This work uses computational fluid dynamics to study the flowfield around a hypersonic missile with two lateral jets to provide control in place of control surfaces. The jets exhaust an H2-O2 mixture at Mach number of 2.9 with a jet pressure ratio of roughly 10,500. The jets are staggered axially and circumferentially in such a way to produce pitch and yaw. The flowfield of such a jet configuration is characterized at several angles of attack and the corresponding force coefficients and amplification factors are provided. The freestream air and H2-O2 plume is treated as inert for the majority of the calculations. Special cases are treated with finite rate chemical kinetics and compared to the inert flowfield to ascertain the effects that chemical reactions have on the force coefficients. It was found that the flowfield was only slightly altered from the familiar one jet flowfield when the second jet is active. The flow topology and vortex structures tend to shift towards the second jet but the overall structure remains the same. The normal force amplification factors are close to unity over the range of angle of attack due to the thrust being so high with the two jet configuration having a lower amplification factor compared to firing a single jet. Treating the flowfield as chemically reacting did not affect the force values much: the difference being 0.3% for an angle of attack of 0°. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection

"One of the general processes of interest in Pulsed Plasma Thrusters is the ablation of the solid fuel. In general, ablation occurs when a short pulse of applied energy removes a portion of the fuel surface. Although this ablation process is relatively straight-forward in simple materials that sublimate, ablation in Pulsed Plasma Thrusters is significantly more complicated. This is caused by the transient conditions and the complex behavior of Teflon that does not sublimate but rather undergoes both physical and chemical changes prior to leaving the surface. These two effects combine to make Teflon ablation a highly nonlinear function of heat flux, material property variations, changing molecular weight, and phase transformation behavior. To gain greater insight into the ablation process, a one-dimensional ablation model is developed that addresses the more detailed thermal and thermodynamic behavior of Teflon during simulated operation of a Pulsed Plasma Thruster. The mathematical model is based on the work of Clark (1971), which focused on two-phase, one-dimensional Teflon ablation in the context of thermal protection systems. The model is modified for use in simulated PPT operations and implemented numerically using an adaptive non-uniform grid, explicit finite-difference techniques, and a volume fraction method to capture the interface between the crystalline and amorphous Teflon phases. The ablation model is validated against analytical heat transfer and ablation solutions and compared with previous experimental results. The Teflon ablation model is used to analyze several general ablation scenarios in addition to specific PPT conditions to gain greater insight into long-duration thruster firing, post-pulse material ablation, variable heat flux effects, variable material property effects, and the impact of surface re-crystallization on particulate emission. These simulations are considered in the context of prior experimental investigations of Pulsed Plasma Thrusters. The results of these simulations demonstrate the success of the numerical ablation model in predicting experimental trend and suggest potential paths of moderately improving thruster efficiency and operational repeatability in the future. "

This thesis presents the author's contribution to the design and implementation of COOLFluiD, an object oriented software platform for the high performance simulation of multi-physics phenomena on unstructured grids. In this context, the final goal has been to provide a reliable tool for handling high speed aerothermodynamic applications. To this end, we introduce a number of design techniques that have been developed in order to provide the framework with flexibility and reusability, allowing developers to easily integrate new functionalities such as arbitrary mesh-based data structures, numerical algorithms (space discretizations, time stepping schemes, linear system solvers, ...),and physical models. Furthermore, we describe the parallel algorithms that we have implemented in order to efficiently read/write generic computational meshes involving millions of degrees of freedom and partition them in a scalable way: benchmarks on HPC clusters with up to 512 processors show their effective suitability for large scale computing. Several systems of partial differential equations, characterizing flows in conditions of thermal and chemical equilibrium (with fixed and variable elemental fractions)and, particularly, nonequilibrium (multi-temperature models) have been integrated in the framework. In order to simulate such flows, we have developed two state-of-the-art flow solvers: 1- a parallel implicit 2D/3D steady and unsteady cell-centered Finite Volume (FV) solver for arbitrary systems of PDE's on hybrid unstructured meshes; 2- a parallel implicit 2D/3D steady vertex-centered Residual Distribution (RD) solver for arbitrary systems of PDE's on meshes with simplex elements (triangles and tetrahedra). The FV~code has been extended to handle all the available physical models, in regimes ranging from incompressible to hypersonic. As far as the RD code is concerned, the strictly conservative variant of the RD method, denominated CRD, has been applied for the first time in literature to solve high speed viscous flows in thermochemical nonequilibrium, yielding some preliminary outstanding results on a challenging double cone flow simulation. All the developments have been validated on real-life testcases of current interest in the aerospace community. A quantitative comparison with experimental measurements and/or literature has been performed whenever possible.

