Contribution à la modélisation de la combustion non-prémélangée turbulente dans les écoulements rapides

This work is dedicated to the study of non-premixed turbulent combustion in high-speed and two-phase flows. From a modeling point of view, it is of primary importance to take into consideration the coupling that exists for those configurations between the effects of compressibility, turbulent mixing, and chemistry. In supersonic reactive flows, the conversion of a portion of kinetic energy into heat or enthalpy is to influence significantly the early developments of chemical reactions and thus, lead to an increase of the chemical conversion of reactants into products of reaction, and contribute to the stabilisation process of the flame. Moreover, the value of the time scale representative of the turbulent mixing and the value of the chemical time scale are expected to be comparable, so that the fast chemistry assumption can be questionned. In this study, an approach based on the estimation of the joint PDF of two scalars, the first quantity describing the local composition of the mixture, and the second characterizing the progress of the reaction, is retained. The model relies on the sudden chemistry assumption, thus permitting a strong but clearly stated functional dependence between the two scalars introduced. As a result, the joint PDF of the two scalars can be simply expressed from the knowledge of the marginal mixture fraction PDF. This approach is extended to the description of supersonic combustion by considering the variations of total enthalpy. Finally, the fluctuations of composition induced by the evaporation of one of the two reactants are also taken into account. The full model is implemented into Computational Fluid Dynamics code, solving the three-dimensional compressible and reactive Navier-Stokes equations. In this work, the representation of the mixing layers and discontinuities is improved thanks to the use of a mesh adaptation strategy, coupled to the CFD code. The numerical and modeling approach is then validated against various configurations : coflowing H2-vitiated air supersonic jets, highly underexpanded jets, and a Scramjet-like combustion chamber. Finally, the modeling framework is also extended to the simulation of the Mascotte configuration (ONERA) with sub-critical liquid oxygen. The results obtained on those configurations are in satisfactory agreement with both underlying physics and experimental data when available, and the numerical code and modeling strategy are shown to be viable tools for further developments and investigations within U-RANS or LES approaches, and for its extension to more extreme conditions (super-critical oxygen).Le travail présenté dans ce mémoire est consacré à la combustion turbulente non-prémélangée dans des écoulements rapides, et éventuellement diphasiques. Pour ce type de conditions, il devient nécessaire, du point de vue de la modélisation, de tenir compte du couplage existant entre les effets de compressibilité, les processus de mélange turbulent et la cinétique chimique. Dans ces écoulements, la conversion de tout ou partie de l'énergie cinétique de l'écoulement sous forme d'enthalpie sensible va influencer le développement des réactions chimiques et peut contribuer notablement à la conversion des réactifs en produits de combustion ainsi qu'à la stabilisation des flammes. De plus, les échelles de temps caractéristiques du mélange turbulent et de la cinétique chimique sont susceptibles d'être du même ordre de grandeur et l'hypothèse de chimie infiniment rapide n'est pas toujours applicable. Dans cette étude, une approche basée sur l'évaluation de la PDF jointe de deux quantités scalaires est retenue : la première variable permet de quantifier la richesse locale du mélange, la seconde caractérise l'écart à l'état d'équilibre chimique. Une hypothèse de "chimie brusque" permet d'introduire une dépendance explicite entre ces deux variables pour s'en tenir à la seule détermination de la PDF de la variable de mélange. Cette approche est étendue au cas de la combustion supersonique en considérant de surcroît les variations d'enthalpie totale. Enfin, les fuctuations de composition induites par la vaporisation d'un des deux réactifs sont elles-aussi prises en compte. Le modèle complet est implanté dans un code de calcul Navier-Stokes tridimensionnel compressible et réactif. Dans le cadre de cette étude, la résolution est couplée à une méthode d'adaptation de maillage qui permet d'améliorer significativement la représentation des zones de mélange et des fortes discontinuités. L'approche proposée est ensuite validée en s'appuyant sur différentes géométries : jets co-courants supersoniques H2-air vicié, jets fortement sous-détendus, chambre de combustion de type Scramjet. Enfin, le modèle est aussi employé pour effectuer un calcul de la configuration Mascotte de l'Onera dans un cas sous-critique. Les simulations numériques correspondantes conduisent à des résultats encourageants et ouvrent de nombreuses perspectives aussi bien quant à l'utilisation du modèle le cadre d'approches U-RANS ou LES que vis-à-vis de son extension à des conditions de combustion extrêmes (super-critiques)

Contribution à la modélisation de la combustion non prémélangée turbulente dans les écoulements rapides

