Numerical Investigation on the Dual Effect of Upstream Steps and Transverse Trenches on Film Cooling Performance

Abstract

This paper presents a numerical investigation of a concept for improving film cooling performance by setting a step upstream the transverse trench. The step, which is placed upstream the transverse trench, is used to modify the approaching boundary-layer flow and its interaction with coolant to improve the lateral spreading of coolant. Five different relative distances between the steps and transverse trenches (upstream distances) are investigated, including −20, 0, 5, 10, and 15 mm. The film cooling performance is evaluated at a density ratio of 0.97, with the blowing ratios ranging from 0.5 to 2.0. The numerical results of film cooling with an upstream step and the numerical results of film cooling with holes embedded in transverse trenches show an agreement with the experimental data when three-dimensional average Navier–Stokes equations are solved with the standard k-ε model. Detailed adiabatic cooling effectiveness and total pressure loss coefficients are simulated. Results obtained indicate that film cooling performance in the region downstream from the film hole is sensitive to upstream distances. In the case with an upstream distance of 0 mm, the lateral spreading of coolant is superior to that in other cases, which leads to a higher lateral adiabatic cooling effectiveness. The case with an upstream distance of 0 mm is a better choice when the improved lateral adiabatic cooling effectiveness and the reduced total pressure loss penalty are taken into account.