A Discrete Immersed Boundary Method for the numerical simulation of heat transfer in compressible flows

In the present study, a discrete forcing Immersed Boundary Method (IBM) is proposed for the numerical simulation of high-speed flow problems including heat exchange. The flow field is governed by the compressible Navier-Stokes equations, which are resolved by using the open source library OpenFOAM. The numerical solver is modified to include source terms in the momentum equation and in the energy equation, which account for the presence of the immersed body. The method is validated on some benchmark test cases dealing with forced convection problems and moving immersed bodies. The results obtained are in very good agreement with data provided in the literature. The method is further assessed by investigating three-dimensional high Mach flows around a heated sphere with different wall temperature. Even for this more complex test case, the method provides an accurate representation of both thermal and velocity fields

Development of an Immersed Boundary Method for the Analysis and Control of Compressible Flows

Cette thèse s'inscrit dans le contexte de la simulation numérique et l'analyse des écoulements compressibles, notamment en géométrie complexe ou mobile. Dans ces situations, la mise en place d'un maillage représentant correctement lesolide sans perte de précision des méthodes de discrétisation s'avère difficile. Une alternative est de travailler en maillage cartésien quelque que soit la géométrie du domaine d'écoulement en introduisant une approche aux frontières immergées.Dans ce contexte, on propose une amélioration et extension d'une méthode formulée pour la simulation des écoulements incompressibles. Les deux principales caractéristiques du modèle proposé sont d'une part l'intégration d'un nouveau terme de forçage des vitesses qui prend en compte les effets de pression et d'autre part l'intégration d'un nouveau terme de correction de température dans le traitement de l'équation de l'énergie.Cette méthode a été intégrée dans deux solveurs compressibles du code OpenFOAM : SonicFOAM et RhoCentralFOAM. La validation a été effectuée en considérant différents cas de complexité croissante sur des corps 2Dfixes et mobiles, pour lesquels on a fait varier les nombres de Mach et de Reynolds. De plus, des cas mettant en jeu des transferts de chaleur pariétaux ont été étudiés. Les résultats ont été comparés à un grand nombre de données numériques et expérimentales issues de la littérature.Enfin, des études sur des configurations plus complexes tridimensionnelles ont été mises en place. Les bifurcations de régime d'écoulement de la sphère ont été investiguées quand le nombre de Mach augmente. Une sphère avec des parois non-adiabatiques a été également analysée. Une géométrie réaliste de drone a été simulée en régime compressible.Ces analyses mettent en évidence de nombreuses caractéristiques favorables de la méthode des frontières immergées en termes de précision, de flexibilité et de coût de calcul.This thesis is related to the numerical simulation and the analysis of compressible flows, especially in complex or mobile geometry. In these situations, the establishment of a mesh correctly representing the solid with out loss of precision of discretization methods is difficult. An alternative is to use Cartesian mesh independently of the geometry of the flow domain by introducing an immersed boundary approach. In this context, we propose an improvement and extension of a method formulated for the simulation of incompressible flows. The two main characteristics of the proposed model are on the one hand the integration of a new velocity forcing term which takes into account the effects of pressure and on the other hand the integration of a new term of temperature correction in the treatment of the energy equation. This method has been integrated in two compressible solvers of OpenFOAM code: SonicFOAM and RhoCentralFOAM. The validation was carried out by considering different cases of increasing complexity on fixed and mobile 2D bodies, for which the Mach and Reynolds numbers were varied. In addition, cases involving parietal heat transfer have been studied. The results were compared to a large number of numerical and experimental data from the literature. Finally, studies on more complex three-dimensional configurations have been done. The flow regime bifurcations of the sphere have been investigated as the Mach number increases. A sphere with non-adiabatic walls was also analyzed. A realistic drone geometry was simulated in a compressible regime.These analyzes highlight many favorable features of the immersed boundary method in terms of accuracy, flexibility and computational cost

Développement d’une méthode des frontières immergées pour l’analyse et le contrôle des écoulements compressibles

