Performance Prediction of a Novel Design for Turbine Vane Film Cooling With Low Aerodynamic Loss and High Effectiveness

Abstract

A new film-cooling scheme for the suction surface of a gas turbine vane in a transonic cascade is studied numerically. The concept of the present design is to inject a substantial amount of coolant at a very small angle, approaching a “wall-jet,” through a single row of relatively few, large holes near the vane leading edge. The near-match of the coolant stream and mainstream momentums, coupled with the low coolant trajectory, theoretically results in low aerodynamic losses due to mixing. A minimal effect of the film cooling on the vane loading is also important to realize, as well as good coolant coverage and high adiabatic effectiveness. A systematic computational methodology, developed in the Advanced Computational Research Laboratory (ACRL) and tested numerous times on film-cooling applications, is applied in the present work. For validation purposes, predictions from two previous turbine airfoil film-cooling studies, both employing this same numerical method, are presented and compared to experimental data. Simulations of the new film-cooling configuration are performed for two blowing ratios, M=0.90 and M=1.04, and the density ratio of the coolant to the mainstream flow is unity in both cases. A solid vane with no film cooling is also studied as a reference case in the evaluation of losses. The unstructured numerical mesh contains about 5.5 million finite-volumes, after solution-based adaption. Grid resolution is such that the full boundary layer and all passage shocks are resolved. The Renormalization Group (RNG) k-ε turbulence model is used to close the Reynolds-averaged Navier-Stokes equations. Predictions indicate that the new film-cooling scheme meets design intent and has negligible impact on the total pressure losses through the vane cascade. Additionally, excellent coolant coverage is observed all the way to the trailing edge, resulting in high far-field effectiveness. Keeping the design environment in mind, this work represents the power of validated computational methods to provide a rapid and reasonably cost-effective analysis of innovative turbine airfoil cooling.