Electrical and aerodynamic characteristics of sliding discharge based on a microsecond pulsed plasma supply

Plasma flow control technology has broad prospects for application. Compared with conventional dielectric barrier discharge plasma actuators (DBD-PA), the sliding discharge plasma actuator (SD-PA) has the advantages of a large discharge area and a deflectable induced jet. To achieve the basic performance requirements of light weight, low cost, and high reliability required for UAV (Unmanned Aerial Vehicle) plasma flight experiments, this work designed a microsecond pulse plasma supply that can be used for sliding discharge plasma actuators. In this study, the topology of the primary circuit of the microsecond pulse supply is determined, the waveform of the output terminal of the microsecond pulse plasma supply is detected using the Simulink simulation platform, and the design of the actuation voltage, the pulse frequency modulation function and the construction of the hardware circuit are achieved. Using electrical diagnosis and flow field analysis, the actuation characteristics and flow characteristics of sliding discharge plasma under microsecond pulse actuation are studied, the optimal electrical actuation parameters and flow field characteristics are described.     

Experimental Investigation on Airfoil Shock Control by Plasma Aerodynamic Actuation

An experimental investigation on airfoil （NACA64-215） shock control is performed by plasma aerodynamic actuation in a supersonic tunnel （Ma -= 2）. The results of schlieren and pressure measurement show that when plasma aerodynamic actuation is applied, the position moves forward and the intensity of shock at the head of the airfoil weakens. With the increase in actuating voltage, the total pressure measured at the head of the airfoil increases, which means that the shock intensity decreases and the control effect increases. The best actuation effect is caused by upwind-direction actuation with a magnetic field, and then downwind-direction actuation with a magnetic field, while the control effect of aerodynamic actuation without a magnetic field is the most inconspicuous. The mean intensity of the normal shock at the head of the airfoil is relatively decreased by 16.33%, and the normal shock intensity is relatively reduced by 27.5% when 1000 V actuating voltage and upwind-direction actuation are applied with a magnetic field. This paper theoretically analyzes the Joule heating effect generated by DC discharge and the Lorentz force effect caused by the magnetic field. The discharge characteristics are compared for all kinds of actuation conditions to reveal the mechanism of shock control by plasma aerodynamic actuation.     

A Study of Variation Patterns of Shock Wave Control by Different Plasma Aerodynamic Actuations

Demonstrative experiments on the variation patterns of the position, angle, and intensity of shock wave are presented. Different means of aerodynamic actuation, such as variations of the distance between discharge channels, the number of discharge channels, the DC discharge voltage, the angle of ramp, and the application of magnetic field, in a supersonic flow of M=2.2 are employed. Results of both the schlieren and pressure test indicated that when the plasma aerodynamic actuation is applied, the starting point of the shock wave was shifted 1 to 8mm upstream on average, the shock wave angle was reduced 4% to 8% on average, and the shock wave intensity was decreased by 8% to 26%. The local plasma aerodynamic actuation could generate an extrusive plasma layer with high temperature and pressure. This plasma layer caused an upstream-shift of the separating point of the boundary layer, which changed the structure of the original shock wave. Moreover, in a simulation study, the plasma aerodynamic actuation was simplified as a thermal source term added to the Navier–Stokes equations, after all, the results obtained showed consistency with the experimental results.     

Discharge Characteristics of SF6 in a Non-Uniform Electric Field Under Repetitive Nanosecond Pulses

The characteristics of high pressure sulphur hexafluoride (SF ₆ ) discharges in a highly non-uniform electric field under repetitive nanosecond pulses are investigated in this paper. The influencing factors on discharge process, such as gas pressure, pulse repetition frequency (PRF), and number of applied pulses, are analyzed. Experimental results show that the corona intensity weakens with the increase of gas pressure and strengthens with the increase of PRF or number of applied pulses. Spark discharge images suggest that a shorter and thicker discharge plasma channel will lead to a larger discharge current. The number of applied pulses to breakdown descends with the increase of PRF and ascends with the rise of gas pressure. The reduced electric field (E/p) decreases with the increase of PRF in all circumstances. The experimental results provide significant supplements to the dielectric characteristics of strongly electronegative gases under repetitive nanosecond pulses.     

Two-Phase Flow Regimes and Discharge Characteristics of a Plasma Electrohydrodynamic Atomization

Experimental investigation was conducted to study the flow regimes and discharge characteristics of plasma electrohydrodynamic atomization (EHDA) for decane (C10H22) under pulsed applied negative voltage. The experimental parameters were set as the flow rate of decane from 0 to 10 mL/min and the dc charging voltage from dc 0 to 12 V with a pulse repetition rates of 200 Hz. The flow regime of decane was observed and the volume-to-electrical charge ratio was measured. Unlike a conventional EHDA system, the results show that a corona discharge was initiated at the edge of the hollow electrode at a specific corona on-set voltage of -17 or -20 kV in the case with or without decane flow, respectively. This phenomenon was defined as plasma EHDA.     

