A new 1D method for assessing volute induced circumferential pressure distortion at the exit of a centrifugal impeller

Volute induced static pressure distortion may degrade impeller performance. In high-pressure applications, it can also severely affect mechanical operation. It is therefore worthwhile, to know the magnitude of pressure distortion at impeller exit. The authors present a detailed study of aerodynamic impeller-volute interaction. Firstly, CFD simulations of a volute stage are analysed: The distortion of radial velocity is a consequence of the volute’s pressure field and remains almost constant throughout the vaneless diffuser. In contrast, at impeller exit, local discharge pressure determines tangential velocity, whereas towards diffuser exit, it is affected by the volute’s pressure field. Aerodynamic blockage within the diffuser reduces static pressure at diffuser exit and hence mitigates absolute distortion. With these findings, a new 1D method for predicting the static pressure distortion at impeller exit is derived. Testing the model against CFD-results of further volute stages yields very good agreement at various operating conditions.