Flow in Annular Diffuser : 1st Report, Internal Flow and Performance

Abstract

The internal flow and the performance of an annular diffuser composed of a cylindrical casing and a conical hub were examined experimentally. When the flow has no whirl component at the inlet, the optimum convergent angle of the hub, giving the best pressure recovery, is about 24 degrees. But with an increment of the whirl component, the component roughly changes to the free vortex pattern at the downstream passage independent of the initial flow pattern and the axial velocity is faster near the hub side than near the casing side. Accordingly, it is possible to prevent the separation by giving an adequate whirl component at the inlet, even if it occurs at the hub wall with a large convergent angle in the case without the whirl component. When the whirl component becomes stronger, a reverse flow occurs along the hub wall at the definite area ratio irrespective of the convergent angle.