Direct numerical simulation of stagnation region flow and heat transfer with free-stream turbulence

Abstract

A direct numerical simulation is performed for stagnation-region flow with free-stream turbulence. A fully implicit second-order time-advancement scheme with fourth-order finite differences and an optimized scheme are employed. The optimized scheme is developed to save computational cost. The free-stream turbulence is a precomputed field of isotropic turbulence. The present DNS results in the “damping” and “attached amplifying” regimes are found to be similar to those of the organized inflow disturbances. Emphasis is placed on the flow and temperature fields in the “detached amplifying” regime. The contours of instantaneous flow field illustrate that streamwise vortices are stretched in the streamwise direction by mean strain rate. The temperature field is also stretched in the streamwise direction near the wall. The surface contours reveal that the temperature field is influenced significantly by streamwise vorticity. Due to the dominance of the mean strain, the log-law region is not observed for ū and T̃, the inner scaling fails, but the outer scaling works. The single-point turbulence statistics and the turbulent statistics budgets are obtained. The flow statistics reflect the typical characteristics of stagnation-region flow which are generically different from those of other canonical shear flows. One of the typical features of the budgets is that the velocity pressure correlation and the turbulent transport play significant roles in the stagnation-region flow. Finally, the present simulation data are compared with experimental results. It is found that the effect of large-scale eddies on the enhancement of wall heat transfer is substantial in the turbulent stagnation-region heat transfer.