In recent studies, a turbine film cooling shaped hole designed by adjoint optimization techniques (X-AOpt) was found to substantially increase film cooling performance with 90% greater adiabatic effectiveness than a reference 7-7-7 shaped hole. Two aspects of the geometry contribute to the high adiabatic effectiveness levels achieved by the X-AOpt holes: the shape of the internal geometry which improves the diffuser performance, and the external protrusions that generate counter-rotating vortices that push the core of the coolant jets towards the wall and spread the coolant laterally. In this study, insight into the relative importance of these two factors was obtained by testing the performance of a row of X-AOpt holes with the protrusions removed from the external surface. Experiments were also performed with varying pitch between X-AOpt holes to determine how the hole spacing affects film cooling effectiveness. Results from the tests of X-AOpt holes without external protrusions showed a 9% increase in adiabatic effectiveness compared to the baseline 15-15-1 holes, while the X-AOpt holes had a 45% higher adiabatic effectiveness than this standard. Experiments were also conducted using X-AOpt holes with varying pitch between holes of P/D = 4.0, 5.45, and 7.0. Results from these experiments showed that a decrease in pitch to P/D = 4.0 provided only a slightly increased adiabatic effectiveness compared to standard P/D = 5.45. However, increasing the pitch to P/D = 7.0 caused a 33% decrease in adiabatic effectiveness compared to the standard spacing. Superposition was found to significantly under predict adiabatic effectiveness for P/D = 4.0 and 7.0, indicating there is a dependence on lateral spacing for the X-AOpt geometry due to vortex interaction.
