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Blade design and tip clearance flow analysis for a compact high-pressure compressor rear stage

One way to mitigate the environmental impact of an aero-engine is the increase of thermal efficiency by implementing higher core engine pressure ratios. A higher core engine pressure ratio inevitably leads to a reduction of the compressor’s cross-sectional area and thus to an increase of the relative rotor tip clearance heights. The large clearances cause detrimental aerodynamic effects, which penalize the compressor’s operational behavior. This paper presents the numerical design efforts for a compact high-pressure compressor rear stage as well as measures to mitigate the detrimental effects resulting from high rotor tip clearances. To reduce turnaround times, an iterative adaption, including 3D features of the rotor and stator, is carried out by steady single blade row calculations on coarse meshes. It appears that the designed compressor blading shows a stall initiation at the rotor tip due to the strong tip leakage flow. A conducted tip clearance sensitivity study substantiates this. As the relative rotor tip clearance is reduced, the stall margin as well as the design point efficiency of the stage increase. Finally, a novel way of analyzing the stability of a tip-critical rotor blade row is presented by analyzing the circumferentially averaged entropy distribution within the rotor tip clearance.