324 Surface flow on the tip surface

For the surface flow pattern on the tip surface in fig. 3.8, we can find that a separation bubble exists immediately along the pressure edge of the tip at t/C = 0.86%. Relatively larger shear stresses show up in the rest part of the tip surface, caused by the high speed shear flow inside the tip clearance. For the larger tip clearance of 1.72%C, this separation bubble increases in size as the separation line moves a little away from the pressure edge of the tip, and a small accumulation appears on the pressure edge near the mid-chord of tip surface, indicating a low pressure zone near the pressure side edge similar to that found by Bindon (1987). A second separation bubble is also evident on the suction side of tip starting from the leading edge up to 20%^. The leakage flow inside the tip clearance travels generally in the direction close to that of the incoming flow at two smallest tip clearances, and the leakage flow exits from the clearance after X/Cx = 0.2.

At the larger tip clearance of 3.45%C, low shear stresses and accumulation areas lie along the pressure side edge and near mid-chord respectively on the second half of the tip surface, showing perhaps the existence of separation exists near the pressure edge and reverse flows on the second half of the tip surface.

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