Bistable flow in lower transition regime of circular cylinder

Abstract

Based on flow visualization, LDA and DPIV, the present study establishes the switching phenomenon of near wake of circular cylinder of low aspect ratios (AR ≤ 4) within the lower transition from the laminar shedding regime to the wake transition regime. The phenomenon occurs at and below the critical Reynolds number, which involves switching between the wide wake mode without the large-scale primary vortex and the regular shedding mode with primary vortices. The switching is suggested to play an important role in the transition. In the switching regime the small-scale secondary vortices and their pairings are identified. Their appearance, pairings and phase difference on the two sides of the wake play important roles in the switching and the enhancement or suppression of the primary vortices. The present study further establishes the fact that the two-dimensionality of the secondary vortices is important in the shift of the transition to high Reynolds number at low aspect ratios. © 2001 Published by The Japan Society of Fluid Mechanics and Elsevier Science B.V. All rights reserved.