Hôpital-Camfrout, France
Hôpital-Camfrout, France

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Ducoin A.,CNRS Laboratory for Hydrodynamics, Energetics & Atmospheric Environment | Loiseau J.-C.,KTH Royal Institute of Technology | Robinet J.-C.,DynFluid Laboratory
European Journal of Mechanics, B/Fluids | Year: 2016

The objective of this work is to investigate numerically the different physical mechanisms of the transition to turbulence of a separated boundary-layer flow over an airfoil at low angle of attack. In this study, the spectral elements code Nek5000 is used to simulate the flow over a SD7003 wing section at an angle of attack of α=4(ring operator). Several laminar cases are first studied from Re=2000 to Re=10000, and a gradual increase of the Reynolds number is then performed in order to investigate one transitional case at Re=20000. Computations are compared with measurements where the instability mechanisms in the separated zone and near wake zone have been analyzed. The mechanism of transition is investigated, where the DMD (Dynamic Mode Decomposition) is used in order to extract the main physical modes of the flow and to highlight the interaction between the transition and the wake flow. The results suggest that the transition process appears to be physically independent of the wake flow, while the LSB shedding process is locked-in with the von Kármán instability and acts as a sub-harmonic. © 2016 Elsevier Masson SAS.

Ducoin A.,Dynfluid Laboratory | Young Y.L.,University of Michigan
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2013

The objective of this research is to derive and validate scaling relationships for flexible lifting bodies in transitional and turbulent flows. The motivation is to help the design and interpretation of reduced-scale experimental studies of flexible hydrofoils, with focus on the influence of viscous effects on the hydroelastic response. The numerical method is based on a previous validated viscous FSI solver presented in [1]. It is based on the coupling between a commercial Computational Fluid Dynamics (CFD) solver, CFX, and a simple two-degrees-of-freedom (2-DOF) system that simulates the free tip section displacement of a cantilevered, rectangular hydrofoil. To validate the scaling relations, sample numerical results are shown for three geometrically similar models: full scale, 1/2 scale and 1/10 scale. On the fluid side, although the effects of gravity and compressibility are assumed to be negligible, three different methods of scaling the velocity are considered: Reynolds scaling, Froude scaling, and Mach scaling. The three scaling methods produce different velocity scales when the fluid properties and gravitational constant are the same between the model and prototype, which will lead to different scaling for the material properties. The results suggest that by applying Mach scaling (which does not mean the flow is compressible, but simply requires the relative inflow velocity and fluid properties to be the same between the model and the prototype) and Re≥ 2×106, the same material as the full scale could be used, which will lead to similar stress distributions, in addition to similar strains, and hence similar hydroelastic response and failure mechanisms. However, if Re≤ 2×106 and Mach scale is used, a viscous correction is required to properly extrapolate the experimental results to full-scale. Copyright © 2013 by ASME.

Hamidi A.,CNRS Process and Engineering in Mechanics and Materials Laboratory | Khelladi S.,DynFluid laboratory | Illoul A.,CNRS Process and Engineering in Mechanics and Materials Laboratory | Shirinbayan M.,CNRS Process and Engineering in Mechanics and Materials Laboratory | And 2 more authors.
International Journal of Material Forming | Year: 2015

During Reactive Rotational Molding (RRM), it is very important to predict the fluid flow in order to obtain the piece with homogeneous shape and high quality. This prediction may be possible by simulation the fluid flow during rotational molding. In this study we have used a mixture of isocyanate and polyol as reactive system. The kinetic rheological behaviors of thermoset polyurethane are investigated in anisothermal conditions. Thanks to these, rheokinetik model of polyurethane was identified. Then, to simulate the RRM, we have applied Smoothed Particles Hydrodynamics (SPH) method which is suited method to simulate the fluid flow with free surface such as occurs at RRM. Modelling and simulating reactive system flow depend on different parameters; one of them is the surface tension of reactive fluid. To implement force tension surface, the interface between polymer and air is dynamically tracked by finding the particles on this border. First, the boundary particles are detected by free-surface detection algorithm developed by Barecasco, Terissa and NAA [1, 2] in two and three dimension. Then, analytical and geometrical algorithms have been used for interface reconstructions. The aim of this work is the implementation of surface tension force in the SPH solver applied to RRM. To illustrate that, we used novel and simple geometric algorithm fitting circle and fitting sphere, in two and three dimensional configurations, respectively. The model has been validated using a well-known dam break test case which covered the experimental data. © 2015 Springer-Verlag France

Aubard G.,Arts et Metiers ParisTech | Aubard G.,DynFluid Laboratory | Gloerfelt X.,Arts et Metiers ParisTech | Gloerfelt X.,DynFluid Laboratory | And 2 more authors.
AIAA Journal | Year: 2013

The simulation of low-frequency unsteadiness in shock wave/turbulent boundary-layer interactions constitutes a challenging case insofar as very long time integrations are required to describe these broadband motions at frequencies two orders of magnitude lower than those of the turbulent motions. A relatively low-cost numerical strategy is established in the present study. The use of quasi-spectral centered finite differences in conjunction with high-order selective filtering provides an efficient method for compressible large-eddy simulations based on explicit filtering regularization. This strategy is extended to flows containing discontinuities by switching between the highorder filter used in regular zones and a low-order filter acting selectively near the shock locations. The accuracy of the current strategy is assessed for a developing turbulent supersonic boundary layer. The case of an oblique shock wave impinging on a flat plate is then successfully validated against previous experimental and numerical studies. The numerical strategy is finally applied to a configuration involving important low-frequency unsteadiness. A database covering dozens of low-frequency cycles is established to characterize the broadband nature of the low-frequency dynamics, which can be associated with a breathing motion of the decelerated zone.Aparticular attention is drawn to the important turbulent activity occurring at medium frequencies. It is shown that it corresponds to vortical structures shed in the developing shear layer.Afrequency-wave number analysis of the wall pressure helps to identify their phase speed. Copyright © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Pont G.,Airbus | Cinnella P.,Dynfluid Laboratory | Robinet J.C.,Dynfluid Laboratory | Brenner P.,Airbus
Notes on Numerical Fluid Mechanics and Multidisciplinary Design | Year: 2015

An automatic HRL (Hybrid RANS/LES) strategy is investigated in FLUSEPA, a finite-volume solver developed by Airbus Defense and Space. A HRL turbulence model is coupled to a high-order hybrid numerical approximation method. Concerning the turbulence model, the well-known k − ε two equations RANS turbulence model is sensitized to the grid as suggested by Perot and Gadebusch (Phy Fluids 19:1–11, 2007). Concerning the numerical strategy, a third-order accurate upwind approximation method is locally re-centered in vortex dominated regions to achieve non-dissipative fourth-order accuracy. Results are presented for a 2D backward facing step and an an axisymmetry backward facing step, which represent good prototypes of after body flows. © Springer International Publishing Switzerland 2015.

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