Heatshield design and analysis has traditionally been a decoupled process, the designer creates the geometry generally without knowledge about how the design variables affect the thermostructural response or how the system will perform under off nominal conditions. Heatshield thermal and structural response analyses are generally performed as separate tasks where the analysts size their respective components and feedback their results to the designer who is left to interpret them. The analysts are generally unable to provide guidance in terms of how the design variables can be modified to meet geometric constraints and not exceed the thermal or structural design specifications. In general, the thermal response analysis of ablative thermal protection systems has traditionally been performed using a one-dimensional finite difference calculation. The structural analyses are generally one, two, or three-dimensional finite element calculations. In this dissertation, the governing differential equations for ablative thermal response are solved in three-dimensions using the finite element method. Darcy' Law is used to model the flow of pyrolysis gas through the ablative material. The three-dimensional governing differential equations for Darcy flow are solved using the finite element method as well. Additionally, the equations for linear elasticity are solved by the finite element method for the thermal stress using temperatures directly from the thermal response calculations. This dissertation also links the analysis of thermal protection systems to their design. The link to design comes from understanding the variation in the thermostructural response over the range of the design variables. Material property sensitivities are performed and an optimum design is determined based on a deterministic analysis minimizing the design specification of bondline temperature subject to appropriate constraints. A Monte Carlo simulation is performed on the optimum design to determine the probability of exceeding the design specifications. The design methodology is demonstrated on the Orion Crew Exploration Vehicle's compression pad design.

Gas turbine engines for aircraft applications are required to meet multiple performance and sizing requirements, subject to constraints established by the best available technology level. The performance requirements and limiting values of constraints that are considered by the cycle analyst conducting an engine cycle design occur at multiple operating conditions. The traditional approach to cycle analysis chooses a single design point with which to perform the on-design analysis. Additional requirements and constraints not transpiring at the design point must be evaluated in off-design analysis and therefore do not influence the cycle design. Such an approach makes it difficult to design the cycle to meet more than a few requirements and limits the number of different aerothermodynamic cycle designs that can reasonably be evaluated. Engine manufacturers have developed computational methods to create aerothermodynamic cycles that meet multiple requirements, but such methods are closely held secrets of their design process. This thesis presents a transparent and publicly available on-design cycle analysis method for gas turbine engines which generates aerothermodynamic cycles that simultaneously meet performance requirements and constraints at numerous design points. Such a method provides the cycle analyst the means to control all aspects of the aerothermodynamic cycle and provides the ability to parametrically create candidate engine cycles in greater numbers to comprehensively populate the cycle design space from which a "best" engine can be selected. This thesis develops the multi-design point on-design cycle analysis method labeled simultaneous MDP. The method is divided into three different phases resulting in an 11 step process to generate a cycle design space for a particular application. Through implementation of simultaneous MDP, a comprehensive cycle design space can be created quickly for the most complex of cycle design problems. Furthermore, the process documents the creation of each candidate engine providing transparency as to how each engine cycle was designed to meet all of the requirements. The simultaneous MDP method is demonstrated in this thesis on a high bypass ratio, separate flow turbofan with up to 25 requirements and constraints and 9 design points derived from a notional 300 passenger aircraft.

