Nanosecond Pulsed Surface Dielectric Barrier Discharge Research Articles

A Numerical Investigation of Supersonic Combustion Flow Control by Nanosecond-Pulsed Actuations

The efficiency of supersonic combustion is largely dependent on inlet and injection parameters. Additional energy input is required in some off-design conditions, and nanosecond discharge actuation can be a solution. In the present study, a phenomenological model of a nanosecond-pulsed surface dielectric barrier discharge (NS-SDBD) actuator was developed to analyze the combustion enhancement effect for a supersonic combustor with transverse H2 injection. A seven-reaction H2–air combustion model was adopted for the numerical simulation. Dynamic mode decomposition (DMD) was employed to acquire temperature perturbation in spatial and temporal domains. The results show that the actuator provides additional temperature-increment and species transportation through compression waves. The combustion enhancement effect is mainly attributed to the flow perturbation in the shear layer, which promotes the turbulent diffusion of fuel. Given the same power input, the combustion efficiency at the shockwave reflection point is increased by 17.5%, and the flame height is increased by 15.4% at its maximum.

Experimental investigation of expansive bending pipe flow separation control using a surface dielectric barrier discharge plasma actuator.

Adverse pressure gradients can cause severe flow separation within typical S-shaped inlets. This results in a total pressure distortion at the aerodynamic interface plane (AIP). The expansive bending pipe, where flow separation also occurs due to the adverse pressure gradient, is the basis for investigations into S-shaped inlets. In this study, surface dielectric barrier discharge (SDBD) plasma actuators are used to moderate the total pressure distortion in the AIP of an expansive bending pipe under a 10 m/s incoming flow. Also, the influences of actuation voltage amplitude and pulsed frequency on the total pressure distortion of the AIP are investigated under two plasma actuation modes, nanosecond pulsed SDBD and alternating current (AC) SDBD. Under optimal actuation parameters, the nanosecond pulsed SDBD and the AC-SDBD can reduce the distortion index by 14.93% and 32.22%, respectively. The results demonstrate the effectiveness of SDBD plasma actuators in suppressing flow separation within expansive bending pipes.

Impact of surface charges on energy deposition in surface dielectric barrier discharge: a modeling investigation

Surface charges have significant impact on the evolution of surface dielectric barrier discharge (SDBD). In this work, the role of residual surface charges on repetitively nanosecond pulsed SDBD in atmospheric air is investigated using a two-dimensional fluid model, based on the assumption of preserving the distribution of surface charges at the end of the previous high voltage (HV) pulse. In the bipolar mode when the polarity of residual surface charges is opposite to that of the current HV pulse, a lower breakdown voltage and more deposited energy can be observed, showing an obvious enhancement of SDBD. In the unipolar mode, residual surface charges suppress the development of discharges and energy deposition. It is found that more residual surface charges are accumulated during the negative pulsed discharge, which have a more pronounced effect on the subsequent positive pulsed one. This is explained by the fact that the negative surface streamers directly contact the dielectric and charge it, while the positive surface streamers float above the dielectric, forming a ion-rich region near the surface. The results in this work demonstrate the mechanism of how residual surface charges affect discharge dynamics, which can be utilized to regulate energy deposition in SDBDs.

Active Flow Control of a Flame-Holder Wake Using Nanosecond-Pulsed Surface-Dielectric-Barrier Discharge in a Low-Pressure Environment

Flame holders are widely used in ramjet combustors. We propose using surface nanosecond-pulsed surface-dielectric-barrier-discharge (NS-DBD) to manipulate the flame-holder flow field experimentally. The electrical characteristics, induced flow performance, and temperature distribution of NS-DBD were investigated via the electrical and optical measurement system. In the filamentary discharge mode, the discharge energy rose with decrease of the ambient pressure. The discharge pattern of NS-DBD changed from filamentous to uniform around 5 kPa. Starting-vortex intensity and jet-flow angle relative to the wall increased at low pressure. The recirculation zone was asymmetrical at pressures above 60 kPa. The recirculation zone’s area and length were smaller at lower pressures, but when the actuator was operating, the recirculation zone was nearly 11.8% longer. The vorticity increased with pressure. When the pulse width was 300 ns, the actuator had the greatest effect, and the low velocity region (LVR) area and the fuel–air-mixture residence time (FMRT) could be increased by 31.8% and 20.5%, respectively. The actuator had a smaller widening effect on the LVR area at lower pressure. Rising-edge time should increase with pressure to optimize LVR increase; it should be above 300 ns to optimize FMRT increase. We conclude that NS-DBD is a viable method of controlling flame-holder airflow at low pressure.

