On the Flow in the Vaneless Diffuser of a Centrifugal Compressor

Abstract

The flow in the vaneless diffuser of a centrifugal compressor is found by means of a series of conformal transformations which map the uniform parallel flow over a semi-infinite flat plate into the flow in a scroll-type diffuser. The method is based on the assumptions that the flow is inviscid, incompressible, and two-dimensional and that the impeller may be replaced by a source vortex for purposes of calculation. The walls of the diffuser are assumed to have the shape of logarithmic spirals, but their divergence may be adjusted arbitrarily within limits. The method is applied to finding the expressions for the velocity and pressure distributions along the upper and lower walls of the diffuser, showing the points of maximum velocity and minimum pressure and making it possible to calculate the thrust on the diffuser due to the flow.