Le travail présenté dans ce mémoire est consacré à la combustion turbulente non-prémélangée dans des écoulements rapides, et éventuellement diphasiques. Pour ce type de conditions, il devient nécessaire, du point de vue de la modélisation, de tenir compte du couplage existant entre les effets de compressibilité, les processus de mélange turbulent et la cinétique chimique. Dans ces écoulements, la conversion de tout ou partie de l'énergie cinétique de l'écoulement sous forme d'enthalpie sensible va influencer le développement des réactions chimiques et peut contribuer notablement à la conversion des réactifs en produits de combustion ainsi qu'à la stabilisation des flammes. De plus, les échelles de temps caractéristiques du mélange turbulent et de la cinétique chimique sont susceptibles d'être du même ordre de grandeur et l' ypothèse de chimie infiniment rapide n'est pas toujours applicable. Dans cette étude, une approche basée sur l'évaluation de la PDF jointe de deux quantités scalaires est retenue : la première variable permet de quantifier la richesse locale du mélange, la seconde caractérise l'écart à l'état d'équilibre chimique. Une hypothèse de "chimie brusque" permet d'introduire une dépendance explicite entre ces deux variables pour s'en tenir à la seule détermination de la PDF de la variable de mélange. Cette approche est étendue au cas de la combustion supersonique en considérant de surcroît les variations d'enthalpie totale. Enfin, les fluctuations de composition induites par la vaporisation d'un des deux réactifs sont elles-aussi prises en compte. Le modèle complet est implanté dans un code de calcul Navier-Stokes tridimensionnel compressible et réactif. Dans le cadre de cette étude, la résolution est couplée à une méthode d'adaptation de maillage qui permet d'améliorer significativement la représentation des zones de mélange et des fortes discontinuités. L'approche proposée est ensuite validée en s'appuyant sur différentes géométries: jets co-courants supersoniques H2-air vicié, jets fortement sous-détendus, chambre de combustion de type Scramjet. Enfin, le modèle est aussi employé pour effectuer un calcul de la configuration Mascotte de l'Onera dans un cas sous-critique. Les simulations numériques correspondantes conduisent à des résultats encourageants et ouvrent de nombreuses perspectives aussi bien quant à l'utilisation du modèle le cadre d'approches U-RANS ou LES que vis-à-vis de son extension à des conditions de combustion extrêmes (super-critiques).This work is dedicated to the study of non-premixed turbulent combustion in high-speed and two-phase flows. From a modeling point of view, it is of primary importance to take into consideration the coupling that exists for those con gurations between the effects of compressibility, turbulent mixing, and chemistry. In supersonic reactive flows, the conversion of a portion of kinetic energy into heat or enthalpy is to influence significantly the early developments of chemical reactions and thus, lead to an increase of the chemical conversion of reactants into products of reaction, and contribute to the stabilisation process of the flame. Moreover, the value of the time scale representative of the turbulent mixing and the value of the chemical time scale are expected to be comparable, so that the fast chemistry assumption can be questionned. In this study, an approach based on the estimation of the joint PDF of two scalars, the first quantity describing the local composition of the mixture, and the second characterizing the progress of the reaction, is retained. The model relies on the sudden chemistry assumption, thus permitting a strong but clearly stated functional dependence between the two scalars introduced. As a result, the joint PDF of the two scalars can be simply expressed from the knowledge of the marginal mixture fraction PDF. This approach is extended to the description of supersonic combustion by considering the variations of total enthalpy. Finally, the fluctuations of composition induced by the evaporation of one of the two reactants are also taken into account. The full model is implemented into Computational Fluid Dynamics code, solving the three-dimensional compressible and reactive Navier-Stokes equations. In this work, the representation of the mixing layers and discontinuities is improved thanks to the use of a mesh adaptation strategy, coupled to the CFD code. The numerical and modeling approach is then validated against various configurations : coflowing H2-vitiated air supersonic jets, highly underexpanded jets, and a Scramjet-like combustion chamber. Finally, the modeling framework is also extended to the simulation of the Mascotte configuration (ONERA) with sub-critical liquid oxygen. The results obtained on those configurations are in satisfactory agreement with both underlying physics and experimental data when available, and the numerical code and modeling strategy are shown to be viable tools for further developments and investigations within U-RANS or LES approaches, and for its extension to more extreme conditions (super-critical oxygen).POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Testicular tumours discovered during infertility workup are predominantly benign and could initially be managed by sparing surgery

International audienceTo evaluate the pathological features and recurrence of incidental testis tumours treated by partial orchiectomy in a population of infertile men

Characteristics of the musculoskeletal symptoms observed among survivors of Ebola virus disease in the Postebogui cohort in Guinea

