Nanosecond Pulsed Dielectric Barrier Discharge Research Articles

Pressure dependency on a nanosecond pulsed dielectric barrier discharge plasma actuator

The behavior of a nanosecond pulsed dielectric barrier discharge (ns-DBD) plasma actuator with the ambient pressure from 30 to 100 kPa was characterized with Schlieren images. Shock wave propagation speed and strength were recorded, showing clear trends with decreasing ambient pressure. Higher ambient pressures result in stronger shock waves; this has been observed irrespective of the actuator thickness. This might be explained with fewer air molecules to ionize at lower ambient pressures and hence a lower temperature from the exothermal recombination reactions. The thickness of the dielectric barrier also influences the shock strength. In accordance with previous findings, it was confirmed that a thinner dielectric barrier results in a greater shock strength. NS-DBD shock waves were modeled numerically using OpenFOAM through a source term added to the energy equation, which controls the amount of thermal energy added to the near-wall deposition region. The compressible, unsteady sonicFoam solver was used with second order schemes. A mesh sensitivity study gives confidence that the solution is grid independent. The overall shock wave structure and propagation speed match well with experimental data. The heat addition required to reproduce experimental results varied with ambient pressure. Less heating of the near-wall region was needed with lower ambient pressures.

Static and dynamic stall control by NS SDBD actuators

In the last two decades, nonequilibrium plasmas have demonstrated the ability to affect a variety of flows of aeronautical interest, including mitigation of stall on steady airfoils as it is a nonintrusive, active control method. Plasma actuation also shows promise to address dynamic stall in rotorcraft because of the absence of moving parts, extremely lightweight and flexible assembly, extremely fast turn-on time and wide range of actuation frequency. In this paper, we summarize the recent advances in flow control both for static and dynamic flow separation control using nanosecond pulsed surface dielectric barrier discharge plasma devices. Topics of discussion include the mechanism of NS plasma actuation, results of experiments at different Reynolds and Mach numbers, dynamics of flow reattachment, and boundary layer separation control on a pitching airfoil. The common issue of retreating blade stall, as experienced in helicopters, was also considered in this study by experimenting with a reverse flow over an airfoil. Increases in lift are demonstrated for separated flows for reduced frequencies up to k = 0.05, angle of attack up to 32°. Instantaneous increase in lift with plasma control was demonstrated to be up to 55%. The 20% integral lift force increase of a helicopter model in hover mode using a constant engine power is also demonstrated with NS SDBD actuation of the flow on the rotating blades.

Nanosecond pulsed plasma assisted dry reforming of CH4: The effect of plasma operating parameters

Dry reforming is a promising approach to converting CH4 and CO2 (i.e., two common greenhouse gases) into clean fuels and valuable chemicals. Non-thermal plasma, acting as an alternative to the traditional reforming processes, achieves considerable gas conversion with low energy consumption under mild operating conditions. In this study, CH4 and CO2 were converted to syngas (i.e., H2 and CO) in a nanosecond pulsed dielectric barrier discharge plasma at a total gas flow rate of 50 sccm. Through evaluating the effects of electrical parameters on reforming performance, the experimental results showed that CH4 and CO2 conversions increased with the increase of pulse repetition frequency owing to the increased energy injection. Shorter rise and fall times resulted in better CH4 and CO2 conversions and higher energy conversion efficiencies, due to the rapid acceleration of electrons in a shorter discharge time. In the case where the optimal pulse peak width was 150 ns, the secondary discharge was improved because of the charge accumulation in the primary discharge, thereby increasing the CH4 and CO2 conversions. Among all experiments, when the pulse repetition frequency was 10 kHz and the discharge power was 55.7 W, the maximum conversions of CH4 and CO2 were 39.6% and 22.9%, respectively, while the total energy conversion efficiencies of the syngas and all detected products were 5.0% and 7.1%, respectively. Furthermore, an optical emission spectroscopy was used to characterize the active species formed during the reforming process.

