pressure side edge on the tip and then separation occurs on the tip-endwall due to the divergent flow in the clearance. The leakage vortex separates from the endwall initially at about 20%CX along the suction edge and deviates from the suction edge further downstream at small tip clearances.

5. The suction flow effect can be clearly found on the pressure surface at all tip clearance levels. On the suction surface, the effect of passage vortex gradually disappears as the leakage vortex becomes stronger and pushes the underdeveloped passage vortex into the blade passage.

6. Separation bubble also exists along the suction edge on the tip close to the leading edge at large tip clearance levels. Incoming flow enters the tip clearance from suction side directly while the development of the passage vortex is delayed. The surface flow pattern on the second half of the tip surface at large tip clearance levels is complicated, including accumulation, separation and reverse flows.

7. Prom the smoke wire visualization, we can find that the leakage vortex is weak and probably incorporated into the passage vortex at small tip clearance levels.

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