Unsteady Boundary Layer Flows Induced by Accelerating Motion

Abstract

To approximate unsteady boundary layer flows induced by an impulsive motion of a body, a model of an external stream preceded by an accelerating process is presented, which might have been realized in the laboratories. The variation with time t of an external stream is assumed to be in the form V(t)=1−exp(−αtⁿ), where α means a coefficient of acceleration. By employing this acceleration process, flows near the forward and rear stagnation points on an infinite plane wall are investigated. Numerical studies show that the time lag of an external stream gives rise to a remarkable lag in time to the response of the boundary layer and evaluated time elapsed before the boundary layer near the rear stagnation point begins to separate is found to disagree with that of impulsive motion when the acceleration is slow and gradual.