Influence of Flow Coefficient, Stagger Angle, and Tip Clearance on Tip Vortex in Axial Compressors

Experiments have been performed on the low speed research compressor (LSRC) at General Electric Aircraft Engines to investigate the effects of flow coefficient, stagger angle, and tip clearance on tip vortex. Time resolved casing pressure distributions over the third stage rotor have been acquired with high-frequency-response pressure transducers. Also, tip vortex strength and trajectory have been estimated from the casing pressure fluctuations which have been obtained simultaneously from various axial locations. As flow coefficient decreases, tip vortex gets strengthened and migrates upstream. The stagger angle increase weakens the tip vortex and moves it downstream slightly because the blade loading is decreased. However, tip leakage vortex is influenced mainly by tip clearance, and there exists a “critical” tip clearance which determines the type of tip vortex trajectory (“straight” or “kinked”). As predicted by others, tip vortex gets strengthened with increasing tip clearance. However, unlike the predictions, the tip vortex trajectory moves upstream with increasing tip clearance. Furthermore, with tip clearance above a “critical” value, the tip vortex trajectory is no longer straight but shows a kink in the passage.