Three-dimensional transient flows past plates translating near a wall

Large eddy simulations are conducted to investigate transient three-dimensional flows past arrays of finite plates translating in the vicinity of a wall. Flows around a single plate are examined for a wide range of wall distances at a Reynolds number based on plate height of 50,000. The drag coefficient decreases rapidly when the plate is placed very close to the wall; it reaches a maximum at an intermediate distance and it asymptotes to the value corresponding to unconfined flows as the gap between the wall and the plate is increased. The reduction in drag coefficient is directly related to the pressure drop caused by vortices generated upstream of the plate induced by the close proximity of the wall. Temporal and spatial characteristics of flows past arrays of yawed plates are examined for the wall distance ratio of 1.5 and the spacing ratios of 2.5 and 5. Drag coefficient of the plates is larger than those placed away from the wall. With suitable spacing the wall proximity effects result in an increase of drag force exerted on the plates. The present study aids in optimizing marine energy harvesting systems that have blades translating beneath ocean platforms or floating river docks.