Conjugate Heat Transfer Validation of an Optimized Film Cooling Configuration for a Turbine Vane Endwall

In this study, to improve overall cooling performance for the endwall of a turbine nozzle guide vane that incorporated internal jet impingement and external purge flow and discrete injection cooling, the external film cooling was re-designed based on the knowledge of film coverage patterns from a baseline design, allowing film injection to overcome the crossflow and to cover more areas of the endwall with a given amount of coolant. Experimental conjugate heat transfer validation of the newly designed cooling geometry was conducted in a linear vane cascade by measuring overall cooling effectiveness over the endwall through an infrared (IR) thermography technique and detecting aero-thermal fields at the cascade exit with five-hole and thermocouple probes. For a given total coolant flowrate, the influence of coolant split among different cooling sources was examined. Additionally, parallel computational simulations were undertaken to elaborate the results observed in the experiments by offering in-passage flow physics. Comparisons with the baseline design proved that the newly designed cooling scheme improved the endwall overall cooling performance in terms of both effectiveness levels and coverage. In addition to optimizing the cooling geometry, more efficient usage of the coolant was found to be linked with the proper coolant split, which helped the re-designed cooling geometry to achieve an improvement of cooling effectiveness by approximately 20%. The computational simulations produced satisfactory overall cooling effectiveness, but failed to capture mixing of coolant with mainstream flow. The coolant with mainstream flow interactions visualized by the simulations provided evidence that the coolant jets from the optimized cooling scheme increased mixing flow loss but those from the pressure side suppressed the inherent vortex flow, resulting in no aerodynamic penalty as compared with the baseline cooling design.