SIMULATION OF VORTEX BREAKDOWN

The phenomenon of vortex breakdown was simulated numerically by solvin g the Navier-Stokes equations for three-dimensional, unsteady, and inc ompressible flows. Results of the simulation were compared with experi mental investigations and showed good agreement. Therefore, the data o f the simulation were used to inquire the phenomenon in more detail. W ith the help of a feedback-model, the initiation process and the devel opment of bubble-type breakdown can be illustrated. Within the frame o f that model, the formation of a free stagnation point can be describe d by the redistribution of axial vorticity into the circumferential an d radial components. The transition from bubble-type to spiral-type br eakdown is explained by the growing asymmetry of the flow-field. The i mportance of the pressure distribution at the lateral boundaries on th e initiation and development of bubble-type breakdown was investigated .