Surge Margin Extension and Circumferential Groove Interaction with the Rotor Tip Clearance Flow Field

Abstract

Experimental and computational studies were conducted to study the role of the tip leakage flow in axial compressor stall and the relationship between the tip clearance flow field and surge margin extension from circumferential groove casing treatment (CGCT). Experimental measurements of surge margin extension from seven CGCT configurations with a fixed groove geometry demonstrated that the contribution of individual grooves in a multi-groove casing to surge margin extension is an (a) additive and (b) linear function of the smooth wall tip clearance axial momentum flux at the location of a each groove. Cameron et al.’s 2013 axial momentum model of the rotor tip clearance was extended to include the influence of a CGCT. Control volume analysis of this model showed that circumferential grooves reduce the tip leakage flow axial momentum through radial transport. The equivalent force due to a circumferential groove was demonstrated to be related to the smooth wall tip clearance axial momentum flux through a coefficient of drag that had a log-linear dependence on groove aspect ratio. The paper closes with a demonstration of how findings from the experiments described above can combine with the one-dimensional momentum balance to make first-order estimates of surge margin extension from a given circumferential groove casing treatment.