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 0 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 <10. The results showed that the heat transfer was dominated by the hole approach flow and this surface area A 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.