Mechanism of Formation of Prandtl’s Secondary Flows of the Second Kind

Turbulent flow in a tube of square cross section is investigated numerically. The concentrated longitudinal vortices responsible for the occurrence of secondary flows are studied. It is shown that the longitudinal vortices are formed as a result of nonlinear interaction of turbulent pulsations in which the pulsations of the longitudinal component of vorticity are specially adjusted in phase with the pulsations of the longitudinalvelocity component. A physical interpretation of this mechanism is given.