Blowing and suction effects on vortex breakdown in an enclosed cylindrical container

Abstract

The phenomenon of vortex breakdown has been studied extensively by numerous researchers. Although some aspects of the flow phenomenon are quite well understood, much remains unclear. Among the experimental set-ups used to study vortex breakdown, an enclosed cylindrical container with one rotating endwall is often used since the boundary conditions are well defined, and there is no flow comes in and out. In this paper, we present vortex breakdown control studies in a confined cylinder container by downstream blowing and suction through a small tubing going through the shaft of the rotating plate. Blowing and suction were realized by a piston mechanism connected to the blowing tubing. It can be observed by flow visualization that downstream blowing and suction can enhance or suppress vortex breakdown. By applying downstream suction, the upstream vortex breakdown bubble can be stretched due to the reduction of the pressure gradient. By applying downstream blowing, the pressure gradient is increased and additional azimuthal vorticity is generated, and another bubble structure can be formed between blowing and the upstream vortex breakdown bubble. The upstream vortex breakdown is not affected for small blowing rate, and its bubble structure is enlarged for higher blowing rate. The higher the suction/blowing rate, or the shorter the distance between the blowing tube mouth and the vortex breakdown, the more vortex breakdown is suppressed/aggravated. This also suggests that the bubble vortex breakdown structure in such confined container is evolution of vortex flow at certain conditions, but rather than instability.