, the glow is weaker and well-distributed by AC- DBD than that by NS-DBD. There are some highlights in order for AC-DBD. C. Particle-Image-Velocimetry and Electro-magnatic Screen The PIV system is manufactured by the DantecDynamic Company. The Nd:YAG Laser, a product of the Beamtech Optronics Co., emits single pulse of energy 2 mj and produces double pulses with a time interval of 5 μ s.the laser sheet is 1 mm thickness, and is set at the position of 5% span-wise length of electrodes to make sure the induced flow is two dimensional. The repeat rate of the laser double-pulse is set at 1 Hz. Consecutive 1 seconds of sampling are performed for each case. The sampling number for ensemble averages is 1. A CCD camera of pixels is used to capture the field-of-view of 2mm 45mm. A software of DynamicStudio 3.31 version is used to calculate the cross-flow velocity vector field from the double-pulse images. 5

6 The rectangular interrogation windows pixels and overlap 5% has been adapted to analyze the experimental data. The flow field must keep steady during the acquisition of PIV data. It takes approximately 5 seconds to start power supple and stabilize the output voltage and nearly 1 seconds are needed to make the flow become steady. In order to obtain a steady flow field, the plasma actuator has to work for 15 seconds before PIV acquisition. It should be noted that no other filtering or smoothing has been applied apart from the processing of the raw PIV data and time averaging. Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / Figure 4. Photograph of the PIV setup 1. Computer system 2. Glass cover 3. Oscilloscope 4. High voltage probe 5. Nanosecond pulsed plasma generator 6. Camera 7. Laser arm 8.Laser lens 9. Radiator 1. plasma actuator 11. Timer box 12. Laser controller 13.Laser bench 14. Suman plasma generator The output voltage is measured by a high voltage probe, while the current is read on the plasma generator, and then displayed on the oscilloscope. The model of voltage probe and oscilloscope is Tektronix P615A and Tektronix DPO 354. The probe can measure high voltage of 2 kv DC/4 kv Peak,while it uses 1X readout coding. The oscilloscope is a 4 Channel 5 MHz Digital Phosphor Oscilloscope and it has 5 M uncompromised long record length comes as standard and up to 2.5 GS/s sample rate on all channels for accurate representation of your signal. It is worth mentioning that nanosecond pulse driven DBD plasma actuator has a large electromagnetic interference on experimental devices, especially on devices which have USB interface. When the voltage of the nanosecond pulse driven DBD plasma actuator gradually goes up, the mouse and keyboard which connected to the computer will be affected, even out of work. In addition, the laser system of PIV is sensitive to electromagnetic interference. When working simultaneously with the power supply, the transmitting frequency cannot be kept constant, causing the frame skipping of the camera. Considering the advice of expert, we take protective measures by using shield over host computer and synchronizer. Also, the camera is shielded by wrapping the front with copper mesh which has good light transmission (and this is the reason why PIV images in the flowing figures are blurred). All the shields are connected to the ground. The fluctuation of voltage curve shown above is subject to electromagnetic interference. III. Experimental Results A. Velocity Vectors and Contours The time averaged flow field actuated by DBD is given in Fig. 5&6. The exposed electrode is located between x = -5 mm and x = mm and the encapsulated electrode is located between x = mm and x=1 mm. The red arrow 6

7 stands for the ensemble-averaged velocity vector and the curve between different colors represents the contour of the ensemble-averaged velocity magnitude. In order to present the velocity field clearly, one of every seven vectors along the x-direction is shown. 2 Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / x(mm) a) Velocity field actuated by AC-DBD (V p-p =12 kv, F=11.75 khz) The maximum velocity is 2.57 m/s at position (4.72 mm, mm) x(mm) U(m/s) U(m/s) b) Velocity field actuated by AC-DBD (V p-p =13 kv, F=11.75 khz) The maximum velocity is 3.97m/s at position (5.68 mm,.72 mm). Figure 5.Velocity field actuated by AC-DBD While at the upstream of exposed electrode a vortex flow exists, there is a wall jet flow at the downstream of encapsulated electrode. The higher the voltage is, the stronger the starting vortex and the wall jet are. 7

8 Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / a) Velocity field actuated by NS-DBD (V=5.76 kv, F=1.712 khz) The maximum velocity is.17 m/s at position (-3.13 mm, 1.57 mm) x(mm) b) Velocity field actuated by NS-DBD (V=7.28 kv, F=1.712 khz) The maximum velocity is.37m/s at position (-11.74mm,.28 mm). U(m/s)

9 2 15 U(m/s) Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / x(mm) (c) Velocity field actuated by NS-DBD (V=11.7kV, F=1.712 khz) The maximum velocity is.49m/s at position (3.49 mm,.49 mm) x(mm) (d) Velocity field actuated by NS-DBD (V=13.4kV, F=1.712 khz) The maximum velocity is.53m/s at position (5.2 mm,.49 mm). U(m/s)

