Experimental study on flow field measurements inside the tip clearance of an axial compressor using PIV

Flow field visualization within the clearance is crucial for understanding the tip leakage flow characteristics. This study introduces an optical window with a distortion-elimination surface and an anti-contamination periscopic laser probe, enabling PIV measurements in a single-stage axial compressor. Results reveal that radial inflow near the blade pressure side drives tip leakage formation, generating a low-speed pressure-side region and a high-speed leakage zone within the gap. As rotational speed increases, the leakage flow exhibits greater deviation, maintaining a velocity ratio of ∼0.3 relative to the tip speed, while the high-speed leakage region expands upstream. Vortex structures formed by the mixing of tip leakage with the main flow, and regions of high-vorticity are observed upstream of the rotor. A high-vorticity region exists at the vortex center, where velocity instability is strong, and the vorticity value increases further along with the increase of the speed, exacerbating flow instability. The leakage vortex is identified as the primary factor contributing to flow instability in the tip clearance region. This measurement approach, along with the visualization results of the internal local flow field within the blade tip clearance, is expected to provide valuable insights into the mechanisms of leakage formation and development.