Numerical exploration of flow topology and vortex stability in a curved duct

We performed incompressible flow simulation in a square duct with 90◦ bend and a curvature radius of 2.3 to extend our understanding of the vortical flow development in the bend. The solutions for the flow investigated at the Reynolds number of Re=790 are obtained in a tri-quadratic element system, where velocities stagger the pressure working variable, using the streamline-upwind finite element model and the BiCGSTAB iterative solver. The simulated results reveal that centrifugal force convects the quickly moving fluid particles towards the outer wall. The axial velocity, as a result, shows twin peaks in the curved channel. At about =66◦, the secondary flow shows three complex pairs of vortices. Also noteworthy is the formation of a downstream spiralling flow motion. To better elucidate the dominating three-dimensional flow nature, the topological study of limiting streamlines was undertaken. Insight into the longitudinal flow instability is gained by tracking the formation and diminishing of limiting cycles. Copyright q 2006 John Wiley & Sons, Ltd