Experimental study of the flow around a near-wall rectangular cylinder

Abstract

This study experimentally investigates the flow around a near-wall rectangular cylinder at a Reynolds number of \(Re_D = 1000\), focusing on the influence of gap ratios (\(G/D = 0.5, 1.0, 2.0\)) and aspect ratios (\(L/D = 3, 6, 9\)). The results demonstrate that both parameters profoundly impact vortex dynamics and turbulence characteristics. At small \(G/D\), near-wall effect suppresses lower leading edge vortex formation and leads to asymmetric recirculation. As \(G/D\) increases, the flow becomes more symmetric, and vortex shedding from both the upper and lower sides intensifies, forming Kármán vortex streets at suitable \(L/D\). The behavior of secondary vortices and their interaction with primary wake vortices vary significantly with geometry, influencing their development into coherent boundary layer structures or their entrainment into the wake. The fluctuations grow with increasing \(G/D\) and are especially strong at \(L/D = 3\) due to enhanced wake oscillations. Wall-normal integrated velocity fluctuations reveal that leading edge and trailing edge vortex shedding contributes comparably to turbulence production, particularly at larger gap ratios, where clear bimodal distributions are observed.