Experimental research of an axial flow compressor performance with stepped tip gap casing configuration

With the help of an axial flow isolated rotor test rig, a special type of casing treatment with different stepped tip gaps was designed and investigated experimentally for two operating speeds. To compare with the test results for a transonic rotor in Ref. [4] the subsonic operating condition was selected. Seven casing geometries with different step profiles under three varied clearance levels were examined. By comparing the test data, it is known that as the tip clearance level increases the compressor performance and its stability will be deteriorated. For the small clearance level (0.517%h), not only the pre-stall performance but also the post-stall behaviors can be improved significantly when the stepped tip gaps are used. Meanwhile it is found that the axial location and size of the stepped tip gap are also the pivotal parameters affecting the compressor performance and the stall margin improvements. Furthermore, the interesting finding is that for the large clearance level (0.741 %h), the radial depth of the stepped tip gaps, different from the axial width, can only display weak influences on the compressor performance and stability.