Viscous vs. inviscid interaction of a vorticity structure with a circular cylinder

The interaction of a given two-dimensional vorticity distribution with a circular cylinder is analyzed by comparing the numerical solutions provided by an inviscid and by a viscous approach. While the vorticity dynamics of high Reynolds flows in free space shows an almost inviscid behavior, at least in the starting phase, this is not the case in the presence of a solid wall where a considerable effect of viscosity is experienced since the initial stage of the evolution. In fact, the vorticity generation process at the wall may significantly influence the overall flow field even in the case of a weak interaction. A multilevel contour dynamics technique plus a vortex sheet at the body surface are introduced to study the inviscid evolution, while a viscous vortex method has been adopted for the solution of the complete Navier-Stokes equations. An energy-like relation involving forces and other global quantities of the flow is proposed together with its use as a way to control the accuracy of the numerical solution. The numerical simulation of a vorticity patch orbiting around a circular cylinder gives an interesting source of information for the study of unsteady separation providing, at the same time, a proper test to devise a simplified model within the limit of vanishing viscosity. © 1994 Kluwer Academic Publishers.