Characteristics of a nanosecond pulsed dielectric barrier plasma actuator with a surface water film

Aircraft icing is one of the most serious hazards for airflight operations. The nanosecond pulsed surface dielectric barrier discharge (NSDBD) plasma actuator is recognized as an extremely promising anti-icing technology. In this paper, a multi-physics coupling simulation is used to study the plasma-discharge characteristics and responses of the air–water flow field generated by an NSDBD plasma actuator with a surface water film. The computational model describes air flows through an NSDBD plasma actuator with a water film at the center of two upper powered electrodes. The multi-physics model is solved using the drift-diffusion and energy-conservation equations for the plasma discharge and the mass, momentum, energy, and concentration equations for the air–water flow. The results show that, at the beginning of the voltage pulse, the surface water film has no effect on the plasma discharge. Then, during the pulse plateau time, the film leads to a longer plasma-discharge time and a larger plasma-discharge region. Furthermore, the film causes the plasma-actuator surface to develop a virtual positive electrode that would otherwise be absent and results in the plasma actuator generating more intense shock waves, higher gas temperatures, and larger heated regions.

Numerical verification of the two-spike-current behavior in the initial stage of plasma formation in a pulsed surface dielectric barrier discharge

Nanosecond pulsed surface dielectric barrier discharge (SDBD) is a hot topic in many fields, but the mechanisms of discharge evolution and micro-channel propagation are still not clearly understood. In this paper, a plasma fluid model of nanosecond pulsed SDBD is established, and the deductions of the two current spikes are verified and improved by simulation. The two current spikes correspond to the two stages of the discharge: the ionization wave propagation and the repeated re-ignition in the gap between the ionization wave and the dielectric surface. In the first stage, the ionization wave develops rapidly at first and propagates very slowly in the end, which produces the first current spike with a very short rise time and a tailing falling edge. The curve profile of the ionization wave velocity is very similar to that of the first current spike. A certain distance is maintained between the bottom of the ionization wave and the dielectric surface in this stage, which forms the gap for the next stage. In the second stage, the charged particle cloud induced by the quasi-uniform electric field in the middle of the gap and the new micro-channel from the edge of the high-voltage electrode propagate at first, and then merge together to establish a new discharge channel. The reverse electric field in the gap induced by the accumulated charges on the dielectric surface restricts the expansion velocity of the second discharge channel, which results in a longer rise time and falling time of the second current spike.

Numerical Investigation on the Effects of Dielectric Barrier on a Nanosecond Pulsed Surface Dielectric Barrier Discharge.

In order to understand the impacts of dielectric barrier on the discharge characteristics of a nanosecond pulsed surface dielectric barrier discharge (NS-DBD), the effects of dielectric constant and dielectric barrier thickness are numerically investigated by using a three-equation drift–diffusion model with a 4-species 4-reaction air chemistry. When the dielectric constant increases, while the dielectric barrier thickness is fixed, the streamer propagation speed (V), the maximum streamer length (L), the discharge energy (), and the gas heating () of a pulse increase, but the plasma sheath thickness (h), the fast gas heating efficiency , and the charge densities on the wall surface decrease. When the dielectric barrier thickness increases, while the dielectric constant is fixed, V, L, , and of a pulse decrease, but h, , and the charge densities on the wall surface increase. It can be concluded that the increase of the dielectric constant or the decrease of the dielectric barrier thickness results in the increase of the capacitance of the dielectric barrier, which enhances the discharge intensity. Increasing the dielectric constant and thinning the dielectric barrier layer improve the performance of the NS-DBD actuators.

Atmospheric-pressure pulsed plasma actuators for flow control: shock wave and vortex characteristics

Pulsed plasma actuators are used for an active flow control application since the 2000s. In this paper, we discuss shock wave and vortex characteristics in pulsed plasma actuators after an introduction of research progress on atmospheric-pressure discharge plasma actuators. First, the shock wave characteristics in surface dielectric barrier discharge (SDBD) actuator operating in diffuse-like and multi-streamer modes are discussed. In the most general case, a shock wave in a diffuse-like SDBD actuator is stronger and faster than in a multi-streamer SDBD actuator. Improved plasma actuators, such as the three-electrode SDBD actuator and the plasma synthetic jet actuator have the enhanced shock wave characteristics. Second, in order to investigate the effects of pulse parameters on the shock wave characteristics in nanosecond-pulse SDBD actuator, a particle image velocimetry system is used to capture the formation of starting vortexes at different pulse rise times, pulse durations, and pulse repetition frequencies (PRFs). It is shown that the velocity of a starting vortex significantly increases when the pulse rise time decreases from 400 ns to 50 ns due to a more significant hydrodynamic effect generated during a shorter rise time. This phenomenon is confirmed by calculating a reduced electric field E/N at a short rise time, which turns out to be higher at a shorter rise time than that at a relatively longer rise time. It is also shown that the velocity of a starting vortex increases and its active area enlarges when the PRF increases.