Investigation of the interaction between NS-DBD plasma-induced vortexes and separated flow over a swept wing

The effect of nanosecond pulsed dielectric barrier discharge(NS-DBD) plasma flow separation control is closely related to the actuation frequency,because it involves the interaction between plasma-induced vortexes and separated flow.In order to study the mechanism of NS-DBD plasma flow separation control over a swept wing,especially the influence of the actuation frequency,at first,experimental studies of the actuation frequencies at 100 Hz are conducted to validate the numerical simulation meth...     

Experimental Study of the Unsteady Actuation Effect on Induced Flow Characteristics in DBD Plasma Actuators

The main aim of this paper is to investigate unsteady actuation effects on the operation of dielectric barrier discharge(DBD) plasma actuators and to study induced flow characteristics of steady and unsteady actuators in quiescent air.The parameters affecting the operation of unsteady plasma actuators were experimentally measured and compared with the ones for steady actuators.The effects of excitation frequency and duty cycle on the induced flow pattern properties were studied by means of hot-wire anemometers,and the smoke visualization method was also used.It was observed that the current and the mean induced velocity linearly increase with increasing duty cycle while they are not sensitive to excitation frequency.Furthermore,with increasing excitation frequency,the magnitude of vortices shedding from the actuator decreases while their frequency increases.Nevertheless,when the excitation frequency grows beyond a certain level,the induced flow downstream of the actuator behaves as a steady flow.However,the results for steady actuators show that by increasing the applied voltage and carrier frequency,the velocity of the induced flow first increases and then decreases with actuator saturation and the onset of the emission of streaky glow discharge.     

Spatiotemporal control of femtosecond laser filament-triggered discharge and its application in diagnosing gas flow fields

Precise control of the discharge in space and time is of great significance for better applications of discharge plasma. Here, we used a femtosecond laser filament to trigger and guide a high-voltage DC pulse discharge to achieve spatiotemporal control of the discharge plasma. In space, the discharge plasma is distributed strictly along the channel generated by the femtosecond laser filament. The breakdown voltage threshold is reduced, and the discharge length is extended. In time, the electrical parameters such as the electrode voltage and the electrode gap affect discharge delay time and jitter. By optimizing the parameters, we can achieve sub-nanosecond jitter of the discharge. Based on the spatiotemporal control of the discharge, we applied filament-triggered discharge for one-dimensional composition measurements of the gas flow field. Besides, the technique shows great potential in studying the spatiotemporal evolution of discharge plasma.     

Temporal evolution of atmospheric cascade glow discharge with pulsed discharge and radio frequency discharge

Atmospheric cascade discharges with pulsed discharge and radio frequency(RF)discharge were experimentally investigated by the temporal evolution of discharge spatial profile and intensity.The indium tin oxide(ITO)coated glass was employed as the transparent electrode to capture the discharge distribution above the electrode surface.It is demonstrated that in the pulsed discharge with dielectric barrier,the first discharge at the rising edge of pulse voltage is uniformly ignited and then forms an expanding plasma ring on the ITO electrode surface,which shrinks to the same diameter as that of bare stainless steel electrode with the generation of second discharge at the falling edge of pulse voltage.The discharge profiles along the electrode surface and discharge gap of the successive RF discharge are dependent on the intensity and spatial distribution of residual plasma species generated by the pulsed discharge,which is determined by the time interval between the pulsed discharge and RF discharge.It is demonstrated that the residual plasma species before the RF discharge ignition help to achieve the stable operation of RF discharge with elevated intensity.     

Simulation of Electrical Discharge Initiated by a Nanometer-Sized Probe in Atmospheric Conditions

In this paper,a two-dimensional nanometer scale tip-plate discharge model has been employed to study nanoscale electrical discharge in atmospheric conditions.The field strength distributions in a nanometer scale tip-to-plate electrode arrangement were calculated using the finite element analysis(FEA) method,and the influences of applied voltage amplitude and frequency as well as gas gap distance on the variation of efective discharge range(EDR) on the plate were also investigated and discussed.The simulation results show that the probe with a wide tip will cause a larger efective discharge range on the plate;the field strength in the gap is notably higher than that induced by the sharp tip probe;the efective discharge range will increase linearly with the rise of excitation voltage,and decrease nonlinearly with the rise of gap length.In addition,probe dimension,especially the width/height ratio,afects the efective discharge range in diferent manners.With the width/height ratio rising from 1:1 to 1:10,the efective discharge range will maintain stable when the excitation voltage is around 50 V.This will increase when the excitation voltage gets higher and decrease as the excitation voltage gets lower.Furthermore,when the gap length is 5 nm and the excitation voltage is below 20 V,the diameter of EDR in our simulation is about 150 nm,which is consistent with the experiment results reported by other research groups.Our work provides a preliminary understanding of nanometer scale discharges and establishes a predictive structure-behavior relationship.     

