Direct numerical simulation of turbulent flow in an axisymmetric supersonic diffuser

Effects of deceleration and mean dilatation on the turbulence structure of supersonic flow in a diffuser with an incoming supersonic fully developed turbulent pipe flow are studied by means of direct numerical simulation. Strong enhancement of the turbulence intensities is observed when the flow undergoes deceleration. Turbulence production and pressure-strain terms in the Reynolds stress budgets are found to increase dramatically leading to increased Reynolds stresses. The central role of pressure-strain correlations in modifying the turbulence structure under these flow conditions is demonstrated and a priori tests of two turbulence models are presented.