Backflow events under the effect of secondary flow of Prandtl's first kind

Abstract

The occurrence of backflow events, defined as negative wall-shear stress, is rare in turbulent flows. It is found that these backflow events are further suppressed in a toroidal flow when compared to a straight pipe flow at a nominally similar Reynolds number. The reduction of backflow is due to the secondary flow of Prandtl's first kind occurring in the toroidal flow.