Numerical Prediction of Film Cooling Effectiveness and the Associated Aerodynamic Losses With a Three-Dimensional Calculation Procedure

Abstract

Film cooling of turbine blades by injecting air through holes or slots affects the main stream flow. A numerical model has been developed to predict the resulting three-dimensional flow and the temperature pattern under steady flow conditions. An elliptic procedure is used in the near injection area to include reverse flow situations, while in the upstream area as well as far downstream a partial-parabolic procedure is applied. As first step an adiabatic wall has been assumed as boundary condition, since for this case experimental data are readily available for comparison. At elevated momentum blowing rates, zones of reverse flow occur downstream of the injection holes resulting in a decrease of cooling efficiency. A variation of the relevant parameters momentum blowing rate m, injection angle α and ratio of hole spacing to diameter s/d revealed the combination of m ≈ 1, α ≈ 30° and s/d ≈ 2 to be the optimum with respect to the averaged cooling efficiency and to the aerodynamic losses. Cooling is more efficient with slots than with a row of holes not considering the related problems of manufacture and service life. The calculated temperature patterns compare well with the experimental data available.

Heat Transfer in Film-Cooled Turbine Blades

“…They introduced the threedimensional effects through an "entrainment fraction". Dibelius et al (1990) developed an elliptic procedure near the injection area but a partially parabolic procedure far downstream for film cooling. They used an eddy viscosity model for turbulence, and presented results for a flat plate.…”

Effect of Velocity and Temperature Distribution at the Hole Exit on Film Cooling of Turbine Blades

“…They specified a uniform coolant temperature but nonuniform velocity profile at the hole exit. Dibelius et al (1990) developed an elliptic procedure near the injection area but a partially parabolic procedure far downstream for film cooling on a flat plate. They prescribed a uniform coolant velocity but slightly nonuniform coolant temperature at the hole exit.…”