Analysis of Secondary Flows in Centrifugal Impellers

Secondary flows are undesirable in centrifugalcompressors as they are a direct cause for flow (head) losses,create nonuniform meridional flow profiles, potentially induceflow separation/stall, and contribute to impeller flow slip; thatis, secondary flows negatively affect the compressor performance.A model based on the vorticity equation for a rotating system wasdeveloped to determine the streamwise vorticity from the normaland binormal vorticity components (which are known from themeridional flow profile). Using the streamwise vorticity resultsand the small shear-large disturbance flow method, the onset,direction, and magnitude of circulatory secondary flows in ashrouded centrifugal impeller can be predicted. This model is alsoused to estimate head losses due to secondary flows in acentrifugal flow impeller. The described method can be employedearly in the design process to develop impeller flow shapes thatintrinsically reduce secondary flows rather than using disruptiveelements such as splitter vanes to accomplish this task