Impact of Vibrational Nonequilibrium on the Simulation and Modeling of Dual-Mode Scramjets

The practical realization of supersonic flight relies on the development of a robust propulsion system. These air-breathing scramjet engines process fuel and high-speed air to generate propulsive thrust. Unlike conventional jet engines, scramjets achieve efficient thrust by compressing air through a system of shocks. As a result, the reliability of the engine is highly sensitive to the stability of these shock structures. Physically, these shocks are located in an engine component called the isolator. The shock structures are spatially distributed leading to a region of pressure increase, which is termed the pseudoshock. As vehicle operating conditions change, the length of the pseudoshock will change, reflecting changes to inflow conditions and operation of downstream combustor component. The overall objective of this thesis is to understand the complex flow inside these isolators. Of particular focus is the role of molecular processes in the development of the shocks. At high enthalpy conditions, the internal motions of the molecules are moved out of equilibrium due to compression shocks, which affects not only the thermophysical properties of air, but more critically the fuel-air mixing and chemical reactions. While there exists a vast body of literature on scramjet isolators, almost all of these works focus on low enthalpy conditions due to laboratory experimental limitations, or simply rely on equilibrium thermodynamics. In this work, the effect of nonequilibrium on isolator and scramjet combustors at high-altitude high-enthalpy flight conditions was studied using high-fidelity numerical simulations. Detailed models for the description of molecular nonequilibrium, in the form of multi-temperature model was used. Computational chemistry derived reaction rates were used to describe the combustion processes. These studies revealed the following key features: a) nonequilibrium of vibrational states greatly increases pseudoshock length, b) contrary to external hypersonics, nonequilibrium accelerates chemical reactions in the combustor, reducing the distance from fuel injection to flame ignition and stabilization, c) while multi-temperature models are adequate to express such nonequilibrium effects, more detailed state-specific representations clearly demonstrate that molecular populations do not follow the Boltzmann relation even at subsonic but compressible flow conditions. In a related study but using equilibrium thermal conditions, it was shown that the isolator shock structure can develop a resonance to inflow perturbations that can vastly increase the pseudoshock spatial oscillations. These results verify that isolator flow is a complex nonlinear process and clearly demonstrate that the design of scramjets needs to include the effect of thermal nonequilibrium. To begin addressing this process, reduced-order models in the form of a flux-conserved one-dimensional formulation for estimating pseudoshock length was developed for thermal equilibrium conditions.PHDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/143909/1/rfievet_2.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/143909/2/rfievet_1.pd

Integrable Deformations of the XXZ Spin Chain

We consider integrable deformations of the XXZ spin chain for periodic and open boundary conditions. In particular, we classify all long-range deformations and study their impact on the spectrum. As compared to the XXX case, we have the z-spin at our disposal, which induces two additional deformations: the short-range magnetic twist and a new long-range momentum-dependent twist.Comment: 24 pages, v2: minor change

An overview of the functioning of Sitobion avenea populations at three spatial scales in France

In this paper we give 3 snapshots of our recent work on S. avenae at field, landscape and country scales. From April to June wheat fields are continuously colonized by winged S. avenae and previously established colonies experience high extinction rates. This leads to changes in spatial distribution of aggregates of aphids and to a progressive spatial homogenisation of the populations in fields, and highlights the role of spring immigrants in the field dynamics of S. avenae. In the surrounding landscape, the S. avenae populations on cultivated cereals (wheat, maize, barley) do not differ genetically. Conversely, aphids from weed margins and pastures (mostly on Poeae) clearly differ from those on cereals, indicating a low level of gene flow between the ‘uncultivated’ (mostly perennial) and cultivated system (annual). Consequently weeds and pasture grasses are probably poor sources of S. avenae for further infestation of cereal fields. The role of surrounding crops and weeds as a source of aphids infesting wheat was assessed by stable isotopic ratios and population genetic tools. In autumn, up to the beginning of October, most S. avenae landing on wheat originated from maize and after this from cereal volunteers. In spring the influx from surrounding cereal volunteers varied between years, but uncultivated Poeae played a minor role. At country scale on cereals, clonal reproduction and parthenogenetic overwintering prevails everywhere in France, but there is a trend toward increasing sexuality northward. The weak genetic differentiation of the regional populations on cereals and the presence of many identical genotypes in most of the regions sampled confirm the high dispersal ability of S. avenae. The high occurrence of widespread genotypes in multiple copies, belonging to the same genetic pool, which persist over several years in France and other countries in Europe, indicates a homogenising effect of selection by millions of hectares of cereal

L’ambivalence de l’honneur dans l’Angleterre de la fin du Moyen Âge : une force compétitive ou modératrice ?

Cet article met en lumière le lien complexe entre honneur et violence dans le contexte de l’Angleterre de la fin du Moyen Âge. Il montre que si la culture de l’honneur, en particulier celle du monde aristocratique, pouvait légitimer et exacerber dans une certaine mesure le recours à la violence, elle pouvait également la freiner. Dans un contexte où la loyauté personnelle constituait la valeur primordiale dans l’éthique de comportement des nobles et gentlemen, personne ne pouvait laisser passer le moindre affront affectant sa valeur sociale, mais personne ne pouvait aller au-delà d’un certain seuil dans l’usage de la force sous peine d’affecter sa réputation. Un tel homme représentait en effet une menace potentielle pour tous ses alliés présents et futurs.This article highlights the complex relationship between honour and violence in late medieval England. It shows that if the culture of honour, especially in the aristocratic world, could legitimize and exacerbate resort to violence, it could also be a moderating force. In a context where personal loyalty was paramount value in the value system of the landowners, no one could leave unpunished offense, but no one could go beyond a certain threshold in the use of force, since such a behaviour could tarnish his reputation. This kind of man indeed represented a potential threat to its allies present and future