Numerical investigations on fully-developed and unsteady flows in a curved duct.

Fully-developed and unsteady flows are dealt with in a curved duct of a rectangular cross-section (aspect ratio = 2, curvature ratio = 8). It is simulated by the MAC method how the flow patterns will evolve under the condition of pressure gradients C suddenly given in the streamwise direction or kept constant. The results are as follows; a pair of stable vortices is obtained at C < 6.90 × 104. At C = 6.90 × 104, the vortex pair begins to fluctuate periodically. It is confirmed that the Hopf bifurcation occurs from steady flow to periodic flow. At about C = 6.93 × 104, the single pair of vortices changes to two pairs of vortices which return shortly through asymmetric vortices. At about C = 30 × 104, asymmetric vortices are obtained after symmetric vortices break down. It is shown that time-dependent flows are predominant over the intermediate Dean numbers in curved ducts.