Prediction of Heat Transfer Characteristics for Discrete Hole Film Cooling for Turbine Blade Applications

Abstract

A two-dimensional (2-D) injection model is used with a 2-D low Reynold’s number k-ε model boundary layer code. The three-dimensional effects of the discrete hole injection process is introduced in the 2-D prediction scheme through an “entrainment fraction” (T). An established correlation between T and the injection parameters obtained in a previous paper is used to predict the film cooling effectiveness (η̄) and heat transfer coefficients for multirow injection, injection into a laminar boundary layer and finally injection on convex curved surfaces. Predictions of η̄ are in good agreement with experimental data for most of the cases tested. Predictions of Stanton numbers defined by St(0) and St(1) are good for low injection ratios (M) but as M increases the values are underpredicted. In spite of some shortcomings, in the authors’ opinion the present 2-D prediction scheme is one of the most comprehensive developed so far. It is seen that the entrainment fraction T is quite universal in its application to 2-D predictions of the discrete hole film cooling process.

Impact of Rotor–Stator Interaction on Turbine Blade Film Cooling

“…The entrainment fraction correlation reported by Tafti and Yavuzkurt (1987) is found to be ill-suited for the cases where the ratio of the coolant-to-main flow densities is large (about 2) or the external flow is compressible. To obtain the dependence of the entrainment fraction on the flow conditions and the coolant hole geometries, an extensive number of flat plate simulations were performed and matched to their corresponding experiments.…”

“…The injection model incorporated into UNSFLO approximates the three-dimensional fluid dynamics at the film holes. This model is an extension of the model proposed by Tafti and Yavuzkurt (1990) for a two-dimensional boundary layer code. At every injection site, an equivalent plane jet is distributed into the viscous computational domain.…”

“…By conserving mass, momentum, and enthalpy of the injected jet, the added fluxes are integrated over each cell surface and the contributions distributed at the cell nodes. In order to account for the effect of three-dimensional entrainment on the temperature profile, Tafti and Yavuzkurt (1990) introduced a source term into the energy equation. The parameters that characterized this source term were T and 7 enI , defined as the "entrainment fraction" and the "entrainment enthalpy," respectively.…”

“…Crawford et al (1980) developed a boundary layer code with an algebraic turbulence model in which the mixing length was "augmented" at the injection site to simulate the enhanced local mixing. Tafti and Yavuzkurt (1987) also developed a model of the injection process in which the three-dimensional mixing of the coolant and the boundary layer was accounted for through an "entrainment fraction." The entrainment fraction was correlated to experimental data and incorporated into a boundary layer code, which was shown to be successful in the prediction of film cooling effectiveness in multirow film cooling configurations (Tafti and Yavuzkurt, 1990).…”

“…Tafti and Yavuzkurt (1987) also developed a model of the injection process in which the three-dimensional mixing of the coolant and the boundary layer was accounted for through an "entrainment fraction." The entrainment fraction was correlated to experimental data and incorporated into a boundary layer code, which was shown to be successful in the prediction of film cooling effectiveness in multirow film cooling configurations (Tafti and Yavuzkurt, 1990). In another approach, Schonung and Rodi (1987) used a three-dimensional elliptic calculation to obtain "dispersion terms," which describe the enhanced mixing at the injection location.…”