A carregar...
Publicação
Modelação Computacional do Escoamento Hipersónico Perante a Influência de Campos Eletromagnéticos
| Nome: | Descrição: | Tamanho: | Formato: | |
|---|---|---|---|---|
| 29.72 MB | Adobe PDF |
Orientador(es)
Resumo(s)
A presente tese tem como objetivo o estudo da magnetoaerodinâmica (MAD) para aplicação em sistemas de proteção térmica (TPS) de veículos hipersónicos e na melhoria da precisão das previsões do escoamento em túneis de vento de plasma (PWT). Os fundamentos que regem o escoamento hipersónico e a MAD foram analisados, conduzindo ao desenvolvimento de um modelo numérico robusto em OpenFOAM. O novo modelo integra as equações de Navier–Stokes–Fourier com interações eletromagnéticas sob condições de não-equilíbrio termoquímico. Foram implementados vários modelos químicos, incluindo um novo modelo multiespécies, desenvolvido para captar as reações de ionização responsáveis por induzir interações MAD, ampliando a capacidade preditiva das simulações em condições pouco exploradas. A validação com dados experimentais revelou elevada precisão na previsão de fenómenos aerotermodinâmicos, em particular o aquecimento aerodinâmico, a relaxação vibracional e as propriedades do escoamento em tubeiras hipersónicas, com discrepâncias inferiores a 2%. Adicionalmente, o novo modelo químico reproduziu fielmente a cinética relevante do plasma, permitindo a simulação de plasma fracamente ionizado com mais de 99% de concordância relativamente a resultados experimentais. Após a consolidação da fiabilidade do modelo numérico, a presente investigação aprofunda o conhecimento científico em múltiplas áreas. Demonstrou-se que os efeitos de não-equilíbrio termoquímico em PWT hipersónicos aumentam com a razão de expansão da tubeira e com a entalpia específica de estagnação. Nestes casos, os efeitos catalíticos da parede tornaram-se mais significativos, enquanto a influência da atividade catalítica da parede nas propriedades do núcleo do escoamento revelou-se desprezável para razões de expansão abaixo de 186, fornecendo orientações precisas para a operação das instalações. Paralelamente, foram desenvolvidas novas tubeiras de perfil em sino, propostas como alternativas às convencionais tubeiras de perfil cónico para o PWT SCIROCCO. As novas tubeiras demonstraram desempenho superior, com um aumento de 19% no número de Mach à saída, uma redução de 33% na angularidade do escoamento central e diminuições adicionais nas perdas de entalpia específica (3,7%) e na geração de entropia específica (18,4%). De forma particularmente significativa, a configuração em sino ampliou em 66% a região de interação MAD sob campo magnético imposto (0,8 T), confirmando a sua superioridade para ensaios MAD, enquanto a configuração cónica permanece preferível para análises aerodinâmicas. Este trabalho evidencia pela primeira vez a relação entre a atividade catalítica da superfície e o controlo do escoamento MAD no desempenho de sistemas de proteção térmica. Para o menor número de Mach considerado (11,3), o escudo térmico MAD revelou-se ineficaz devido ao baixo parâmetro de interação magnética e à reduzida intensidade da força de Lorentz. Em contraste, a Mach 17,1, a aplicação do escudo térmico MAD conduziu a reduções significativas nos fluxos de calor superficial: 38% em superfícies não catalíticas e 49% em superfícies totalmente catalíticas. Estes resultados representam um marco no estudo do controlo de escoamentos hipersónicos assistidos por MAD, ao estabelecerem simultaneamente a relevância da atividade catalítica e a influência do número de Mach na eficácia do escudo térmico MAD. Em conjunto, as conclusões apresentadas expandem o conhecimento sobre os fenómenos aerotermodinâmicos, catalíticos e eletromagnéticos que caracterizam o voo hipersónico e oferecem metodologias que reforçam o desenvolvimento, a certificação e a otimização de veículos hipersónicos e de tecnologias de proteção térmica suportadas pela MAD.
