Measurement of Tip-Clearance Flow in a Multistage, Axial Flow Compressor

Detailed measurements using pneumatic probe traverses, blade static pressure tappings, and laser anemometry are made in the third stage of a large-scale, low-speed, four-stage, axial flow, research compressor. Inlet conditions show well-ordered “two-dimensional” flow from approximately 40 to 85 percent annulus span. Outside of this region, reduced total pressure due to upstream leakage losses and endwall effects results in high incidence to the following blade row. As a result, peak suction surface static pressure moves forward along the blade chord for both the hub and tip of stators and rotors. At the blade tip, however, the peak suction pressure is maintained with chord due to radial flow on the suction surface being entrained into the tip leakage jet. The extent of rotor chord for which this “entrainment” occurs increases with increasing rotor tip clearance gap. The leakage jet from both stators and rotors is seen to “roll up” into a vortex downstream of their respective blade rows.