A hybrid LES-RANS approach for effusion cooling prediction

Cooling techniques for solid parts in the combustor and turbine are essential for both the performances and the life time of jet engine components. Experiments of the jet engine components are costly to set up, and it is sometimes difficult to access the 3D flow structures and heat transfer in key regions. Due to the fast development of high performance computing in recent decades, Large-Eddy Simulation (LES) is widely used not only in fundamental studies of the flow structures and heat transfer, but also to help the design and optimisation of jet engine components. This thesis focuses on the development of an LES based approach and the prediction of effusion cooling schemes for combustor liners. In this work, a novel hybrid LES-RANS approach based on wall proximity is further developed based on an existing in-house code to extend its capability, especially for unsteady heat transfer studies. Two synthetic methods for free-stream turbulence generation are studied. The hybrid LES-RANS approach is first validated by a canonical unsteady heat transfer case, a heated square cylinder in cold crossflow. The accuracy of the approach in predicting the unsteady flow field and surface heat transfer is assessed by comparison with relevant measurements. Analysis of turbulent structures is performed to help understand their effects on the surface heat transfer, as well as show how well those structures are resolved on modest grids. Free-stream turbulence is introduced in the heated cylinder case to study the effects of inflow turbulence on both the flow field and surface heat transfer. Two effusion cooling cases are studied using the hybrid LES-RANS approach. A singlerow film cooling configuration is first studied. Results of the simulations are validated against the experimental dataset. Good prediction is obtained for velocity and surface adiabatic cooling effectiveness. A multi-row effusion cooling configuration under scaled representative combustor conditions is also investigated. Agreement with the measurements and further studies of turbulent structures suggest that the hybrid LES approach is a promising tool for the investigation of complex industrial configurations with highly unsteady flow features.