Tesis de maestría:
Sensitivity study and improvement of a film cooling configuration of a high-pressure turbine blade



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Much effort has been expended in the aerospace industry in order to achieve the highest quality standards required for nowadays technical and environmental necessities. This involves the increase of specific power and overall engine performance, together with the reduction of noise, specific fuel and heat to fuel consumption. Fundamentally, thermal efficiency and power output increase while increasing turbine rotor inlet temperatures. For this purpose, it is necessary to optimize engines with regard to the overall thermodynamic process. Advanced gas turbine engines operate at high temperatures to improve thermal efficiency and power output. As the turbine inlet temperature increases, the heat transferred to the turbine blades also increases. The level and variation in the temperature within the blade material, which causes thermal stresses, must be restricted to achieve reasonable durability goals. The operating temperatures for aircraft engines are far above the permissible metal temperatures, therefore it is necessary to cool the blades internally and externally. The blades are cooled by extracted air from the compressor of the engine and, since this extraction incurs in a reduction of thermal efficiency, it is necessary to understand and optimize the cooling techniques, operating conditions, and turbine blade geometry. Increasing demands confront the cooling systems of turbine blades. High temperature material development, such as thermal barrier coating (TBC) or highly sophisticated cooling schemes, are a necessary challenge to overcome, in order to ensure high-performance gas turbines for the upcoming years. The suggested designs hereby are to achieve an optimum cooling by a minimum use of cooling air and minimum aerodynamic losses which are an unwanted consequence of film cooling injection. Cooling techniques in advanced gas turbine engines can be distinguished between internal and external cooling. In convection cooling or internal cooling, the secondary flow extracts the heat flux through the blade walls and transports it away via channels inside the turbine blade. A vast amount of studies for different types of geometry arrangements have been carried out and applied, in order to increase heat flux transfer. These geometries include rib turbulators, pin fins, dimpled surfaces, surfaces with arrays of protrusions, swirl chambers, and rough surfaces. For external cooling, film cooling technology made possible the nowadays achievements in high efficiency gas turbine engines. The art and science of film cooling concerns the bleeding of internal cooling air through the external walls to form a protective layer between the hot gases and the component external surfaces. The application of effective film-cooling techniques provides a reliable defense for hot gas path surfaces against the high heat fluxes, serving to directly reduce the incident convective heat flux on the surface. Several investigations have been made regarding the major effects of cooling holes arrangements, turbulence, interaction between flows and vorticity production in order to improve film cooling technology. To address the main challenges of designing an optimal film cooling configuration, it is necessary to understand the behaviour of the main gas flow and the coolant flow. For this purpose, CFD calculations are carried out to visualise and understand the complex physical phenomena under study. However, numerical models should be validated with experimental data as this path leads not only to the understanding of the physical phenomena involved in the experiment, but also provides correct guidance on how the different variables under study can lead to engineering improvement. A test rig at the Institute for Thermal Turbomachinery (ITS) at the Karlsruhe Institute of Technology (KIT) is used to validate the related CFD set-up. In this work, a sensitivity study of different conventional film cooling configurations is introduced. This involves the study and modification of different geometrical variables in specific regions of the blade. Also, the complex vortex structures generated due to the interaction of the main hot gas with the coolant, that enhances heat flux transfer through the blade, is analysed. The most promising configurations in terms of blade temperature reduction, will be considered as possible candidates for blade manufacturing


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