Interaction Fluide-Structure pour les corps élancés

Cet article présente le couplage du solveur fluide ISIS-CFD du LMF et d’un solveur structure de type poutre appliqué à des problèmes 3D complexes d’interaction fluide-structure des corps élancés en grand déplacement, comme les risers. Le couplage temporel s’appuie sur un algorithme itératif. Un soin tout particulier a été porté au couplage spatial, en particulier au processus de déformation de maillage. Afin de valider le code IFS, le cas-test 2D d’Hübner a été traité

Experimental Investigation and Large-Eddy Simulation of the Turbulent Flow past a Smooth and Rigid Hemisphere

Computations carried out on the German Federal Top-Level Computer SuperMUC at LRZ Munich under the contract number pr84na.International audienceThe objective of the present paper is to provide a detailed experimental and numerical investigation on the turbulent flow past a hemispherical obstacle (diameter D). For this purpose, the bluff body is exposed to a thick turbulent boundary layer of the thickness δ = D/2 at Re = 50,000. In the experiment this boundary layer thickness is achieved by specific fences placed in the upstream region of the wind tunnel. A detailed measurement of the upstream flow conditions by laser-Doppler and hot-film probes allows to mimic the inflow conditions for the complementary large-eddy simulation of the flow field using a synthetic turbulence inflow generator. These clearly defined boundary and operating conditions are the prerequisites for a combined experimental and numerical investigation of the flow field relying on the laser-Doppler anemometry and a finite-volume Navier-Stokes solver for block-structured curvilinear grids. The results comprise an analysis on the unsteady flow features observed in the vicinity of the hemisphere as well as a detailed discussion of the time-averaged flow field. The latter includes the mean velocity field as well as the Reynolds stresses. Owing to the proper description of the oncoming flow and supplementary numerical studies guaranteeing the choice of an appropriate grid and subgrid-scale model, the results of the measurements and the prediction are found to be in close agreement

Interaction Fluide-Structure pour les corps élancés

The current computational resources lead the different scientific disciplines to get closer to each other, in order to consider more and more complex phenomena. Thus, one of the axis of research of the CFD Team from École Centrale Nantes is the Fluid-Structure Interaction (FSI). In this context, the development of a large displacement structural solver for elongated bodies and its coupling with the non-structured finite volume RANSE solver, ISIS, has been done. This thin beam solver relies on the Cosserat theory and on the 'geometrically exact' approach. The space coupling on the interpolations and the information transfer at the fluid-structure interface were realised with caution, in order to be as accurate as possible and to fulfill the load conservation. Since the beam solver can be used for great displacements, an original technique had to be built to update the fluid computational domain. It is based on the pseudo solid approach, which allows a precise control over the mesh deformation through a local behaviour law of the pseudo-solid. Each part of the FSI code has been checked: the structural solver on 2D/3D test-cases, in statics and in dynamics, in small and large displacements; the remeshing module has been tested on various geometries and with MPI. Finally, some FSI applications have been performed: two bidimensional examples, a steady case and a fully unsteady one; then, the program has shown its capabilities in 3D on a deformable cable in a current with a fixed end. The computation of a riser towed in a multifluid environment at rest has also been done and studied.Les moyens de calcul actuels conduisent les différentes disciplines scientifiques à se rapprocher, afin de prendre en compte des phénomènes physiques de plus en plus complexes. Ainsi, un axe de recherche de l'Équipe de Modélisation Numérique du Laboratoire de Mécanique des fluides UMR6598 de l'École Centrale Nantes est l'Interaction Fluide-Structure (IFS). Dans ce contexte, le développement d'un solveur structure grand déplacement, limité aux corps élancés, puis son couplage avec le code RANSE volumes-finis non-structuré ISIS ont été réalisés. Le solveur poutre s'appuie sur la théorie de Cosserat et sur la méthode dite 'géométriquement exacte'. Une attention particulière a été portée au couplage en espace sur les interpolations et au transfert des informations à l'interface fluide-structure, afin d'être le plus précis possible et d'assurer la conservation des efforts. Le code poutre pouvant prendre en compte de grands mouvements, une technique originale a dû être écrite pour mettre à jour le domaine de calcul fluide. Elle se base sur l'approche pseudo-solide, et permet via une loi de comportement locale du pseudo-solide, de contrôler finement la déformation du maillage. Chaque partie du code IFS a été validée : le solveur poutre sur des cas-tests 2D/3D, en statique et en dynamique, en petit et grand déplacement; le module de remaillage sur des géométries variées et en calcul parallèle. Enfin, quelques applications IFS ont été traitées : deux exemples bidimensionnels, l'un stationnaire, l'autre très instationnaire; puis, le programme a montré ses possibilités en tridimensionnel sur un câble déformable fixé à une extrémité et subissant un courant, ou encore un riser tracté dans un environnement multifluide au repos

