Conjugate Heat Transfer Assessment of a 3-D Vane with Film Cooling and Comparison to Experiments

Abstract

Heat transfer characteristics were predicted here on a full-scale 3-D model of a modern high pressure turbine vane with 648 film cooling holes called the High Impact Technologies Research Turbine Vane (HIT RTV). A Reynolds-Averaged Navier Stokes (RANS) computational fluid dynamics (CFD) code called Leo simulated the internal cooling plenums, cooling hole passages, external main flow passages as well as the solid vane metal in realistic turbine-representative conditions at a typical film cooling blowing ratio using an unstructured mesh. This conjugate assessment of both the solid and fluid domains allows for a more accurate representation of the heat transfer environment for the vane. Surface data including heat flux, net heat flux reduction (NHFR), and surface temperature are computed and compared to full-scale annular blow-down rig experimental measurements from the same vane in the Turbine Research Facility (TRF) of the Air Force Research Laboratory (AFRL). Predictions from the conjugate heat transfer (CHT) CFD are compared to experimental measurements for six span locations on both the suction side (SS) and pressure side (PS) of the vane. These are also compared to CFD predictions from previous simulations that only model the external main flow and estimate the cooling influx using a transpiration boundary condition. The heat transfer information gleaned from this study helps validate the maturing CHT CFD code used, helps realize the problem areas and conduction trends on the surface of a typical modern turbine vane with film cooling in true geometry and operational conditions, and provides critical information about the level of CFD integrity required for axial turbomachinery flows. This work also provides a thorough benchmarking of a film cooling array on a modern vane design for ongoing cooling optimization studies to be reported in the future. Results show that heat flux is generally over-predicted on the vane surface, especially without film cooling but shows some areas with fair agreement for both the cooled and uncooled cases. Surface temperature is much more accurately predicted for both sides of the cooled and uncooled vanes. Prediction of NHFR is fair but inconclusive due to the limited available experimental measurements. Meanwhile, a rarely reported parameter, net temperature reduction (NTR), is more accurately predicted by the CFD. The challenges in predicting heat transfer in such a realistic environment is primarily, but not exclusively, attributed to the necessity for more heat transfer measurements on the cooling air in the rig cooling channels and inside the vane and due to the fact that the experiments may have more isothermal wall temperatures at over the run time than expected.