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CFD Analysis of the Blade Cooling of a Gas Turbine
Language: Italian This thesis is written in Italian
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Original Italian title:
Studio CFD del raffreddamento delle pale di una turbina a gas
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Gennaro Bozza, Università degli Studi di Napoli - Federico II, 2008-09
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The research carried out during this thesis work, focused on optimizing the cooling system of the first stage of a modern gas turbine. More precisely, we worked on the cooling system of the stator vanes row, which is directly invested by the flow of exhaust gas straight out of the combustion chamber. In particular it has been studied, through new methods of computational fluid dynamics (CFD), the "film cooling" technique which provides for the creation, around the entire surface of the blade/vane (that is lapped against exhaust fumes), of an adherent layer of cold air (which is at the temperature at the end of compression). Such air layer isolates the blade/vane from the gas flow. The development of a highly sophisticated cooling system is justified by the need to increase as much as possible the maximum cycle temperature (T3) in order to improve efficiency and power of the gas turbine cycle, with a view of wide relevance of reducing energy consumption.
In the first chapter an overview on modern gas turbines will be presented, primarily illustrating the thermodynamic principles that underlie its reference cycle, then the new frontiers of development. The second chapter is exclusively dedicated to the turbine blades. The state of the art of the blades and their cooling systems is presented: materials, the (complex) geometry of cooling channels, the influence of cooling on the thermodynamic cycle. The third chapter is finally exclusively dedicated to the simulation of the blades cooling, with CFD techniques. We started from the presentation of the methods used for the CAD modeling of the blades, then it is described in detail how they were modeled. Finally all the results of the simulations are presented. Such simulations have been realized using the CAD/CAE software package Fluent/Gambit. We focused attention on both the generation of the computational grid, illustrating the characteristics and the different types, and on physical-mathematical models used and their numerical integration techniques that Fluent implements. The chapter ends with the presentation of simulation results, which concern distributions of temperature, pressure, velocity and many other parameters in the calculation domain, together with the values of efficiency, effectiveness, and loss coefficient for various configurations of cooling holes and for different values of cooling air mass flow. The results are widely illustrated by tables, charts and graphs.