EXPERIMENTAL INVESTIGATION OF STEPPED TIP GAP EFFECTS ON THE PERFORMANCE OF A TRANSONIC AXIAL-FLOW COMPRESSOR ROTOR

The effects of stepped-tip gaps and clearance levels on the performanc e of a transonic axial-flow compressor rotor were experimentally deter mined. A two-stage compressor with no inlet guide vanes was tested in a modem transonic compressor research facility. The first-stage rotor was unswept and was tested for an optimum tip clearance with variation s in stepped gaps machined into the casing near the aft tip region of the rotor. Nine casing geometries were investigated consisting of thre e step profiles at each of three clearance levels. For small and inter mediate clearances, stepped tip gaps were Sound to improve pressure ra tio, efficiency, and flow range for most operating conditions. At 100 percent design rotor speed, stepped tip gaps produced a doubling of ma ss flow range with as much as a 2.0 percent increase in mass flow and a 1.5 percent improvement in efficiency. This study provides guideline s for engineers to improve compressor performance for an existing desi gn by applying an optimum casing profile.