The effects of stepped tip gaps and clearance levels on the flowfield of a transonic axial-flow compressor rotor were experimentally and computationally determined. This paper complements a previous experimental study by the authors regarding the effects of stepped tip gaps and clearance levels on the performance of an axial-flow compressor rotor. In the current study, the generation of blockage associated with the variation of geometry in the rotor tip region was examined. The shock-vortex interaction generating the blockage was characterized, and a theory and mechanism for relocation of blockage in the rotor tip region was developed. A two-stage compressor with no inlet guide vanes was tested in a modern transonic compressor research facility. The first-stage rotor was unswept and was tested with stepped gaps machined into the casing near the aft tip region of the rotor. Nine casing geometries were investigated consisting of three step profiles at each of three clearance levels. Computational Fluid Dynamic modeling of tip geometry effects also was performed. Increased tip clearance was found to increase the amount of flow blockage near the rotor tip. Stepped tip gaps were found to be an effective means of reducing the effects of tip region blockage, resulting in improved pressure ratio, efficiency, and mass flow. This study provides guidelines for engineers to improve compressor performance for an existing design by applying an improved casing profile.

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