Browsing by Author "Lopes, Joao Pedro Ramalho"
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- Design of a Supersonic NozzlePublication . Lopes, Joao Pedro Ramalho; Brojo, Francisco Miguel Ribeiro ProençaAs new engines are built, the necessity of improving the initial design grows. The preliminary design of nozzles is one of the most important parts due to being the component that increases the speed of the flow even more than the rest of the engine. There are a lot of factors involved in the selection of the nozzle: the cruise speed intended for the aircraft, the cruise altitude and others. As the design methods evolved from paper drafts, in the beginning of the history of aviation, to digital designs, in the present days, the methods employed to do it also changed. The Method of Characteristics was one of the methods that gain some popularity around the 1980’s being first used in paper drafts and then with computer software. This dissertation utilizes the Method of Characteristics to design the supersonic section of the nozzle, and describes how such factors, as the altitude, influence the shape of the contour, as the main goal. The State of the art, chapter 2, introduces a brief description of the types of nozzles that exist and the application for each one of them. From the basics of thermodynamics to advanced Aerothermodynamics, it is explained the knowledge required to accomplish the results presented on chapter 5. The theoretical foundation, 3, explains the relationship between work and heat as well as the specific heat ratio, the speed of sound and the Mach number, the types of flow, the shocks, the expansion fans and how the variations of pressure affect the flow inside a nozzle. The Design method chapter lays out step by step how to apply the Method of Characteristics, starting with an introduction to the method, then a linear method to design the convergent section, requiring only a few step to do it, and the design of the divergent section of the nozzle, which is the hardest part to attain. The code, in MATLAB, behind the design, is also explained step by step. The Results chapter depicts what appears to the user when initiating the code and what inputs are required for the code to work and give results.There are three cases described and explained, where some variables were changed to observe the difference between those cases. The results of this dissertation indicated that the nozzle was operating with an overexpanded flow, and the convergent section could not achieve a choked flow at the throat, but the pressure decrease along the nozzle had a similar behavior to a choked isentropic supersonic flow.