Numerical Simulation of Transition in Boundary Layers

Abstract

Transition in boundary layers is a spatially evolving process. In natural transition it is initiated by environmental disturbances such as pressure fluctuations, sound, vortical disturbances, etc. By virtue of certain receptivity mechanisms, which are enhanced for example by strong local wall variations, such as steps, protuberances (roughness elements) or suction slots, the disturbances generate instability waves within the boundary layers. Ideally, if no such disturbances were present, the transition process would not evolve, or if disturbances that were present initially are then suppressed, an already initiated transition process would come to a halt and the flow would relax to the laminar undisturbed state. In short, the dynamic events occurring during the transition process are initiated and derived by the continual forcing of the flow system under consideration which, in this case, is the wall boundary layer.