Effect of rise time on nanosecond pulsed surface dielectric barrier discharge actuator

Nanosecond pulsed surface dielectric barrier discharge (ns-SDBD) actuator is a novel technology for active flow control due to its high control capability and low power consumption. The electrical, and aerodynamic, characteristics of ns-SDBD actuator with different rise times are investigated by electrical measurement system, Schlieren optical system, and particle image velocimetry (PIV) system. Experimental results show that the short rise time leads to a high current amplitude and a diffuse-like plasma layer. The deposited energy reaches its maximum (9.26 mJ) at a rise time of 50 ns, and then declines, finally, slight changes occur when the rise time is increased from 150 ns to 500 ns. Furthermore, a circular arc wave and a plane wave are produced due to the localized heating. The intensity of the circular arc wave increases when the rise time decreases and the propagation distance of induced pressure waves in the vertical direction increases in a quasi-linear manner. In addition, due to the greater ability to transmit output energy to the surroundings, and the stronger tangential acceleration ability in the case of a short rise time, the area of action for the starting vortex is larger when rise time decreases and two vortexes are formed, which is conducive to mixing with the airflow and improving flow control capability.

나노세컨드 펄스 DBD 플라즈마의 멀티스케일 모델링을 위한 비평형 플라즈마 유동 해석 및 검증

In a nanosecond pulse discharge, the computational cost is high because of the characteristic time difference between the plasma and the flow. In order to reduce the computational cost, multi-scale modeling study of nanosecond pulse discharge plasma is needed. In this study, we developed and verified a non-equilibrium plasma solver for nanosecond-pulse Dielectric Barrier Discharge(NS-DBD) multi-scale modeling study. To simulate the non-equilibrium phenomena, 17 chemical species / 54 chemistry reaction models were used. The governing equations included chemical species continuity equations, a electrical potential equation, and Navier-Stokes equations. Numerical results show that streamer velocity and micro shock wave speed are comparable to those of other experimental results. This study is expected to contribute to the future study of NS-DBD multi-scale modeling.

Numerical investigation on the effects of discharge conditions on a nanosecond pulsed surface dielectric barrier discharge

In order to understand the impacts of discharge conditions on the discharge characteristics of a nanosecond pulsed surface dielectric barrier discharge, the effects of gas pressure, temperature, and velocity are numerically investigated by using a three-equation drift-diffusion model with a 4-species 4-reaction air chemistry. The scaling laws of plasma morphology and gas heating on pressure are obtained for further reduced modeling in the flow-control application. Theoretical discussions on the scaling laws are carefully conducted. When the pressure increases in the studied range, while the temperature is fixed, the streamer propagating velocity (V), the plasma sheath thickness (h), the maximum streamer length (L), the total discharge energy (QD_ei), and the gas heating (QGH) decrease. The plasma morphology and the gas heating have different scalings on the pressure according to V∼ep, h∼p−0.8, L∼p−0.8, QD_ei∼p−0.5, and QGH∼p−0.5. When the temperature decreases in the investigated range, while the pressure is kept constant, V, h, L, QD_ei, and QGH also decrease. When the gas velocity increases from 0m/s to 258m/s, while the pressure and the temperature are kept fixed, V and h increase. The total QD_ei and QGH increase by 4.3% and 4.6%, respectively. It is concluded that, on the one hand, the discharge characteristics are mainly dominated by the gas number density, which can be equivalently changed by the gas pressure and temperature. On the other hand, when the gas pressure and temperature are kept constant, the uniform gas velocity has weak effects on the discharge characteristics.

Silver nanoparticle-loaded filter paper: Innovative assembly method by nonthermal plasma and facile application for the reduction of methylene blue

In this study, silver nanoparticles (AgNPs) were loaded onto commercial filter paper using a simple “suspending-discharging-washing” process. Nanosecond pulse dielectric barrier discharge (NP-DBD) plasma was used to perform the in-situ reduction-loading process in a plate-to-plate DBD reactor during the five-minute fabrication process. Gaseous ethanol was used as the reducing agent under an argon gas plasma treatment. There was no thermal treatment, which prefers the formation of small nanoparticles. Transmission electron microscopy showed that the synthesized AgNPs were well-dispersed over the surface of the filter paper. The synthesized nanoparticles were hemispherical and crystalline. Fourier transform infrared spectroscopy showed that the cellulose skeletons had been mostly maintained after the plasma discharge. The catalytic activity of the AgNPs paper was evaluated by the reduction reaction of methylene blue (MB) with sodium borohydride (NaBH4) using a straightforward filtration process.