This thesis is related to the numerical simulation and the analysis of compressible flows, especially in complex or mobile geometry. In these situations, the establishment of a mesh correctly representing the solid with out loss of precision of discretization methods is difficult. An alternative is to use Cartesian mesh independently of the geometry of the flow domain by introducing an immersed boundary approach. In this context, we propose an improvement and extension of a method formulated for the simulation of incompressible flows. The two main characteristics of the proposed model are on the one hand the integration of a new velocity forcing term which takes into account the effects of pressure and on the other hand the integration of a new term of temperature correction in the treatment of the energy equation. This method has been integrated in two compressible solvers of OpenFOAM code: SonicFOAM and RhoCentralFOAM. The validation was carried out by considering different cases of increasing complexity on fixed and mobile 2D bodies, for which the Mach and Reynolds numbers were varied. In addition, cases involving parietal heat transfer have been studied. The results were compared to a large number of numerical and experimental data from the literature. Finally, studies on more complex three-dimensional configurations have been done. The flow regime bifurcations of the sphere have been investigated as the Mach number increases. A sphere with non-adiabatic walls was also analyzed. A realistic drone geometry was simulated in a compressible regime.These analyzes highlight many favorable features of the immersed boundary method in terms of accuracy, flexibility and computational cost.Cette thèse s'inscrit dans le contexte de la simulation numérique et l'analyse des écoulements compressibles, notamment en géométrie complexe ou mobile. Dans ces situations, la mise en place d'un maillage représentant correctement lesolide sans perte de précision des méthodes de discrétisation s'avère difficile. Une alternative est de travailler en maillage cartésien quelque que soit la géométrie du domaine d'écoulement en introduisant une approche aux frontières immergées.Dans ce contexte, on propose une amélioration et extension d'une méthode formulée pour la simulation des écoulements incompressibles. Les deux principales caractéristiques du modèle proposé sont d'une part l'intégration d'un nouveau terme de forçage des vitesses qui prend en compte les effets de pression et d'autre part l'intégration d'un nouveau terme de correction de température dans le traitement de l'équation de l'énergie.Cette méthode a été intégrée dans deux solveurs compressibles du code OpenFOAM : SonicFOAM et RhoCentralFOAM. La validation a été effectuée en considérant différents cas de complexité croissante sur des corps 2Dfixes et mobiles, pour lesquels on a fait varier les nombres de Mach et de Reynolds. De plus, des cas mettant en jeu des transferts de chaleur pariétaux ont été étudiés. Les résultats ont été comparés à un grand nombre de données numériques et expérimentales issues de la littérature.Enfin, des études sur des configurations plus complexes tridimensionnelles ont été mises en place. Les bifurcations de régime d'écoulement de la sphère ont été investiguées quand le nombre de Mach augmente. Une sphère avec des parois non-adiabatiques a été également analysée. Une géométrie réaliste de drone a été simulée en régime compressible.Ces analyses mettent en évidence de nombreuses caractéristiques favorables de la méthode des frontières immergées en termes de précision, de flexibilité et de coût de calcul

Direct numerical simulation of compressible flows around spherical bodies using the immersed boundary method

2e Journée Française des utilisateurs d'OpenFOAM, 2017, Nevers, France.International audienc

DIRECT NUMERICAL SIMULATION OF COMPRESSIBLE FLOWS AROUNDSPHERICAL BODIES USING THE IMMERSED BOUNDARY METHOD

International audienc

‘No place for a woman’: Access, exclusion, insecurity and the mobility regime in grand tunis

Drawing on an innovative peer researcher method, this paper uses mobility diaries and in-transit interviews to examine the everyday travel experiences of women from socio-economically marginalised neighbourhoods in metropolitan Grand Tunis. It situates those experiences, and the practices they deploy to navigate them, within a meso-level discussion of women’s social condition in Tunisia and a macro-level political economy of the Tunis transport system. Together these shed light on the multi-layered intersecting disadvantages which shape women’s place in the prevailing mobility regime, pushing already marginalised women into transport poverty and social exclusion. The paper highlights the subsequent constraints on women’s access to the resources which might allow them to improve their lives, and the significance of travel-related violence and insecurity on their everyday lives

Alpha-mannosidosis in Tunisian consanguineous families: Potential involvement of variants in GHR and SLC19A3 genes in the variable expressivity of cognitive impairment

International audienceAlpha-Mannosidosis (AM) is an ultra-rare storage disorder caused by a deficiency of lysosomal alpha-mannosidase encoded by the MAN2B1 gene. Clinical presentation of AM includes mental retardation, recurrent infections, hearing loss, dysmorphic features, and motor dysfunctions. AM has never been reported in Tunisia. We report here the clinical and genetic study of six patients from two Tunisian families with AM. The AM diagnosis was confirmed by an enzymatic activity assay. Genetic investigation was conducted by Sanger sequencing of the mutational hotspots for the first family and by ES analysis for the second one. In the first family, a frameshift duplication p.(Ser802GlnfsTer129) was identified in the MAN2B1 gene. For the second family, ES analysis led to the identification of a missense mutation p.(Arg229Trp) in the MAN2B1 gene in four affected family members. The p.(Ser802GlnfsTer129) mutation induces a premature termination codon which may trigger RNA degradation by the NMD system. The decrease in the levels of MAN2B1 synthesis could explain the severe phenotype observed in the index case. According to the literature, the p.(Arg229Trp) missense variant does not have an impact on MAN2B1 maturation and transportation, which correlates with a moderate clinical sub-type. To explain the intra-familial variability of cognitive impairment, exome analysis allowed the identification of two likely pathogenic variants in GHR and SLC19A3 genes potentially associated to cognitive decline. The present study raises awareness about underdiagnosis of AM in the region that deprives patients from accessing adequate care. Indeed, early diagnosis is critical in order to prevent disease progression and to propose enzyme replacement therapy