A Study on the Effect of Periodic Wake on a Separation Flow : On the Changes of the Fluctuation Frequency of Separation Flow

Abstract

Te vortex structure within a separated flow region changes when the disturbance is introduced in a mean-flow. This change was investigated by numerical simulation. The periodic velocity fluctuation introduced into the mean-flow at the upstream of separation shear layer, and its amplitude is 30% of the mean-flow velocity. By this periodic fluctuation, the shear layer is flapped to make vortices be shed with the frequency of fluctuation. For making the separation region narrow, it is found that the most effective frequency is about twice of the frequency which is dominant in the separation flow without fluctuation. Furthermore, first sub and super harmonics of that frequency make the flow be periodic. These resonance are explained by using the wave number which is equivalent to the vortex scale.