Abstract

The Role of Acoustic Radiation During the Interaction of a Shock Wave with a Turbulent Flow

F.Shugaev, L.S.Shtemenko, E.A.Bratinkova (Faculty of Physics, Moscow State University, Moscow, Russia); O.A.Azarova (Computing Center RAS, Moscow, Russia)

e-mail: shugaev@phys.msu.su

Density fluctuations were investigated ahead of and behind a shock wave propagating through a turbulent gas flow both experimentally and theoretically. Experiments were fulfilled in a shock tube. A turbulence grid was used. Density fluctuations were recorded with the aid of a laser-schlieren technique. Structure and correlation functions and a turbulent lengthscale were found from the experimental values. We found out that after the passage of the shock wave the turbulent lengthscale is ten times as small as its value ahead of the wave. The possible mechanism of this phenomenon is as follows. Vortices in the turbulent flow emit acoustic waves while changing their velocity. The acoustic radiation becomes intensive after the passage of the shock wave. The interaction of acoustic waves with vortices may be resonant or not. If there is no resonance then the vortex oscillates as a whole. If the frequency of the acoustic waves is a multiple of the natural frequency of the core of the vortex then it becomes unstable and destroys. As a result, the turbulent lengthscale diminishes. A numerical simulation was also performed. The Euler equations for two-dimensional flow were used. Theoretical results agree qualitatively with experimental ones.

Section : 7