A Detailed Analysis of Film Cooling Physics: Part II — Compound–Angle Injection With Cylindrical Holes

Abstract

Detailed analyses of computational simulations with comparisons to experimental data were performed to identify and explain the dominant flow mechanisms responsible for film cooling performance with compound angle injection, Φ, of 45°, 60°, and 90°. A novel vorticity and momentum based approach was implemented to document how the symmetric, counter–rotating vortex structure typically found in the crossflow region in streamwise injection cases, becomes asymmetric with increasing Φ. This asymmetry eventually leads to a large, single vortex system at Φ = 90° and fundamentally alters the interaction of the coolant jet and hot crossflow. The vortex structure dominates the film cooling performance in compound angle injection cases by enhancing the mixing of the coolant and crossflow in the near wall region, and also by enhancing the lateral spreading of the coolant. The simulations consist of fully–elliptic and fully–coupled solutions for field results in the supply plenum, film–hole, and crossflow regions and includes surface results for adiabatic effectiveness η and heat transfer coefficient h. Realistic geometries with length–to–diameter ratio of 4.0 and pitch–to–diameter ratio of 3.0 allowed for accurate capturing of the strong three–way coupling of flow in this multi–region flowfield. The cooling configurations implemented in this study exactly matched experimental work used for validation purposes and were represented by high quality computational grid meshes using a multi–block, unstructured grid topology. Blowing ratios of 1.25 and 1.88, and density ratio of 1.6 were used to simulate realistic operating conditions and to match the experiments used for validation. Predicted results for η and h show good agreement with experimental data.