Numerical investigation on the CH4/CO2 nanosecond pulsed dielectric barrier discharge plasma at atmospheric pressure

The excellent non-equilibrium characteristic of the nanosecond pulsed dielectric barrier discharge (NPDBD) plasma can overcome thermodynamically barriers of reactions in the dry reforming of methane (DRM), so that the NPDBD plasma coupled with catalyst provides an attractive alternative to the traditional catalytic method of the DRM. In this work, the one-dimensional fluid model, including 68 species and 276 reactions, is built up to numerically investigate the atmospheric-pressure CH4/CO2 plasma driven by the nanosecond pulsed power supply. Discharge current densities, discharge gap voltages, dissipated power densities, spatial averaged particle densities and spatial distributions of the high-density species, and generating reaction pathways of the significant species in CH4, CO2, and CH4/CO2 NPDBD plasmas at atmospheric pressure are systematically illustrated and discussed. The simulation results should be valuable for optimizations of both existing and emerging DRM approaches using the NPDBD plasma, the plasma-assisted catalyst, and other novel plasma-based fuel reforming technologies.

Time-resolved characterization of plasma properties in a CH4/He nanosecond-pulsed dielectric barrier discharge

Non-equilibrium plasmas for plasma-assisted combustion, pollutant remediation, fuel reforming, and catalysis rely on the production of energetic electrons that ionize, dissociate, and excite the fuel and oxidizer molecules. Experimental characterization of the electron temperature, electron density, and vibrational temperature are necessary to validate and improve plasma kinetic models. An experimental apparatus capable of Thomson scattering and vibrational Raman scattering measurements in the same discharge with molecular admixtures was developed. Both diagnostics are necessary to study the induced vibrational non-equilibrium from electron impact. Thomson scattering spectra were resolved by placing a physical mask at the output of a single grating spectrometer. The electron temperature and density and the impact of hydrocarbon addition was measured for a 60 Torr CH4/He nanosecond pulsed plane-to-plane dielectric barrier discharge with 0%–2% CH4 addition. Electron densities as low as 1 × 1012 cm−3 and electron temperatures ranging from 0.5 eV to 9 eV were observed. A decrease in the electron temperature and density was observed even with 1% CH4 addition. Moreover, the addition of N2 to the discharge enabled vibrational Raman scattering and quantification of the first level vibrational temperature starting from 75 ns after the voltage pulse. The electron temperature and density were also measured in this CH4/N2/He mixture by Thomson scattering. Addition of N2 led to a faster electron temperature decay than in the original CH4/He mixture. The advantages and disadvantages of this detection scheme for Thomson scattering over the triple grating spectrometer and the volume Bragg grating notch filter is discussed.

Hysteresis characteristics of the initiating and extinguishing boundaries in a nanosecond pulsed DBD

The dielectric barrier discharge (DBD) is presently used in many fields, including plasma medicine, surface modification, and ozone synthesis; the influence of airflow on the DBD is a widely investigated topic. In this work, a hysteresis characteristic on the initiating and extinguishing boundaries is observed in a nanosecond pulsed DBD, which is sensitive to the variation in the airflow velocities and pulse repetition frequencies (PRFs). It is found that, at a certain airflow velocity, the initiating PRF is higher than the extinguishing PRF. This difference between the initiating PRF and the extinguishing PRF leads to a hysteresis phenomenon on the initiating and extinguishing boundaries. When the airflow velocity is increased, both the initiating and extinguishing PRFs are increased and the difference between the initiating PRF and the extinguishing PRF also increased. The hysteresis width between the initiating and extinguishing boundaries is enhanced. To explain these results, the physical processes involved with the seed particles and the mechanisms of forming discharge channels are discussed.

Investigation of the transition from streamer to uniform ‘overvoltage’ mode of atmospheric air nanosecond-pulsed dielectric barrier discharge

A nanosecond-pulsed dielectric barrier discharge ignited in atmospheric air was studied by optical emission spectroscopy to investigate the time- and space-resolved development of the reduced electric field. The discharge operated in two distinct modes that correlate with the values of the applied electric field: non-uniform streamer regime and uniform breakdown regime. It is shown that the reduced electric field in the non-uniform mode corresponds to the propagation of cathode-directed streamers, while in uniform discharge both molecular nitrogen emission and the reduced electric field are uniformly distributed along the gap during the initial discharge development stage with corresponding lower reduced electric field values.

