Vaneless Diffuser Rotating Stall Based on Two-Dimensional Inviscid Flow Analysis : 1st Report, Linear Analysis

Abstract

Rotating stalls in vaneless diffusers are studied from the viewpoint that they are basically two-dimensional inviscid flow instability under the boundary conditions of vanishing velocity disturbance at the diffuser inlet and of vanishing pressure disturbance at the diffuser outlet. The linear analysis in the present report shows that the critical flow angle and the propagation velocity are functions of only the diffuser radius ratio. It is shown that the present analysis can reproduce most of the general characteristics observed in experiments : critical flow angle, propagation velocity, velocity and pressure disturbance field. It is shown that the venishing velocity disturbance at the diffuser inlet is caused by the nature of impellers as a "resistance" and an "inertial resistance", with is generally strong enough to suppress the velocity disturbance at the diffuser inlet. This explains the general experimental observations that veneless diffuser rotating stalls are not largely affected by the impeller.