THE INFLUENCE OF ENTROPY FLUCTUATIONS ON THE INTERACTION OF TURBULENCE WITH A SHOCK-WAVE

Direct numerical simulation and inviscid linear analysis are used to s tudy the interaction of a normal shock wave with an isotropic turbulen t field of vorticity and entropy fluctuations. The role of the upstrea m entropy fluctuations is emphasized. The upstream correlation between the vorticity and entropy fluctuations is shown to strongly influence the evolution of the turbulence across the shock. Negative upstream c orrelation between u' and T' is seen to enhance the amplification of t he turbulence kinetic energy, vorticity and thermodynamic fluctuations across the shock wave. Positive upstream correlation has a suppressin g effect. An explanation based on the relative effects of bulk compres sion and baroclinic torque is proposed, and a scaling law is derived f or the evolution of vorticity fluctuations across the shock. The valid ity of Morkovin's hypothesis across a shock wave is examined. Linear a nalysis is used to suggest that shock-front oscillation would invalida te the relation between u(rms) and T-rms as expressed by the hypothesi s.