Unsteady separation past moving surfaces

Unsteady boundary-layer development over moving walls in the limit of infin ite Reynolds number is investigated using both the Eulerian and Lagrangian formulations. To illustrate general trends, two model problems are consider ed, namely the translating and rotating circular cylinder and a vortex conv ected in a uniform flow above an infinite flat plate. To enhance computatio nal speed and accuracy for the Lagrangian formulation, a remeshing algorith m is developed. The calculated results show that unsteady separation is del ayed with increasing wall speed and is eventually suppressed when the speed of the separation singularity approaches that of the local mainstream velo city. This suppression is also described analytically. Only 'upstream-slipp ing' separation is found to occur in the model problems. The changes in the topological features of the flow just prior to the separation that occur w ith increasing wall speed are discussed.