Axial turbine tip desensitization by injection from a tip trench part 2: Leakage flow sensitivity to injection location

In Part 1 of this paper it was shown that discrete jets issuing from a tip platform trench were successful in reducing the total pressure deficit due to tip leakage flow. The specific tip cooling system used in Part 1 had all four injection locations active. This paper examines the effect of the individual location of the injection hole on the tip leakage flow. The investigation was carried out in a large-scale rotating rig. Total pressure downstream of the rotor exit was measured using a Kulite sensor. The measurements were phase-locked and ensemble averaged over 200 rotor revolutions. The injection holes are located at 61%, 71%, 81%, and 91% blade axial chord, in the tip trench of a single blade with a clearance of 1.40% blade height. Individual injection at 61% and 71% chord reduced the leakage vortex size. Coolant injection at 81% chord was the most successful in reducing the total pressure deficit in the leakage vortex. Injection from 91% chord had no effect on the leakage vortex. Injection from combinations of holes had greater effect in reducing the leakage vortex size and the total pressure deficit associated with the vortex. It can be concluded that the individual jets most likely turn the leakage flow towards the trailing edge. Most of the leakage flow that is responsible for the greatest total pressure deficit occurs around 80% chord.