Heat Transfer Augmentation in the Region Downstream of a Backward-Facing Step : Effects of a Cylinder Mounted near the Top Corner of the Step

A study was conducted to see if it is possible to enhance the heat transfer in the downstream region of a backward-facing step, where heat transfer is normally deteriorated, by the insertion of a cylinder near the top corner of the step. The flow Reynolds number, cylinder size and streamwise position of the cylinder were kept constant but the cross-stream position of the cylinder was changed in three steps. The results of the heat transfer experiment, flow visualization and measurement of the averaged and fluctuating flow fields were reported. When the cylinder was mounted in a position a little higher than the step top surface, a jetlike flow pattern appeared in the averaged velocity profile beneath the cylinder, and the recirculating flow was intensified. Therefore, the velocity of recirculating flow near the wall is increased at some streamwise positions. Additionally, velocity fluctuation is intensified, not only in the shear layer between the jetlike flow and the recirculating flow regions but also in the near wall region. These intensifications result in the effective augmentation of heat transfer in this case. Therefore, it is concluded that the mounting of a cylinder is effective if it is mounted in the proper position.