COMPRESSIBLE MIXING LAYER GROWTH-RATE AND TURBULENCE CHARACTERISTICS

Direct numerical simulation databases have been used to study the effe ct of compressibility on mixing layers. The simulations cover convecti ve Mach numbers from 0.2 to 1.2 and all contain a fully resolved turbu lent energy cascade to small spatial scales. Statistical information i s extracted from the databases to determine reasons for the reduced gr owth rate that is observed as the convective Mach number is increased. It is found that the dilatational contribution to dissipation is negl igible even when eddy shocklets are observed in the how. Also pressure -dilatation is not found to be significant. Using an accurate relation between the momentum thickness growth rate and the production of turb ulence kinetic energy together with integrated equations for the Reyno lds stress tensor it is shown that reduced pressure fluctuations are r esponsible for the changes in growth rate via the pressure-strain term . A deterministic model for the required pressure fluctuations is give n based on the structure of variable-density vortices and the assumpti on that the limiting eddies are sonic. Simple anisotropy consideration s are used to close the averaged equations. Good agreement with turbul ence statistics obtained from the simulations is found.