Simulations of heat transfer in a boundary layer subject to free-stream turbulence

The present study investigates the effects of ambient free-stream turbulence (FST) on the momentum and heat transfer in a spatially developing, turbulent flat-plate boundary layer via large-eddy simulations using the ADM-RT model. Due to a local turbulence intensity Tu of 7% in the free stream, the skin-friction coefficient cf and Stanton number St are substantially elevated up to 25% and 32%, respectively, in the fully turbulent region (Re=300). This observation is in qualitative agreement with earlier experimental studies. Moreover, the Reynolds analogy factor is found to increase with the FST intensity Tu. The depression of both mean velocity and temperature profiles in the wake region due to FST is observed. In addition, the pre-multiplied spanwise spectra show that the outer peak residing in the logarithmic region in the case without FST is replaced by a new peak located near the boundary layer edge with a spanwise scale of about 3-495. It is suggested that these large-scale events and their imprint throughout the boundary layer cause the elevation of both the skin friction and heat transfer on the solid surface.