Study on flow of centrifugal impeller. 3rd Report. The effects of tip clearance on the characteristics and secondary flow of the impeller.

Abstract

To examine the effects of a secondary flow induced by tip leakage, the velocity and pressure distributions are measured within an unshrouded centrifugal impeller with a large tip clearance. The changes of the characteristics between shrouded and unshrouded impellers are discussed in comparison with the previous reports. In spite of the considerable difference of the tip clearance, the secondary flow pattern is similar to the first report. Though a wake in the shrouded impeller of the second report is found on the suction side, the wake in the unshrouded impeller exists on the midposition of blade-to-blade near the casing because of the effects of tip leakage. The position of the largest blade loading in the unshrouded impeller changes to midpassage from first-half-passage in shrouded impeller. Therefore the absolute circumferential velocity at the exit in the unshrouded impeller is larger than that in the shrouded impeller.