An effort has been made in this paper to numerically estimate the critical rotational speeds for which the steady separation bubble completely disappears behind a circular cylinder. The cylinder is subjected to an unconfined free stream flow, however, fictitious confining boundaries are considered for computationalconvenience. The Reynolds numbers computed from the free stream flow velocity are considered in the range of 10–40. In this range of Reynolds number, the flow around a stationary circular cylinder remains steady and separated with the formation of a recirculation zone through counter-rotating vortices (separation bubble) behind the body. Rotational motion is provided to the cylinder that causes stabilization of the flow field. The separation bubble vanishes and an attached type flow feature is observed. The rotational speeds at which the recirculating zone behind the cylinder completely vanishes in the said range of Reynolds number are considered as the critical rotation rates. The aerodynamic coefficients are obtained for the specific operating conditions and a regimediagram is produced depicting the separated and the attached flows.

A channel confined flow around a bluff object is significantly different from its unconfined counterpart. A confined flow is presumably more stabilized due to the presence of the confinement. This causes a delay in the onset of flow separation and vortex shedding in comparison to the unconfined flow. While the abovefacts have been reported for the confined flow around a circular object in a channel, the same for a square object is infrequent. The present study focuses on the steady flow past a stationary square cylinder placed in a channelat low Reynolds numbers (1≤Re≤30). The behavior of the flow is observed through numerical simulation for various channel confinements (0:01≤B≤0:9, blockage ratio). The steady state laminar two-dimensional incompressible flow equations are solved using a finite volume based technique. An effort is made to find the separation critical Reynolds number at all blockages. It is observed that the separation critical Reynolds number increases with an increase in the blockage ratio. Unsteady flow characteristics at various blockages are alsostudied at Re = 100. In the unsteady regime, the frequency of vortex shedding increases with an increase in the blockage.