Huimin Song

Influence of operating pressure on surface dielectric barrier discharge plasma aerodynamic actuation characteristics

This letter reports an experimental study of surface dielectric barrier discharge plasma aerodynamic actuation characteristics’ dependence on operating pressure. As the pressure decreases, the N2(CПu3) rotational temperature decreases, while its vibrational temperature decreases initially and then increases. In addition, the discharge mode changes from a filamentary type to a glow type at 45Torr. In the filamentary mode, the electron density decreases with pressure, while the electron temperature remains almost unchanged. In the glow mode, however, both the electron density and the electron temperature increase while the pressure decreases. The induced velocity shows a maximum value at 445Torr.

Influence of geometrical parameters on performance of plasma synthetic jet actuator

Plasma synthetic jet actuator (PSJA) has shown wide and promising application prospects in a high speed flow control field, due to its rapid response, high exhaust velocity, and non-moving components. In this paper, the total pressure profile of a plasma synthetic jet (PSJ) is measured and a new method is developed to evaluate the pulsed thrust of the PSJA. The influence of geometrical parameters including the electrode distance, the orifice diameter, and the throat length on PSJA performance is analyzed based on the pulsed thrust, the discharge characteristics, and the schlieren images. When varying the electrode distance, the dominant factor determining the jet intensity is the heating volume instead of the discharge energy. For the arc discharge, the electrode distance should be extended to increase both the jet velocity and the jet duration time. The design of the orifice diameter should be based on the controlled flow field. A large orifice diameter produces a strong perturbation with short time duration, while a small orifice diameter induces a lasting jet with low mass flux. In order to obtain better high frequency performance, the throat length should be shortened on the condition that the structural strength of the PSJA is maintained, while there is almost no influence of the throat length on the single cycle performance of the PSJA. Once the discharge energy is fixed, the pulsed thrust remains almost unchanged with different orifice diameters and throat lengths. These three geometrical parameters are independent to some extent and can be optimized separately.

Effects of plasma aerodynamic actuation on oblique shock wave in a cold supersonic flow

Wedge oblique shock wave control using an arc discharge plasma aerodynamic actuator was investigated both experimentally and theoretically. Schlieren photography measurements in a small-scale short-duration supersonic wind tunnel indicated that the shock wave angle decreased and its start point shifted upstream with the plasma aerodynamic actuation. Also the shock wave intensity weakened, as shown by the decrease in the gas static pressure ratio of flow downstream and upstream of the shock wave. Moreover, the shock wave control effect was intensified when a static magnetic field was applied. Under test conditions of Mach 2.2, magnetic control and input voltage 3 kV, the start point of the shock wave shifted 4 mm upstream, while its angle and intensity decreased 8.6% and 8.8%, respectively. A thermal choking model was proposed to deduce the change laws of oblique shock wave control by surface arc discharge. The theoretical result was consistent with the experimental result, which demonstrated that the thermal choking model can effectively forecast the effect of plasma actuation on an oblique shock wave in a cold supersonic flow.

Analytic model and frequency characteristics of plasma synthetic jet actuator

This paper reports a novel analytic model of a plasma synthetic jet actuator (PSJA), considering both the heat transfer effect and the inertia of the throat gas. Both the whole cycle characteristics and the repetitive working process of PSJA can be predicted with this model. The frequency characteristics of a PSJA with 87 mm3 volume and different orifice diameters are investigated based on the analytic model combined with experiments. In the repetitive working mode, the actuator works initially in the transitional stage with 20 cycles and then in the dynamic balanced stage. During the transitional stage, major performance parameters of PSJA experience stepped growth, while during the dynamic balanced stage, these parameters are characterized by periodic variation. With a constant discharge energy of 6.9 mJ, there exists a saturated frequency of 4 kHz/6 kHz for an orifice diameter of 1 mm/1.5 mm, at which the time-averaged total pressure of the pulsed jet reaches a maximum. Between 0.5 mm and 1.5 mm, a larger orifice diameter leads to a higher saturated frequency due to the reduced jet duration time. As the actuation frequency increases, both the time-averaged cavity temperature and the peak jet velocity initially increase and then remain almost unchanged at 1600 K and 280 m/s, respectively. Besides, with increasing frequency, the mechanical energy incorporated in single pulsed jet, the expelled mass per pulse, and the time-averaged density in the cavity, decline in a stair stepping way, which is caused by the intermittent decrease of refresh stage duration in one period.

Optical emission characteristics of surface nanosecond pulsed dielectric barrier discharge plasma

This paper reports an experimental study of the optical emission characteristics of the surface dielectric barrier discharge plasma excited by nanosecond pulsed voltage. N2(C3Пu) rotational and vibrational temperatures are almost the same with upper electrode powered with positive polarity and lower electrode grounded or upper electrode grounded and lower electrode powered with positive polarity. While the electron temperature is 12% higher with upper electrode powered with positive polarity and lower electrode grounded. When the frequency is below 2000 Hz, there is almost no influence of applied voltage amplitude and frequency on N2(C3Пu) rotational, vibrational temperature and electron temperature. As the pressure decreases from 760 Torr to 5 Torr, N2(C3Пu) rotational temperature remains almost unchanged, while its vibrational temperature decreases initially and then increases. The discharge mode changes from a filamentary type to a glow type around 80 Torr. In the filamentary mode, the electron tempera...

