Flow visualization and heat transfer experiments between two parallel plates with an insertion of a square rod

Flow visualization and heat transfer measurements were made for a turbulent channel flow between two parallel plates obstructed by an insertion of a square rod. The space between the square rod and the duct wall was changed in five steps. The intermittent dye injection method was introduced to visualize the Karman vortex shed from the rod, and the locations of the Karman vortices were visualized as they move downstream. The results reveal that the Karman vortex shows crisscross motion. In accordance with the motion of the Karman vortex, a high-vorticity wall layer is intermittently lifted from the wall. The second peak in the streamwise distribution of local Nusselt number is caused by the action of vorticity island, which is produced periodically from the tip of the lifted wall layer.