Fomin V.M.   Yakovlev V.I.  

Original cause and mechanisms for structure instability of strong shock waves in gases

Reporter: Yakovlev V.I.

Sufficiently strong shock waves (SW) in atomic and molecular gases are characterized by two qualitatively different flow modes, which are classified as stable and unstable regimes, displaying regular or irregular flow structure. Results of many efforts to explain experimental data of some decades were represented in [1–3]. For the first time in work [1] was pointed out a possible decisive role of experimental conditions: channel’s walls influence, method used to generate shock waves, from which depends wave’s dynamics.
Data of work [2] serve as evidence, which ascertain, that wall’s heating by emitted radiation of shock-heated gas give rise to 1D flow structure failure because of thermal effect. Thus it is supposed, that original cause for irregular flow mode is boundary of a flow – channel’s walls. Besides such boundary serve as a source of week gasdynamic perturbations as well as flow nonuniformity caused by growing boundary layer behind SW front.
An analysis for atomic gas ionization relaxation under influence of stated factors (week perturbations with different frequencies, no uniform flow behind SW front) performed in [3] revealed that physical mechanisms causing structure instability are various depending on initial experimental conditions. 
At low Mach numbers with thermal effect absence the decisive role play week gasdynamic perturbations, which exert significant influence upon kinetic mechanism of associative ionization by atom/excited atom collisions. When Mach number increasing an electric field increased and its vector change direction (no uniform flow effect caused by boundary layer). When electric field reach critical value near wall behind SW front a local energy input in gas implemented similar to thermal effect.
Thus the original cause for irregular SW flow mode is the boundary influence, which: a) induce week gasdynamic (specifically temperature) perturbations, b) give rise to no uniform flow behind SW front as well as gas stratification ahead of it. The pointed original cause is general for SW penetrating various atomic and molecular gases. Though the mechanisms, causing unstable flow modes may be different depending on initial experimental conditions.
1. Kuznetsov N.M.// Usp. Fiz. Nauk. 1989. V.159. I.3. P.493-527. (in Russian).
2. М.B. Zheleznyak, А.H. Mnatsakyan, V.E. Pasternak, E.A. Philimonova. // Izvestia AN, MZhG. 1991.№.3.   С. 124-131. (in Russian).

3. V.M. Fomin. V.I.Yakovlev. Energy exchange in supersonic gas/plasma flows and shock waves. – M.:FIZMATLIT, 2017. – 368 p. (in Russian)

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