Secondary flow due to the tip clearance at the exit of centrifugal impellers. 2nd report. Relationship between secondary flow and slip coefficient.

The velocity distributions measured at the exit of two different types of unshrouded centrifugal impellers respectively under four different tip clearance conditions were reexamined with respect to the shroud wall surface. By increasing the tip clearance, the hub-to-shroud velocity distribution was hardly changed at the exit of the radial blade impeller, by contrast, the relative flow angle was reduced significantly and monotonously in the backward-leaning blade impeller. The change in input power due to the tip clearance was clearly related to the change of flow pattern at the exit of the impeller due to the secondary flow, which must be induced by the component, normal to the blade, of the shear force to support the fluid in the clearance space against the pressure gradient in the meriodional plane without blades.