Adaptive wall treatment for the elliptic blending Reynolds stress model

International audienceWall functions are widely used in CFD in order to significantly reduce the computational cost compared to so called Low-Reynolds number formulations. They are, however, particularly restrictive in terms of meshing as they require the first calculation point to fall into the logarithmic region. Industrial simulations of internal flows, such as the ones encountered in nuclear applications, are particularly challenging due to their inherent complexity that makes it difficult to satisfy those conditions everywhere.The present study focuses on a new algebraic adaptive wall treatment for the Elliptic Blending Reynolds Stress Model (EB-RSM) by extending some of those recently proposed approaches. Blending functions that ensure a correct asymptotic behaviour at the wall for the velocity and the turbulent variables are introduced and boundary conditions are prescribed at the first near-wall cell. The approach shows very promising results on fully developed channel flows, comparable to what is obtained using a numerical integration down to the wall

Extension to various thermal boundary conditions of the elliptic blending model for the turbulent heat flux and the temperature variance

International audienceA new formulation of the model used in the near-wall region for the turbulent heat flux is developed, in order to extend the Elliptic Blending Differential Flux Model of Dehoux et al., Int. J. Heat Fluid Fl. (2017), to various boundary conditions for the temperature: imposed wall-temperature, imposed heat flux or Conjugate Heat Transfer (CHT). The new model is developed on a theoretical basis in order to satisfy the near-wall budget of the turbulent heat flux and, consequently, its asymptotic behavior in the vicinity of the wall, which is crucial for the correct prediction of heat transfer between the fluid and the wall. The models of the different terms are derived using Taylor series expansions and comparisons with recent direct numerical simulation data of channel flows with various boundary conditions. A priori tests show that this methodology makes it possible to drastically improve the physical representation of the wall/turbulence interaction. This new differential flux model relies on the thermal-to-mechanical timescale ratio which depends on the thermal boundary condition at the wall. The key element entering this ratio is ε θ , the dissipation rate of the temperature variance θ 2. Thus, a new near-wall model for this dissipation rate is proposed, in the framework of the second-moment closure based on the elliptic-blending strategy. The computations carried out in order to validate the new differential flux model demonstrate the very satisfactory prediction of heat transfer in the forced convection regime for all kinds of thermal boundary condition

Rapid testing versus karyotyping in Down's syndrome screening: cost-effectiveness and detection of clinically significant chromosome abnormalities

In all, 80% of antenatal karyotypes are generated by Down's syndrome screening programmes (DSSP). After a positive screening, women are offered prenatal foetus karyotyping, the gold standard. Reliable molecular methods for rapid aneuploidy diagnosis (RAD: fluorescence in situ hybridization (FISH) and quantitative fluorescence PCR (QF-PCR)) can detect common aneuploidies, and are faster and less expensive than karyotyping

Guidelines for Diagnosis and Management of Infective Endocarditis in Adults: A WikiGuidelines Group Consensus Statement.

IMPORTANCE Practice guidelines often provide recommendations in which the strength of the recommendation is dissociated from the quality of the evidence. OBJECTIVE To create a clinical guideline for the diagnosis and management of adult bacterial infective endocarditis (IE) that addresses the gap between the evidence and recommendation strength. EVIDENCE REVIEW This consensus statement and systematic review applied an approach previously established by the WikiGuidelines Group to construct collaborative clinical guidelines. In April 2022 a call to new and existing members was released electronically (social media and email) for the next WikiGuidelines topic, and subsequently, topics and questions related to the diagnosis and management of adult bacterial IE were crowdsourced and prioritized by vote. For each topic, PubMed literature searches were conducted including all years and languages. Evidence was reported according to the WikiGuidelines charter: clear recommendations were established only when reproducible, prospective, controlled studies provided hypothesis-confirming evidence. In the absence of such data, clinical reviews were crafted discussing the risks and benefits of different approaches. FINDINGS A total of 51 members from 10 countries reviewed 587 articles and submitted information relevant to 4 sections: establishing the diagnosis of IE (9 questions); multidisciplinary IE teams (1 question); prophylaxis (2 questions); and treatment (5 questions). Of 17 unique questions, a clear recommendation could only be provided for 1 question: 3 randomized clinical trials have established that oral transitional therapy is at least as effective as intravenous (IV)-only therapy for the treatment of IE. Clinical reviews were generated for the remaining questions. CONCLUSIONS AND RELEVANCE In this consensus statement that applied the WikiGuideline method for clinical guideline development, oral transitional therapy was at least as effective as IV-only therapy for the treatment of IE. Several randomized clinical trials are underway to inform other areas of practice, and further research is needed