10 2 15 Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / x(mm) (e) Velocity field actuated by NS-DBD (V=14.1kV, F=1.712 khz) The maximum velocity is.49m/s at position (5.2 mm,.7 mm). Figure 6.Velocity field actuated by NS-DBD U(m/s) Velocity field induced by NS-DBD is completely different from AC-DBD. Both sides of the actuator location have velocity field, and the main velocity flow field at upstream of the exposed electrode. Flow velocity and range induced by NS-DBD increases while the voltage increasing. B. Convergence of Time-Averaged Velocity Components (u, v) The origin of the coordinate system is located at the downstream upper edge of the exposed electrode as shown in Fig. 1. In order to show that the results presented in this paper are convergent, the time averaged u and v induced by plasma are given in Fig. 7,8,9,1&11. A line A (x=-2 mm) is chosen arbitrarily to check whether the flow is steady. We can clearly see that the results are almost convergent with 2 seconds sampling time a) u b) v Figure 7. Convergence of Time-Averaged u and v, F = khz, V = 5.76kV, x = -2 mm. 1

11 Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / a) u b) v Figure 8. Convergence of Time-Averaged u and v, F = khz, V = 7.28kV, x = -2 mm. a) u b) v Figure 9. Convergence of Time-Averaged u and v, F = khz, V = 11.7kV, x = -2 mm. 11

12 Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / a) u b) v Figure 1. Convergence of Time-Averaged u and v, F = khz, V = 13.4kV, x = -2 mm. a) u b) v Figure 11. Convergence of Time-Averaged u and v, F = khz, V = 14.1kV, x =-2 mm. 12

13 C. Distributions of (u, v) along Lines Parallel to Coordinate Axes AC12kV AC13kV NS5.76kV NS7.28kV NS11.7kV NS13.4kV NS14.1kV AC12kV AC13kV NS5.76kV NS7.28kV NS11.7kV NS13.4kV NS14.1kV Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / u(m/s) u(m/s) a) u b) v Figure 12.Mean velocity profiles for NS and AC-DBD plasma actuators operating in quiescent air measured at x=2 mm AC12kV AC13kV NS5.76 NS7.28 NS11.7kV NS13.4kV NS14.1kV U[m/s] AC12kV AC13kV NS5.76 NS7.28 NS11.7kV NS13.4kV NS14.1kV V[m/s] a) u b) v Figure 13.Mean velocity profiles for NS and AC-DBD plasma actuators operating in quiescent air measured at x=-3 mm. 13

14 D. Contours and Time-Averaged vorticity Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / (a) Vorticity field actuated by AC-DBD( V =12kV, F=11.75kHz) The maximum value of the vorticity is (1/sec) at position(2.37mm,1.14mm). The minimum value of the vorticity is (1/sec) at position(2.3mm,.49mm). p p (b) Vorticity field actuated by AC-DBD( V =13kV, F=11.75kHz) The maximum value of the vorticity is (1/sec) at position (5.7mm,1.4mm). The minimum value of the vorticity is (1/sec) at position (6.11mm,.61mm). Figure 14.Vorticity field actuated by AC-DBD p p 14

15 Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / (a) Vorticity field actuated by NS-DBD(V=5.76kV, F=11.75kHz) The maximum value of the vorticity is 318.8(1/sec) at position (-24.1mm,3.12mm). The minimum value of the vorticity is (1/sec) at position (1.16mm,.25mm). (b) Vorticity field actuated by NS-DBD (V=7.28kV, F=1.712kHz) The maximum value of the vorticity is (1/sec) at position (-13.75mm,3.88mm). The minimum value of the vorticity is (1/sec) at position (-12.69mm,.12mm). 15

16 Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / ( c) Vorticity field actuated by NS-DBD(V=11.7kV, F=1.712kHz) The maximum value of the vorticity is (1/sec) at position(4.12mm,.12mm). The minimum value of the vorticity is (1/sec) at position(-22.97mm,2.51mm). ( d) Vorticity field actuated by NS-DBD(V=13.4kV, F=1.712kHz) The maximum value of the vorticity is (1/sec) at position(6.64mm,.13mm). The minimum value of the vorticity is (1/sec) at position(5.94mm,1.4mm). 16