Fast gas heating of nanosecond pulsed surface dielectric barrier discharge: spatial distribution and fractional contribution from kinetics

The effect of heat release in reactions with charged and electronically excited species, or so-called fast gas heating (FGH), in nanosecond surface dielectric barrier discharge (nSDBD) in atmospheric pressure air is studied. Two-dimensional numerical simulations based on the PArallel Streamer Solver with KinEtics code are conducted. The code is based on the direct coupling of a self-consistent fluid model with detailed kinetics, an efficient photoionization model, and Euler equations. The choice of local field approximation for nSDBD modeling with simplified kinetics is discussed. The reduced electric field and the electron density are examined at both polarities for identical high-voltage pulses 24 kV in amplitude on a high-voltage electrode and 20 ns full width at half maximum. The distribution of the FGH energy and the resulting gas temperature field are studied and compared with findings in the literature. The input of different reactions to the appearance of hydrodynamic perturbations is analyzed.

Uniformity analysis of nanosecond and sub-nanosecond pulsed DBD in atmospheric air

In this study we report the results of atmospheric air nanosecond-pulsed dielectric barrier discharge (DBD) uniformity analysis as a function of applied electric field. We quantify the uniformity of the discharge by analyzing the discharge images obtained with fast intensified charge-coupled device camera using chi-square test. The results show that uniformity of DBD strongly depends on applied electric field with a weak effect on the high voltage pulse rise time. The nanosecond-pulsed air DBD operates in two distinct modes, namely, non-uniform streamer regime and uniform ‘overvoltage’ regime, with transition applied electric field of around 130 kV cm−1.

Temporal variation of the spatial density distribution above a nanosecond pulsed dielectric barrier discharge plasma actuator in quiescent air

The thermal perturbation caused by a nanosecond pulsed dielectric barrier discharge (ns-DBD) plasma actuator may lead to boundary layer transition. Hence, understanding of the thermal flow induced by the ns-DBD plasma actuator will contribute to the development of an efficient flow control device for various engineering applications. In this study, the spatial density distribution related to the thermal flow was experimentally investigated using both qualitative and quantitative schlieren techniques. The focus of this study is to understand the initial temporal variation of the spatial density distribution above the ns-DBD plasma actuator in quiescent air. The quantitative visualisation showed that a hot plume is generated from the edge of the exposed electrode and moves slightly towards the ground electrode. A possible explanation is that an ionic wind and/or an induced jet leads to the movement of the hot plume. However, the plasma-induced flow (the ionic wind and the induced jet) is generated after the primary plasma discharges; namely, the hot plume does not move immediately after the first plasma discharge. At almost the same time as the movement of the hot plume, consecutive plasma discharges enhance the density of the hot plume; thereafter, the density reaches almost a steady state.

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.

Analysis of flow separation control using nanosecond-pulse discharge plasma actuators on a flying wing

Dielectric barrier discharge (DBD) plasma is one of most promising flow control method for its several advantages. The present work investigates the control authority of nanosecond pulse DBD plasma actuators on a flying wing model’s aerodynamic characteristics. The aerodynamic forces and moments are studied by means of experiment and numerical simulation. The numerical simulation results are in good agreement with experiment results. Both results indicate that the NS-DBD plasma actuators have negligible effect on aerodynamic forces and moment at the angles of attack smaller than 16°. However, significant changes can be achieved with actuation when the model’s angle of attack is larger than 16° where the flow separation occurs. The spatial flow field structure results from numerical simulation suggest that the volumetric heat produced by NS-DBD plasma actuator changes the local temperature and density and induces several vortex structures, which strengthen the mixing of the shear layer with the main flow and delay separation or even reattach the separated flow.

Nanosecond pulsed uniform dielectric barrier discharge in atmospheric air: A brief spectroscopic analysis.

