Influence of wake vortices induced by rotating circular cylinder on flat-plate boundry layer

Abstract

Unsteady boundary layer development over a flat plate under the influence of wake vortices induced from a rotating circular cylinder has been investigated by numerical computations. The ratio of peripheral speed of the rotating cylinder to the free stream velocity, a is varied from 0.5 to 1.75 keeping the rotating cylinder positioned at different locations from the plate. The unsteady two-dimensional flow is simulated numerically using finite element formulation. Quadratic triangular elements and discontinuous linear triangular elements are used for velocity and pressure interpolation respectively. A finite element package FEMLAB is used for the present computation. Investigations are carried out for low Reynolds number based on cylinder diameter and undisturbed free stream velocity in the range of 200 to 800. Initial development of the flow field up to certain time period is considered. Instantaneous streamlines of the disturbed flow field, instantaneous velocity field, instantaneous boundary layer integral parameters, and skin friction are presented on different streamwise locations. The location of the onset of transition is also identified. The wake vortices strongly affect the boundary layer development compared to undisturbed flow over flat plate. The computational results showed two types of interactions, one is the strong wake-boundary layer interaction and another being the weak wake-boundary layer depending on the speed ratio, a and the cylinder to plate relative positions. Comparisons are also shown between the parameters . obtained for the rotating cylinder to those of the stationary cylinder.