Visualization of the interaction region of an oblique shock wave with a boundary layer by the radiation of a nanosecond surface sliding discharge

Abstract

The spatial structure of radiation of a surface sliding discharge with a duration of ~ 300 ns (plasma sheet) in inhomogeneous supersonic air flows including oblique shock wave in a discharge chamber of shock tube was experimentally investigated. The flows were created behind plane shock waves with Mach numbers 2.8-4.2; flow Mach numbers were 1.30-1.60. The flow in the discharge chamber included an oblique shock wave generated by the interaction of a supersonic flow with a small obstacle, and then reflected from the upper wall of the discharge chamber. In this case, the shock wave interacted with the boundary layer of the supersonic flow, which formed on the streamlined wall. A surface sliding discharge with a length of 100 mm and 30 mm wide was initiated on a streamlined surface at a certain moment in time. The discharge current, emission spectra, and spatial characteristics of the radiation under various conditions of discharge initiation were obtained and analyzed in experiments. The time dependence of geometry of the discharge glow region was obtained by digital processing of discharge images in flows. CFD simulation was performed to determine the shock-wave structure of the flow in the channel with an obstacle under experimental conditions. The comparison of experimental data with the results of numerical calculation of the supersonic flow field was done. It was shown that the spatial distribution of radiation from a surface sliding discharge visualizes the low density areas and the separation zone formed under the interaction of an oblique shock wave with a boundary layer.

High-Speed Shadowgraphy of the Interaction of an Oblique Shock Wave in a Channel with a Surface Sliding Discharge

“…Analysis of high-speed imaging showed that the formation of a quasi-stationary flow occurs within 90-150 μs after the plane shock wave passes the obstacle. Its duration is about 150-500 μs, which corresponds to numerical simulation [15]. The total duration of a homogeneous co-current flow behind a plane shock wave is 180-650 μs depending on the Mach number of the initial shock wave (Fig.…”

“…Therefore, in an inhomogeneous air flow with an oblique shock wave, a surface sliding discharge develops as a single channel located in a region of low density formed during the interaction of an oblique shock wave with the boundary layer (Fig. 5 c, d), [15]. In experimental photo images, the discharge channel looks like an intensively emitting band about 10 mm wide.…”

“…Interaction with the boundary layer can be with separation of the flow or without separation [6][7][8]. In both cases, a region of low density is formed [15].…”

“…Moreover it is necessary to determine the structure of the supersonic flow after discharge. In high-speed flows in the channels, the formation of separation zones is possible when the boundary layer interacts with an oblique shock wave [10,11], and the search for methods for controlling such zones remains relevant [12,13], including the study of physical processes in the plasma of nanosecond discharges discharge in an inhomogeneous flow [14,15].…”

“…The near-surface flow influences the discharge channels [3,6]. The interaction of vortex zone and the relaxing plasma can lead to inhomogeneous discharge current [14,15]. This study is focused on the structure of a supersonic flow in a shock tube channel with inclined shock wave and on the details of surface sliding discharge dynamics in a supersonic airflow, which is important for understanding of the discharge physics and processes of plasma-flow interaction.…”