SHOCK-INDUCED TURBULENCE IN COMPOSITE-MATERIALS AT MODERATE REYNOLDS-NUMBERS

Numerical simulation is used to study the turbulence generated by the passage of strong shocks (typical Mach number 7.3) through an inhomoge neous fluid at moderate Reynolds numbers. Before passage of the shock, the material consists of mass-density inhomogeneities embedded in a b ackground fluid. The entire system is initially at uniform temperature , pressure, and number density, with the nonuniform mass density resul ting from differing mass species in different regions. In the present application, the substances are treated as ideal gases, though in the motivating physical problems they are more complex materials, The shoc k retains its identity and a sharp front, but leaves behind it a turbu lent state whose locally averaged properties only slowly become spatia lly uniform. The shock acquires a turbulent ''thickness'' (the linear dimension of the nonuniform region behind the shock front) that seems ultimately damped by viscous and thermally conducting properties that are dependent on transport coefficients and (highly uncertain) Reynold s numbers, Typically, the turbulence is highly compressible, with comp arable mean divergences and curls in the velocity field, and fractiona l rms density fluctuations of the order of 0.25 in the parameter range s studied. The rms vorticity generated can be estimated reasonably wel l from dimensional considerations. The effect of the high density inho mogeneities is primarily to create a wide region of compressible turbu lence behind the shock. The inhomogeneities create both a succession o f reflected shocks and considerable vorticity. (C) 1998 American Insti tute of Physics.