SDBD based plasma anti-icing: A stream-wise plasma heat knife configuration and criteria energy analysis

Ice accretion is one of the potential dangers of the aircraft. Surface dielectric barrier discharge (SDBD) based plasma anti-icing is one of the novel methods that has the advantage of energy efficient, fast response and geometrical simplicity. A “stream-wise plasma heat knife” configuration was proposed based on nanosecond pulsed SDBD for better anti-icing performance. A set of wind tunnel experiments were conducted to study the performance of the “stream-wise plasma heat knife” quantitatively. Spatial-temporal distribution and the dynamic process of icing on a NACA0012 airfoil model were obtained. An analysis of the balance between discharge energy and anti-icing energy was introduced, an energy efficiency ηtotal ≈ 15.6–21.6% was found to be appropriate as the ratio between heating energy and total deposited energy during discharge. A good agreement between analytical results and existing experiments was achieved, providing a good prediction of the anti-icing performance for nSDBD based plasma anti-icing devices.

Two Typical Charge Transportation Characteristics in Nanosecond-Pulse Surface Dielectric Barrier Discharge

Charge transportation expressed as a Lissajous figure usually is a standard method for the analysis of discharge power and energy in surface dielectric barrier discharge (SDBD). In this paper, the charge transportation characteristics under different parameters of power supply and actuator configurations are investigated, and the mechanisms of two typical Lissajous figures are discussed theoretically. Experimental results show that when the plasma distribution is quasi-diffuse mode, the Lissajous figure is almond shape correspondingly, while the plasma distribution looks like separated-channel mode, the Lissajous figure presents a parallelogram shape. Based on an improved time-varying lumped-element circuit model, two equivalent circuits of SDBD under two plasma distributions are built, and the Lissajous figures are calculated theoretically. Calculations and analysis results indicate that the two kinds of Lissajous figures under different plasma distribution modes are due to the current pulse durations and equivalent dielectric capacitances caused by plasma distributions acting together. The protrusions of Lissajous figures are caused by the current narrow pulses in the characteristics of separated-channel mode, while Lissajous figures under quasi-diffuse mode have no protrusions.

Control of Shock-Wave/Boundary-Layer Interaction Using Nanosecond-Pulsed Plasma Actuators

Nanosecond-pulsed surface dielectric barrier discharge plasma actuators are used to control shock-wave/boundary-layer interactions. Characterization of the separation region without plasma actuation is conducted to understand the interaction based on measurements of pressure distribution, schlieren imaging, and velocimetry by the femtosecond laser electronic excitation tagging technique. The results show a weak separation due to the interaction. Three types of plasma actuators are applied to control the separation. Schlieren images are taken by a high-speed camera to evaluate the magnitude of the interaction. It is shown that the plasma actuators affect the flow in two different ways: heat generation in the boundary layer, and generation of vorticity near the surface. When the first effect is dominant, the shock-wave/boundary-layer interaction becomes stronger and the size of the separation bubble increases. If the vorticity generation prevails, it suppresses the separation due to the momentum transfer from the main flow to the boundary layer. The experimental results of the three actuator’s geometries provide the design guidelines for nanosecond-pulse-driven electrodes to control the interaction. An optimal actuation frequency is found through an investigation of the frequency response of the flow.

Investigation of the electrode surface geometry effects driven by nanosecond-pulsed surface dielectric barrier discharge

Nanosecond-pulsed surface dielectric barrier discharge (NS-DBD) plasma actuations with powered electrodes of different surface geometries were investigated numerically by solving the coupled plasma discharge equations, electron energy equations and the Navier–Stokes equations in quiescent air at atmospheric pressure. The plasma discharge characteristics and the air flow features were simulated numerically using a simple chemical kinetics plasma model for three powered electrodes with serrated, rectangular and semicircular surfaces, respectively. The results show that the reduced electric field of the serrated electrode is globally the strongest, while that of the rectangular electrode the second strongest, and that of the semicircular electrode the weakest. The maximum values of the reduced electric field, the mean electron energy and the electron density are found to occur immediately near the right upper tips of the powered electrodes, and the streamers of the mean electron energy and electron density in the serrated electrode case are larger in size and higher in value than in the rectangular and semicircular electrode cases. On the other hand, the pressure wave in the serrated electrode case is more intensive, and propagates slightly faster than in the other two electrode cases. Besides, the heated region in the serrated electrode case is greater with a higher temperature than in the other two electrode cases. The comparison results indicate that the performance of NS-DBD plasma actuators depends significantly on the powered electrode surface geometry, and the serrated surface design is a very promising means of flow control.

