Heat transfer enhancement behind an obstacle in a channel flow undergoing transition to turbulence

Direct numerical simulation of heat transfer behind a spanwise obstacle was carried out in a steady channel flow. Reynolds numbers corresponded to transition to turbulence in the separation region behind the obstacle. The obstacle was mounted either on the channel wall or with a gap from the wall. Thorough verification of numerical results (visual flow pattern and flow statistics) against experimental data was carried out. Distributions of local coefficients of heat transfer and skin friction behind the obstacle were found to correlate with vortical structure of the flow. For both positions of the obstacle relative to the channel wall, the study discovered principal regularities in the behavior of local and averaged across the channel values of heat transfer behind the obstacle with the varying Reynolds number of the oncoming flow. The effect of obstacle position on the total increase in heat transfer coefficient on the wall behind the obstacle was estimated in comparison with the smooth wall.