Prediction of Film Cooling by Discrete-Hole Injection

This paper presents a study on film cooling performance resulting from injection through a single row and alternatively through two staggered rows of holes onto a flat plate. The objective is to use an appropriate computational method for the simulation of the film cooling process in order to improve our understanding of the complex flow and heat transfer phenomena downstream of the coolant injection holes. A multi-grid and segmentation method is used to solve the transport equations of the film cooling process to achieve good local flow resolution and rapid convergence. The turbulence is represented by the k-ϵ model combined with a nonisotropic eddy-viscosity formulation and a near-wall k model. New experimental results are obtained for comparison with the numerical simulations. Cooling through single and double rows of orifices is investigated computationally; for the same overal mass injection, the double row cooling has better spanwise averaged film cooling effectiveness for the range of parameters investigated. The effects of mass flow ratios and injection angles on the double row cooling performance are investigated computationally. Comparison between the predicted and measured spanwise averaged effectiveness shows good agreement for mass flow ratios of 0.2 and 0.4 but also shows that the numerical values are consistently lower than the measured results for mass flow ratios of 0.8. This difference suggests that the k-ϵ turbulence model under-predicts the turbulence production resulting from the shear flow between the main stream and jets when the cross flow momentum is high and the associated streamwise vorticity is strong and therefore that the turbulence stresses and scalar fluxes are not correctly predicted in these cases. Some possible improvements are suggested.