Laminar swirling flow and vortex breakdown in a pipe

A problem of asymmetric swirling flow in a pipe has been analyzed by the finite volume numerical simulation of the three-dimensional incompressible Navier-Stokes equations expressed in cylindrical polar coordinates. The swirl is generated by one tangential inlet near the closed base of the duct. Because of the high value of the swirl number, S, a vortex breakdown forms near the base of the cylinder; it is of bubble-like shape. Downstream of the bubble the axial flow is at first wavy and finally tends toward the Poiseuille profile, while the swirl decays exponentially. At high enough axial Reynolds number, Re, the flow becomes time dependent.