Coherent structures in trailing-edge cooling and the challenge for turbulent heat transfer modelling |
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| Institution: | 1. Karlsruhe Institute of Technology, Institute for Thermal Turbomachinery, Kaiserstraße 12, 76128 Karlsruhe, Germany;2. Karlsruhe Institute of Technology, Institute for Hydromechanics, Kaiserstraße 12, 76128 Karlsruhe, Germany;3. King Abdulaziz University, Jeddah, Saudi Arabia;1. Shaanxi Engineering Laboratory of Turbomachinery and Power Equipment, Institute of Turbomachinery, School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, China;2. Shanghai Center of Research for Commercial Aircraft Engine Engineering Techniques, AECC Commercial Aircraft Engine Co., LTD, Shanghai 200241, China;3. Department of Mechanical Engineering, University of Minnesota Twin Cities, Minneapolis, MN 55455, USA;1. Tianjin Key Laboratory of Nonlinear Dynamics and Chaos Control, Tianjin 300072, China;2. Key Laboratory of Efficient Utilization of Low and Medium Grade Energy, MOE, School of Mechanical Engineering, Tianjin University, Tianjin 300350, China |
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| Abstract: | The present paper tests the capability of a standard Reynolds-Averaged Navier–Stokes (RANS) turbulence model for predicting the turbulent heat transfer in a generic trailing-edge situation with a cutback on the pressure side of the blade. The model investigated uses a gradient-diffusion assumption with a scalar turbulent-diffusivity and constant turbulent Prandtl number. High-fidelity Large-Eddy Simulations (LES) were performed for three blowing ratios to provide reliable target data and the mean velocity and eddy viscosity as input for the heat transfer model testing. Reasonably good agreement between the LES and recent experiments was achieved for mean flow and turbulence statistics. The LES yielded coherent structures which were analysed, in particular with respect to their effect on the turbulent heat transfer. For increasing blowing ratio, the LES replicated an also experimentally observed counter-intuitive decrease of the cooling effectiveness caused by the coherent structures becoming stronger. In contrast, the RANS turbulent heat transfer model failed in predicting this behaviour and yielded significantly too high cooling effectiveness. It is shown that the model cannot predict the strong upstream and wall-directed turbulent heat fluxes caused by large coherent structures, which were found to be responsible for the counter-intuitive decrease of the cooling effectiveness. |
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| Keywords: | Turbulence simulation Coherent structures Turbulent heat transfer Film cooling |
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