Effects of centrifugal and coriolis forces on secondary flow phenomena in rotating curved square channels: Visualizations for positive and negative rotations

Abstract

Flow visualization results for secondary flow phenomena are presented to study the destabilizing effects of Coriolis forces on fully developed flow in rotating curved square channels (cross section = 5.08×5.08 cm2, radius of curvature Rc = 25.4 cm) at Reynolds numbers Re = 500 and 600, and rotating speeds in the range n = 0 to approximately 374 rpm for both positive and negative rotations. The flow visualization was realized by a smoke injection method. The early transition process from laminar to turbulent flow due to channel rotation is illustrated by presenting numerous pictures for secondary flow. Within the scope of the present investigation, the existence of multiple solutions for each Reynolds number, the nature of non-steady flow, nonsymmetric secondary flow and a complete destruction of the original pair of counter-rotating vortices at higher rotating speeds are observed. At relatively low rotating speeds in the case of negative rotation. Coriolis instability problem similar to Dean's instability problem for laminar flow in stationary curved square channels exists and Coriolis vortices similar to Dean vortices are shown clearly.