Small Diameter Film Cooling Hole Heat Transfer: The Influence of the Hole Length

Abstract

The overall surface averaged heat transfer was determined for air passing through arrays of small diameter holes drilled at 90° through thin metal walls. The influence of the wall metal thickness, L, was investigated for a range of hole diameters, D, and pitch, X. L/D was varied from 0.43 to 8.3 using 13 different test geometries. It was found that although the influence of L/D was significant, there was only a ±20% data scatter on a correlation of the results that ignored the influence of L/D for 0.8<L/D<10. The results showed that the heat transfer was dominated by the hole approach flow and this surface area Ax was the appropriate heat transfer area for the determination of the heat transfer coefficient. The dominant parameters that affected the heat transfer were G and X/D. An improved correlation for a range of L/D was achieved if the heat transfer surface area was taken as the sum of Ax and Ah, the hole internal surface area.