Aerodynamic characteristics and flow mechanism of rectangular cylinders with a small corner radius ratio

In practical applications, the inflow direction for rectangular cylinders with small corner radius ratios is often variable, yet research on aerodynamic characteristics and flow mechanisms has largely focused on cross-flow. The effects of wind direction angle on their aerodynamic behavior, and how they differ from standard rectangular cylinders, remain unclear, as do the underlying flow mechanisms. This study investigates these aspects by examining aerodynamic characteristics and flow field characteristics across different wind direction angles, aiming to clarify how a small corner radius ratio influences performance. Wind tunnel tests were conducted on cylinders with an aspect ratio of 2 and corner radius ratios (R/D, where R is the corner radius and D is the section thickness) of 0.1 and 0.2 under uniform flow, across wind direction angles from 0° to 90°, with comparisons to a standard cylinder. Results show five typical flow regimes for all cylinders. Compared to the standard cylinder, those with R/D = 0.1 and 0.2 exhibit narrower ranges for Regime I and V, wider ranges for Regime III and IV, and a similar but shifted range for Regime II toward smaller wind direction angles. As the corner radius ratio increases, the mean drag coefficient decreases (maximum reductions: 27% for R/D = 0.1, 55% for R/D = 0.2), while the mean lift coefficient increases (maximum increases: 94% for R/D = 0.1, 116% for R/D = 0.2). The Strouhal number rises with the corner radius ratio. A sharp rise in Strouhal number occurs during the I–II transition, and abrupt changes in force coefficients are observed during the IV–V transition.