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Modelling of Turbulent Flow and Heat Transfer in Porous Media for Gas Turbine Blade Cooling

Al-Aabidy, Qahtan Abdulzahra Flaiyh

[Thesis]. Manchester, UK: The University of Manchester; 2018.

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Abstract

This thesis focuses on the study of flow and heat transfer in porous media in both laminar and turbulent flow regimes, by using Volume Averaged Reynolds Navier Stokes (VARNS) approach. The main concern is to investigate the possibility of using porous media for the gas turbine blade cooling. Very recently, using this technique in blade cooling, particularly with internal cooling, has motivated many researchers due to an effective enhancement in the blade cooling. In this study turbulence is represented by using the Launder-Sharma low-Reynolds-number k-Îµ turbulence model, which is modified via proposals by Nakayama and Kuwahara (2008) and Pedras and de Lemos (2001) for extra source terms in the turbulent transport equations to account for the porous structure, which is treated as rigid and isotropic. Due to the changing of the effective porosity as the clear fluid region is approached, the porosity and additional source term in the macroscopic Reynolds averaged Navier-Stokes equations are relaxed across a thin transitional layer at the edges of the porous media. This is achieved by utilizing exponential damping relations to consider these changes. The Local Thermal Equilibrium (LTE) (one-energy equation) model is used for the thermal analysis in porous media. In order to investigate the validity of the extended model, laminar and turbulent flow in different cases, fully developed and developing flows, have been considered. For laminar flows, fully developed plane channel flows with one and two porous layers, a channel with a single porous block and partially filled porous channel flows have been examined for the purpose of validating the extra drag terms in the momentum equations. For the validation purpose for turbulent flows in porous media, the extended model has been tested in homogeneous porous media, turbulent porous channel flows, turbulent solid/porous rib channel flows, and repeated turbulent porous baffled channel flows. Results of all laminar cases show excellent qualitative agreements with the available numerical calculations and experimental data. Results of all turbulent cases show that the extended model returns generally satisfactory accuracy through the comparisons with the available data, except for some predictive weaknesses in regions of either impingement or adverse pressure gradients, both of which are largely due the underlying eddy-viscosity model formulation employed. Thus, from all results, it can be confirmed that the extended model is promising for engineering applications.