Strengths of horseshoe vortices around a circular cylinder with an upstream cavity

Horseshoe vortices are formed at the junction of an object immersed in fluid-flow and endwall plate as a result of three-dimensional boundary layer separation. This study presents the variation of the strengths of such horseshoe vortices around a circular cylinder with a cavity (slot) placed upstream. Through the cavity, no mass flow addition (blowing) or reduction (suction) is applied. With the upstream cavity, adverse pressure gradient is weakened upstream of the cavity whereas it is strengthened downstream of the cavity. Furthermore, a single vortex system is found to form immediately upstream of the cylinder instead of a typical two vortex (primary and secondary vortices) system observed in the absence of the upstream cavity. The strength of the primary vortex is weakened due to the fluid stream engulfed in to the upstream cavity, resulting in diffusion of the mainstream. Consequently, the circulation of the primary vortex is weakened. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. Seung Jin Song has received his undergraduate and graduate degrees from Duke University and MIT, respectively. He has taught in the Department of Aerospace Engineering at Inha University from 1995 to 1999. Since 1999, he has been teaching in the School of Aerospace Engineering at Seoul National University. His research interests include turbomachinery, propulsion, and fluid engineering.