Viscous flow induced by counter-rotating vortices

The nature of the viscous boundary-layer flow induced near a wall, caused by a pair of counter-rotating vortices above the wall, is investigated. Solutions for the unsteady flow that develops near the wall are obtained numerically for a variety of cases. The vortices are taken to be of equal strength with cores located at equal distances from the wall; depending upon the assumed sense of rotation, the vortices either move toward the wall or recede from it, creating a region of either inflow or outflow near the wall, respectively. The calculated results show that the adverse pressure gradient near the wall induced by the vortex motion gives rise to explosively growing regions of recirculating flow near the wall. The possible relevance of these results to Görtler vortex instability and turbulent flow near walls is discussed.