Turbulent heat transport in a perturbed channel flow

The recovering boundary layer downstream of a separation bubble is known to have a highly perturbed turbulence structure which creates difficulty for turbulence models. The present experiment addressed the effect of this pert urbed structure on turbulent heat transport. The turbulent diffusion of hea t downstream of a heated wire was measured in a perturbed channel flow and compared to that in a simple fully developed channel flow. The turbulent di ffusivity of heat was found to be more than 20 times larger in the perturbe d flow. The turbulent Prandtl number increased to 1.7, showing that the tur bulent eddy viscosity as affected even more strongly than the eddy thermal diffusivity. This result corroborates previous work showing that boundary l ayer disturbances generally have a stronger effect on the eddy viscosity, r endering prescribed turbulent Prandtl number models ineffective in perturbe d flows.