Coexistence of natural and forced vortex dislocations in step cylinder flow

Abstract

The wake behind a step cylinder [consisting of a small diameter cylinder (d) and a large diameter cylinder (D)] with diameter ratio D/d=2 at Reynolds number ReD = 200 (the mode A* regime) is simulated by direct numerical simulations. New detailed information of the interaction between natural vortex dislocations and forced vortex dislocations is described. In the large cylinder wake, the forced and natural vortex dislocations coexist. The regular formation of forced vortex dislocation is found to be delayed under the effect of natural vortex dislocations. The occurrence of natural vortex dislocations is suppressed in the large cylinder wake close to the small cylinder. Moreover, the effect of vortex dislocations on structural loads is described. The results of this paper provide a more thorough understanding of the formation and interaction between the natural and forced vortex dislocations.