On identification of flow separation and vortices in internal periodic flows

To permit simplified analysis of complex time‐dependent flows, possible relationship between the near‐wall flow, flow separation and vortices are studied numerically for a flow in a constricted two‐dimensional channel. The pulsating incoming wave‐form consists of a steady flow, followed by a half‐sinus flow superimposed on the steady component. One pair of vortices is created in each cycle, one vortex near each wall. The vortices propagate downstream in the next cycles, promoting flow separation as they move. Existing flow separation criteria were not found to be uniformly valid. A relation between the near‐wall flow and the vortical system exists only during the steady incoming flow phase of the cycle. It seems that local criteria of flow separation cannot be found for complex internal pulsating flow fields. However, the vorticity field can be utilized, even in complex time‐periodic flows, for identifying vortices that have been formed by the roll‐up of shear layers.