This thesis is dedicated to the study of magnetoaerodynamics (MAD) for application in thermal protection systems (TPS) for hypersonic vehicles and to improving the accuracy of flow predictions in plasma wind tunnels (PWTs). The fundamental governing equations of hypersonic flow and MAD were examined, leading to the development of a robust numerical model in OpenFOAM. The new model integrates the Navier–Stokes–Fourier equations with electromagnetic interactions under thermochemical non-equilibrium conditions. Several chemical models were implemented, including a newly developed multispecies formulation designed to capture the ionisation reactions underlying MAD interactions, thereby extending the predictive fidelity of simulations in previously underexplored conditions. Validation against experimental data showed high accuracy in predicting aerothermodynamic phenomena, particularly aerodynamic heating, vibrational relaxation, and flow parameters in hypersonic nozzles, with discrepancies limited to less than 2%. The new chemistry model further reproduced the relevant reaction kinetics, enabling simulation of weakly ionized plasma with over 99% agreement with ground-based experimental results. After consolidating the reliability of the numerical model, the present investigation deepens scientific knowledge across multiple areas. It was demonstrated that the effects of thermochemical non-equilibrium in hypersonic plasma wind tunnels (PWTs) increase with the nozzle expansion ratio and the stagnation enthalpy. In these cases, the catalytic effects of the wall became more significant, whereas the influence of wall catalytic activity on the core flow properties was shown to be negligible for expansion ratios below 186, providing precise guidelines for facility operation. In parallel, new bell-shaped nozzles were developed and proposed as alternatives to conventional conical-profile nozzles for the SCIROCCO PWT. These new configurations demonstrated superior performance, yielding a 19% increase in Mach number at the exit, a 33% reduction in the angularity of the core flow, and additional decreases in enthalpy losses (3.7%) and entropy generation (18.4%). Particularly noteworthy is that the bell-shaped configuration expanded the MAD interaction region by 66% under an imposed magnetic field (0.8 T), confirming its superiority for MAD testing, while the conical configuration remains preferable for aerodynamic analyses. This work reveals, for the first time, the relationship between surface catalytic activity and MAD flow control in the performance of thermal protection systems. For the lowest Mach number considered (11.3), the MAD heat shield proved ineffective due to the low magnetic interaction parameter and the reduced intensity of the Lorentz force. In contrast, at Mach 17.1, the application of the MAD heat shield led to significant reductions in surface heat flux: 38% for non-catalytic surfaces and 49% for fully catalytic surfaces. These results represent a milestone in the study of MAD-assisted hypersonic flow control, by establishing both the relevance of catalytic activity and the critical influence of Mach number on the effectiveness of the MAD heat shield. Collectively, the conclusions presented expand the knowledge on the aerothermodyna mic, catalytic, and electromagnetic phenomena that characterise the hypersonic flows and offer methodologies that strengthen the development, certification, and optimisation of hypersonic vehicles and MAD-assisted thermal protection technologies.
This thesis is dedicated to the study of magnetoaerodynamics (MAD) for application in thermal protection systems (TPS) for hypersonic vehicles and to improving the accuracy of flow predictions in plasma wind tunnels (PWTs). The fundamental governing equations of hypersonic flow and MAD were examined, leading to the development of a robust numerical model in OpenFOAM. The new model integrates the Navier–Stokes–Fourier equations with electromagnetic interactions under thermochemical non-equilibrium conditions. Several chemical models were implemented, including a newly developed multispecies formulation designed to capture the ionisation reactions underlying MAD interactions, thereby extending the predictive fidelity of simulations in previously underexplored conditions. Validation against experimental data showed high accuracy in predicting aerothermodynamic phenomena, particularly aerodynamic heating, vibrational relaxation, and flow parameters in hypersonic nozzles, with discrepancies limited to less than 2%. The new chemistry model further reproduced the relevant reaction kinetics, enabling simulation of weakly ionized plasma with over 99% agreement with ground-based experimental results. After consolidating the reliability of the numerical model, the present investigation deepens scientific knowledge across multiple areas. It was demonstrated that the effects of thermochemical non-equilibrium in hypersonic plasma wind tunnels (PWTs) increase with the nozzle expansion ratio and the stagnation enthalpy. In these cases, the catalytic effects of the wall became more significant, whereas the influence of wall catalytic activity on the core flow properties was shown to be negligible for expansion ratios below 186, providing precise guidelines for facility operation. In parallel, new bell-shaped nozzles were developed and proposed as alternatives to conventional conical-profile nozzles for the SCIROCCO PWT. These new configurations demonstrated superior performance, yielding a 19% increase in Mach number at the exit, a 33% reduction in the angularity of the core flow, and additional decreases in enthalpy losses (3.7%) and entropy generation (18.4%). Particularly noteworthy is that the bell-shaped configuration expanded the MAD interaction region by 66% under an imposed magnetic field (0.8 T), confirming its superiority for MAD testing, while the conical configuration remains preferable for aerodynamic analyses. This work reveals, for the first time, the relationship between surface catalytic activity and MAD flow control in the performance of thermal protection systems. For the lowest Mach number considered (11.3), the MAD heat shield proved ineffective due to the low magnetic interaction parameter and the reduced intensity of the Lorentz force. In contrast, at Mach 17.1, the application of the MAD heat shield led to significant reductions in surface heat flux: 38% for non-catalytic surfaces and 49% for fully catalytic surfaces. These results represent a milestone in the study of MAD-assisted hypersonic flow control, by establishing both the relevance of catalytic activity and the critical influence of Mach number on the effectiveness of the MAD heat shield. Collectively, the conclusions presented expand the knowledge on the aerothermodyna mic, catalytic, and electromagnetic phenomena that characterise the hypersonic flows and offer methodologies that strengthen the development, certification, and optimisation of hypersonic vehicles and MAD-assisted thermal protection technologies.
Descrição
Palavras-chave
Investigação numérica Escoamento hipersónico Não-equilíbrio Termoquímico Magnetoaerodinâmica Túnel de Vento de Plasma Sistema de Proteção Térmica Condição Catalítica da Parede Tubeiras Hipersónicas Numerical Investigation Hypersonic Flow Thermochemical Non-equilibrium Magnetohydrodynamics Plasma Wind Tunnel Thermal Protection System Wall Catalytic Condition Hypersonic Nozzles