Abstract
We experimentally investigate the effect of thermal boundary conditions on the heat transfer characteristics in a turbulent boundary layer developing over a heated flat plate. The flat walls are independently heated, thus yielding rapidly changing thermal boundary conditions in contrast to the uniformly heated case. It is found that in the case of stepwise cooling, the wall-normal turbulent heat flux near the wall becomes opposite in sign to that in the uniformly heated case. On the other hand, in the stepwise heating case, the turbulent heat flux becomes larger than that observed in the uniformly heated case. Interestingly, both of changes in the wall-normal turbulent heat fluxes are caused by the quasi-coherent motions of the same velocity field.
