The aim in the development of future aircraft is to be more environmentally friendly through the implementation of various innovative technologies. Over the past few decades, the efficiency of gas turbines has been improved by using film cooling on components that experience thermal stress. Up until now, there have been mostly three film cooling techniques used in gas turbines e.g. slot film cooling, discrete round effusion holes, and fan-shaped holes - the latter being the state of the art. To further enhance gas turbine efficiency, this study focuses on investigating discrete film cooling holes placed in a groove, referred to as a trench. The study explores different coolant to hot gas momentum ratios that are relevant for both the combustor and turbine. Additionally, external turbulence boundary conditions, typical to the hot gas section of gas turbines, are generated and applied in the research. The analyses are carried out using Computational Fluid Dynamics (CFD) and involve the utilization of two distinct approaches: scale-resolved Large Eddy Simulations (LES) and turbulence-modelled Reynolds-averaged Navier-Stokes (RANS) simulations. The study employs established turbulence models. Notably, a novel steady-state RANS model, wherein the model's coefficients are trained using a neural network, is introduced for the first time in film cooling simulations. One of the research goals is to examine and computationally generate inflow conditions with a turbulence characteristic similar to those found in combustors. This involves achieving turbulence with an intensity of 10-20% and a length scale of up to 3.5 times the diameter of the film cooling hole. In order to accomplish this, active turbulence generators are simulated using Large Eddy Simulations (LES) with the implementation of moving meshes. LES simulations are conducted with realistic external turbulence boundary conditions for three film cooling designs: untrenched, transverse trench, and segmented trench. These simulations allow for the assessment of adiabatic film cooling efficiency, heat transfer coefficient, and resulting net heat flux reduction in a single LES simulation, a novel approach. The results show that the segmented trench design outperforms the other tested designs under both realistic and zero turbulence boundary conditions. Furthermore, the simulations reveal unsteady effects in the centerplane, which closely resemble experimental findings, emphasizing the importance of accounting for turbulence in simulations. By conducting a numerical analysis of conjugate heat transfer, an observation is made regarding the presence of an issue in existing trenched film cooling designs. Normally, a trench is formed by eliminating a section of the outer wall that necessitates cooling. The simulations illustrate that the trench has a tendency to draw in hot gas, leading to concentrated heating on the inner surface of the exposed metal wall within the trench. The idea is to create new trench designs with inclined walls in order to minimize hot gas ingestion. Through an automated parametric optimization study conducted under realistic turbulence conditions, innovative three-dimensional trench shapes are developed, almost eliminating hot gas entrainment. Among these designs, one stands out, providing higher film cooling efficiency, more even coolant distribution, and reduced hot gas ingestion compared to conventional transverse and segmented trench designs, particularly regarding film cooling efficiency. These novel designs have the potential to rival the current state-of-the-art fan-shaped film cooling designs and offer more efficient gas turbines in the future.     «

The aim in the development of future aircraft is to be more environmentally friendly through the implementation of various innovative technologies. Over the past few decades, the efficiency of gas turbines has been improved by using film cooling on components that experience thermal stress. Up until now, there have been mostly three film cooling techniques used in gas turbines e.g. slot film cooling, discrete round effusion holes, and fan-shaped holes - the latter being the state of the art. To...    »