Full Coverage Discrete Hole Film Cooling: The Influence of the Number of Holes and Pressure Loss

Experimental measurements of the overall cooling effectiveness for full coverage discrete hole effusion cooling are presented for a wide range of practical geometries and for a density ratio between the coolant and combustion gases of 2.5. The influence of the number of holes per unit surface area was investigated at two fixed total hole areas or design pressure losses of 3% and 0.1%, at a relatively low coolant flow rate per unit surface area. Hole configurations suitable for both combustor and turbine blade cooling were investigated with hole sizes from 1.4 to 0.6mm at 3% design pressure loss and 1.3 to 3.3mm at 0.1% design pressure loss. The diameter change at a fixed pressure loss was for a constant total hole area with more holes as the size was reduced. This was shown to increase the cooling effectiveness through improved film cooling. Enlarging the hole size for a fixed number of holes and hence reducing the pressure loss for a fixed coolant mass flow was also shown to improve the cooling effectiveness through better film cooling. Major reductions in current combustor wall cooling flows were demonstrated for some full coverage effusion geometries.