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Progress in conventional rocket engine technologies, based on constant pressure combustion, has plateaued in the past few decades. Rotating detonation engines (RDEs) are of particular interest to the rocket propulsion community as pressure gain combustion may provide improvements to specific impulse relevant to booster applications. Despite recent significant investment in RDE technologies, little research has been conducted to date into the effect of nozzle design on rocket application RDEs. Proper nozzle design is critical to capturing the thrust potential of the transient pressure ratios produced by the thrust chamber. A computational fluid dynamics study was conducted based on hotfire conditions tested in the Purdue V1.3 RDE campaign. Three geometries were investigated: nozzleless/blunt body, internal-external expansion (IE-) aerospike, and flared aerospike. The computational study found the RDE's dynamic exhaust plume enhances the ejection physics beyond that of a typical high pressure device. For the nozzleless geometry, the base pressure was drawn down below constant pressure estimates, increasing the base drag on the engine. For the aerospike geometries, the occurrance of flow separation on the plug was delayed, which has ramifications on nozzle design for operation at a range of pressure altitudes. The flared aerospike design, which has the ability to achieve much higher area ratios, was shown to have potential performance benefits over the limited IE-aerospike geometry. A new test campaign with the Purdue RDE V1.4 was designed with instrumentation to capture static pressures on the nozzleless and aerospike surfaces. These results were used to validate the results from the computational study. The computational and experimental studies were used to identify new flow physics associated with a rocket RDE important to future nozzle design work. Future computational work is necessary to explore the effect of different parameters on the nozzle performance. More testing, including with an altitude simulation chamber, would help quantify the possible benefit of new aerospike nozzle designs, including the flared aerospike geometry.

Dans le but d’améliorer le rendement des propulseurs aérospatiaux, on s’intéresse à l’utilisation de ladétonation dans le cycle moteur. Cette thèse porte sur le développement et l’utilisation d’un codepour la compréhension du fonctionnement d’un moteur à détonation continue (CDWE). Le 1erchapitre place le cadre de l’étude, et positionne le CDWE par rapport à différents concepts demoteurs à détonation. Un état des lieux des simulations numériques concernant le fonctionnementd’un CDWE est établi afin de justifier l’approche numérique à utiliser. Cette approche numérique estdétaillée dans le 2e chapitre. Les équations d’Euler, les modèles thermochimiques, ainsi que lesschémas cinétiques utilisés dans cette étude y sont présentés. Le 3e chapitre décrit les méthodesnumériques implémentées dans le code. Le schéma WENO d’ordre 5 est utilisé pour l’évaluation desflux numériques. L’avancement temporel est assuré par le schéma semi-implicite d’ordre 2 ASIRK2Cou explicite d’ordre 3 RK3. Le 4e chapitre est consacré à la technique de raffinement adaptatif demaillage (AMR) et à la bibliothèque choisie. Le code est testé dans le 5e chapitre sur différents cas etappliqué à la simulation d’une onde de détonation afin de préparer les simulations présentées dans ledernier chapitre. Le 6e chapitre présente les résultats des simulations d’un CDWE. La structure 2Dd’une onde de détonation continue est présentée et comparée avec la structure 3D. L’influence durayon de courbure du canal et l’effet d’une injection par une fente sur la structure de l’écoulementsont étudiés. / In order to improve the performance of aerospace propulsion systems, it is interesting to use detonation in the engine cycle. This thesis focuses on the development and use of a code for understanding the operation of a continuous detonation wave engine (CDWE). The first chapter establishes the framework of the study and compares the CDWE with different concepts of detonation engines. An overview of numerical simulations concerning the operation of a CDWE is made to justify the numerical approach to use. This numerical approach is detailed in the second chapter. The Euler equations, thermochemical models and kinetic mechanisms used in this study are presented. The third chapter describes the numerical methods implemented in the code. The 5th order WENO scheme is used for the evaluation of numerical fluxes. The time-stepping is provided by the 2nd order semi-implicit ASIRK2C scheme or the 3rd order explicit RK3 scheme. The fourth chapter describes the technique of adaptive mesh refinement (AMR) and the selected library. The code is tested in the fifth chapter on different cases and applied to the simulation of a detonation wave in order to prepare the simulations presented in the last chapter. The sixth chapter presents the results of simulations of a CDWE. The 2D structure of a continuous detonation wave is presented and compared with the 3D structure. The influence of the radius of the curvature of the duct and the effect of a slot injection on the structure of the flowfield are discussed.

