Computation of Low Mach Inviscid Compressible Flows around a Prolate Spheroid

The numerical simulation of low Mach compressible flows around a prolate spheroid is investigated using a Godunov-like numerical method. The hyperbolic differential problem -the three-dimensional Euler equations- is solved on unstructured meshes by a finite volume scheme based on Roe's upwind scheme and Turkel's low Mach preconditioner. The effects of artificial viscosity and preconditioning on the computation of Drag and Lift coefficients are investigated. The classical Roe's scheme and its low Mach preconditioned variant are both considered using a sequence of three meshes of different fineness for solutions comparison and convergence. The numerical results show the preponderant part played by the low Mach preconditioner in terms of accuracy and robustness when very subsonic flows are considered, and the importance of using a small amount of numerical dissipation

Computation of Low Mach Inviscid Compressible Flows around a Prolate Spheroid

The numerical simulation of low Mach compressible flows around a prolate spheroid is investigated using a Godunov-like numerical method. The hyperbolic differential problem -the three-dimensional Euler equations- is solved on unstructured meshes by a finite volume scheme based on Roe's upwind scheme and Turkel's low Mach preconditioner. The effects of artificial viscosity and preconditioning on the computation of Drag and Lift coefficients are investigated. The classical Roe's scheme and its low Mach preconditioned variant are both considered using a sequence of three meshes of different fineness for solutions comparison and convergence. The numerical results show the preponderant part played by the low Mach preconditioner in terms of accuracy and robustness when very subsonic flows are considered, and the importance of using a small amount of numerical dissipation

Prevalence of macular complications related to myopia – Results of a multicenter evaluation of myopic patients in eye clinics in France

Purpose: Uncorrected refractive errors are the first cause of vision impairment worldwide. High myopia is a frequent cause of sight‐threatening chorioretinal complications. The aim of this study was to evaluate the prevalence of macular complications, visual impairment and blindness in patients with myopia. Methods: A cross‐sectional multicenter study carried out in French eye clinics mainly dedicated to refractive errors. Myopia severity was defined as mild (−0.5 to −3 D), moderate (−3 to −6 D), high (−6 to −10 D) and very high (more than −10 D). Macular complications related to myopia included lacquer cracks, myopic choroidal neovascularization, chorioretinal atrophy and retinoschisis. The prevalences of macular complications, blindness and vision impairment were estimated with respect to degree of myopia and age. Eligibility criteria were myopia on the left eye of −0.5 D or more. Exclusion criteria included any missing data related to subjective refractive error, age, gender and any history of cataract or refractive surgery. Results: Data files from 198 641 myopic individuals with a mean age of 34 years (SD: 15 years) were analysed. The prevalence of mild, moderate, high and very high myopia was, respectively, 65.95%, 26.14%, 6.72% and 1.19%. The prevalence of macular complications in the high and very high myopia groups was 0.5% [0.39–0.64] and 4.27% [3.49–5.17]. The prevalence of blindness or vision impairment was observed in 10.10% [8.91–11.39%] of the very high myopic group. At 60 years old or over, the prevalences of blindness or vision impairment were, respectively, 9.75% [7.91–11.85%] and 25.71% [21.00–30.87%] in the high and very high myopia groups. Conclusions: This multicenter cross‐sectional study provides new insights in terms of prevalence of macular complications related to myopia. To our knowledge, this is one of the largest European studies focusing on individuals with myopia, particularly on the macular complications and the functional consequences in relation to myopia

Modélisation et simulation numérique de la turbulence par des approches statistiques bas-Reynolds et hybride Rans/Les

Le travail présenté dans cette thèse s'inscrit dans le contexte de la modélisation et de la simulation numérique des écoulements turbulents à grand nombre de Reynolds, avec intégration des équations jusqu'à la paroi. L'objectif principal est de reconsidérer les approches existantes de la turbulence, en s'appuyant sur des outils numériques récents, afin d'obtenir des résultats plus précis sur des maillages non-structurés, notamment en proche paroi. Dans la perspective d'une hybridation avec l'approche LES, nous étudions tout d'abord les performances d'un modèle k- bas-Reynolds linéaire. Nous le comparons ensuite à une extension non-linéaire cubique qui permet de tenir compte de l'effet d'anisotropie. Le solveur Navier-Stokes compressible utilise une approche mixte éléments/volumes finis instationnaire implicite. Dans deux cas d'écoulements stationnaires nous obtenons des résultats satisfaisants avec le modèle linéaire, alors que l'extension non-linéaire montre une forte sensibilité au paramètre de viscosité turbulente C . Dans le cas instationnaire, le modèle non-linéaire s'est montré bien plus performant. Nous proposons ensuite une combinaison originale entre les approches de type RANS et LES. L'idée de base consiste à résoudre le champ moyen par les équations de type RANS, puis à le corriger en ajoutant les fluctuations résolues par l'approche VMS (Variational Multi-Scale) de la LES. Le terme de correction est amorti par une fonction d'hybridation continue à travers le domaine de calcul. Le modèle obtenu est appliqué à l'écoulement 3D autour d'un cylindre circulaire à séparation turbulente. Nous analysons les différentes régions de l'écoulement ainsi que sa topologie.The work presented in this thesis concerns the turbulence modelling and numerical prediction of high Reynolds number flows by performing the integration of the governing equations up to the wall. The main objective is to reconsider existing turbulence models, using recent numerical tools, in order to obtain more accurate results on unstructured meshes, particularly in the near-wall region. In the perspective of hybridisation with a LES approach, we study first a linear low-Reynolds k- model. Then, we compare it with a cubic eddy-viscosity model, which allows accounting for anisotropy effect. The compressible Navier-Stokes solver uses an implicit unsteady mixed finite element/volume method. In two steady flow cases (turbulent channel and backward-facing step flows), we obtain satisfactory results with the linear model, whereas the nonlinear extension shows a substantial sensitivity to the eddy-viscosity parameter C . In the unsteady flow (circular cylinder), the nonlinear model shows higher performances. Next, we propose a novel combination of RANS and LES approaches. The basic idea is to solve the averaged flow field by the RANS equations, and to correct it by adding the remaining resolved fluctuations with VMS (Variational Multi-Scale) approach of LES. The correction term is damped by a smooth blending function across the computational domain. The obtained model is applied to a three-dimensional flow past a circular cylinder with turbulent separation. We analyse the different flow regions and the flow topology. The statistics computed from numerical simulations are consistent with the experimental data and the hybrid approach of DES-type.PAU-BU Sciences (644452103) / SudocSudocFranceF

