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Abstract(s)
Nos últimos anos, a combustão por detonação tem sido revolucionária no setor
aeronáutico e aerospacial com elevado interesse na sua aplicação no motor de detonação
rotativa (RDE – Rotating Detonation Engine) que realiza o processo de combustão de
forma contínua, proporcionando reduções no consumo específico de combustível e
ganhos significativos de eficiência comparativamente a motores de foguetes e turbinas
de gás. A simplicidade mecânica do RDE requer apenas uma sequência de ignição para
iniciar a onda de detonação que se propaga a velocidades supersónicas numa onda de
choque de compressão autossustentada pelo calor libertado na combustão.
Esta dissertação apresenta uma análise termodinâmica da propagação de ondas de
combustão, através da teoria da dinâmica de gases que, juntamente com o critério de
Chapman e Jouguet (CJ), permitem determinar a velocidade apropriada da detonação
para uma mistura explosiva. O modelo de Zeldovich-von Neumann-Döring é enunciado
para justificar a teoria CJ incompleta. De facto, este modelo envolve a estrutura da
detonação e considera as detonações patológicas de von Neumann e as detonações não
ideais. Todos os processos reais envolvem viscosidade e as detonações são
intrinsecamente instáveis tridimensionais e transientes. Neste sentido, com o intuito de
se analisar o impacto dos efeitos viscosos no desempenho do RDE e na estrutura da
detonação, esta tese apresenta duas simulações numéricas tridimensionais do fenómeno
de detonação no RDE desenvolvidas por Peter A. T. Cocks et al: uma simulação de Euler
e uma simulação do modelo de turbulência, considerando a mistura de ar/hidrogénio
totalmente pré-misturada em condições estequiométricas. A estrutura da detonação, as
velocidades de detonação previstas e o impulso específico foram analisados, verificandose que a viscosidade num RDE provoca perdas de desempenho, sendo que o impulso
específico é superior na simulação de Euler.
O desempenho do RDE é degradado pela presença das irreversibilidades que devem ser
consideradas no seu projeto, tendo em vista a produção da tração necessária e
estabilidade da detonação em escoamento de fluido real. A minimização das perdas num
RDE é um dos grandes desafios que esta tecnologia promissora acarreta, pelo que a
compreensão da termodinâmica e dinâmica de gases na propagação da detonação é
fundamental para o projeto do RDE.
In recent years, detonation combustion has been revolutionary in the aeronautical and aerospace sector with great interest in its application in the Rotating Detonation Engine (RDE) which performs the combustion process continuously, providing reductions in specific fuel consumption and gains in efficiency compared to rocket engines and gas turbines. The mechanical simplicity of RDE requires only one ignition sequence to initiate the detonation wave that propagates at supersonic speeds in a compression shock wave self-sustained by the heat release in combustion. This dissertation presents a thermodynamic analysis of propagating combustion waves, through the gasdynamic theory which, together with the Chapman and Jouguet (CJ) criterion, determine the appropriate detonation velocity for an explosive mixture. The Zeldovich-von Neumann-Döring model is announced to justify the incomplete CJ theory. In fact, this model involves the detonation structure and considers the pathological detonation of von Neumann and nonideal detonations. All real processes involve viscosity and detonations are intrinsically unstable, three-dimensional and transient. In this sense, in order to analyse the impact of viscous effects on the RDE performance and on the detonation structure, this thesis presents two three-dimensional numerical simulations of the detonation phenomenon in the RDE created by Peter A. T. Cocks et al: an Euler simulation and a simulation of the turbulence model, considering a fully premixed air/hydrogen mixture under stoichiometric conditions. The detonation structure, the predicted detonation velocities and the specific impulse were analysed, proving that the viscosity in an RDE causes performance losses, with the specific impulse being higher in the Euler simulation. The performance of the RDE is degraded by the presence of irreversibilities that must be considered in its design, mindful of producing the required thrust and stability of detonation in real fluid flow. Minimizing losses in an RDE is one of the great challenges that this promising technology entails, thus understanding the thermodynamics and gas dynamics in detonation propagation is fundamental to the RDE design.
In recent years, detonation combustion has been revolutionary in the aeronautical and aerospace sector with great interest in its application in the Rotating Detonation Engine (RDE) which performs the combustion process continuously, providing reductions in specific fuel consumption and gains in efficiency compared to rocket engines and gas turbines. The mechanical simplicity of RDE requires only one ignition sequence to initiate the detonation wave that propagates at supersonic speeds in a compression shock wave self-sustained by the heat release in combustion. This dissertation presents a thermodynamic analysis of propagating combustion waves, through the gasdynamic theory which, together with the Chapman and Jouguet (CJ) criterion, determine the appropriate detonation velocity for an explosive mixture. The Zeldovich-von Neumann-Döring model is announced to justify the incomplete CJ theory. In fact, this model involves the detonation structure and considers the pathological detonation of von Neumann and nonideal detonations. All real processes involve viscosity and detonations are intrinsically unstable, three-dimensional and transient. In this sense, in order to analyse the impact of viscous effects on the RDE performance and on the detonation structure, this thesis presents two three-dimensional numerical simulations of the detonation phenomenon in the RDE created by Peter A. T. Cocks et al: an Euler simulation and a simulation of the turbulence model, considering a fully premixed air/hydrogen mixture under stoichiometric conditions. The detonation structure, the predicted detonation velocities and the specific impulse were analysed, proving that the viscosity in an RDE causes performance losses, with the specific impulse being higher in the Euler simulation. The performance of the RDE is degraded by the presence of irreversibilities that must be considered in its design, mindful of producing the required thrust and stability of detonation in real fluid flow. Minimizing losses in an RDE is one of the great challenges that this promising technology entails, thus understanding the thermodynamics and gas dynamics in detonation propagation is fundamental to the RDE design.
Description
Keywords
Análise Cfd Detonação Escoamento Viscoso Modelo Znd Ondas de Combustão Rde Teoria Cj