The paper proposes a simple and convenient approach to represent the discharge uniformity of nanosecond-pulse dielectric barrier discharge (DBD) in air by observation of the ratio of N2+ (B3Σu+ → X3Σg+, 0-0, 391.4 nm) to N2 (C3Πu → B3Πg, 2-5, 394.3 nm) intensities. The DBDs at different pulse peak voltages, discharge gap distances, dielectric materials and thicknesses were investigated by recording their single-pulse-shot discharge images and N2+/N2 ratios to verify the feasibility of the above innovative approach. The results show that the ratios of N2+/N2 are in the range of 0.18-0.6within our experimental parameters, which is respect to the reduced electric field (E/N, where E is the field strength and N is gas number density) strength of 260-440 Td (1 Td = 10-17 V·cm2). And it is indicated that a lower N2+/N2 ratio would be found in a higher pulse peak voltage or/and a lower discharge gap distance, which benefits for improving the discharge uniformity of nanosecond-pulse DBD. The thickness and permittivity of dielectric material also affect the E/N strength and discharge uniformity to a certain extent, but the effects are ambiguous due to additional factors of dielectric materials. In addition, the theoretical basis and application scope of this approach were also discussed.

Propagation of Ionization Waves in Nanosecond-Pulse Dielectric Barrier Discharge in Atmospheric Air

This paper presents an experimental investigation of ionization waves’ (IWs’) propagation in a nanosecond-pulse dielectric barrier discharge at atmospheric pressure in air. The effect of the rise time and pulse duration on IW propagation is studied by an intensified charge-coupled device, and the mechanism of the discharge propagation is analyzed. The experimental results show that the discharge produced in the rise time of the applied voltage develops in a structure of discontinuous sphere, while the discharge produced in the falling time exhibits a continuous form due to the effect of space charge. Furthermore, the rise time of the applied voltage has a significant influence on the velocity of IWs, and the maximal velocity of IWs rapidly decreases from 0.08 to 0.008 mm/ns when the rise time of the applied voltage increases from 50 to 300 ns. However, the pulse width has almost no influence on the velocity of IWs. The electric field distortion caused by both the propagation of IWs and the accumulation of surface charges is responsible for the formation and propagation of IWs.

Hydrophilicity modification of aramid fiber using a linear shape plasma excited by nanosecond pulse

In this paper, a linear shape nanosecond pulsed dielectric barrier discharge is generated at atmospheric pressure for improving the hydrophilic property of aramid fibers. The discharge images, waveforms of voltage and current, and optical emission spectra of discharge are obtained to investigate plasma characteristics, and the water contact angles, scanning electron microscopy, and X-ray photoelectron spectroscopy are employed to estimate the modifying effects of plasma and investigate modification mechanisms. It is found that 75 s is an optimal treatment time in air under 2 mm discharge gap, 28 kV pulse peak voltage, and 100 Hz pulse repetition rate, and the energy density of discharge is about 2.1 J/cm2. The improvement of aramid fiber hydrophilicity is due to the increasing of surface roughness and the formation of polar functional groups such as CN and OCO. Besides, the content of O2 has an obvious influence on plasma treatment, and CC is more easily oxidized under a high O2 concentration owing to the role of O atoms.

Effect of parallel magnetic field on repetitively unipolar nanosecond pulsed dielectric barrier discharge under different pulse repetition frequencies

A magnetic field, with the direction parallel to the electric field, is applied to the repetitively unipolar positive nanosecond pulsed dielectric barrier discharge. The effect of the parallel magnetic field on the plasma generated between two parallel-plate electrodes in quiescent air is experimentally studied under different pulse repetition frequencies (PRFs). It is indicated that only the current pulse in the rising front of the voltage pulse occurs, and the value of the current is increased by the parallel magnetic field under different PRFs. The discharge uniformity is improved with the decrease in PRF, and this phenomenon is also observed in the discharge with the parallel magnetic field. By using the line-ratio technique of optical emission spectra, it is found that the average electron density and electron temperature under the considered PRFs are both increased when the parallel magnetic field is applied. The incremental degree of average electron density is basically the same under the considered PRFs, while the incremental degree of electron temperature under the higher-PRFs is larger than that under the lower-PRFs. All the above phenomena are explained by the effect of parallel magnetic field on diffusion and dissipation of electrons.