Shock wave interaction with a thermal layer produced by a plasma sheet actuator

Abstract

This paper explores the phenomena associated with pulsed discharge energy deposition in the near-surface gas layer in front of a shock wave from the flow control perspective. The energy is deposited in 200 ns by a high-current distributed sliding discharge of a ‘plasma sheet’ type. The discharge, covering an area of mm2, is mounted on the top or bottom wall of a shock tube channel. In order to analyse the time scales of the pulsed discharge effect on an unsteady supersonic flow, we consider the propagation of a planar shock wave along the discharge surface area 50–500 μs after the discharge pulse. The processes in the discharge chamber are visualized experimentally using the shadowgraph method and modelled numerically using 2D/3D CFD simulations. The interaction between the planar shock wave and the discharge-induced thermal layer results in the formation of a lambda-shock configuration and the generation of vorticity in the flow behind the shock front. We determine the amount and spatial distribution of the electric energy rapidly transforming into heat by comparing the calculated flow patterns and the experimental shadow images. It is shown that the uniformity of the discharge energy distribution strongly affects the resulting flow dynamics. Regions of turbulent mixing in the near-surface gas are detected when the discharge energy is deposited non-uniformly along the plasma sheet. They account for the increase in the cooling rate of the discharge-induced thermal layer and significantly influence its interaction with an incident shock wave.

Methods for Panoramic Visualization and Digital Analysis of Thermophysical Flow Fields. A Review.

“…Figure 26 presents the calculated and experimental images of the density fields of a complex gas-dynamic quasi-two-dimensional flow in a shock tube after the shock wave interaction with a pulsed volume discharge with preionization from plasma electrodes. Comparison of experimental shadow images with the results of CDF images based on the Euler and Navier -Stokes equations made it possible to calculate the value of the energy input to the flow by solving the inverse problem [145][146][147]. In the 90th the first computerized interferograms of two-dimensional flows were published [148,149].…”

Edge Detection and Machine Learning Approach to Identify Flow Structures on Schlieren and Shadowgraph Images

“…Local high-energy cylindrical channels form semi-cylindrical shock waves and the following convective plumes. It was previously shown that the plume dynamics is explained by the forced convection, caused by the discharge-induced shock wave [19]. Fig.…”

“…Flat shock wave spreads from the plasma sheet surface and the cylindrical one is created by the local high-energy surface discharge channel. The physics of the convective plume is based on the forced convection, caused by the shock wave [19]. The air pressure of quiescent air was p = 93 Torr.…”

“…Thus, the developed software allows us to automatically process hundreds of shadowgraph images within a minute. Previously, it took several hours to process one sequence of such frames manually [19]. To detect the shock wave position, two CNNs are working together.…”

Dynamics of dual-pulse laser energy deposition in a supersonic flow

“…In both cases, a vortex strength could be manipulated by the change of the density gradient and local non-uniformity created by the formed plasma plume. Authors of the paper [14], considering a plasma sheet actuator interaction with a shock wave, concluded that the effect of the non-uniform energy deposition cannot be neglected and can lead to the generation of large-scale coherent vortices and transition to turbulence. A parametrical study [15] suggested that the vortex energy strength is proportional to the radius of the low-density region generated by the laser discharge.…”