Flow Over Two Circular Disks in Tandem

Abstract

Placing two or more bluff-bodies in tandem is known to lead, in some cases, to configurations with relatively low overall drag. The present study concerns one particular case where two disks of unequal diameters, normal to the flow, are placed in tandem for the purpose of drag reduction. It shows that very significant drag reductions may be achieved by proper sizing of the disk diameters and of the gap between them. Placing a properly sized disk at an optimum distance ahead of a single reference disk can result in a configuration whose total drag is up to 81 percent lower than that of the reference disk alone. If the additional disk is placed behind into the near-wake of the reference disk, the drag of the two-disk configuration can be up to 70 percent lower than for the reference disk alone. Four different flow regimes have been identified, depending on the diameter ratio of the two disks, two with relatively steady flows and two with unsteady flows. The absolute drag minimum was found to occur in one of the two steady-flow regimes.