Leading-Edge Film-Cooling Physics: Part I — Adiabatic Effectiveness

Abstract

A systematic, computational methodology was employed to study film cooling on a turbine airfoil leading edge. In this paper, numerical predictions are compared with surface effectiveness measurements from a code-validation quality experiment in the open literature, and a detailed discussion of the physical mechanisms involved in leading edge film cooling is presented. The leading edge model was elliptic in shape to accurately simulate a rotor airfoil, and other geometric parameters were in the range of current design practice for aviation gas turbines. Three laterally-staggered rows of cylindrical film-cooling holes were investigated. One row of holes was centered on the stagnation line, and the other rows were located 3.5 hole-diameters downstream, mirrored about the stagnation line. All holes had an injection angle of 20° with the surface, and a 90° compound angle (radial injection). The average blowing ratio was varied from 1.0 to 2.5, and the coolant-to-mainstream density ratio was 1.8 in all simulations. Converged and grid independent solutions were obtained using a high-quality, multi-topology grid with 3.6 million cells and a fully-implicit, pressure correction-based Navier-Stokes solver. Turbulence closure was obtained with a realizable k-ε model, which has been demonstrated to be especially effective in controlling spurious production of turbulent kinetic energy in regions of rapid, irrotational strain. The predictions of laterally averaged effectiveness agreed well with the experimental data, especially at low-range blowing ratios. Highly nonuniform coolant coverage was seen to exist downstream of the second row of holes, caused mainly by interaction between the two rows of jets and by a strong vortex that reduced the spread of coolant from the downstream row. The results of the present study demonstrate that computational methods can accurately model the highly-complex film-cooling flowfield in the stagnation region.