Improving of Film Cooling Effectiveness Using a Reverse Injection

Abstract

Film cooling is a cooling technique widely used in high performance gas turbines to protect the turbine's airfoils from damage by hot gases. Film injection holes are placed in the blade body to allow the coolant to pass from the inner cavity to the outer surface. The cooling injection gas results a layer film cooling gas flowing along the outer surface of the airfoil. This study consists of a 3D numerical film cooling simulation. The CFD code used ANSYS CFX is based on the finite volume method for the resolution of the averaged Navier-Stokes equations. The objective of the study is to test a geometrical configuration with an injection hole in the reverse direction to a mainstream flow. The goal is to modify the flow structure to destroy the two kidney-shaped secondary vortexes (Kidney Vorticies) that are primarily responsible for the deterioration of cooling effectiveness. The geometric configuration is combined with different injection rates that have been simulated to evaluate the influence of the reverse injection. The computational domain is discredited using a structured mesh with highly refined multi-blocks including the region of the distribution box (plenum). The turbulence is modeled by the RNG k-epsilon turbulence model. The coolant was fed by a film cooling hole with an inclination angle of 30 ° in both directions. Three blowing ratio are tested respectively (0.5, 1 and 2). It has been found that the reverse injection hole improves the cooling performance across the entire computational field compared to the forward injection hole. The numerical results of forward and reverse holes are compared with the experimental study of Singh et al.