Effects of different non-uniform tip clearance layouts on compressor performance and flowfield characteristics

Circumferentially non-uniform tip clearances in rotors would significantly affect the overall performance of axial compressors, particularly the stability margin. The amplitude and wavelength of clearance nonuniformity are two key parameters. To investigate the effects of these two parameters on compressor performance and flowfields, a series of numerical simulations were conducted on a 1.5-stage transonic compressor with different non-uniform clearance layouts using the time-space collocation (TSC) method. The results indicate that non-uniform tip clearances have little influence on the compressor’s efficiency, but exert significant effects on its peak total pressure ratio and stability margin. The maximum absolute loss of stability margin occurs in the 1-Lobed configuration with an amplitude of 0.20 mm, reaching approximately 3.59 %. The detrimental impact of non-uniform tip clearances on compressor performance attenuates as the clearance variation amplitude and wavelength decrease, since smaller amplitude and wavelength lead to weaker tip blockage effects. Additionally, N-Lobed tip clearances result in circumferential fluctuations resembling N-Lobed patterns in rotor performance parameters. The maximum fluctuation amplitude of inlet mass flow rate among different rotor passages occurs in the 1-Lobed configuration with a clearance variation amplitude of 0.20 mm, reaching approximately 3.6 % of the baseline result. Furthermore, N-Lobed clearances subject the rotor blades to alternating loads with a fundamental frequency of N times the rotation frequency. The maximum fluctuation amplitudes of axial force and torque among different rotors both occur in the 4-Lobed configuration with a clearance variation amplitude of 0.20 mm, reaching approximately 2.9 % and 3.4% of the baseline results, respectively.