Effects of Local Convection of Flow Over Periodic Roughness

The effects of local convection on turbulent flow structures over periodic roughness were experimentally investigated in the Union College water channel. k-type roughness was used with a pitch-to-height ratio of p/k = 11. A heated bar was manufactured to have the same geometry as the other roughness elements. The temperatures of the front face, top face, and back face of the heated bar were controlled individually using proportional integral derivative (PID) temperature controllers. The heated bar was kept at a constant T_s ≈ 42 °C. Two experiments were performed: one with heating and one without. Both experiments were performed at a Reynolds number of 618. The experiment with heating had a Richardson number of 0.229, which implies forced convection. The flow was measured using 2D particle image velocimetry (PIV). The results suggest that the buoyancy effects introduced by the heated bar had minimal to no effects on the time-averaged streamwise velocity. However, the buoyancy effects had a significant impact on the time-averaged wall-normal velocity in front of and above the heated bar. Buoyancy effects were also seen to create a greater magnitude of Reynolds shear stress in front of and downstream of the heated bar. Similar results were seen in the turbulent kinetic energy, which was higher for the heated case in front of and downstream of the heated bar.