The Use of 3D Viscous Flow Calculations in the Design and Analysis of Industrial Centrifugal Compressors

The 3D viscous codes of Denton and Dawes have been used to predict the flow field and performance of a back-swept industrial centrifugal impeller without an inducer (the Eckardt impeller “B”). The calculated flow field and performance agree very well with measurements at several operating points from surge to choke. Both codes predict that the suction surface flow near the impeller inlet is on the verge of separation at the design point. Calculations with tip clearance using the Dawes code predict a thin region of backflow in the clearance jet near the casing wall. The secondary flows arising from the meridional curvature in the impeller redistribute the losses generated on the blades and give rise to a spanwise stratification of the circumferentially mass-averaged losses. The resulting spanwise entropy gradient can be included in a throughflow calculation to improve the prediction of the meridional velocity distribution at impeller exit.