Investigation and Application of Nanosecond Discharges for Supersonic Flow Structure Visualization

An experimental study was carried out on the spatial distribution of glow in a nanosecond surface sliding discharge and a combined volume discharge in supersonic air flows around a streamlined axisymmetric body in a channel. The flow in the discharge chamber included shock waves generated by the flow around the body and those reflected from the channel walls. Flow visualization was performed by the direct shadowgraphy and by recording the discharge glow with photo cameras and ICCD camera. Supersonic air flows with Mach numbers of 1.36–1.60 were generated behind plane shock waves with Mach numbers of 3.0–4.4 in a in a rectangular shock tube channel. Discharges were initiated under a voltage pulse of 25 kV either along the surface or within the volume, extending up to 100 mm along the flow direction. Spatial emission characteristics of the discharge initiated at various stages of gas-dynamic flow were analyzed. Digital image processing and analysis of the glow captured during discharge development were carried out and compared with shadowgraphy images of the flow field. A correlation was demonstrated between the emission distribution of the sliding surface discharge in supersonic flows and the state of the boundary layer on the channel wall where the discharge develops. Comparison of volume discharge images with shadowgraphy frames enabled the reconstruction of the three‑dimensional structure of the supersonic flow, featuring a bow shock in front of the body and the oblique shock waves downstream.