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A Study of Compressible Turbulence
Final rept. 1 Jun-30 Nov 1991
NIELSEN ENGINEERING AND RESEARCH INC MOUNTAIN VIEW CA
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This work involves theoretical analyses of turbulence in high speed flow and large eddy simulation results for the mixing layer. Analysis indicates that turbulence is dominated by streamwise vortices as the Mach number approaches infinity. A conceptual model based on swept vortices makes predictions about the sweep angle of these vortices from spanwise at low speeds to streamwise at high speeds, and about the reduced spreading rate at high speeds. Simulations of planar shear layers, started from random initial disturbances, validate these structural predictions. Some interesting characteristics about high speed turbulence have been identified. Shocks are generally rare and weak, even at a convective Mach number of 2.5, because the flow normal to the swept vortices is subcritical. The turbulence kinetic energy is dominated by streamwise fluctuations, while the other energy components are much smaller. The pressure velocity correlations promote weak transfer of energy from the streamwise fluctuations to the other components of energy, and they strongly suppress the shear stress. These statistics are, in general, compatible with the swept vortex structure of turbulence at high Mach number. Compressible turbulence, Flow simulation mathematical models.
APPROVED FOR PUBLIC RELEASE