Numerical FSI Investigation based on LES: Flow past a cylinder with a flexible splitter plate involving large deformations (FSI-PfS-2a)

International audienceThe objective of this paper is to provide a detailed numerical investigation on the fluid-structure interaction (FSI) test case presented in Kalmbach and Breuer (Journal of Fluids and Structures, 42, (2013), pp. 369-387). It relies on detailed experimental investigations on the fluid flow and the structure deformation using modern optical measurement techniques such as particle-image velocimetry and laser triangulation sensors. The present numerical study is based on an efficient partitioned FSI coupling scheme especially developed for turbulent flow simulations around light-weight structures using large-eddy simulation. The current FSI configuration is composed of a fixed cylinder with a flexible thin rubber plate and a rear mass inducing a turbulent flow (Re = 30,470). Mainly based on a movement-induced excitation the flexible structure oscillates in the second swiveling mode involving large deformations. Thus, particular attention has been paid to the computational model and the numerical set-up. Special seven-parameters shell elements are applied to precisely model the flexible structure. Structural tests are carried out to approximate the optimal structural parameters. A fine and smooth fluid mesh has been generated in order to correctly predict the wide range of different flow structures presents near and behind the flexible rubber plate. A phase-averaging is applied to the numerical results obtained, so that they can be compared with the phase-averaged experimental data. Both are found to be in close agreement exhibiting a structure deformation in the second swiveling mode with similar frequencies and amplitudes. Finally, a sensitivity study is carried out to show the influence of different physical parameters (e.g. Young’s modulus) and modeling aspects (e.g. subgrid-scale model) on the FSI phenomenon

Interaction fluide-structure pour les corps élancés

Les moyens de calcul actuels conduisent les différentes disciplines scientifiques à se rapprocher, afin de prendre en compte des phénomènes physiques de plus en plus complexes. Ainsi, un axe de recherche de l'Équipe de Modélisation Numérique du Laboratoire de Mécanique des fluides UMR6598 de l'École Centrale Nantes est l'Interaction Fluide-Structure (IFS). Dans ce contexte, le développement d'un solveur structure grand déplacement, limité aux corps élancés, puis son couplage avec le code RANSE volumes-finis non-structuré ISIS ont été réalisés. Le solveur poutre s'appuie sur la théorie de Cosserat et sur la méthode dite géométriquement exacte''. Une attention particulière a été portée au couplage en espace sur les interpolations et au transfert des informations à l'interface fluide-structure, afin d'être le plus précis possible et d'assurer la conservation des efforts. Le code poutre pouvant prendre en compte de grands mouvements, une technique originale a dû être écrite pour mettre à jour le domaine de calcul fluide. Elle se base sur l'approche pseudo-solide, et permet via une loi de comportement locale du pseudo-solide, de contrôler finement la déformation du maillage. Chaque partie du code IFS a été validée : le solveur poutre sur des cas-tests 2D/3D, en statique et en dynamique, en petit et grand déplacement; le module de remaillage sur des géométries variées et en calcul parallèle. Enfin, quelques applications IFS ont été traitées : deux exemples bidimensionnels, l'un stationnaire, l'autre très instationnaire; puis, le programme a montré ses possibilités en tridimensionnel sur un câble déformable fixé à une extrémité et subissant un courant, ou encore un riser tracté dans un environnement multifluide au repos.The current computational resources lead the different scientific disciplines to get closer to each other, in order to consider more and more complex phenomena. Thus, one of the axis of research of the CFD Team from École Centrale Nantes is the Fluid-Structure Interaction (FSI). In this context, the development of a large displacement structural solver for elongated bodies and its coupling with the non-structured finite volume RANSE solver, ISIS, has been done. This thin beam solver relies on the Cosserat theory and on the geometrically exact'' approach. The space coupling on the interpolations and the information transfer at the fluid-structure interface were realised with caution, in order to be as accurate as possible and to fulfill the load conservation. Since the beam solver can be used for great displacements, an original technique had to be built to update the fluid computational domain. It is based on the pseudo solid approach, which allows a precise control over the mesh deformation through a local behaviour law of the pseudo-solid. Each part of the FSI code has been checked: the structural solver on 2D/3D test-cases, in statics and in dynamics, in small and large displacements; the remeshing module has been tested on various geometries and with MPI. Finally, some FSI applications have been performed: two bidimensional examples, a steady case and a fully unsteady one; then, the program has shown its capabilities in 3D on a deformable cable in a current with a fixed end. The computation of a riser towed in a multifluid environment at rest has also been done and studied.NANTES-BU Sciences (441092104) / SudocNANTES-Ecole Centrale (441092306) / SudocSudocFranceF

