Effects of Vaneless Diffuser Geometries on Rotating Stall

Detailed experimental investigation was carried out primarily to document the effects of vaneless diffuser diameter and width ratios on the fundamental characteristics of flow perturbation in the vaneless diffuser of a centrifugal blower. A benchmark set of experimental data is provided to aid numerical investigation of instabilities in the vaneless diffuser flow field in particular and the entire compression system in general. The synchronous speed was also varied to study the effect of shaft speed on stall features. The current data showed that a decrease of the diffuser width, at constant impeller angular speed, resulted in an increase of the critical flow coefficient. The data further revealed that an increase in the diffuser diameter ratio resulted in an increase in the frequency of rotating stall. Unlike diffuser diameter ratio, variation of the diffuser width ratio does not have an appreciable effect on the frequency of rotating stall.