Dependence of vortex breakdown on angular momentum parameter in draft tubeflows

The present study has shown that a rotating runner is a powerful means of i nvestigating draft tube flows because of the convenience in using the hot w ire anemometry. A rotating runner acts as a powerful mixing device giving g ood pressure recovery even in the presence of considerable inlet swirl. Spe ctrum analysis of the hot wire signal reveals the phenomenon similar to vor tex breakdown that introduces oscillations outside a narrow range of unit s peed surrounding the design point. There is every indication that water tur bine surge and the oscillations observed in the present experiments are one and the same. There is also some evidence that classical vortex break down may not be identical to what happens in the draft tube.