Numerical investigation on the influence of nonuniform tip clearance on rotor tip-clearance flow field structure.

A numerical study was conducted on an axial compressor, the NASA Stage 35, with three nonuniform tip clearances to understand the effect of a different shape tip clearances rotor on the compressor's performance. The results demonstrated that by modifying the traditional parallel tip clearance to sine-type tip clearance (STC), hump-type tip clearance (HTC), and concave-type tip clearance (CTC), the compressor's peak efficiency showed remarkable improvement and the SMI was significantly improved. In comparison to the design rotor, the SMI of STC, HTC, and CTC increased by 3.102 %, 2.672 %, and 0.645 %, respectively. The leakage distribution at the tip-clearance region from LE to TE exhibited an inverse pattern to that of the tip curve. The leakage's magnitude could not reflect the TLF's intensity, and the leakage in the middle of the blade tip had a role in the size of the TLV. Leakage at the tip's TE influenced the corner separation's scale in the casing. The STC and HTC schemes' total pressure ratio improved, the low-velocity zone's area, high-entropy area, and high absolute vorticity area at the LE of rotor's PS decreased, the detached shock moved backward, the leading-edge spillage flow decreased, the shock action position of the rotor suction surface moved forward, the BLS increased, the TPL in the stator channel decreased, and the CTC exhibited the opposite trend. A nonuniform tip clearance was achieved by reducing the leakage and TLV intensity, thereby reducing the size of the TLV, induced vortex, or CSV in rotor passage and increasing the compressor's SMI.