The increasing electrification of ultra-high bypass turbo fan engines requires further development of waste heat management. Since waste heat is generated at a low temperature, providing a low driving temperature difference for heat transfer, structured surfaces are used as heat exchangers to transfer waste heat to the bypass duct. Dimple structures have been shown to be effective in increasing the heat transfer area and heat transfer coefficient while maintaining low pressure loss. However, previous studies have only considered dimples at Mach and Reynolds numbers well below those in the bypass duct. A comparison of experiments and RANS simulations shows that the turbulence and heat flux modelling significantly influences the velocity and temperature profiles. Deviations of up to 25% are caused, on the one hand, by the different capturing of the secondary flows caused by the structures via the turbulence models and, on the other hand, by the spatial directions considered in the heat flux model. The accuracy of the heat flux model is strongly influenced by the quality of the flow solution and the coupling between the turbulence model and the heat flux model. This work extends the Reynolds and Mach number range via RANS simulations to bypass duct flow conditions. It compares different turbulence and heat flux models with each other. The study is carried out using a simplified setup of fully developed channel flow. This is done using a numerical setup with periodic inlet and outlet boundary conditions. The dimples are referenced against a smooth channel. Empirical correlations are used to validate the results. Since empirical correlations only apply to smooth and rough channels but not to specific geometries, scale-resolving simulations are performed as part of this work and used for validation.