Research on the Peristaltic Flow Acceleration Performance of Asynchronous and Duty Cycle Pulsed DBD Plasma Actuation

Using a plexiglas plate model, the performance of peristaltic flow acceleration in- duced by multiple DBD （dielectric barrier discharge） plasma actuators was studied based on PIV （particle image velocimetry）. The asynchronous and the duty cycle pulsed actuation modes were proposed and tested. The velocity fields induced by multiple DBD plasma actuators with different phase angles and duty cycle ratios were acquired and the momentum transfer characteristics of the flow field were discussed. Consequently, the mechanism of the peristalsis-acceleration multi- ple DBD plasma actuation was analyzed. The results show that the peristaltic flow acceleration effect of multiple plasma actuators occurs mainly in paraelectric direction, and the mechanism of peristaltic flow acceleration is ejection pushing effect rather than injection pumping effect. The asynchronous and the duty cycle pulsed actuation modes can, with energy consumption increase of merely 10%, achieve 65% and 42% increase of downstream velocity, and thus are promising in velocity improvement and energy saving.     

Spectral Measurement of Atmospheric Pressure Plasma by Means of Digital camera

A digital camera measuring system has been used sucessfully to measure the space fluctuation behaviors of Induced Dielectric Barrier Discharge (IDBD) plasma at atmospheric pressure.The experimental results showed that:(1) The uniformity of elctron Temperature of space depends on discharge condition and structure of web electrode,For a certain web electrode the higher the discharge volgage is ,the more uniform distribution of electron temperature in space will be.For a certain discharge the finer and denser the holes on web electrode are,the more uniform distribution of electron temperature in space will be(2).Digital camera is an available equipment to measure some behaviors of the plasma working at atmospheric pressure.     

The detailed characteristics of positive corona current pulses in the line-to-plane electrodes

The corona current pulses generated by corona discharge are the sources of the radio interference from transmission lines and the detailed characteristics of the corona current pulses from conductor should be investigated in order to reveal their generation mechanism. In this paper, the line-to-plane electrodes are designed to measure and analyze the characteristics of corona current pulses from positive corona discharges. The influences of inter-electrode gap and line diameters on the detail characteristics of corona current pulses, such as pulse amplitude, rise time, duration time and repetition frequency, are carefully analyzed. The obtained results show that the pulse amplitude and the repetition frequency increase with the diameter of line electrode when the electric fields on the surface of line electrodes are same. With the increase of inter-electrode gap,the pulse amplitude and the repetition frequency first decrease and then turn to be stable, while the rise time first increases and finally turns to be stable. The distributions of electric field and space charges under the line electrodes are calculated, and the influences of inter-electrode gap and line electrode diameter on the experimental results are qualitatively explained.     

Investigation of the Flow Structure on a Flat Plate Induced by Unsteady Plasma Actuation with DNS Methods

An investigation into the flow characteristic on a flat plate induced by an unsteady plasma was conducted with the methods of direct numerical simulations(DNS).A simplified model of dielectric barrier discharge(DBD) plasma was applied and its parameters were calibrated with the experimental results.In the simulations,effects of the actuation frequency on the flow were examined.The instantaneous flow parameters were also drawn to serve as a detailed study on the behavior when the plasma actuator was applied to the flow.The result shows that induced by the unsteady actuation,a series of vortex pairs which showed dipole formation and periodicity distribution were formed in the boundary layer.The production of these vortex pairs indicated a strong energy exchange between the main flow and the boundary layer.They moved downstream under the action of the free stream and decayed under the influence of the fluid viscosity.The distance of the neighboring vortices was found to be determined by the actuation frequency.Interaction of the neighboring vortices would be ignored when the actuation frequency was too small to make a difference.     

Investigation of nanosecond-pulsed dielectric barrier discharge actuators with powered electrodes of different exposures

Nanosecond-pulsed dielectric barrier discharge actuators with powered electrodes of different exposures were investigated numerically by using a newly proposed plasma kinetic model. The governing equations include the coupled continuity plasma discharge equation, drift-diffusion equation, electron energy equation, Poisson's equation, and the Navier–Stokes equations.Powered electrodes of three different exposures were simulated to understand the effect of surface exposure on plasma discharge and surrounding flow field. Our study showed that the fully exposed powered electrode resulted in earlier reduced electric field breakdown and more intensive discharge characteristics than partially exposed and rounded-exposed ones. Our study also showed that the reduced electric field and heat release concentrated near the right upper tip of the powered electrode. The fully exposed electrode also led to stronger shock wave, higher heating temperature, and larger heated area.     