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<p>  The wave dynamics within a rotating detonation engine were investigated using a combustor where the fuel injector was varied continuously relative to the oxidizer throat. Both natural gas and a hydrocarbon fuel blend containing the major components of a "cracked" kerosene fuel were characterized using high speed imaging, pressure sensors, and photomultiplier tubes. Major detonation features were visualized with high-speed cameras through a 360 optical outerbody. The detonation region, oblique shock, contact surface where fresh reactants mixed with products of a previous wave, and burning above the fuel injectors in a stratified zone beneath the detonation wave were studied as fuel conditions and fuel injector position were changed. As the inner body of the engine was translated away from the oxidizer throat, or started at a position far from the oxidizer throat, the combustor was not able to support coherent detonation behavior. At these points, the region of highest heat release remained close to the fuel injectors, and there was very little heat release processed behind the front edge of the wave compared to the level of deflagrative combustion occurring inside the chamber. The surrogate hydrocarbon blend is more representative of a composition that high speed vehicles would use, so the operability limits of the fuel and the fuel with nitrogen dilution were characterized using a metal and an optical outerbody on the combustor. With a larger amount of ethylene in the fuel composition compared to the amount of methane, the chamber tended towards slower waves and higher wave modes, and the combustor was able to sustain a coherent detonative mode with up to 40% nitrogen. When all chosen fuel blend components were present in the fuel except ethane, the combustion kinetics of the fuel was slowed significantly, and there was a measured decrease in thrust. No fuel tested was able to support coherent detonative modes with 50% nitrogen in the oxidizer.  </p>

Detonation cycles are identified as an efficient alternative to the Brayton cycles used in power and propulsion applications. Rotating Detonation Engine (RDE) operating on a detonation cycle works by compressing the working fluid across a detonation wave, thereby reducing the number of compressor stages required in the thermodynamic cycle. Numerical analyses of RDEs are flexible in understanding the flow field within the RDE, however, three-dimensional analyses are expensive due to the differences in time-scale required to resolve the combustion process and flow-field. The alternate two-dimensional analyses are generally modeled with perfectly premixed fuel injection and do not capture the effects of improper mixing arising due to discrete injection of fuel and oxidizer into the chamber. To model realistic injection in a 2-D analysis, the current work uses an approach in which, a Probability Density Function (PDF) of the fuel mass fraction at the chamber inlet is extracted from a 3-D, cold-flow simulation and is used as an inlet boundary condition for fuel mass fraction in the 2-D analysis. The 2-D simulation requires only 0.4% of the CPU hours for one revolution of the detonation compared to an equivalent 3-D simulation. Using this method, a perfectly premixed RDE is comparing with a non-premixed case. The performance is found to vary between the two cases. The mean detonation velocities, time-averaged static pressure profiles are found to be similar between the two cases, while the local detonation velocities and peak pressure values vary in the non-premixed case due to local pockets fuel rich/lean mixtures. The mean detonation cell sizes are similar, but the distribution in the non-premixed case is closer due to stronger shock structures. An analytical method is used to check the effects of fuel-product stratification and heat loss from the RDE and these effects adversely affect the local detonation velocity. Overall, this method of modeling captures the complex physics in an RDE with the advantage of reduced computational cost and therefore can be used for design and diagnostic purposes. / Master of Science / The conventional Brayton cycle used in power and propulsion applications is highly optimized, at cycle and component levels. In pursuit of higher thermodynamic efficiency, detonation cycles are identified as an efficient alternative and gained increased attention in the scientific community. In a Rotating Detonation Engine (RDE), which is based on the detonation cycle, the compression of gases occurs across a shock wave. This method of achieving high compression ratios reduces the number of compressor stages required for operation. In an RDE (where combustion occurs between two coaxial cylinders), the fuel and oxidizer are injected axially into the combustion chamber where the detonation is initiated. The resultant detonation wave spins continuously in the azimuthal direction, consuming fresh fuel mixture. The combustion products expand and exhaust axially providing thrust/mechanical energy when coupled with a turbine. Numerical analyses of RDEs are flexible over experimental analysis, in terms of understanding the flow physics and the physical/chemical processes occurring within the engine. However, three-dimensional numerical analyses are computationally expansive, and therefore demanding an equivalent, efficient two-dimensional analysis. In most RDEs, fuel and oxidizer are injected from separate plenums into the chamber. This type of injection leads to inhomogeneity of the fuel-air mixture within the RDE which adversely affects the performance of the engine. The current study uses a novel method to effectively capture these physics in a 2-D numerical analysis. Furthermore, the performance of the combustor is compared between perfectly premixed injection and discrete, non-premixed injection. The method used in this work can be used for any injector design and is a powerful/efficient way to numerically analyze a Rotating Detonation Engine.

Approved for public release, distribution is unlimited / Operational characteristics of a valveless pulse detonation engine system were characterized by experimental measurements of thrust, fuel flow, and internal gas dynamics. The multi-cycle detonation experiments were performed on an axis-symmetric engine geometry operating on an ethylene/air mixtures. The detonation diffraction process from a small 'initiator' combustor to a larger diameter main combustor in a continuous airflow configuration was evaluated during multi-cycle operation of a pulse detonation engine and was found to be very successful at initiating combustion of the secondary fuel/air mixture at high frequencies. The configuration was used to demonstrate the benefit of generating an overdriven detonation condition near the diffraction plane for enhanced transmission of the larger combustor. Results have shown that the addition of optical sensors, such as tunable diode lasers, to provide fuel profile data are invaluable for providing high fidelity performance results. The performance results demonstrated the ability of the valveless pulse detonation engine to run at efficiencies similar to valved pulse detonation engine geometries and may be a low cost alternative to conventional air-breathing propulsion systems. / Funded By: N00014OWR20226. / Lieutenant, United States Navy