79 research outputs found

    Simulation of forced deformable bodies interacting with two-dimensional incompressible flows: Application to fish-like swimming

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    International audienceWe present an efficient algorithm for simulation of deformable bodies interacting with two-dimensional incompressible flows. The temporal and spatial discretizations of the Navier-Stokes equations in vorticity stream-function formulation are based on classical fourth-order Runge-Kutta and compact finite differences, respectively. Using a uniform Cartesian grid we benefit from the advantage of a new fourth-order direct solver for the Poisson equation to ensure the incompressibility constraint down to machine zero. For introducing a deformable body in fluid flow, the volume penalization method is used. A Lagrangian structured grid with prescribed motion covers the deformable body interacting with the surrounding fluid due to the hydrodynamic forces and moment calculated on the Eulerian reference grid. An efficient law for curvature control of an anguilliform fish, swimming to a prescribed goal, is proposed. Validation of the developed method shows the efficiency and expected accuracy of the algorithm for fish-like swimming and also for a variety of fluid/solid interaction problems

    France South Pilot Centre - Main activities of the MSNM-GP laboratory

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    ERCOFTAC Bulletin 77Presentation of the main activities of the MSNM-GP laborator

    Simulation of fish escape and swimming toward a predefined goal

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    We present an immersed boundary method for numerical simulation of a swimming fish. The vorticity transport equation is solved on a Cartesian grid using compact finite dif- ferences. A Lagrangian structured grid defines the fish body and is moving in the surrounding incompressible flow due to the exerted hydrodynamic forces and the torque. An efficient law determining the curvature of a swimming fish is presented which is based on the geometrically exact theory of nonlinear beams and quaternions. Validation of the solver shows the efficiency and expected accuracy of the algorithm for swimming fish simulations. The structure of the wake of a swimming fish is studied, and some common features with the wake of a flapping plate are demonstrated

    High-order Large Eddy Simulations of Confined Rotor-Stator Flows

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    International audienceIn many engineering and industrial applications, the investigation of rotating turbulent flow is of great interest. In rotor-stator cavities, the centrifugal and Coriolis forces have a strong influence on the turbulence by producing a secondary flow in the meridian plane composed of two thin boundary layers along the disks separated by a non-viscous geostrophic core. Most numerical simulations have been performed using RANS and URANS modelling, and very few investigations have been performed using LES. This paper reports on quantitative comparisons of two high-order LES methods to predict a turbulent rotor-stator flow at the rotational Reynolds number Re=400000. The classical dynamic Smagorinsky model for the subgrid-scale stress (Germano et al., Phys Fluids A 3(7):1760-1765, 1991) is compared to a spectral vanishing viscosity technique (Séverac & Serre, J Comp Phys 226(2):1234-1255, 2007). Numerical results include both instantaneous data and postprocessed statistics. The results show that both LES methods are able to accurately describe the unsteady flow structures and to satisfactorily predict mean velocities as well as Reynolds stress tensor components. A slight advantage is given to the spectral SVV approach in terms of accuracy and CPU cost. The strong improvements obtained in the present results with respect to RANS results confirm that LES is the appropriate level of modelling for flows in which fully turbulent and transition regimes are involved

    Transition vers la turbulence dans un fluide supercritique en configuration de Rayleigh-Bénard

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    Des simulations numériques directes de la convection de Rayleigh-Bénard dans un fluide, légèrement au dessus de son point critique liquide-vapeur, sont présentées pour des nombres de Rayleigh compris entre 10^6 and 10^8. Une description spatio-temporelle de l'écoulement est réalisée depuis le début du régime convectif jusqu'à l'établissement du régime turbulent. Cette description concerne principalement la structure du champ de température ainsi que l'équilibre thermique global de la cavité. On insiste sur l'influence de la forte stratification du fluide induite par sa compressibilité élevée sur la pénétrabilité des structures convectives et sur l'équilibre thermique global de la cavité, et une comparaison avec le cas d'un gaz parfait, à nombre de Rayleigh équivalent, est présentée

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    A pseudo-spectral solution of vorticity-stream function equations using the influence matrix technique

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    International audienceA method for computing unsteady two dimensional incompressible flows, using the vorticity and the stream function as dependent variables approximated by Chebyshev polynomial expansions is presented. Boundary conditions for the vorticity are derived by the influence matrix technique. The theoretical and numerical difficulties associated with the two-dimensional formulation of the method are discussed. Numerical results illustrate the properties of the method
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