Mesh and polynomial adaptation for high-order discretizations of compressible flows

The aerospace research and industry sectors are relying increasingly on numerical simulations to gain insight into aerodynamic flows. However, the complexity of these flows and the broad range of scales they exhibit still represent a serious challenge to the current generation of computational methods. This thesis presents developments to high-order accurate (> 2nd order) schemes aimed at addressing these limitations. The topic is tackled from the perspectives of enhanced resolution and adaptive error-control. Firstly, an extension of the Lifting-Collocation-Penalty (LCP) scheme to spatially-varying polynomial approximations is presented. This formulation is used to perform efficient polynomial-adaptive computations of compressible flows. The focus is put on the adequate inter-cell flux transfer, and stability analysis of the resulting scheme. Secondly, improved error-control via adjoint-driven mesh refinement is demonstrated. The connection between the global error-norm and the truncation error is established through an adjoint problem. This link provides valuable information about error-propagation patterns, and is shown to be useful for adaptive mesh refinement.La recherche aérospatiale et le secteur industriel font un usage intensif des méthodes de simulations aérodynamiques. Cependant, les écoulements aérodynamiques présentent une grande plage de longueurs caractéristiques, qui constituent un défi de taille pour les méthodes actuelles. Cette thèse présente des avancées dans le domaine des méthodes d'ordre élevé (ordre de précision > 2) visant à contourner ces limitations. Le premier axe concerne le schéma Lifting-Collocation-Penalty (LCP), qui est étendu aux approximations polynomiales variables dans l'espace. Cette formulation est conçue afin de permettre des calculs d'écoulements compressibles avec adaptation polynomiale. Nous discutons le traitement adéquat du transfert des flux numériques et présentons une analyse de stabilité du schéma. Le second axe est consacré au contrôle accru de l'erreur numérique grâce à une nouvelle méthode de raffinement de maillage. En utilisant une formulation adjointe, nous établissons une connexion entre la norme globale de l'erreur et l'erreur de troncature du schéma numérique. Ce lien révèle les mécanismes de propagation d'erreur, dont nous démontrons l'utilité dans le cadre de raffinement automatique de maillage

A non linear frequency domain-spectral difference scheme for unsteady periodic flows /

This research presents a new, more efficient computational scheme for complex periodic flows, and brings forward two novel ideas. The first consists in the use of a Fourier space time representation in conjunction with a high-order spatial discretization. The second is based on the efficient treatment of the resulting set of equations using a fast, implicit solver. This thesis describes the formulation and implementation of the proposed framework. Firstly, a high-order spectral difference scheme for the Euler equations is introduced. Secondly, the non-linear frequency domain method resolving the unsteady behavior of the flow is discussed. Thirdly, a mathematical and experimental validation of the proposed algorithm is carried out. Numerical experiments performed in this thesis suggest that the methodology could be an attractive new avenue for large scale time-dependent problems, alleviating the computational cost traditionally associated with such simulations

A discontinuous Galerkin model for multiphysics welding simulations

This paper describes the development of a multiphysics welding simulation model based on the discontinuous Galerkin (DG) finite-element method. Our numerical model implements a classical enthalpy-porosity constitutive law accounting for hydrodynamic and thermal effects occurring during the phase transition from solid to liquid metal. The objective of the study is to present the verification of our numerical framework and explore the applicability of the DG formulation to the simulation of welding processes. Three computational examples of increasing complexity are presented.</jats:p

LARGE EDDY SIMULATION OF A LOW PRESSURE COMPRESSOR CASCADE AT HIGH INCIDENCE

peer reviewe

Kinins and Their Receptors as Potential Therapeutic Targets in Retinal Pathologies

The kallikrein-kinin system (KKS) contributes to retinal inflammation and neovascularization, notably in diabetic retinopathy (DR) and neovascular age-related macular degeneration (AMD). Bradykinin type 1 (B1R) and type 2 (B2R) receptors are G-protein-coupled receptors that sense and mediate the effects of kinins. While B2R is constitutively expressed and regulates a plethora of physiological processes, B1R is almost undetectable under physiological conditions and contributes to pathological inflammation. Several KKS components (kininogens, tissue and plasma kallikreins, and kinin receptors) are overexpressed in human and animal models of retinal diseases, and their inhibition, particularly B1R, reduces inflammation and pathological neovascularization. In this review, we provide an overview of the KKS with emphasis on kinin receptors in the healthy retina and their detrimental roles in DR and AMD. We highlight the crosstalk between the KKS and the renin–angiotensin system (RAS), which is known to be detrimental in ocular pathologies. Targeting the KKS, particularly the B1R, is a promising therapy in retinal diseases, and B1R may represent an effector of the detrimental effects of RAS (Ang II-AT1R)

Influence of the numerical strategy on wall-resolved LES of a compressor cascade

peer reviewe

Dyslipidemia in retinal metabolic disorders

Abstract The light‐sensitive photoreceptors in the retina are extremely metabolically demanding and have the highest density of mitochondria of any cell in the body. Both physiological and pathological retinal vascular growth and regression are controlled by photoreceptor energy demands. It is critical to understand the energy demands of photoreceptors and fuel sources supplying them to understand neurovascular diseases. Retinas are very rich in lipids, which are continuously recycled as lipid‐rich photoreceptor outer segments are shed and reformed and dietary intake of lipids modulates retinal lipid composition. Lipids (as well as glucose) are fuel substrates for photoreceptor mitochondria. Dyslipidemia contributes to the development and progression of retinal dysfunction in many eye diseases. Here, we review photoreceptor energy demands with a focus on lipid metabolism in retinal neurovascular disorders

Dyslipidemia in retinal metabolic disorders

The light-sensitive photoreceptors in the retina are extremely metabolically demanding and have the highest density of mitochondria of any cell in the body. Both physiological and pathological retinal vascular growth and regression are controlled by photoreceptor energy demands. It is critical to understand the energy demands of photoreceptors and fuel sources supplying them to understand neurovascular diseases. Retinas are very rich in lipids, which are continuously recycled as lipid-rich photoreceptor outer segments are shed and reformed and dietary intake of lipids modulates retinal lipid composition. Lipids (as well as glucose) are fuel substrates for photoreceptor mitochondria. Dyslipidemia contributes to the development and progression of retinal dysfunction in many eye diseases. Here, we review photoreceptor energy demands with a focus on lipid metabolism in retinal neurovascular disorders

Comparison of Various CFD Codes for LES Simulations of Turbomachinery: From Inviscid Vortex Convection to Multi-Stage Compressor

peer reviewedSome possible future High Fidelity CFD codes for LES simulation of turbomachinery are compared on several test cases increasing in complexity, starting from a very simple inviscid Vortex Convection to a multistage axial experimental compressor. Simulations were performed between 2013 and 2016 by major Safran partners (Cenaero, Cerfacs, CORIA and Onera) and various numerical methods compared: Finite Volume, Discontinuous Galerkin, Spectral Differences. Comparison to analytical results, to experimental data or to RANS simulations are performed to check and measure accuracy. CPU efficiency versus accuracy are also presented. It clearly appears that the level of maturity could be different between codes and numerical approaches. In the end, advantages and disadvantages of every codes obtained during this project are presented