Numerical Studies of Unsteady Compressible Turbulent Shear Flows

摘要

We have shown that in all cases when the integral scale (L sub i) of turbulenceis of the order of the size of the system (L), flow parameters and characteristics of the turbulence fluctuate strong on a time scale of one turn-over time. DNS of Kolmogorov flow has been used to establish this effect. Experimental data on jet and mixing layers, where the integral scale is L sub i (approx. =) 1/2L, supports this basic observation. Strong fluctuations invalidate the ordinary 'eddy viscosity' concept which in these cases requires finite time corrections. It has been shown that for those strongly time dependent flows the Smith/Yakhot modification of RNG gives a good description of the flow. The derived equations are being used for investigation of the onset of nonstationarity in flow over bluff bodies, including a rocket-like body at finite angle of attack. We have studied the optimization of physical characteristics of a 'Spoiler' used to reduce or eliminate vortex shedding using VLES. It has been shown that the process parameters depend on the device length and relative position. The validated theoretical concepts numerical codes have been used for a set of exploratory simulations of a 3-D flow over rocket-like body at the Reynolds number Re approx. 10(exp7).