CMB-S4: Forecasting Constraints on Primordial Gravitational Waves

CMB-S4---the next-generation ground-based cosmic microwave background (CMB) experiment---is set to significantly advance the sensitivity of CMB measurements and enhance our understanding of the origin and evolution of the Universe, from the highest energies at the dawn of time through the growth of structure to the present day. Among the science cases pursued with CMB-S4, the quest for detecting primordial gravitational waves is a central driver of the experimental design. This work details the development of a forecasting framework that includes a power-spectrum-based semi-analytic projection tool, targeted explicitly towards optimizing constraints on the tensor-to-scalar ratio, $r$, in the presence of Galactic foregrounds and gravitational lensing of the CMB. This framework is unique in its direct use of information from the achieved performance of current Stage 2--3 CMB experiments to robustly forecast the science reach of upcoming CMB-polarization endeavors. The methodology allows for rapid iteration over experimental configurations and offers a flexible way to optimize the design of future experiments given a desired scientific goal. To form a closed-loop process, we couple this semi-analytic tool with map-based validation studies, which allow for the injection of additional complexity and verification of our forecasts with several independent analysis methods. We document multiple rounds of forecasts for CMB-S4 using this process and the resulting establishment of the current reference design of the primordial gravitational-wave component of the Stage-4 experiment, optimized to achieve our science goals of detecting primordial gravitational waves for $r > 0.003$ at greater than $5\sigma$, or, in the absence of a detection, of reaching an upper limit of $r < 0.001$ at $95\%$ CL.Comment: 24 pages, 8 figures, 9 tables, submitted to ApJ. arXiv admin note: text overlap with arXiv:1907.0447

CMB-S4: Forecasting Constraints on Primordial Gravitational Waves

Abstract: CMB-S4—the next-generation ground-based cosmic microwave background (CMB) experiment—is set to significantly advance the sensitivity of CMB measurements and enhance our understanding of the origin and evolution of the universe. Among the science cases pursued with CMB-S4, the quest for detecting primordial gravitational waves is a central driver of the experimental design. This work details the development of a forecasting framework that includes a power-spectrum-based semianalytic projection tool, targeted explicitly toward optimizing constraints on the tensor-to-scalar ratio, r, in the presence of Galactic foregrounds and gravitational lensing of the CMB. This framework is unique in its direct use of information from the achieved performance of current Stage 2–3 CMB experiments to robustly forecast the science reach of upcoming CMB-polarization endeavors. The methodology allows for rapid iteration over experimental configurations and offers a flexible way to optimize the design of future experiments, given a desired scientific goal. To form a closed-loop process, we couple this semianalytic tool with map-based validation studies, which allow for the injection of additional complexity and verification of our forecasts with several independent analysis methods. We document multiple rounds of forecasts for CMB-S4 using this process and the resulting establishment of the current reference design of the primordial gravitational-wave component of the Stage-4 experiment, optimized to achieve our science goals of detecting primordial gravitational waves for r > 0.003 at greater than 5σ, or in the absence of a detection, of reaching an upper limit of r < 0.001 at 95% CL

Adaptive wall treatment for a second order turbulence model in an industrial context

