Perspectives in Modeling Film Cooling of Turbine Blades by Transcending Conventional Two-Equation Turbulence Models

Abstract

The paper presents recent trends in modeling jets in crossflow with relevance to film cooling of turbine blades. The aim is to compare two classes of turbulence models with respect to their predictive performance in reproducing near-wall flow physics and heat transfer. The study focuses on anisotropic eddy-viscosity/diffusivity models and explicit algebraic stress models, up to cubic fragments of strain and vorticity tensors. The first class of models are direct numerical simulation (DNS) based two-layer approaches transcending the conventional k−ε model by means of a nonisotropic representation of the turbulent transport coefficients; this is employed in connection with a near-wall one-equation model resolving the semi-viscous sublayer. The aspects of this new strategy are based on known channel-flow and boundary layer DNS statistics. The other class of models are quadratic and cubic explicit algebraic stress formulations rigorously derived from second-moment closures. The stress-strain relations are solved in the context of a two-layer strategy resolving the near-wall region by means of a nonlinear one-equation model; the outer core flow is treated by use of the two-equation model. The models are tested for the film cooling of a flat plate by a row of streamwise injected jets. Comparison of the calculated and measured wall-temperature distributions shows that only the anisotropic eddy-viscosity/diffusivity model can correctly predict the spanwise spreading of the temperature field and reduce the strength of the secondary vortices. The wall-cooling effectiveness was found to essentially depend on these two particular flow features. The non-linear algebraic stress models were of a mixed quality in film-cooling calculations.

Investigation of density ratio effects on normally injected cold jets into a hot cross flow

“…Azzi and Lakehal [14] studied two classes of turbulence models, namely anisotropic eddy-viscosity/diffusivity and explicit algebraic stress models in modeling film cooling of turbine blades. They investigated the predictive performance of the turbulence models in reproducing near-wall flow physics and heat transfer on a flat plate by a row of streamwise injected jets for a density ratio of 2.0.…”

Computational research on rotating channel by a modified anisotropic turbulence model

“…Many experimental researches and DNS (Direct Numerical Simulation) results revealed that in the vicinity of walls, the turbulent fluctuation w w   in flow direction is generally larger than the normal turbulent fluctuation u u   . However, the traditional eddy-viscosity turbulence model with the Boussinesq approximation could not catch this feature, which can be proved by Azzi and Lakehal [12]. So in the present study, w w   / u u   is calculated by the correlation fitted by experimental data [13].…”

Large-eddy simulations of leading edge film cooling: Analysis of flow structures, effectiveness, and heat transfer coefficient

“…In another study by Azzi and Lakehal (2001), two classes of k-e model and Reynolds stress transport model were used to simulate both a flat plate and a symmetrical turbine blade. In the first case, a two-layer approach was used where a DNS-based one-equation model was applied in the viscous region and k-e model was applied in the outer region.…”