Secondary currents in straight wide channels (Q1100033)

We examine the transverse flow (commonly known as secondary flow) which exists for fully developed turbulent flow in straight channels of noncircular cross section. We show that the basic macroscopic features of this secondary flow in straight wide channels can be found, assuming that the axial mean flow is in hydrodynamic instability, which is the result of a competition between destabilizing and stabilizing effects. The two opposite effects in the rectilinear flow are the normal stresses which tend to produce a motion of the fluid away from the wall and the viscosity v which tends to prevent this motion. This study predicts that the width of the secondary flow cells in a straight wide channel is equal to the depth of the flow. Experimental evidence agrees with this finding.