Wake Dynamics of a Rotating Cylinder With Cactus-Shaped Surface Elements

Abstract

Flow controls have been applied to a cylinder for a Reynolds number of Re = 2 x 103. The results have been procured by Particle Image Velocimetry (PIV). Rotation rates have been considered up to alpha = 1.26 as active control. Apex angles of cactus-shaped surfaces from beta = 7.5 degrees to beta = 45 degrees have been evaluated as passive control. Maximum streamwise values have been observed in regions externally to the wake. Minimum values have been recorded within wakes. Positive cross-stream values have been observed over stationary cylinders. However, these were in the far wake regions. In contrast, negative values have been detected below the stationary cylinders, with these readings occurring over the far wake regions. Beyond influence of apex angles, rotational rates also affected the spatial cluster distributions. Rotation changed the number and distributions of foci and saddle points. Analysis of fluctuating streamwise and cross-stream components revealed two distinct clusters and only one cluster, respectively. As apex angles and rotation rates increased, clusters tended to converge towards the cylinders. These were indicative of dominance stemming from wake and separated flows. It led to two clusters of Reynolds stress correlations. Apex angle impact on vorticity is comparatively limited. Influence of rotational dynamics proved to be more pronounced. Consequently, two vortical structures have been discerned with the positive ones emerging as more dominant because of the rotation. To sum up, the overall effects of active control are more overarching than those attained by passive ones.