2011 IEEE Congress on Evolutionary Computation (CEC). June 5-8, 2011, Ritz-Carlton, New Orleans, LA, USA

A numerical investigation on the combustion mechanics of a hybrid rocket engine is performed through unsteady Reynolds-averaged Navier-Stokes simulation. The hybrid rocket engine model is based on an experimental laboratory scale engine design operating on GOX and HDPE as a propellant. A simple convection heat flux model is used to determine the heat transfer to the fuel wall. The project is done with the goal of finding the fuel regression rate in mind, as it is an essential parameter for determining engine performance. The results show early results of the fluid- and thermodynamics occurring in the combustion chamber. Propellant mixing is shown to not be optimal as a significant part of the exit flow consists of high concentrations of oxidizer that has not reacted with the fuel. The flame temperature is shown to be relatively high inside the combustion chamber. It is concluded from the simulations that the model needs further improvement in order to accurately compute the flow as well as the heat transfer to the fuel. To determine the regression rate, radiation should be implemented into the heat transfer model.

Rocket propulsion using the hybrid-propellant scheme is a technology that offers much promise in applications where high-performance liquid rocket engines are deemed too complex and solid rocket motors are considered to lack performance or safety. However, despite extensive research, there is still a lack of knowledge in the theoretical aspects of hybrid rocketry, especially in the area of fuel-oxidizer mixing and fuel regression rate. This lack of a good theoretical model makes the implementation of good, practical solutions and mature, well-functioning designs more diffcult. This disadvantages the hybrid rocket engine when compared to liquid rocket engines or solid rocket motors.In this study, a hybrid rocket engine burning polymethyl methacrylate (PMMA) with compressed air has been designed to the point of a preliminary design defnition. PMMA is a transparent material, and this has been utilized to create a transparent-chamber rocket engine where engine processes can be studied with various optical methods withoutinterrupting or disturbing the operation of the engine. The function of hybrid rocket engines, the technological solutions involved in designing working hybrid rocket engines and the constituent parts of hybrid rocket engines have been studied. The nature of the trade-offs between performance and simplicity that occur when designing a rocket engine are also studied, with a focus on maximizing simplicity, safety and minimizing expenses, while still designing an engine that fulfills basic requirements. The results include a design defnition with a preliminary user’s guide, a feasibility study, and a summary of the results of the hybrid rocket performance model that was used to determine appropriate design parameters.

Les moteurs-fusées hybrides combinent les technologies des deux autres catégories de moteurs à propulsionchimique, et associent un combustible et un oxydant stockés respectivement sous phase solide et liquide.Cette architecture offre un certain nombre d’avantages, comme par exemple des coûts plus faibleset une architecture simplifiée par rapport à la propulsion bi-liquide; la possibilité de réaliser de multiplesextinctions et ré-allumages et une bonne impulsion spécifique théorique par rapport à la propulsion solide,et enfin une sécurité de mise en œuvre accrue et un impact environnemental faible vis-à-vis de ces deuxautres modes de propulsion. Comme toutes les chambres de combustion, celles des moteurs hybrides peuvent subir des oscillations de pression sous certaines conditions de fonctionnement. Ces instabilités se traduisent par des fluctuationsde poussée qui peuvent dégrader la structure d’un lanceur ou d’un satellite. Des phénomènes diverspeuvent être à l’origine des fluctuations de pression observées dans les moteurs hybrides.L’objectif de la thèse est de proposer une modélisation des instabilités d’origine hydrodynamique quiapparaissent dans les moteurs hybrides. Une exploitation nouvelle de la base de données disponible àl’ONERA a servi de support pour la modélisation, ainsi que des simulations numériques instationnaires 2Det 3D réalisées à l’aide du code CFD CEDRE. Les instabilités sont provoquées par la formation périodiquede structures tourbillonnaires dans la chambre de combustion, qui génèrent des fluctuations de pressionlors de leur passage dans le col de la tuyère. L’originalité du modèle, basé sur la théorie classique degénération tourbillonnaire dans une cavité, consiste à prendre en compte les variations géométriques dela chambre de combustion au cours des tirs. Ces variations ont un effet sur la vitesse de l’écoulement, surla zone de recirculation dans la post-chambre, ainsi que sur les tourbillons eux-mêmes. Enfin, plusieursnouveaux essais du moteur hybride HYCOM ont été effectués et confrontés au modèle développé dans lecadre de la thèse. / Hybrid rocket motors combine solid and bi-liquid chemical propulsion technologies and associate asolid fuel and a liquid oxidizer in its classical configuration. This architecture offers several advantagesover liquid propulsion such as lower costs and a simplified architecture. The possibility of performingmultiple extinctions and re-ignitions and a good theoretical specific impulse is also an improvement inregard to solid propulsion. Hybrid engines also have improved safety and a lower environmental impactthan other chemical propulsion systems. As in all combustion chambers, hybrid engines suffer from pressure oscillations under specific operating conditions. These instabilities provoke thrust fluctuations that can damage the launcher and payloads.Various phenomena can induce the pressure oscillations observed in hybrid rocket engines.The objective of this thesis is to propose a model of hydrodynamics instabilities that appear in hybridengines. A new exploitation of the database available at ONERA, and unsteady 2D and 3D numericalsimulations were used for the modeling. The instabilities are provoked by the periodic formation ofvortices in the combustion chamber that generate pressure fluctuations when passing through the nozzlethroat. The originality of the model, which is based on the classical theory of vortices generation ina cavity, consists in taking into account the geometrical variations of the combustion chamber duringoperation. These variations have an effect on the flow velocity, on the recirculation area in the postchamberand on the vortices. Finally, several new firing tests of the hybrid engine HYCOM have beenperformed and compared to the model developed in this thesis.