A new turbulent three-dimensional FSI benchmark FSI-PFS-3A: definition and measurements

In the last decade, the demand for the prediction of complex multi-physics prob- lems such as fluid-structure interaction (FSI) has strongly increased. For the development and improvement of appropriate numerical tools several test cases were designed in order to vali- date the numerical results based on experimental reference data [4, 12, 13, 8, 9, 10]. Since FSI problems often occur in turbulent flows also in the experiments similar conditions have to be provided. In the test-case FSI-PfS-1a [7] presented in the first contribution to this session, a cylinder is used with an attached flexible rubber plate. The resulting FSI problem is nearly two-dimensional regarding the phase-averaged flow and the structure deformations. The ac- tual test case FSI-PfS-3a is the reasonable further development step of this two-dimensional benchmark to a forced fully three-dimensional flow, which now also leads to a significant three- dimensional structure deformation. The cylinder is replaced by a truncated cone. Similar to FSI-PfS-1a [7] a rubber plate is attached at the backside. This geometrical setup is exposed to a constant flow at Re = 32,000 which is in the subcritical regime. Due to the linearly increasing diameter of the cone the alternating eddies in the wake even become larger resulting in corre- spondingly increasing structural displacements. Owing to these challenging flow and structure effects, this benchmark will be the next step for validating FSI predictions for real applications. The experiments are performed in a water channel with clearly defined and controllable bound- ary and operating conditions. For measuring the flow a two-dimensional mono-particle-image velocimetry (PIV) system is applied. In order to characterize the three-dimensional behavior of the flow, phase-averaged PIV measurements are performed at three different planes. The structural deformations are measured along a line on the structure surface with a time-resolved laser distance sensor. The resulting FSI problem shows a quasi-periodic deformation behavior so that a phase averaging of the results is reasonable. By phase-averaging turbulent fluctua- tions are averaged out and thus a comparison with corresponding numerical simulations based on LES [3] and RANS [12, 13] approaches is possible

Identifier des enjeux environnementaux grâce aux chorèmes : retour d’expériences en Poitou-Charentes

Le raisonnement spatial permet-il l’émergence d’enjeux environnementaux intégrés, prenant en compte la complexité d’un territoire ? Nous verrons d’abord en quoi la Méthode de Diagnostic Partagé Territorial permet d'établir une autre compréhension du territoire par une démarche participative et multithématique s’appuyant sur les chorèmes. Puis, à partir d’un exemple en Poitou-Charentes, nous mettrons en débat l’expression des enjeux environnementaux

FSI simulations of wind gusts impacting an air-inflated flexible membrane at Re = 100,000