A hybrid temporal LES/RANS formulation based on a two-equation subfilter model

International audienceA novel hybrid model for statistically stationary flow simulations at moderate to high Reynolds numbers is presented. Based on a consistent formalism developed for seamless hybrid temporal LES/RANS methodologies (Fadai-Ghotbi et al., 2010b; Schiestel and Dejoan, 2005), the Temporal Partially-Integrated Transport Model (TPITM) approach is used to derive a two-equation subfilter model, consistent with the k − ω SST model in the RANS limit, i.e., when the temporal filter width goes to infinity. Comparisons are made with a widespread hybrid RANS/LES model, the DES-SST formulation (Menter et al., 2003), which tends to the same RANS model in the RANS zones, but uses the Detached Eddy Simulation (DES) methodology to control the transition from RANS to LES. The paper discusses the features and capabilities of both approaches

Numerical prediction of wall-bounded flows with low-Reynold k-e turbulence models

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Low Mach investigation of compressible airflow around a generic airship

The numerical simulation of low Mach compressible flows around a generic airship is investigated using a Godunov-like numerical method. The hyperbolic differential problem -the three-dimensional Euler equations- is solved on unstructured meshes by a finite volume scheme based on Roe's upwind scheme [7] and Turkel's low Mach preconditioner [12, 5, 9, 10]. The effects of artificial viscosity and preconditioning on the computation of Drag and Lift coefficients are investigated. The classical Roe's scheme and its low Mach preconditioned variant are both considered using a sequence of three meshes of different fineness for solutions comparison and convergence. The numerical results show the preponderant part played by the low Mach preconditioner in terms of accuracy and robustness when very subsonic flows are considered, and the importance of using a small amount of numerical dissipation

A numerical method for simulating turbulent shear flows with low Reynolds k-e models

We present a new numerical model for the simulation of turbulent flows. New numerics rely on a 3D upwind compressible solver which applies to (possibly unstructured) tetrahedrizations. Accuracy in boundary layers is increased by a new type of tetrahedrization. The Reynolds-Averaged Navier-Stokes (RANS) equations are solved using a mixed element-volume method for the spatial discretization and an implicit scheme is applied to advance the equations in time. Two low Reynolds number k-e RANS models are implemented with this numerical technique. A linear model, the low Reynolds number k-e turbulence model of Goldberg et al., and a nonlinear one using a cubic relation between the strain and vorticity tensors and the stress tensor, as originally proposed by Craft et al. These models are applied to the study of a turbulent flow past a backward-facing step. The results obtained are compared to experimental dat

Prevalence of unknown ocular hypertension, glaucoma suspects, and glaucoma in patients seen in an ophthalmology center in France

indexation en cours.International audienceINTRODUCTION: The rate of unknown glaucoma is around 50% in industrialized countries. The purpose of our study was to estimate the prevalence of unknown cases of ocular hypertension, glaucoma suspects, and glaucoma in patients consulting for refractive disorders in France. METHODS: A retrospective study in the Point Vision ophthalmology center was led in Toulouse, France. All participants consulting for refractive disorders between June 2015 and June 2017 in the ophthalmology center were included. The cases were identified by the assessment of intraocular pressure, optic nerve head structure, and visual field. Ocular hypertension was defined as an intraocular pressure >21 mm Hg. Glaucoma was defined as the association of a glaucomatous papilla and two successive pathological visual fields. Glaucoma suspect was defined as the association of a glaucomatous papilla without visual field defect. The primary endpoint was the prevalence of unknown ocular hypertension, glaucoma suspects, and glaucoma in patients seen in an ophthalmology center. RESULTS: A total of 66,068 patients (mean age = 37 years) consulted for a refraction visual assessment during the study period. Among them, 234 had a visual field and a retinal nerve fiber layer assessment for ocular hypertension and/or suspicious papilla. The prevalence of unknown cases of ocular hypertension, glaucoma suspect, and glaucoma was 2.6, 0.8, and 0.5 per 1,000 consultants, respectively. Median age at diagnosis of ocular hypertension, glaucoma suspect, and glaucoma was 52, 53, and 65 years, respectively. CONCLUSION: The present study highlights the importance of glaucoma screening in people over 40 years old with the measurement of intraocular pressure and an optic nerve head assessment