Study on the aerodynamic characteristics and flow mechanism of square cylinders with rounded corners

In order to elucidate the variation patterns of the aerodynamic characteristics of square cylinders with rounded corners with respect to corner radius ratio and angles of incidence, and to reveal their underlying mechanisms, a wind tunnel test was performed to examine the surface wind pressure of square cylinders with a corner radius ratio R/D (where R represents the corner radius and D signifies the characteristic dimension of the object) of 0, 0.1, 0.2, 0.3, and 0.4. The experiment was conducted at a Reynolds number of 120,000 while varying the angles of incidence between 0 degrees and 45 degrees. In this study, aerodynamic forces, Strouhal numbers, and wind pressure were analyzed. Additionally, the flow field was visualized using a large eddy simulation (LES). The results indicate that the critical angle of incidence alpha(cr) of square cylinders with rounded corners decreases as the corner radius ratio increases. alpha(cr) represents the angle at which the mean drag and fluctuating lift are minimum and the mean lift and Strouhal number are maximum. Significant negative pressure is observed near the windward rounded corner of the square cylinders with rounded corners in the vicinity of alpha(cr), with the highest value occurring at an R/D of 0.2. Fluctuating wind pressures could attain larger values in the vicinity of the leeward rounded corners where alpha = 12.5 degrees similar to 20 degrees and alpha = 45 degrees. Increasing R/D to a certain value significantly alters the flow structure compared to a square cylinder with R/D= 0. This is due to the shear layer flowing close to the wall, as it does not separate at the windward rounded corner.