Direct numerical simulation of spatially developing turbulent boundary layer for skin friction drag reduction by wall surface-heating or cooling

Direct numerical simulation (DNS) of spatially developing turbulent boundary layer with uniform heating or cooling is performed aiming at skin friction drag reduction. The Reynolds number based on the free-stream velocity, the 99% boundary layer thickness at the inlet and the kinematic viscosity is set to be 3000 and the Prandtl number is 0.71. A constant temperature is imposed on the wall. The Richardson number for the buoyancy Ri is varied in the range of −0.02 ≤ Ri ≤ 0.02. The DNS results show that uniform cooling (UC) reduces the skin friction drag, while uniform heating (UH) enhances it. The trend is similar to that in channel flow s tudied by Iida & Kasagi (1997) and Iida et al. (2002). An analysis using the FIK identity clarifies that UC can reduce skin friction drag by stabilizing the turbulent in the flow, while UH has the opposite trends; UC generates stable density stratification and UH does unstable one.