A Detailed Analysis of Film–Cooling Physics: Part I — Streamwise Injection With Cylindrical Holes

Abstract

A previously documented systematic computational methodology is implemented and applied to a jet–in–crossflow problem in order to document all of the pertinent flow physics associated with a film–cooling flowfield. Numerical results are compared to experimental data for the case of a row of three–dimensional, inclined jets with length–to–diameter ratios similar to a realistic film–cooling application. A novel vorticity based approach is included in the analysis of the flow physics. Particular attention has been paid to the downstream coolant structures and to the source and influence of counter–rotating vortices in the crossflow region. It is shown that the vorticity in the boundary layers within the film hole is primarily responsible for this secondary motion. Important aspects of the study include: (1) a systematic treatment of the key numerical issues, including accurate computational modeling of the physical problem, exact geometry and high quality grid generation techniques, higher–order numerical discretization, and accurate evaluation of turbulence model performance; (2) vorticity–based analysis and documentation of the physical mechanisms of jet–crossflow interaction and their influence on film–cooling performance; (3) a comparison of computational results to experimental data; and (4) comparison of results using a two–layer model near–wall treatment versus generalized wall functions. Solution of the steady, time–averaged Navier–Stokes equations were obtained for all cases using an unstructured/adaptive grid, fully explicit, time–marching code with multi–grid, local time stepping, and residual smoothing acceleration techniques. For the case using the two–layer model, the solution was obtained with an implicit, pressure–correction solver with multi–grid. The three–dimensional test case was examined for two different film–hole length–to–diameter ratios of 1.75 and 3.5, and three different blowing ratios, from 0.5 to 2.0. All of the simulations had a density ratio of 2.0, and an injection angle of 35°. An improved understanding of the flow physics has provided insight into future advances to film–cooling configuration design. In addition, the advantages and disadvantages of the two–layer turbulence model are highlighted for this class of problems.