Transition to turbulence and relaminarization phenomena in rotating radial straight pipes

Abstract

Flow visualization results for secondary flow patterns at the exit of a rotating radial-axis straight tube (length l = 82 cm, inside diameter d = 3.81 cm, l/d = 21.52) are presented to study the stabilizing and destabilizing effects of Coriolis forces for Reynolds numbers Re = 500, 2,000, 3,000 and 4,000 and rotating speeds n = 24 to approximately 350 rpm. The flow visualization was realized by smoke injection method. The photographic results provide insight into the transition process from laminar to turbulent flow at the lower Reynolds number Re = 500 and relaminarization phenomena at Re = 3,000 and 4,000 for a rotating radial-axis straight tube with outward main flow. The stabilizing and destabilizing effects of Coriolis forces are shown for Reynolds number Re = 2,000 in the transition flow regime. The present flow visualization investigation on secondary flow phenomena involving Coriolis forces complements the existing measurements and theoretical studies. At Re = 3,000, the Coriolis vortices relating to Coriolis instability problem are identified clearly by visualization.