The effect of blow and suction at permeable walls on flows at high Reynolds number

The effect of blow or suction on the external flow and on the boundary layer is studied for a stationary, steady, and incompressible flow at permeable walls. Laminar and turbulent boundary layers are separately considered. In the laminar case, theoretical and experimental research results on a thin Joukowsky profile and on a circular cylinder are used to determine the volume of exhaust or suction flow at which transition to asymptotic solutions takes place. Special attention is given to the attainable reduction of resistance under higher order effects and to the normal velocity distribution at the wall. For turbulent boundary layers with weak exhaust or blow, asymptotic methods for classifying orders of magnitude are discussed and the results are compared with known relationships. Boundary layer measurements at porous walls are used to derive a developed asymptotic concept applicable to strong exhaust.