Conjugate Heat Transfer Predictions of Effusion Cooling with Shaped Trench Outlet

The influence of the application of a filleted shape trench hole outlet on the overall cooling effectiveness of a flat hot effusion Nimonic 75 metal wall with a 770K hot gas crossflow was investigated using conjugate heat transfer (CHT) CFD and the Ansys Fluent code. The baseline effusion wall had ten rows of holes with an X/D of 4.65 and a wall thickness of 6.35mm with normal injection holes. This was modelled and showed good agreement with the experimental results for overall cooling effectiveness. The aim of the work was to use these validated CHT CFD procedures to investigate improved hole outlet designs with 30° inclined effusion of X/D = 4.65 with improved hole outlet designs using various trench designs. The predictions involved the use of a gas tracer in the cooling air to simultaneously separate the predicted adiabatic film cooling effectiveness from the overall cooling effectiveness. The shaped trench outlet effusion wall designs were predicted to have a superior performance compared with the 90° effusion wall cooling design. This was due to the improved adiabatic film cooling. An increase in the trailing edge vertical wall depth of the trenched effusion wall design from 0.5D to 0.75D increased the overall and adiabatic cooling effectiveness. The filleted shaped trench outlet effusion wall only required a small amount of cooling air to achieve a satisfactory cooling performance. It was predicted that this new effusion wall design could enable a significant reduction in the coolant mass flow for cooled metal surfaces in in future high performance gas turbines.