Three-dimensional vorticity measurements in the wake of a yawed circular cylinder

Abstract

Using a phase-averaged technique, the dependence of the wake vortical structures on cylinder yaw angle α (=0°–45°) was investigated by measuring all three-velocity and vorticity components simultaneously using an eight-hot wire vorticity probe in the intermediate region (x/d = 10) of a yawed stationary circular cylinder wake. For all yaw angles, the phase-averaged velocity and vorticity contours display apparent Kármán vortices. It is found that when α ≤ 15°, the maximum coherent concentrations of the three vorticity components do not change with α. However, when α is increased to 45°, the maximum concentrations of the coherent transverse and spanwise vorticity components decrease by about 33% and 50%, respectively, while that of the streamwise vorticity increases by about 70%, suggesting that the strength of the Kármán vortex shed from the yawed cylinder decreases and the three dimensionality of the flow is enhanced. The maximum coherent concentrations of u and v contours decrease by more than 20% while that of w increases by 100%. Correspondingly, the coherent contributions to the velocity variances 〈u²〉 and 〈v²〉 decrease, while that of 〈w²〉 increases. These results may indicate the generation of the secondary axial vortices in yawed cylinder wakes when α is larger than 15°. (See Article file for details of the abstract.)