Mémoire (M.Sc.A.)--Université du Québec à Chicoutimi, 1987. / Document électronique également accessible en format PDF. CaQCU

Thesis (M.Sc.) - University of Queensland, 2004. / Includes bibliography.

Dévoiler les mystères du système solaire pour comprendre les mécanismes de la formation de la Terre, pour rechercher des signes de vie ou pour développer des colonies sur d’autres planètes, dépend de notre capacité à repousser les limites de l'ingénierie et de la science. Pour cela, il est important de développer des technologies de pointe pour permettre aux véhicules spatiaux de survivre la phase d'entrée ou de rentrée atmosphérique. Lors de l’entrée ou de la rentrée, l’engin spatial peut être exposé à flux radiatifs intenses qui ne peuvent pas encore être prédits avec précision, imposant ainsi des marges de sécurité sur la conception des systèmes de protection thermique. Ces incertitudes augmentent lorsque le bouclier thermique est constitué d'un matériau ablatif car sa dégradation introduit de nouvelles espèces chimiques réagissant avec le plasma produit devant le véhicule, ce qui affecte le rayonnement. Le but de cette thèse est d’étudier les flux de chaleur radiatifs sur un véhicule de rentrée de petite taille en présence d’un bouclier ablatif (Thermal Protection System, ou TPS), en utilisant des simulations numériques et des expériences pour développer un instrument de vol qui sera embarqué à bord du CubeSat QARMAN.Une évaluation de la trajectoire de rentrée du véhicule QARMAN (masse : 5 kg) a été réalisée en utilisant un code maison à 6 degrés de liberté. Un ensemble de simulations Monte Carlo ont permis de quantifier les incertitudes et ont montré un maximum de ± 15% écart par rapport à la trajectoire nominale. Les spectres sans ablation ont alors été déterminés en utilisant une approche découplée avec deux codes : Stagline (VKI) et SPECAIR (EM2C, CentraleSupélec). Ces simulations ont été effectuées pour la trajectoire nominale ainsi que pour la gamme des incertitudes. Elles ont permis de mettre en évidence un comportement non-linéaire des caractéristiques spectrales par rapport aux valeurs nominales, avec une augmentation drastique vers la fin de la mission.Les effets de l'ablation ont été étudiés avec une nouvelle technique de mesure développée au cours de cette thèse. Basée sur deux sondes de mesure de rayonnement, l’une refroidie et l’autre recouverte d’un matériau ablatif, cette méthode permet de quantifier l'émission et l'absorption induite par tout type de TPS ayant des interactions gaz-surface avec l'écoulement, dans l’hypothèse que les raies d’émission et d’absorption des espèces ablatives ne soient pas superposées. La méthode a été validée sur un échantillon de graphite TPS. Elle a ensuite été appliquée à la prédiction du rayonnement attendu lors de la mission QARMAN (Cork P50 TPS). Cette étude a également permis de sélectionner un spectromètre d’émission adapté à la mission QARMAN et aux objectifs de la thèse (plage de 350 à 800 nm pour une masse de 68 g).Un instrument de mesure de rayonnement standard a été testé et les limites de cet appareil ont été établies. Deux nouvelles technologies ont été développées et la charge utile (spectromètre d’émission INES) a été construite et intégrée au véhicule QARMAN. Un étalonnage spectral et thermique dédié a également été développé pour maximiser la qualité du retour scientifique en prenant en compte les variations de température dans la baie de charge utile de QARMAN.L’instrument proposé est, à ce jour, la seule charge utile non intrusive capable d’effectuer des mesures radiatives sans limitations liées à la contamination par les poussières et gaz d'ablation. L’instrument peut aussi fournir des mesures de la récession, de la sublimation et du gonflement du TPS avec une précision d'au moins 0,2 mm. Le fonctionnement de l'appareil a été démontré pour une grande variété de conditions de test, y compris différents profils d'enthalpie, mélanges de gaz et matériaux de TPS. / Unveiling the mysteries of the solar system to understand the mechanisms of Earth’s formation, to search for signs of life, or to develop settlements on other planets, depends on our abilities to push the limits of engineering and science. One of the key aspects of space exploration is the development of advanced technologies to sustain the entry/reentry phase. During entry or reentry, the spacecraft may be exposed to intense radiative fluxes that cannot be accurately predicted yet, thus imposing high safety margins on the design of thermal protection systems. These uncertainties rise when the heat shield is made of an ablative material as its degradation introduces new chemical species reacting with the flow affecting radiation processes. The goal of this thesis is to study the radiative heat fluxes onto a small size reentry vehicle in the presence of an ablative TPS, using numerical simulations and experiments to develop a flight instrument that will be carried onboard the QARMAN CubeSat.An assessment of the reentry trajectory of the 5-kg QARMAN vehicle was performed using a custom 6-degree of freedom code. An extensive set of Monte Carlo simulations allowed to quantify uncertainties and showed a maximum of ±15% deviation from the nominal trajectory. The spectra without ablation were then computed using a decoupled approach with two codes: Stagline (VKI) and SPECAIR (EM2C, CentraleSupélec). These simulations were performed for the nominal trajectory as well as for the range of uncertainties. They showed a nonlinear behavior of the spectral features deviations from nominal with a drastic increase toward the end of the mission.The effects of ablation were studied with a new measurement technique developed during this thesis. Based on two radiation measurement probes, one cooled and the other with an ablative surface, it allows to quantify the emission and absorption induced by any kind of TPS having gas-surface interactions with the flow, provided that the radiative emission or absorption features of the ablative species do not fully overlap. The method was validated on a graphite TPS sample. It was then applied to determine the radiation expected during the QARMAN mission (Cork P50 TPS). This study also allowed to select an emission spectrometer (350-800 nm range for a 68-g mass).A standard radiation instrument was tested and the limits of this device shown. On those lessons learned, two new technologies were developed and an emission spectrometer payload (INES) was built and integrated into the QARMAN reentry CubeSat. A dedicated spectral and thermal calibration was also developed to maximize the quality of the scientific return by tackling the non-standard internal temperature variations of QARMAN’s payload bay.Relying on two inventions made during this study, the apparatus is at the time of writing, the only non-intrusive payload capable of making radiative measurements without limitations due to ablation dust contamination. The instrument can also provide measurements of recession, sublimation and swelling of the TPS with a precision of at least 0.2 mm. Operation of the apparatus was demonstrated for a wide variety of test conditions, including different enthalpy profiles, gas mixtures and TPS materials.

