Sliding Surface Discharge Research Articles

Исследование течения, создаваемого скользящим разрядом, с помощью методов компьютерного зрения

A quantitative study has been made of the flow with shock waves generated in air by a sliding surface discharge lasting less than one microsecond. The high-speed flow was visualized using the shadowgraph method, the process was recorded at a rate of 124 000 frames/s, the exposure time was 1 μs. The aim of this work is to study the dynamics of the two discontinuities: the cylindrical shock wave and the contact surface generated by the discharge. Each experiment allowed several hundred images to be taken of a short-lived gas-dynamic process lasting up to 1 ms. A YOLOv8 convolutional neural network was trained and used to determine the positions of the discontinuities. A data set of 984 markups was labeled. The model on the mAP50 metric achieved 0.887 and the mAP50-95 was 0.557. The model was used to automatically measure the vertical dimensions of the contact discontinuity. It expands at times up to 0.4 - 0.8 ms to a vertical size of 5 - 11 mm. The x-t plots and the velocities of the cylindrical shock waves were measured. It is shown that up to 1 ms after the discharge, the flow development is due to the blast wind motion behind the shock wave. It is shown that the use of computer vision can significantly speed up the analysis of high-speed flow visualizations and the extraction of quantitative information.

Dynamics of Radiation from Nanosecond Surface Sliding Discharge in Airflow with Shock Waves

Spatio-temporal distributions of radiation from pulsed sliding surface discharge of ~300-ns duration in quiescent air at pressures within 2–200 Torr and in the presence of shock waves in supersonic flow with Mach numbers M = 2.8–3.3 have been experimentally studied. The dynamics of radiation from discharge was analyzed based on processing of the streak images and nine-frame images of discharge glow intensity, emission spectra, and discharge current kinetics. It is established that variation of the radiation intensity from discharge interacting with shock waves is correlated with a model temporal dependence of the population of C3Πu states of nitrogen during shock compression of the discharge plasma region.

The Characteristics of a Nanosecond Surface Sliding Discharge in a Supersonic Airflow Flowing around a Thin Wedge

The characteristics of a distributed sliding surface discharge with a duration of ∼300 ns (plasma sheet) in a non-uniform supersonic airflow with a vortex zone behind a thin wedge have been studied in a shock tube channel. The spatial distribution of the discharge radiation, the spectra of the discharge radiation, and the discharge current are analyzed in the flows behind plane shock waves with Mach numbers 2.4–3.5 (the Mach numbers of flows are 1.16–1.47 and the density is 0.02–0.20 kg/m3). It is shown that in an airflow with a vortex zone, the surface discharge develops as a 1–3-mm-wide channel located in the region of low density behind the wedge. The calculated electron concentration in the discharge channel is an order of magnitude higher than the electron concentration when a discharge is initiated in a homogeneous medium.

Analysis of Plasmadynamic Nanosecond-Range Processes in the Formation of Shock Waves from Pulsed Discharges

We have studied the dynamics of the plasma glow of pulsed discharges (sliding surface discharge and combined volume discharge with plasma electrodes) in the nanosecond range (100–12 000 ns) in stationary air and in the flow behind the front of a plane shock wave with Mach numbers 1.7–5.0 in the shock tube channel. The temporal characteristics of the flow, the radiation spectra, and the discharge currents in air are compared in the pressure range 5–150 Torr, a pulsed voltage of 20–30 kV, and a current of about 1 kA. It is shown that the time of current under various conditions does not exceed 400 ns, and the duration of the glow can reach a few microseconds. It is shown that as a result of energy supply near the planar shock wave front, the decay of discontinuities occurs with the formation of shock waves and contact surfaces. The positions of the plasma glow regions are compared with the positions of discontinuity surfaces of numerically calculated gasdynamic parameters in the flow.

Influence of shock waves from plasma actuators on transonic and supersonic airflow

This paper presents experimental and numerical investigations of high-current sliding surface discharges of nanosecond duration and their effect on high-speed flow as plasma actuators in a shock tube. This study deals with the effectiveness of a sliding surface discharge at low and medium air pressure. Results cover the electrical characteristics of the discharge and optical visualization of the discharge and high-speed post-discharge flow. A sliding surface discharge is first studied in quiescent air conditions and then in high-speed flow, being initiated in the boundary layer at a transverse flow velocity of 50–950 m s−1 behind a flat shock wave in air of density 0.04–0.45 kg m−3. The discharge is powered by a pulse voltage of 25–30 kV and the electric current is ~0.5 kA. Shadow imaging and particle image velocimetry (PIV) are used to measure the flow field parameters after the pulse surface discharge. Shadow imaging reveals shock waves originating from the channels of the discharge configurations. PIV is used to measure the velocity field resulting from the discharge in quiescent air and to determine the homogeneity of energy release along the sliding discharge channel. Semicylindrical shock waves from the channels of the sliding discharge have an initial velocity of more than 600 m s−1. The shock-wave configuration floats in the flow along the streamlined surface. Numerical simulation based on the equations of hydrodynamics matched with the experiment showed that 25%–50% of the discharge energy is instantly transformed into heat energy in a high-speed airflow, leading to the formation of shock waves. This energy is comparable to the flow enthalpy and can result in significant modification of the boundary layer and the entire flow.

