Mixing enhancement in flow past rectangular cavities as a result of periodically pulsed fluid motion

Periodic elimination of the shear layer separating the mainstream from recirculatory regions in a multicavity channel is possible by imposing a pulsatile component on an otherwise steady flow. Numerical and experimental results are correlated to show that the unsteadiness during half of a cycle leads to the destruction of the trapped vortex while simultaneously generating its replacement. During the other half of the cycle, when there is only steady fluid motion, a new vortex grows to fill the cavity and protrudes into the mainstream, thus further enhancing mainstream and cavity mixing. The fluid motion is characterized by three nondimensional parameters: a Reynolds number based on the steady velocity component, a Reynolds number based on the unsteady velocity component, and a Strouhal number based on the frequency of oscillation and the unsteady velocity component.>