Experimental investigation on wake characteristics behind a yawed square cylinder

Abstract

The wake vortical structures of a square cylinder at different yaw angles to the incoming flow (α=0°, 15°, 30° and 45°) are studied using a one-dimensional (1D) hot-wire vorticity probe at a Reynolds number (Re) of about 3600. The results are compared with those obtained in a yawed circular cylinder wake. The Strouhal number (StN) as well as the mean drag coefficient (CDN), normalized by the velocity component normal to the cylinder axis, follow the independent principle (IP) satisfactorily up to α=40°. Using the phase-averaging analysis, both the coherent and the remaining contributions of velocity and vorticity are quantified. The flow patterns of the coherent spanwise vorticity (ωz) display obvious Kármán vortex streets and their maximum concentrations decrease as α increases. Similar phenomena are also shown in the coherent contours of the streamwise (u) and transverse (v) velocities as well as the Reynolds shear stress (uv). The contours of the spanwise velocity (w) and Reynolds shear stress (uw), however, experience an increasing trend for the maximum concentrations with increasing yaw angle. These results indicate an enhancement of the three-dimensionality of the wake and the reduction of vortex shedding strength as α increases. While general similarities to the wake behind a yawed circular cylinder are found in terms of flow features, some differences between the two wakes at different yaw angles are highlighted.