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tip clearance.

2. The effects of the corner vortices on the mass transfer near the endwall of the pressure surface with no tip clearance, as well as the effects of the secondary flows on the mass transfer near the endwall on the suction surface with no tip clearance, are identified and analyzed.

3. The effect of tip clearance on the mass transfer on the pressure surface is limited to 10%C at smaller tip clearances, while at the largest tip clearance high mass transfer rates are induced at 15%S,p by the strong acceleration of the fluids into the clearance.

4. The effect of tip clearance on the mass transfer is not very evident for Ss/C < 0.20 on the suction surface. However, much higher mass transfer rates are caused at Ss/C = 0.60 — 1.0 by the tip leakage vortex at the smallest tip clearance level. At the largest tip clearance level, the high mass transfer region becomes smaller, probably because the strong leakage vortex pushes the passage vortex away from the suction surface.

5. The entrance flow effect induces mass transfer rates 3-4 times as large along the pressure edge of the tip surface at the smallest tip clearance level of 0.86%C. It is also found that the leakage flow after the reattachment is turbulent. As the tip clearance level increase the peaks of the mass transfer move away from the pressure edge due to the increase of separation bubble size near the pressure edge. At the two largest tip clearances, the separation bubble could cover the whole width of the tip on the second half of the tip surface. A low mass transfer region on the first half of the tip is caused by low leakage flow rate at small tip clearance levels, but by leakage flow from suction side at large tip clearances. The average mass transfer rate is highest at the tip clearance level of 1.72%C.

6. The high mainstream turbulence level of 12.0% reduces the local as well as averaged mass transfer rates on the near-tip and the tip surfaces, while the higher mainstream Reynolds number generates higher local and average mass transfer rates on the near-tip and the tip surfaces. The Reynolds number and mainstream turbulence intensity also affect the entrance flow at the smallest tip clearance level by changing the separation bubble size and position of reattachment on the pressure side edge of the tip.

Table 4.1: Surface averaged Sh measured at different tip clearance levels (Reex = 5.8 105,Tu=0.2%) _

r/C(%)

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