Investigation on the Characteristics of Dielectric Barrier Surface Discharge Driven by Repetitive Nanosecond Pulses in Airflows

Recently, more and more attention has been drawn to nanosecond pulsed surface dielectric barrier discharge (NPSDBD) due to its potential applications in flow control. A study of the interaction between high-speed airflows and NPSDBD generated by different nanosecond waveforms is presented in this paper. The effects of airflows on the discharge characteristics, such as plasma morphology, discharge current, the inception voltage of discharge, are investigated at different pulse rise times and flow velocities. The results show that the NPSDBD sustained by pulses with a fast rise time ( $\sim 20$ ns) is quasi-uniform, and relatively stable in the airflows. While the NPSDBD driven by pulses with a rise time more than 50 ns, it seems easier to be influenced by a flowing air of 60 m/s, with a filamentary pattern and a typical discharge current, which has two or more current peaks in the pulse front. In the case of pulses with slow rise time, the inception voltage of discharge increases with the flow velocity, but it almost remains constant in the case of fast rise time. In addition, the deposited energy of discharge generated by the pulses with slow rise time increases slightly with the influence of flowing air. The emission spectrum of NPSDBD is also examined. The variation of the emission spectrum with pulse waveforms is basically consistent with the different discharge behaviors driven by different pulse waveforms.

The discharge characteristics of surface dielectric barrier discharge sustained by repetitive nanosecond pulses in open air

A nanosecond pulsed surface dielectric barrier discharge (NPSDBD) is a promising method for flow control and combustion. We systematically investigated the influence of pulse parameters on the discharge characteristics of NPSDBD, especially on the conduction current of discharge and the energy deposition curves. Meanwhile, the differences of the characteristics of the discharge generated by positive pulses and negative pulses are focused in this paper. The underlying physics is also discussed. Four different discharge regimes of NPSDBD are presented, which can be distinguished by the temporal emission behaviors of discharge and the conduction current of discharge. The transitions of four discharge regimes were also investigated by changing the pulse amplitude, repetitive rate, and voltage polarity. It was found that it is easier to translate quasi-uniform discharge to filamentary discharge or transition mode for the repetitive pulses with a negative polarity. A phenomenological model was proposed to explain the differences between a positive repetitive pulse discharge and a negative repetitive pulse discharge.

OES characterization of streamers in a nanosecond pulsed SDBD using N2 and Ar transitions

The characterization of non-thermal homogeneous plasmas is possible using optical emission spectroscopy (OES), notably by estimating the reduced electric field. This method was applied to characterize streamers generated by a nanosecond pulsed surface dielectric barrier discharge (SDBD) operated in quiescent air at atmospheric pressure and also at 0.5 atm. The average reduced electric field associated with the surface streamers was determined using four different sets of transitions occurring in air plasmas, the first negative system (FNS) of , the first positive system (FPS) and second positive system (SPS) of and argon transitions . The analysis of the results allowed to critically assess the validity of the estimated reduced electric field for the present conditions. It is shown experimentally that the inhomogeneous nature of the streamer head influences significantly the estimation of the reduced electric field. Moreover, the estimated reduced electric field is not sufficient to characterize the processes taking place in the streamer head, due to the steep variation of both the reduced electric field E/N and the electron density ne in space and time. To overcome this limitation, a new method is proposed to take into account the spatial structure of a streamer head. The applicability of the new method is demonstrated for these experimental conditions and shows a very good agreement for the transitions tested.

A novel method of calculating the energy deposition curve of nanosecond pulsed surface dielectric barrier discharge

To obtain the energy deposition curve is very important in the fields to which nanosecond pulse dielectric barrier discharges (NPDBDs) are applied. It helps the understanding of the discharge physics and fast gas heating. In this paper, an equivalent circuit model, composed of three capacitances, is introduced and a method of calculating the energy deposition curve is proposed for a nanosecond pulse surface dielectric barrier discharge (NPSDBD) plasma actuator. The capacitance Cd and the energy deposition curve ER are determined by mathematically proving that the mapping from Cd to ER is bijective and numerically searching one Cd that satisfies the requirement for ER to be a monotonically non-decreasing function. It is found that the value of capacitance Cd varies with the amplitude of applied pulse voltage due to the change of discharge area and is dependent on the polarity of applied voltage. The bijectiveness of the mapping from Cd to ER in nanosecond pulse volumetric dielectric barrier discharge (NPVDBD) is demonstrated and the feasibility of the application of the new method to NPVDBD is validated. This preliminarily shows a high possibility of developing a unified approach to calculate the energy deposition curve in NPDBD.

