Activ and Passive Control of Turbulent Channel Flow over Backward-Facing Step

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An experimental study has been performed for a turbulent channel flow over a backword-facing step. In this work, the backword-facing step flow is passively controlled by equipping the slit in upstream of the step, and deducing the high-speed fluid from this slit in the recirculating region. Angle of the slit is changed 30 degrees and 45 degrees, and width of the slit is changed in several steps in ranging 2mm〜12mm. for active control, low momentum fluids in the recirculating are sucked from the slit at the step corner. The width of the slit is changed 2, 3 and 5mm, and suction flow rate is varied from 0. 00 to 0. 15. The heat transfer coefficient and the wall static pressure are measured behind the backword-facing step. In addition, the velocity profiles, turbulence intensities and wall shear stress are measured using the split hot film probe and the micro flow sensor. The relationship between fluid fluid and heat transfer characteristics is investigated. The results are summarized as follows ;In the case of passive control, when angle of slit is 30 degrees and width of the slit is 10mm, the highest performance is obtained. Enhancement of the heat transfer is related to the increase of streamwuse velocity in the near-wall region and the increase of turbulence energy due to Karman-like vortex shedding.In the case of active control, the suction decreases the pressure drop and the heat transfer characteristics are improve. When suction flow rate is 0. 08, the highest performance is obtained.