17 Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / ( e) Vorticity field actuated by NS-DBD(V=14.1kV, F=1.712kHz) The maximum value of the vorticity is (1/sec) at position(6.25mm,.12mm). The minimum value of the vorticity is (1/sec) at position(5.58mm,1.1mm). Figure 15.Vorticity field actuated by NS-DBD The time averaged vorticity actuated by DBD is given in Fig. 14&15. The main vorticity induced by AC source is on the right while that induced by NS source is on the left or right. The range and value of vorticity increase with higher voltage. IV. Conclusions The results show that the flow induced by AC-DBD aerodynamic actuation comes out as starting wall jet. The maximal velocity induced by AC-DBD is about 4 m/s when the actuation voltage is 13 kv. While the maximal velocity induced by NS-DBD aerodynamic actuation is about.5 m/s. The higher the voltage is, the stronger the vortex and the wall jet are.there are flow induced by NS-DBD at both sides of the actuator and in a large field, which is different from that of induced by AC-DBD. The discharge of the NS power source results mainly in a pair of vortices above the plasma actuator, which are counter-clockwise and clockwise on the downstrean and upstream side, respectively, as shown by the streamlines overlaped on vorticity contours; and, thus induces a jet stream normal the body surface towards the expoxed electrode. This may be a mechanism which causes the repetitive nanosecond plasma actuation more effective at higher speed than the AC power source.future investigations should be pursued to study the cases of higher voltages for the nanosecond pulse voltage sources and to compute the phase-locked time-averaged vorticity field based on the PIV mesurements. Acknowledgments The present work is supported by National Natural Science Foundation of China ( ,511711),the Specialized Research Fund for the Doctoral Program of Higher Education ( ).The authors would like to express their gratitude to master students Jinan Zhao and Mingyang Li for their valuable support in the experiments. 17

18 References 1 Post, M. L. and Corke, T. C., Separation Control on High Angle of Attack Airfoil using Plasma Actuators, AIAA Journal, Vol. 42, No. 11, 24, pp Liu, F., Luo, S. J., Gao, C., Meng, X. S., Hao, J. N., Wang, J. L. and Zhao, Z. J., Flow Control over a Conical Forebody Using Duty-Cycled Plasma Actuators, AIAA J., Vol. 46, No. 11, 28, pp Jukes, T. N., Choi, K., Johnson, G. A., and Scott, S. J., Turbulent Drag Reduction by Surface Plasma through Spanwise Flow Oscillation, 3rd AIAA Flow Control Conference, Vol. 3, 26, pp Thomas, F.O., Kozlov, A. and Corke, T. C., Plasma Actuators for Cylinder Flow Control and Noise Reduction, AIAA Journal, Vol. 45, No. 8, Aug. 28, pp Jacob, J. D., Rivir, R., Carter, C., and Estevadeordal, J., Boundary Layer Flow Control Using AC Discharge Plasma Actuators, Downloaded by NORTHWESTERN POLYTECHICAL UNIV. on January 3, DOI: / nd AIAA Flow Control Conference, Huang, J., Corke, T. C., and Thomas, F. O., Plasma Actuators for Separation Control of Low-Pressure Turbine Blades, AIAA Journal, Vol. 44, 26, pp Seraudie, A., Aubert, E., Naude, N., and Cambronne, J. P., Effect of Plasma Actuators on a Flat Plate Laminar Boundary Layer in Subsonic Conditions, 3rd AIAA Flow Control Conference, Vol. 2, 26, pp Grundmann, S. and Tropea, C., Active Cancellation of Artificially Introduced Tollmien Schlichting Waves using Plasma Actuators, Experiments in Fluids, Vol. 44, No. 5, 28, pp Moreau, E., "Airflow Control by Non-Thermal Plasma Actuators," Journal of Physics D: Applied Physics, Vol. 4, 27, pp Jesse Little and Keisuke Takashima, High Lift Airfoil Leading Edge Separation Control with Nanosecond Pulse Driven DBD Plasma Actuators 5th AIAA Flow Control Conference,21 11 Keisuke Takashima, Yvette Zuzeek, Walter R. Lempert, and Igor V. Adamovich. Characterization of Surface Dielectric Barrier Discharge Plasma Sustained by Repetitive Nanosecond Pulses. AIAA Paper , Little J, Takashima K, Nishihara M, et al. Separation Control with Nanosecond Pulse Driven Dielectric Barrier Discharge Plasma Actuators. AIAA Journal, 212, 5(2): Patel M P, Ng T T, Vasudevan S, Thomas C. Corke et al. Scaling effect s of an aerodynamic plasma actuator [C]. 27, AIAA Li Yinghong,Liang Hua,Ma Qingyuanet al. Experimental Investigation on Airfoil Suction Side Flow Separation by Pulse Plasma Aerodynamic Actuation. Acta Aeronautica Et Astronautica Sinica, 28, 29(6): D V Roupassov, A A Nikipelov, M M Nudnova, A Yu Starikovskii. Flow Separation Control by Plasma Actuator with Nanosecond Pulsed Periodic Discharge[J]. AIAA J, 29, 47(1):