4. Flow visualization

I.A. Znamenskaya, I.A. Doroshchenko, D.S. Naumov, T.D. Naumova, T.A. Kuli-zade
Lomonosov Moscow State University, Russia, Moscow.

High-speed recording of the blast waves created by the pulsed discharge.

An experimental investigation of pulsed combined discharge glow characteristics, and analysis of flow with blast waves, created by the discharge, are presented in the report. The localization of the discharge behind the wedge in the flow was investigated too. The contracted volume discharge was considered as electrical breakdown - vertical plasma column 24 mm long. As a result of the nanosecond-lasting breakdown, the internal energy of the gas increased, that led to flow with cylindrical shock (blast) waves formation. The flow evolution was visualized via highspeed shadowgraphy. Blast waves were recorded, their position and speed were measured; instability of post-discharge hot gas channel also was visualized. A 2D numerical simulation of flow based on the Euler equations was performed. The model of pulse cylindrical energy deposition was used; initial conditions were taken from the experimental data. Inverce problem was solved comparing CFD and experimental shock waves position. It was shown that 20-22% of the combined discharge energy, stored in the capacitor was converted into internal gas energy (about 140 - 155 mJ). Shock waves from surface discharges were visualized and analyzed as well. In case of
initiation of a discharge in a nonuniform gas-dynamic flow contraction mechanism is different. Breakdown occurs in the lowest density region because density reduction leads to an increase of a normalized electric field parameter E / N. Thus, it is possible to control the energy input into the low-density areas in the flow separation zone. It is shown that the luminescence time for both localization regimes substantially exceeds time of the current - 200 ns, and, respectively, the energy input time, which is equal to current time. There is a long afterglow phase in both of the contraction regimes, which is absent in the volume discharge regime. The duration of the afterglow phase is up to 12.5 μs.
Full text paper