Investigation of the performance characteristics of a plasma synthetic jet actuator based on a quantitative Schlieren method

A quantitative Schlieren method is developed to calculate the density field of axisymmetric flows. With this method, the flow field structures of plasma synthetic jets are analysed in detail. Major performance parameters, including the maximum density increase behind the shock wave, the expelled mass per pulse and the impulse, are obtained to evaluate the intensity of the shock wave and the jet. A high-density but low-velocity jet issues out of the cavity after the precursor shock wave, with a vortex ring at the wave front. The vortex ring gradually lags behind the center jet during the propagation, and its profile resembles a pair of kidneys in shape. After the jet terminates, the vortex ring breaks down and the whole density field is separated into two regions. In one period, the jet front velocity first increases and then decreases, with a maximum value of 270 m s−1. The precursor shock wave velocity decays quickly from 370 m s−1 to 340 m s−1 in the first 50 μs. The variation in the maximum density rise behind the precursor shock wave is similar to that of the jet front velocity. The averaged exit density drops sharply at around 50 μs and then gradually rises. The maximum mass flow rate is about 0.35 g s−1, and the total expelled mass in one period occupies 26% of the initial cavity gas mass. The impulse produced in the jet stage is estimated to be 5 μN s–1. The quantitative Schlieren method developed can also be used in the research of other compressible axisymmetric flows.

Efficiency Characteristic of Plasma Synthetic Jet Actuator Driven by Pulsed Direct-Current Discharge

The greatest weakness of the plasma synthetic jet actuator is low working efficiency. In this paper, a novel sequential discharge (trigger discharge/pulsed direct-current discharge) power supply is designed, and the efficiency characteristics of the plasma synthetic jet actuator are analyzed in detail. The total working efficiency is divided into three subefficiencies: discharge efficiency, equivalent uniform heating efficiency, and ideal thermodynamic cycle efficiency. The discharge efficiency of a pulsed direct-current discharge is proportional to the arc voltage. Either increasing the electrode distance or reducing the discharge current can improve the discharge efficiency. The ideal thermodynamic cycle efficiency in previous works was estimated to be less than 30%. Both increasing the nondimensional energy deposition and reducing the heating time are good for improving the ideal thermodynamic cycle efficiency. The equivalent uniform heating efficiency is inversely proportional to the discharge current...

Influence of excitation voltage waveform on dielectric barrier discharge plasma aerodynamic actuation characteristics

Plasma flow control, based on the plasma aerodynamic actuati on generated by air discharge, is an active field in aerodynamics due to its potential application in performance improvement of future aircraft. In order to better understand the underlying physical mechanism of plasma flow control, it is i mportant to investigate the relationship between the operating parameters and the plasma aerodynamic actuation characteristics. This paper reports the electrical, optical and mech anical characteristics of surface dielectric barrier discharge p lasma aerodynamic actuation excited by microsecond and nanosecond high voltage waveforms. The nanosecond discharge is more diffuser than the microsecond discharge and the discharge current is much larger at the same applied voltage amplitude. The optical emission intensity of the nanosecond discharge plasma is stronger than that of the microsecond discharge plasma, while the rotational and vibrational temperatures of N2 in the nanosecond discharge plasma are less. In addition, the relative intensity of the first negative system of N + 2 (B 2 � + u ! X 2 � + g ) and the second positive system of N2(C 3 �u ! B 3 �g) is much less in the nanosecond discharge plasma. The velocity measurements indicate that the air flow induced by the nanose cond discharge plasma aerodynamic actuation is vertical to the dielectric surface, while that induced by the microsecond discharge actuation is parallel to the dielectric surface.

Modeling and optimization of the multichannel spark discharge

This paper reports a novel analytic model of this multichannel spark discharge, considering the delay time in the breakdown process, the electric transforming of the discharge channel from a capacitor to a resistor induced by the air breakdown, and the varying plasma resistance in the discharge process. The good agreement between the experimental and the simulated results validated the accuracy of this model. Based on this model, the influence of the circuit parameters on the maximum discharge channel number (MDCN) is investigated. Both the input voltage amplitude and the breakdown voltage threshold of each discharge channel play a critical role. With the increase of the input voltage and the decrease of the breakdown voltage, the MCDN increases almost linearly. With the increase of the discharge capacitance, the MDCN first rises and then remains almost constant. With the increase of the circuit inductance, the MDCN increases slowly but decreases quickly when the inductance increases over a certain value. There is an optimal value of the capacitor connected to the discharge channel corresponding to the MDCN. Finally, based on these results, to shorten the discharge time, a modified multichannel discharge circuit is developed and validated by the experiment. With only 6-kV input voltage, 31-channels discharge is achieved. The breakdown voltage of each electrode gap is larger than 3 kV. The modified discharge circuit is certain to be widely used in the PSJA flow control field.

Electric and plasma characteristics of RF discharge plasma actuation under varying pressures

The electric and plasma characteristics of RF discharge plasma actuation under varying pressure have been investigated experimentally. As the pressure increases, the shapes of charge–voltage Lissajous curves vary, and the discharge energy increases. The emission spectra show significant difference as the pressure varies. When the pressure is 1000 Pa, the electron temperature is estimated to be 4.139 eV, the electron density and the vibrational temperature of plasma are 4.71×1011 cm−3 and 1.27 eV, respectively. The ratio of spectral lines which describes the electron temperature hardly changes when the pressure varies between 5000–30000 Pa, while it increases remarkably with the pressure below 5000 Pa, indicating a transition from filamentary discharge to glow discharge. The characteristics of emission spectrum are obviously influenced by the loading power. With more loading power, both of the illumination and emission spectrum intensity increase at 10000 Pa. The pin–pin electrode RF discharge is arc-like at power higher than 33 W, which results in a macroscopic air temperature increase.