In the McMurdo Dry Valleys, Victoria Land, East Antarctica, melting of glacial ice is the primary source of water to streams, lakes, and associated ecosystems. To better understand meltwater production, three hypotheses are tested: 1) that small changes in the surface energy balance on these glaciers will result in large changes in melt, 2) that subsurface melt does not contribute significantly to runoff, and 3) that melt from 25-m high terminal cliffs is the dominant source of baseflow during cold periods. These hypotheses were investigated using a surface energy balance model applied to the glaciers of Taylor Valley using 14 years of meteorological data and calibrated to ablation measurements. Inclusion of transmission of solar radiation into the ice through a source term in a one-dimensional heat transfer equation was necessary to accurately model summer ablation and ice temperatures. Results showed good correspondence between calculated and measured ablation and ice temperatures over the 14 years using both daily and hourly time steps, but an hourly time step allowed resolution of short duration melt events and melt within the upper 15 cm of the ice. Resolution of short duration melt events was not important for properly resolving seasonal ablation totals. Across the smooth surfaces of the glaciers, ablation was dominated by sublimation and melting was rare. Above freezing air temperatures did not necessarily result in melt, and low wind speed was important for melt initiation. According to the model, subsurface melt between 5 and 15 cm depth was extensive and lasted for up to six weeks in some summers. The model was better able to predict ablation if some subsurface melt was assumed to drain, lowering ice density, consistent with observations of a low density weathering crust that forms over the course of the summer on Dry Valley glaciers. In extreme summers, drainage of subsurface melt may have contributed up to half of the observed surface lowering through reduction of ice density and possibly through collapse of highly weathered ice. When applied spatially, the model successfully predicted proglacial streamflow at seasonal and daily time scales. This was despite omitting a routing scheme, and instead assuming that all melt generated exits the glacier on the same day, suggesting refreezing is not substantial. Including subsurface melt as runoff improved predictions of runoff volume and timing, particularly for the recession of large flood peaks. Because overland flow was rarely observed over much of these glaciers, these model results suggest that runoff may be predominantly transported beneath the surface in a partially melted permeable layer of weathered ice. According to the model, topographic basins, particularly the low albedo basin floors, played a prominent role in runoff production. Smooth glacier surfaces exhibited low melt rates, but were important during high melt conditions due to their large surface area. Estimated runoff contributions from cliffs and cryoconite holes was somewhat smaller than suggested in previous studies. Spatial and temporal variability in albedo due to snow and debris played a dominant role in flow variations between streams and seasons. In general, the model supported the existing assumption that snowmelt is insignificant, but in extreme melt years snowmelt in the accumulation area may contribute significantly to runoff in some locations.

