Effect of incidence angle on the wake of a wall mounted slotted cylinder in an open channel flow

Abstract

This experimental study investigates the wake flow generated by a vertically, wall-mounted slotted-cylinder in shallow channel flow. The slot, uniformly cut along the central plane of the cylinder, has a thickness equal to 0.1 times the cylinder diameter. The primary parameter examined is the incidence angle θ between the slot axis and the main flow direction, selected by rotating the slotted-cylinder clockwise to four different positions. The study aims to understand the impact of θ on the wake flow characteristics by investigating both the instantaneous and mean velocity fields, as well as the coherent structures. The Reynolds number, based on the water depth, is approximately 25,000. Particle image velocimetry (PIV) measurements were conducted along the vertical mid-plane and on three horizontal planes.

The results revealed the formation of three-dimensional (3D) mean recirculation zones in the wake of the cylinder without a slot, resembling a counter-rotating U-shaped vortical structure. For θ ≥ 60°, this 3D shape persists, while for θ < 60°, it varies by the angle. The jet emanating from the slot suppresses velocity fluctuations when injected into the wake region at incidence angles θ < 60° In contrast, at θ ≥ 60°, there is a transition to a stimulating effect that enhances turbulent kinetic energy (TKE) production. Proper orthogonal decomposition (POD) results highlight differences in kinetic energy transfer to the turbulent flow across various cases of the slotted-cylinder. Moreover, the slot flow exhibits both blowing and suction effects, with varying intensity and dominance throughout the shallow water layer.