Numerical Study of Fluid Dynamics and Heat Transfer Induced by Plasma Discharges

A numerical investigation is conducted to explore the evolution of a plasma discharge and its interaction with the fluid flow based on a self-consistent fluid model which couples the discharge dynamics with the fluid dynamics.The effects of the applied voltage on the distribution of velocity and temperature in initially static air are parainetrically studied.Furthermore,the spatial structure of plasma discharge and the resulting force contours in streamwise and normal directions are discussed in detail.The result shows that the plasma actuator produces a net force that should always be directed away from the exposed electrode,which results in an ionic wind pushing particles into a jet downstream of the actuator.When the energy added by the plasma is taken into account,the ambient air temperature is increased slightly around the electrode,but the velocity is almost not affected.Therefore it is unlikely that the induced flow is buoyancy driven.For the operating voltages considered in this paper,the maximum induced velocity is found to follow a power law,i.e.,it is proportional to the applied voltage to the 3.5 power.This promises an efficient application in the flow control with plasma actuators.     

Experimental investigation on DBD plasma reforming hydrocarbon blends

To improve the'detonation-supporting'performance of fuel-rich catalytic combustion products,DBD plasma,stimulated by adjustable nanosecond pulse power supply,was used to further regulate the components and concentrations of the hydrocarbon blends.In this paper,the parameters including load voltage,frequency,rising(falling)edge,pulse width and feeding flow rate were changed respectively,and the corresponding concentration and proportion change of the components in blend gas were investigated.According to the experiment result,it was found that when the discharge frequency is low,the plasma mainly promotes the transformation of light gaseous substances,while it mainly promotes the conversion to heavy hydrocarbons when the frequency is larger.Increasing load voltage will strengthen this trend.The controlling and reforming effect of plasma on the blend gas will decrease with the increase of voltage rising(falling)edge and the feeding flow rate.The regulation effect will be strengthened with the increase of pulse width under 200 ns.With the increase of discharge intensity,the'carbon'settles on the walls of the reactor,which will change the dielectric constant,leading to the loss of control of the discharge.     

Measurements of plasma parameters in a hollow electrode AC glow discharge in helium

Measurements of the plasma parameters of coaxial gridded hollow electrode alternating current(AC)discharge helium plasma were carried out using an improved probe diagnostic technology.The measurements were performed under well-defined discharge conditions(chamber geometry,input power,AC power frequency,and external electrical characteristics).The problems encountered in describing the characteristics of AC discharge in many probe diagnostic methods were addressed by using an improved probe diagnostics design.This design can also be applied to the measurement of plasma parameters in many kinds of plasma sources in which the probe potential fluctuates with the discharge current.Several parameters of the hollow electrode AC helium discharge plasma were measured,including the plasma density,electron temperature,plasma density profiles,and changes in plasma density at different input power values and helium pressures.The characteristics of the coaxial gridded hollow electrode plasma determined by the experiments are suitable for comparison with plasma simulations,and for use in many applications of hollow cathode plasma.     

Plasma propagation in single-particle packed dielectric barrier discharges: joint effects of particle shape and discharge gap

In this work, a single Al₂O₃ particle packed dielectric barrier discharge (DBD) reactor with adjustable discharge gap is built, and the influences of the particle shape (ball and column) and the residual gap between the top electrode and particle on the electrical and optical characteristics of plasma are studied. Our research confirms that streamer discharge and surface discharge are the two main discharge patterns in the single-particle packed DBD reactor. The strong electric field distortion at the top of the ball or column caused by the dielectric polarization effect is an important reason for the formation of streamer discharge. The length of streamer discharge is proportional to the size of the residual gap, but the number of discharge times of a single voltage cycle shows an opposite trend. Compared to the column, a smooth spherical surface is more conducive to the formation of large and uniform surface discharges. The surface discharge area and the discharge intensity reach a maximum when the gap is equal to the diameter of the ball. All in all, the results of this study will provide important theoretical support for the establishment of the synergistic characteristics of discharge and catalysis in plasma catalysis.     

Characteristics and application of diffuse discharge of water electrode in air

Plasma water treatment technology, which aims to produce strong oxidizing reactive particles that act on the gas–liquid interface by way of discharging, is used to treat the organic pollutants that do not degrade easily in water. This paper presents a diffuse-discharge plasma water treatment method, which is realized by constructing a conical air gap through an uneven medium layer. The proposed method uses water as one electrode, and a dielectric barrier discharge electrode is constructed by using an uneven dielectric. The electric field distribution in the discharge space will be uneven, wherein the long gap electric field will have a smaller intensity, while the short one will have a larger intensity. A diffuse glow discharge is formed in the cavity. With this type of plasma water treatment equipment, a methyl orange solution with a concentration of 10 mg l^-1 was treated, and the removal rate was found to reach 88.96%.