The present study investigates the effect of gap ratio on the turbulent flow characteristics downstream of a square cylinder positioned in an open channel. Detailed velocity measurements were performed using a particle image velocimetry (PIV) system for gap ratios, G/h = 0.5 and 1, where G is the distance from the bottom face of the cylinder to the nearby wall and h is the cylinder height. Each set of experiments was conducted using a water depth of 65 mm and a Reynolds number of 2000 based on the height of the cylinder and the freestream velocity. Mean velocities, Reynolds stresses and Reynolds shear stress producing events of the quadrant decompositions were compared for the different gap ratios investigated. The results showed that as gap ratio decreased from 1 to 0.5 cylinder heights, the length of the separated region increased by 50%. Furthermore, the Reynolds stresses were found to decrease with decreasing gap ratio. Further downstream of the cylinder, the turbulent kinetic energy decreased, while the Reynolds shear stress increased for G/h = 0.5 compared to G/h = 1.

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