Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Department of Aeronautics and Astronautics

First Advisor

Paul I. King, PhD


The effects of stepped tip gaps and clearance levels on the performance, flowfield, and stall characteristics of a transonic axial-flow compressor rotor were experimentally and numerically determined. 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 the Wright Laboratories Compressor Research Facility located at Wright-Patterson Air Force Base, Ohio. The first-stage rotor was unswept and was tested for an optimum tip clearance with variations in 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. For small and intermediate clearances, stepped tip gaps were found to improve pressure ratio, efficiency, and flow range for most operating conditions. At 100% design rotor speed, stepped tip gaps produced a doubling of mass flow range with as much as a 2.0% increase in mass flow and a 1.5% improvement in efficiency The flowfield characteristics associated with performance improvements were experimentally and numerically analyzed. Stepped tip gaps were found to have no significant effect on the stall characteristics of the rotor; the stability characteristics attributable to tip geometry were determined by the clearance over the forward portion of the rotor blade. This study provides guidelines for engineers to improve compressor performance for an existing design by applying an optimum casing profile.

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