Experiments have been performed for a turbulent channel flow over a backward-facing step. The backward-facing step flow is actively controlled by equipping a slit at the bottom corner of the step and low momentum fluids in the recirculating region are sucked from the slit. The width of the slit is changed between 2, 3 and 5 mm, and suction flow ratio is varied from 0.00 to 0.15. The wall static pressure and local heat transfer coefficient are measured behind the backward-facing step. In addition, the velocity profiles and turbulent intensities are measured by a split hot film probe. It is found that improvement in the heat transfer coefficient at the recirculating region and decreases in pressure loss are obtained by the suction. The heat transfer and pressure drop characteristics are controlled by the suction flow ratio, independently of suction velocities. When the suction flow ratio is 0.08, the highest performance is obtained.

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