Vortex shedding patterns past a rectangular cylinder near a free surface

Abstract

The effects of asymmetric boundary conditions on the flow past rectangular cylinders are relevant for many engineering applications. Pertinently, the influence of wall proximity on the flow around cylinders has been widely investigated, and the flow regimes depending on the distance to the wall have been identified. However, a comprehensive study of the flow around rectangular cylinders near a free surface is lacking. The classifications of the flow have not been tackled and the connection between the flow behaviors and the force variations with the depth has not been demonstrated. In this study, multiphase simulations over a broad range of depth-to-length ratios (0.3–4.5) and width-to-length ratios (0.7–5.0) were conducted. Flow results show that the anti-symmetric vortex shedding becomes asymmetric and then suppressed as the depth decreases. Three patterns of asymmetric flow depending on the width-to-length ratio were observed: “asymmetrically separated”, “one-sidedly reattached” and “asymmetrically reattached”. The force variations with the depth for rectangular cylinders with 0.7 <w/l < 1.5, 1.5 ≤ w/l < 2.8 and 2.8 <w/l ≤ 5.0 show different trends due to the occurrence of different asymmetric flows. The boundaries between different flow patterns were defined based on the force variations.