International audienceThe paper addresses the simulation of turbulent wind gusts hitting rigid and flexible structures. The purpose is to show that such kind of complex fluid-structure interaction (FSI) problems can be simulated by high-fidelity numerical techniques with reasonable computational effort. The main ingredients required for this objective are an efficient method to inject wind gusts within the computational domain by the application of a recently developed source-term formulation, an equally effective method to prescribe the incoming turbulent flow and last but not least a reliable FSI simulation methodology to predict coupled problems based on a partitioned solution approach combining an LES fluid solver with a FEM/IGA solver for the structure. The present application is concerned with a rigid and a membranous hemisphere installed in a turbulent boundary layer and impacted by wind gusts of different strength. The methodology suggested allows to inject the gusts in close vicinity of the object of interest, which is typically well resolved. Therefore, the launch and transport of the wind gust can be realized without visible numerical dissipation and without large computational effort. The effect of the gusts on the flow field, the resulting forces on the structure and the corresponding deformations in case of the flexible structure are analyzed in detail. A comparison between the rigid and the flexible case makes it possible to work out the direct reaction of the deformations on the force histories during the impact. Furthermore, in case of the flexible structure the temporal relationships between local or global force developments and the local deformations are evaluated. Such predictions pinpoint the areas of high stresses and strains, where the material is susceptible to failure

Test case on QNET ERCOFTAC database (Underlying Flow Regime 2-14): Fluid-structure interaction in turbulent flow past cylinder/plate configuration II (Second swiveling mode)

New fluid-structure interaction test case for turbulent flows with experimental and numerical data available for download.The objective of the present contribution is to provide a second well-defined benchmark case for fluid-structure interaction as a growing branch of research in science and industry. Similar to the previous case UFR 2-13 (denoted FSI-PfS-1a in Kalmbach (2014) and De Nayer et al. (2014); Note that the PhD thesis of Kalmbach (2014) comprises further test cases for FSI-PfS-1x and FSI-PfS-2x denoted by lower case appendages x=b or x=c not considered here) the entire study relies on a complementary experimental and numerical investigation. The same measuring techniques (planar particle image velocimetry (PIV), volumetric three-component velocimetry (V3V), multiple-point laser triangulation sensor) and the same numerical methodology (partitioned FSI coupling scheme based on large-eddy simulation (LES)) is applied and will thus only partially repeated here for the sake of brevity. However, all details are available at UFR 2-13. What are the differences between the previous case and the present one? For the previous configuration (FSI-PfS-1a, UFR 2-13) the flexible structure deforms in the first swiveling mode inducing only moderate structural displacements by an instability-induced excitation. In contrast, the new case denoted FSI-PfS-2a is a movement-induced excitation with significantly larger deformations of the flexible structure in the second swiveling mode. In order to achieve these more challenging features of the flow and the structure, the previous test case UFR 2-13 (FSI-PfS-1a) is slightly modified: A 2 mm thick flexible plate is clamped behind the fixed cylinder. However, this time a rear mass is added at the extremity of the flexible structure. Moreover, the material (para-rubber) is less stiff than in FSI-PfS-1a. The Reynolds number is again Re = 30,470. The three-dimensional fluid velocity results show shedding vortices behind the structure, which reaches the second swiveling mode with a frequency of about 11.25 Hz corresponding to a Strouhal number of St = 0.179. Providing phase-averaged flow and structure measurements, precise experimental data for coupled computational fluid dynamics (CFD) and computational structure dynamics (CSD) validations are available for this new benchmark case. The test case possesses four main advantages: (i) The geometry is rather simple; (ii) Kinematically, the rotation of the front cylinder is avoided; (iii) The boundary conditions are well defined; (iv) Nevertheless, the resulting flow features and structure displacements are challenging from the computational point of view. Besides these experimental investigations detailed predictions based on LES are available. Particular attention has been paid to the computational model and the numerical set-up. Special seven-parameters shell elements are applied to precisely model the flexible structure. Structural tests are carried out to approximate the optimal structural parameters. A fine and smooth mesh for the flow calculation has been generated in order to correctly predict the wide range of different flow structures presents near and behind the flexible rubber plate. In accordance with the measurements, phase-averaging is applied to the numerical results allowing a detailed comparison with the phase-averaged experimental data. Both are found to be in close agreement exhibiting a structure deformation in the second swiveling mode with similar frequencies and amplitudes. Finally, a sensitivity study is carried out to show the influence of different physical parameters (e.g. Young's modulus) and modeling aspects (e.g. subgrid-scale model) on the FSI phenomenon