Evaluation of the cooling performance for adjoint optimized film cooling hole geometries

Advancement in additive manufacturing (AM) methods along with the application to gas turbine component manufacturing has expanded the feasibility of creating complex hole geometries to be used in gas turbines. The design possibilities for new hole geometries have become unlimited as these improved AM methods allow for the creation of holes with complex hole geometries such as rounded inlets, protrusions in the surface of the inlet and outlet of holes, among others. This advancement in such technology has sparked interest among turbine research groups for the design and creation of optimized versions of holes that showcase sophisticated geometries, which would otherwise not be possible to be manufactured using conventional manufacturing methods. Recently, a computational adjoint based optimization method by a past student in our lab (Fraser B. Jones) was used to design shaped film cooling holes fed by internal co-flow and cross-flow channels. The CFD simulations for said hole geometries predicted that the holes optimized for use with cross-flow (X-AOpt) and co-flow (Co-AOpt) would significantly increase adiabatic effectiveness. However, only the X-AOpt hole was tested experimentally in this previous study. In this study, adiabatic and matched Biot number models were built for 5X engine scale models of the X-AOpt and Co-AOpt shaped holes and tested experimentally in a low speed wind tunnel facility. The optimized shaped holes are experimentally evaluated using measurements of adiabatic effectiveness and overall cooling effectiveness. Coolant was fed to the holes with an internal co-flow channel and tested at various blowing ratios (M=0.5-4). For reference, experiments were also conducted with 5X engine scale models for the baseline 7-7-7 sharp inlet (SI) shaped hole, and a 15-15-1 rounded inlet (RI) shaped hole (shown in a previous parametric optimization study by Jones to be the optimum expansion angles for a shaped hole). Discharge coefficient, C [subscript d], measurements for the Co-AOpt geometry are analyzed in greater detail and compared against the other hole geometries tested for the study. In addition, computational predictions of C [subscript d] for a 15-15-1 RI hole will be compared against experimental measurements from this study. Results from the experiments performed at the low speed facility for 5X scale models confirmed that the X-AOpt hole had a 75% increase in adiabatic effectiveness compared to the 7-7-7 SI shaped hole. However, the Co-AOpt hole had only a 30% increase in adiabatic effectiveness, which is substantially less than had been computationally predicted.