Capacitances and energy deposition curve of nanosecond pulse surface dielectric barrier discharge plasma actuator.

Nanosecond pulse surface dielectric barrier discharge (NPSDBD) plasma actuator is preferred to generate aerodynamic actuation which relies on the deposited energy during nanosecond time scale, named as the mechanism of fast thermalization. It is very important to understand the energy deposition process of NPSDBD plasma actuator. In this paper, an equivalent circuit model is presented to describe a typical asymmetric NPSDBD plasma actuator first. Of the three key capacitances in the equivalent circuit, the values of Capacitance C(m) and C(g) can be gotten by the calculation of the electric field, with the method of undetermined coefficients, while the value of Capacitance C(d) is determined from the charge-voltage (Q-V) plot, also called Lissajous figure. It is found that the value of Capacitance C(d) varies with the amplitude of applied pulse voltage, due to the change of the dimension of plasma sheet. Based on the circuit parameters and the measured waveforms of discharge voltage and current, the time varying characteristics of deposited energy can be obtained finally. It is indicated that the calculated results of deposited energy show a good agreement with conventional method.

Time behaviour of discharge current in case of nanosecond-pulse surface dielectric barrier discharge

Nanosecond-pulse surface dielectric barrier discharge is a promising method used for airflow control application. In our letter, atmospheric-pressure plasmas in open air are produced in a configuration of discharge actuators by repetitive nanosecond pulses. The electrical parameters including applied voltage, total discharge current, and transported charge are measured and analysed, especially it is aimed at the time behaviour of the total discharge current. Experimental results show that the total discharge current pulse includes two obvious spikes during the rise time of the applied pulse voltage. According to the simulation, it is concluded that the first current spike is due to the discharge propagation in the form of wave ionization and displacement current. The second current spike is caused by the repeated re-ignition of the surface dielectric barrier discharge on the area covered previously by the wave ionization.

Numerical simulation on a nanosecond-pulse surface dielectric barrier discharge actuator in near space

Lift-enhancement–drag-reduction technology is strongly required by near-space vehicles with low Reynolds number. It is known that a flow control method by a surface dielectric barrier discharge (SDBD) plasma can play an important role in this field. In order to obtain the discharge characteristics and evaluate the flow control effect of a SDBD actuator, the nanosecond-pulse discharge and induced flow field by the SDBD plasma are simulated at various altitudes using discharge-aerodynamics models. The results show that the ignition voltage decreases with altitude and it is very easy to discharge in near space. Compared with a SDBD at ground level, the plasma is produced on both sides of the exposed electrode and distributes more uniformly in near space. Although the body force generated by the SDBD actuator is less effective in inducing a jet with nanosecond-pulse excitation than that with alternating voltage excitation, the induced jet by body force is with longer extent, thicker profile and higher velocity in near space than at ground level. The plasma bulk heating should be taken into account for nanosecond-pulse excitation. The Joule heating of electrons is the main source of plasma bulk heating which acts as a micro-explosion and mainly induces pressure perturbation. The discharge at ground level is like a ‘point explosion’, but a ‘region explosion’ in near space, which indicates a diffuse distribution of energy, should be responsible for the fact that the effect of bulk heating is reduced in near space.

纳秒脉冲表面介质阻挡放电特性实验研究

The characteristics of nanosecond-pulse surface dielectric barrier discharge (DBD)are investigated in air at atmospheric pressure with the domestic repetitive unipolar nanosecond-pulse generator， the characteristic of surface DBD is investigated in this paper. It is found that nanosecond-pulse surface DBD is a filamentary discharge in essence. The discharge happens during the rising time of the applied voltage pulse. Higher applied voltage and Higher repetitive frequency lead to intenser and more uniform discharge. Voltage amplitudeaffects the discharge uniformity more， while pulse repetition frequency affects the discharge intensity more. There is an optimum electrode gap width to get the best electrical characteristics of surface DBD. Moreover， surface flashover is prone to happen when glass is chosen as dielectric barrier.