Les calculs de CFD industriels pour les écoulements turbulents commencent par une phase complexe de réalisation de maillage (calculs de fond de cuve, de plénum supérieur ou d’assemblages combustibles par exemple dans le domaine nucléaire). Les premières contraintes prises en compte sont le plus souvent géométriques (complexité, détail, intuition ou retour d'expérience concernant les endroits « importants » où le maillage doit être raffiné). On doit cependant respecter des contraintes inhérentes aux modèles de turbulence RANS (Reynolds Averaged Navier Stokes) utilisés notamment la taille de la première cellule de calcul à la paroi. Si on utilise un modèle dit « Haut-Reynolds » (k- ε standard, SSG, …), on ne devrait trouver que des cellules de paroi ayant un centre à une distance adimensionnelle au moins égale à 20 pour pouvoir d’une part justifier l'utilisation de la loi « universelle » logarithmique pour la vitesse et d’autre part, ce qui souvent occulté, respecter le fait que ces modèles ne sont pas conçus pour des distances plus basses. En revanche, si on utilise un modèle dit « Bas-Reynolds » (BL-v²/k, EB-RSM, …), on devrait partout avoir des cellules de paroi ayant un centre à une distance adimensionnelle de la paroi très faible. Si ces modèles sont utilisés avec une partie des cellules en paroi ayant une distance adimensionnelle nettement supérieure, les résultats peuvent être catastrophiques (le calcul peut ou bien diverger ou bien donner des résultats avec une physique totalement fausse). Cette thèse propose le développement d'un nouveau modèle de turbulence avec lois de paroi adaptatives qui donne des résultats satisfaisants quelque soit le type de maillage utilisé, en particulier quand ce dernier contient à la fois des cellules dont le centre est à une distance « Bas-Reynolds » et « Haut-Reynolds ». Étant donné les écoulements complexes des configurations industrielles, ce nouveau modèle s'appuie sur l'utilisation d'un modèle du second ordre connu pour son bon comportement : le modèle EB-RSM. Ce modèle permet de reproduire l'anisotropie de la turbulence et comble certaines lacunes des modèles du premier ordre. Ce modèle est disponible dans Code_Saturne, code open source développé par EDF et au sein duquel les développements ont été réalisés.CFD computations of turbulent flows always begin with a complex meshing process (upper plenum, fuel assembly in the nuclear industry for example). Geometrical constraints are the first ones to be satisfied (level of details, important zones to refine regarding “user experiences”). One has however to satisfy constraints that are inherent to the RANS model (Reynolds Averaged Navier Stokes) used for the computation. For example, if a « High-Reynolds » (k-ε standard, SSG, …) model is used one should only have wall cells with a dimensionless distance to the wall greater or equal to 20 to justify the use of the universal “law of the wall”. On the other hand, if a « Low-Reynolds » (BL-v²/k, EB-RSM, …) model is used, one should only find wall cells with a dimensionless distance to the wall below 1. If those models are used in an inappropriate way the results could be dramatic (computations can either diverge or give unphysical results). This thesis proposes the development of a new turbulence model with adaptive wall treatments that gives satisfactory results on all types of meshes. In particular, the model will be able to cope with meshes containing both « High-Reynolds » and « Low-Reynolds » wall cells. Given the complex flows encountered in the nuclear industry this thesis will use a model known for its good behavior: the EB-RSM model. This model is able to reproduce the anisotropy of the turbulence and give more satisfactory results than eddy viscosity models in different configurations. This model is available in Code_Saturne, an open source code developed at EDF. Al the developments are made in this code

Lois de paroi adaptatives pour un modèle de fermeture du second ordre dans un contexte industriel

