This article presents results from a numerical study of a turbulent slot jet impinging on a concave surface. Five different low Reynolds number k-e models were evaluated to predict the heat transfer under a two dimensional steady turbulent jet. The effects of flow and geometrical parameters (e. g. jet Reynolds number and jet-to-target separation distance) have been investigated. The Yap correction is applied for reducing the over-prediction of Nusselt number in the near wall region. It is shown that among the models tested in this study, the LS-Yap model is capable of predicting local Nusselt number in good agreement with the experimental data in both stagnation and wall jet region. Moreover, after implementation of Yap correction, no significant effect of the nozzle-to-surface distance, h/B, on the predicted stagnation Nusselt number has been found. Finally it is demonstrated that the higher values of turbulent Prandtl number reduces the heat diffusion along the wall and consequently the predicted local Nusselt number is reduced especially in the wall jet region.
SUMMARYThe present study addresses a new effort to improve the prediction of turbulent heat flux in the film cooling flow by applying the implicit algebraic flux (IAF) model of Rogers et al. A three-dimensional symmetry case is investigated using a film hole length-to-diameter ratio of 1.75 and an injection angle of 35 • . The low Reynolds number second moment closure (SMC) model with a wall-reflection term is employed for simulating the turbulent flow field right up to the wall. Results obtained from the IAF model are compared with two other algebraic turbulent heat flux models, namely, the simple eddy diffusivity (SED) with a constant turbulent Prandtl number and the generalized gradient diffusion hypothesis (GGDH). Comparisons of the turbulent heat flux components calculated by these models show that the major difference appears in the streamwise turbulent heat flux. These models demonstrate a significant effect on the prediction of film cooling effectiveness. The SED model with a constant prescribed value for the turbulent Prandtl number fails to predict the cooling air spreading in the lateral direction while by employing the GGDH and IAF models, the spreading of the cooling air and the decay of the effectiveness in the core region are reasonably predicted. A combination of the SMC and IAF models for simulating the turbulent flow and heat transfer is capable of predicting the streamwise and lateral film cooling effectiveness in very good agreement with the available experimental data.
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