This thesis examines the modeling of the shock-layer radiative heating associated with hypersonic vehicles entering the atmospheres of Earth and Titan. For Earth entry, flight conditions characteristic of lunar-return are considered, while for Titan entry, the Huygens probe trajectory is considered. For both cases, the stagnation region flowfield is modeled using a two-temperature chemical nonequilibrium viscous shock layer (VSL) approach. This model is shown to provide results that are in agreement with the more computationally expensive Navier-Stokes solutions. A new radiation model is developed that applies the most up-to-date atomic and molecular data for both the spectrum and non-Boltzmann modeling. This model includes a new set of atomic-lines, which are shown to provide a significant increase in the radiation (relative to previous models) resulting from the 1 - 2 eV spectral range. A new set of electronic-impact excitation rates was compiled for the non-Boltzmann modeling of the atomic and molecular electronic states. Based on these new rates, a novel approach of curve-fitting the non-Boltzmann population of the radiating atomic and molecular states was developed. This new approach provides a simple and accurate method for calculating the atomic and molecular non-Boltzmann populations. The newly-developed nonequilibrium VSL flowfield and nonequilibrium radiation models were applied to the Fire II and Apollo 4 cases, and the resulting radiation predictions were compared with the flight data. For the Fire II case, the present radiation-coupled flowfield model provides intensity values at the wall that predicted the flight data better than any other previous study, on average, throughout the trajectory for the both the 0.2 - 6.0 eV and 2.2 - 4.1 eV spectral ranges. The present results over-predicted the calorimeter measurements of total heat flux over most of the trajectory. This was shown to possibly be a result of the super-catalytic assumption for the wall boundary condition, which caused the predicted convective heating to be too high. For the Apollo 4 case, over most of the trajectory the present model over-predicted the flight data for the wall radiative intensity values between 0.2 - 6.2 eV. For the analysis of Huygens entry into Titan, the focus of the radiation model was the CN violet band. An efficient and accurate method of modeling the radiation from this band system was developed based on a simple modification to the smeared rotational band (SRB) model. This modified approach, labeled herein as SRBC, was compared with a detailed line-by-line (LBL) calculation and shown to compare within 5% in all cases. The SRBC method requires many orders-of-magnitude less computational time than the LBL method, which makes it ideal for coupling to the flowfield. The non-Boltzmann modeling of the CN electronic states, which govern the radiation for Huygens entry, is discussed and applied. The radiation prediction resulting from the non-Boltzmann model is up to 70% lower than the Boltzmann result. A new method for treating the escape factor in detail, rather than assuming a value equal to one, was developed. This treatment is shown to increase the radiation from the non-Boltzmann model by about 10%. / Ph. D.