CFD computations of turbulent flows always begin with a complex meshing process (upper plenum, fuel assembly in the nuclear industry for example). Geometrical constraints are the first ones to be satisfied (level of details, important zones to refine regarding “user experiences”). One has however to satisfy constraints that are inherent to the RANS model (Reynolds Averaged Navier Stokes) used for the computation. For example, if a « High-Reynolds » (k-ε standard, SSG, …) model is used one should only have wall cells with a dimensionless distance to the wall greater or equal to 20 to justify the use of the universal “law of the wall”. On the other hand, if a « Low-Reynolds » (BL-v²/k, EB-RSM, …) model is used, one should only find wall cells with a dimensionless distance to the wall below 1. If those models are used in an inappropriate way the results could be dramatic (computations can either diverge or give unphysical results). This thesis proposes the development of a new turbulence model with adaptive wall treatments that gives satisfactory results on all types of meshes. In particular, the model will be able to cope with meshes containing both « High-Reynolds » and « Low-Reynolds » wall cells. Given the complex flows encountered in the nuclear industry this thesis will use a model known for its good behavior: the EB-RSM model. This model is able to reproduce the anisotropy of the turbulence and give more satisfactory results than eddy viscosity models in different configurations. This model is available in Code_Saturne, an open source code developed at EDF. Al the developments are made in this code.Les calculs de CFD industriels pour les écoulements turbulents commencent par une phase complexe de réalisation de maillage (calculs de fond de cuve, de plénum supérieur ou d’assemblages combustibles par exemple dans le domaine nucléaire). Les premières contraintes prises en compte sont le plus souvent géométriques (complexité, détail, intuition ou retour d'expérience concernant les endroits « importants » où le maillage doit être raffiné). On doit cependant respecter des contraintes inhérentes aux modèles de turbulence RANS (Reynolds Averaged Navier Stokes) utilisés notamment la taille de la première cellule de calcul à la paroi. Si on utilise un modèle dit « Haut-Reynolds » (k- ε standard, SSG, …), on ne devrait trouver que des cellules de paroi ayant un centre à une distance adimensionnelle au moins égale à 20 pour pouvoir d’une part justifier l'utilisation de la loi « universelle » logarithmique pour la vitesse et d’autre part, ce qui souvent occulté, respecter le fait que ces modèles ne sont pas conçus pour des distances plus basses. En revanche, si on utilise un modèle dit « Bas-Reynolds » (BL-v²/k, EB-RSM, …), on devrait partout avoir des cellules de paroi ayant un centre à une distance adimensionnelle de la paroi très faible. Si ces modèles sont utilisés avec une partie des cellules en paroi ayant une distance adimensionnelle nettement supérieure, les résultats peuvent être catastrophiques (le calcul peut ou bien diverger ou bien donner des résultats avec une physique totalement fausse). Cette thèse propose le développement d'un nouveau modèle de turbulence avec lois de paroi adaptatives qui donne des résultats satisfaisants quelque soit le type de maillage utilisé, en particulier quand ce dernier contient à la fois des cellules dont le centre est à une distance « Bas-Reynolds » et « Haut-Reynolds ». Étant donné les écoulements complexes des configurations industrielles, ce nouveau modèle s'appuie sur l'utilisation d'un modèle du second ordre connu pour son bon comportement : le modèle EB-RSM. Ce modèle permet de reproduire l'anisotropie de la turbulence et comble certaines lacunes des modèles du premier ordre. Ce modèle est disponible dans Code_Saturne, code open source développé par EDF et au sein duquel les développements ont été réalisés

Validation of adaptive wall treatment for the EB-RSM

International audienceMotivations:- Turbulence models impose constraints on the mesh.- Industrial meshing processes make those constraints difficult to meet in the whole computational domain.- Divergence/wrong physical behaviour.Objectives:- A new model able to cope with all wall cell sizes.- Convergence towards Low-Reynolds EB-RSM.- Improve the High-Reynolds behaviour of standard wall function

Adaptive wall treatment for the elliptic blending Reynolds stress model

International audienceWall functions are widely used in CFD in order to significantly reduce the computational cost compared to so called Low-Reynolds number formulations. They are, however, particularly restrictive in terms of meshing as they require the first calculation point to fall into the logarithmic region. Industrial simulations of internal flows, such as the ones encountered in nuclear applications, are particularly challenging due to their inherent complexity that makes it difficult to satisfy those conditions everywhere.The present study focuses on a new algebraic adaptive wall treatment for the Elliptic Blending Reynolds Stress Model (EB-RSM) by extending some of those recently proposed approaches. Blending functions that ensure a correct asymptotic behaviour at the wall for the velocity and the turbulent variables are introduced and boundary conditions are prescribed at the first near-wall cell. The approach shows very promising results on fully developed channel flows, comparable to what is obtained using a numerical integration down to the wall