Current film-cooling hole-geometry research is attempting to clarify the mechanism of film cooling effectiveness and its relation to the counter-rotating vortex pair (CRVP), in this paper a mechanism of film cooling heat transfer has been proposed. The coolant expansion in this mechanism is likely to improve film cooling effectiveness. It was characterized by developing a high aspect ratio (AR), hence named high-aspect-ratio (HAR) scheme. Typical AR values investigated experimentally and numerically in this work were 17.5 and 35. The transient thermochromic liquid crystal technique and the steady Reynolds-Averaged Navier-Stokes simulation with realizable κ-epsilon turbulence model were used. The results were assessed against available data hence demonstrating the high performance of the new scheme. The film cooling effectiveness of the full expansion cases is close to 1, achieved the so call “ideal” performance. Meanwhile, CRVP was still very strong, demonstrating that the CRVP did not result in decaying performance in the new scheme. Consequently, the HAR scheme achieved successfully the high performance of the proposed film cooling heat transfer mechanism.
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