Secondary Flow Phenomena in Rotating Radial Straight Pipes

Flow visualization results for secondary flow phenomena near the exit of a rotating radial-axis straight pipe (length € = 82 cm, inside diameter d = 3.81 cm, €/d = 21.52) are presented to study the stabilizing (relaminarization) and destabilizing (early transition from laminar to turbulent flow) effects of Coriolis forces for Reynolds numbers Re = 500 ~ 4,500 and rotating speeds η = 0 ~ 200 rpm. The flow visualization was realised by smoke injection method. The main features of the transition phenomena are disclosed for Re = 1,500 and 4,500. The observed secondary flow patterns are found to be quite different from those obtained by theoretical or numerical analysis with one pair of symmetric and steady counter-rotating vortices. The practical implications of the visualization study are pointed out.