Experimental research of sliding surface distributed nanosecond discharge in supersonic air flow

Results are presented from the experimental study of the spatial structure and spectrum of the nanosecond distributed sliding surface discharge (plasma sheet) in quiescent air and in a supersonic and transonic gas flow behind a plane shock wave. Discharge investigations were carried out in air flow with velocities up to 1600 m/s within density range of 0.08-0.40 kg/m3. Different structures of plasma glow were observed for the laminar and turbulent flow regimes in the boundary layer. Analysis of the obtained images clearly shows that character of the glow of the discharge changes with change of the boundary layer structure. The analysis of the experimental data shows that the radiation spectrum of sliding surface discharge changes in gas flow after a shock wave

Shock-wave structure formation by nanosecond discharge in helium

We have experimentally studied and numerically simulated the shock-wave flow that arises as a result of the development of a system of microchannels of pulsed sliding surface discharge in helium at low pressure. Using numerical simulations based on a solution of the system of regularized Grad equations (R13) and Navier-Stokes equations, results obtained for various Knudsen numbers are compared and it is shown that the influence of rarefaction on the discharge-plasma-induced shock-wave flow is manifested in a transient regime at Kn = 10−1.

Sliding discharges in steam: effects of dielectric surface and hydrocarbon additives on hydrogen, oxygen and hydrogen peroxide generation

A sliding surface discharge was formed on a dielectric layer in steam at ∼100 °C and atmospheric pressure. The material properties and the thickness of the dielectric layer were found to strongly affect the energy deposition into the plasma. With a 0.32 cm thick dielectric the energy deposition was 1.4 times greater than with a 0.48 cm thick dielectric, and with window glass it was 1.3 times greater than with Macor of the same thickness. Product gases were H2 (73 ± 4%) and O2 (27 ± 1%), and H2O2 accumulated in the condensed water up to 0.4 g l−1. The energy yield for hydrogen was 1.2 ± 0.1 g H2 kWh−1 and independent of the input power and thickness or material of the dielectric. However, for hydrogen peroxide the energy yield, which varied between 0.61 and 3.2 g H2O2 kWh−1, was found to depend strongly on the thickness and material of the dielectric. The addition of benzene to the steam increased the energy efficiency of hydrogen to 2.3 g kWh−1, and decreased oxygen and hydrogen peroxide by about 3 and 6 times, respectively. It also caused the deposition of phenol and polymer-like layers on the dielectric. The results are explained on the basis of reactions of H and OH radicals adsorbed on the surface and/or in gas phase.

Energy deposition in boundary gas layer during initiation of nanosecond sliding surface discharge

The process of rapid gas heating in the region of distributed pulsed sliding surface gas discharge (plasma sheet) of nanosecond duration has been studied. The fraction of electric energy converted into heat during the passage of discharge current has been estimated from a detailed analysis of the dynamics of shock wave fields arising upon the initiation of discharge. Experiments are performed in quiescent gases (air, nitrogen, helium) and in supersonic airflows behind a plane shock wave in a shock tube at gas densities within 0.04–0.45 kg/m3 and flow velocities up to 1600 m/s.

Development of gas-dynamic perturbations propagating from a distributed sliding surface discharge

Results are presented from experimental studies of the plasma layer structure of a distributed sliding surface discharge excited in quiescent air and in a uniform gas flow behind a plane shock wave at gas densities of 0.03–0.30 kg/m3. The dynamics of weak shock waves generated after discharge initiation was studied. According to the experimental and simulation results, 40% of the discharge energy transforms into heat within a surface gas layer in the energy input stage, which lasts up to 200 ns.

The effect of voltage pulse polarity on the performance of a sliding discharge pumped HF laser

The influence of the applied voltage pulse polarity on the performance of a HF laser pumped by a sliding surface discharge is investigated. Details are presented for the polarity dependence of the discharge properties as well as for their relation to the physical processes that affect the sliding discharge evolution. The output energy and efficiency were higher when the initiating or stressed electrode was in relative positive potential, irrespective of which electrode was grounded. The experimental results indicate that for positive polarity the discharge was more uniform, self terminating in type, with reduced electron density and temperature. The increase in output energy and efficiency is attributed to the improvement of the spatial uniformity of laser pumping, to a more efficient utilization of discharge input energy due to an increase in the steady state discharge time phase, as well as to the reduced electron temperature and to the increased steady state voltage which may also result in more efficient laser pumping.