Objective.: Previous studies show that arthralgia is the most common symptom experienced by Ebola virus disease (EVD) survivors. Nevertheless, specific analyses of rheumatological sequelea are still lacking. Methods.: The Postebogui study is a prospective, multicentre cohort aiming to evaluate the long-term outcomes of EVD survivors infected during the 2014-15 outbreak in Guinea. Of the 216 participants enrolled in the study in October 2015, 44 patients with arthralgia/myalgia underwent a physical examination by a rheumatologist (the Eborheum cohort). Data were collected using a standardized questionnaire. Results.: In the Eborheum cohort, 61% of patients were female, the median age was 31.1 years, and the median time from Ebola Treatment Centre discharge was 8.8 months. Pain manifestation started after Ebola infection in all but one patient. Patients had mainly both mechanical and inflammatory pain (45%) and low back pain (77%). All patients reported pain in at least one peripheral joint. Pain in large joints was more frequently reported than in small joints (73 vs 41%). Oligo- and polyarticular presentations were similar, with symmetrical pain distribution. Furthermore, 36 patients had at least one painful 18-tender point count, most of whom reported extensive pain (n = 19) and symmetrical distribution (91%). Diagnoses were mainly non-specific musculoskeletal disorders (59%) and mechanical back pain (52%). No polyarthritis was observed. We found a higher percentage of depressed patients compared with the remaining Postebogui group (42 vs 11%; P < 0.001). Conclusion.: Results from the study come from the first complete rheumatological examination of a cohort of EVD survivors, nearly 9 months after Ebola Treatment Centre discharge. Importantly, we found that patients with arthralgia/myalgia included in the Eborheum cohort were more likely to experience depression than survivors not reporting these symptoms, highlighting the impact of pain symptoms among survivors

Cryptic splice site poisoning and meiotic arrest caused by a homozygous frameshift mutation in RBMXL2 : A case report

International audienceGene expression in meiotic cells in the testis is characterized by intense transcriptional activity and alternative splicing. These processes are mainly controlled by RNA-binding proteins expressed strongly in germ cells. Functional impairments in any of these proteins' functions can lead to defects in meiosis and thus severe male infertility. Here, we have identified a homozygous frameshift mutation (NM_014469.4:c.301dup; p.Ser101LysfsTer29) in the RNA-binding motif protein, X-linked like 2 (RBMXL2) gene in a man with an azoospermia due to meiotic arrest. As RBMXL2 is known to be crucial for safeguarding the meiotic transcriptome in mice testes, we hypothesized that this variant leads to cryptic splice site poisoning. To determine the variant's impact on spermatogenesis, we confirmed the absence of RBMXL2 protein in the patient's testis tissue and then evidenced abnormal expression of several spermatogenesis proteins (e.g. meiosis-specific with coiled-coil domain) known to be altered in rbmxl2 knock-out mice with meiotic arrest. Our results indicate that RBMXL2's function in spermatogenesis is conserved in mammals. We hypothesize that deleterious variant in the RBMXL2 gene can result in male infertility and complete meiotic arrest, due to the disruption of gene expression by cryptic splice site poisoning

Cohesive strength of iron ore granules

International audienceWe present an experimental and numerical investigation of the mechanical strength of crude iron ore (Hematite) granules in which capillary bonds between primary particles are the source of internal cohesion. The strength is measured by subjecting the granules to vertical compression between two plates. We show that the behavior of the granules is ductile with a well-defined plastic threshold which increases with the amount of water. It is found that the compressive strength scales with capillary cohesion with a pre-factor that is nearly independent of size polydispersity for the investigated range of parameters but increases with friction coefficient between primary particles. This weak dependence may be attributed to the class of fine particles which, due to their large number, behaves as a cohesive matrix that controls the strength of the granule

Cohesive strength of iron ore granules

We present an experimental and numerical investigation of the mechanical strength of crude iron ore (Hematite) granules in which capillary bonds between primary particles are the source of internal cohesion. The strength is measured by subjecting the granules to vertical compression between two plates. We show that the behavior of the granules is ductile with a well-defined plastic threshold which increases with the amount of water. It is found that the compressive strength scales with capillary cohesion with a pre-factor that is nearly independent of size polydispersity for the investigated range of parameters but increases with friction coefficient between primary particles. This weak dependence may be attributed to the class of fine particles which, due to their large number, behaves as a cohesive matrix that controls the strength of the granule

En Europe, les nations

Face à l'émergence des nationalismes et des versions interethniques en Europe, l'ethnologie propose ses analyses de situations concrètes et sa réflexion sur les deux traditions de pensée l'une française, l'autre allemande - qui fondent l'idée européenne de nation