EXPERIMENTAL INVESTIGATIONS ON MIXED FLOW IMPELLER AND VANE DIFFUSER UNDER VARIOUS OPERATING CONDITIONS

摘要

Experimental Investigations are carried out to study the effect of tip clearance flow in a mixed flow compressor stage. Two configurations, namely; constant and variable clearance gaps between impeller and stationary shroud are considered. For the purpose of the present investigations, a mixed flow compressor stage is designed and fabricated. The flow investigations were carried out in a closed circuit compressor rig. Detailed steady and unsteady measurements were carried out for three clearance gaps, namely; 0.5 mm, 0.75 mm, 0.9 mm. From the experimental investigations it is shown that constant tip clearance configurations show better performance in terms of pressure ratio and efficiency compared to variable clearance configurations. For a given configuration the pressure ratio and efficiency of the stage decrease with increase in the tip gap without indicating any optimum value. Tip clearance flow has considerable effect on the flow through the diffuser and the unsteady flow gets amplified and carried away into the vane diffuser.