On the wake of a large depth ratio wall-mounted prism at a normal incident angle

Abstract

The wake characteristics of a large depth-ratio (depth-to-height) prism at the incident angle of 90° is numerically examined at Reynolds number of 250. An arc type, symmetric vortex shedding is observed in the wake with periodicity of St=0.087. The flow periodicity reduced with increasing incidence angle to 90°. A Hexapole-type cross-sectional wake topology is observed in the wake, corresponding to the formation of two downwash inducing pairs and a single upwash inducing (base vortex) pair. The base-vortex dominate the wake, resulting in a strong upwash flow, while a relatively smaller tip-vortex induced downwash flow is limited to the near vicinity of the prism. The unsteady flow is attributed to fluctuations that arise from the lateral positioning of the prism by means of changing incidence angle, and consecutively increased projected width of the prism. The multiple downwash inducing vortices are formed due to the shear layer detachment from the side and top surfaces of the prism, which itself is attributed to the large depth-ratio in normal incident angle configuration and the base vortex that originated from the legs of the arc-type structure. This constitutes a new wake topology that differs with previous observations at lower incidence angles.