142 results on '"Robinet, J."'
Search Results
2. Instability mechanisms in meandering streamwise vortex pairs of upswept afterbody wakes
- Author
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Ranjan, Rajesh, Robinet, J.-Ch., and Gaitonde, Datta
- Published
- 2022
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3. Predicting degradation of organic molecules in cementitious media
- Author
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Bagaria, F., Riba, O., Albrecht, A., Robinet, J.-C., Madé, B., and Román-Ross, G.
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- 2021
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4. Implant removal of osteosynthesis. Results of a survey among Spanish orthopaedic surgeons
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Mingo-Robinet, J. and Pérez Aguilar, M.
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- 2021
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5. Global transition dynamics of flow in a lid-driven cubical cavity
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Ranjan, Rajesh, Unnikrishnan, S., Robinet, J.-C., and Gaitonde, Datta
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- 2021
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6. 3D global optimal forcing and response of the supersonic boundary layer
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Bugeat, B., Chassaing, J.-C., Robinet, J.-C., and Sagaut, P.
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- 2019
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7. Nonlinear optimal large-scale structures in turbulent channel flow
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Farano, M., Cherubini, S., De Palma, P., and Robinet, J.-C.
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- 2018
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8. Turbulent transition in a channel with superhydrophobic walls: anisotropic slip and shear misalignment effects.
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Jouin, A., Cherubini, S., and Robinet, J. C.
- Subjects
CROSS-flow (Aerodynamics) ,SUPERHYDROPHOBIC surfaces ,CHANNEL flow ,FLOW velocity ,TRANSITION flow ,GROUNDWATER flow - Abstract
Superhydrophobic surfaces dramatically reduce skin friction of overlying liquid flows. These surfaces are complex and numerical simulations usually rely on models to reduce this complexity. One of the simplest consists of finding an equivalent boundary condition through a homogenisation procedure, which in the case of channel flow over oriented riblets, leads to the presence of a small spanwise component in the homogenised base flow velocity. This work aims at investigating the influence of such a three-dimensionality of the base flow on stability and transition in a channel with walls covered by oriented riblets. Linear stability for this base flow is investigated: a new instability region, linked to cross-flow effects, is observed. Tollmien-Schlichting waves are also retrieved but the most unstable are three-dimensional. Transient growth is also affected as oblique streaks with non-zero streamwise wavenumber become the most amplified perturbations. When transition is induced by Tollmien-Schlichting waves, after an initial exponential growth regime, streaky structures with large spanwise wavenumber rapidly arise. Modal mechanisms appear to play a leading role in the development of these structures and a secondary stability analysis is performed to retrieve successfully some of their characteristics. The second scenario, initiated with cross-flow vortices, displays a strong influence of nonlinearities. The flow develops into large quasi-spanwise-invariant structures before breaking down to turbulence. Secondary stability on the saturated cross-flow vortices sheds light on this stage of transition. In both cases, cross-flow effects dominate the flow dynamics, suggesting the need to consider the anisotropicity of the wall condition when modelling superhydrophobic surfaces. [ABSTRACT FROM AUTHOR]
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- 2024
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9. Technical aspects and complications in the surgical treatment of poliomyelitis-affected lower limb fractures
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Mingo-Robinet, J., Alonso, J.A., Moreno-Barrero, M., González-García, L., Garcia-Virto, V., and Aguado, H.J.
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- 2018
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10. Impinging shear layer instability in over-expanded nozzle dynamics.
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Tarsia Morisco, C., Robinet, J.-C., Herpe, J., and Saucereau, D.
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FLOW separation , *BOUNDARY layer (Aerodynamics) , *ROCKET engines , *SPEED of sound - Abstract
When rocket engine nozzles operate at a high degree of over-expansion, an internal flow separation occurs with a strong unsteady shock–wave boundary layer interaction. The global dynamics results in a low-frequency mode, which is associated with the shock displacement, and a high-frequency mode, which is correlated with the shear layer–boundary layer interaction. While the mechanism responsible for the low-frequency oscillation is known, the one in charge of the high-frequency unsteadiness is not yet clear. The scope of this paper is to provide a physical explanation for this mechanism. To do that, a delayed detached eddy simulation is used to numerically reproduce the flow in the case of a sub-scale cold-gas truncated ideal contour nozzle. The obtained results are successfully compared to the experiments and confirm the presence of two non-axisymmetric wall pressure signatures at Strouhal numbers S t = f D j / U j ≃ 0.2 and 0.3 with different azimuthal selections. To reveal the origin of such modes, a power spectral density analysis is performed in the separated region. The analysis shows that both modes originate from the external shear layer and behave as "twins" in the separated region. The reason is that both modes are two sides of the same impinging shear layer instability: the acoustic mode propagates with the sound velocity, while the hydrodynamic one propagates with the supersonic shear layer velocity. In this context, the resulting self-sustained dynamics may be due to an acoustic–hydrodynamic feedback loop involving the impinging shear layer instability of the external supersonic shear layer and the separated region. [ABSTRACT FROM AUTHOR]
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- 2023
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11. Numerical investigation of the interaction between laminar to turbulent transition and the wake of an airfoil
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Ducoin, A., Loiseau, J.-Ch., and Robinet, J.-Ch.
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- 2016
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12. A Nonlinear Control Strategy for Finite-amplitude Perturbations in a Boundary-layer Flow
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Cherubini, S., Robinet, J.-C., and Palma, P. De
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- 2015
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13. Nonlinear optimal perturbation of turbulent channel flow as a precursor of extreme events.
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Ciola, N., De Palma, P., Robinet, J.-C., and Cherubini, S.
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CHANNEL flow ,TURBULENT flow ,TURBULENCE ,PROPER orthogonal decomposition ,PROBABILITY density function - Abstract
This work aims at studying the mechanisms behind the occurrence of extreme dissipation events in a channel flow, identifying nonlinear optimal perturbations as potential precursors of these events. Nonlinear optimal perturbations with respect to a generic turbulent instantaneous snapshot are computed for the first time using a direct-adjoint algorithm in the channel flow at $Re_{\tau }\approx 180$. The resulting initial perturbation displays the upstream tilting characteristic of Orr's mechanism and is positioned along the interfaces between two opposite-sign velocity streaks of the pre-existing turbulent field. Such a perturbation induces a sudden breakdown of the pre-existing structures and a heavier tail in the dissipation probability density function distribution. Different mechanisms are at play during this process: the high shear present at the interface between coherent low- and high-momentum regions is exploited to break down the larger structures and drive energy to small scales. This energy cascade is fed by an enhanced lift-up effect that produces intense streaks near the wall. It is found that the optimal perturbation grows exponentially during the first phase of its evolution reflecting the existence of a secondary modal instability of the streaks. To corroborate the results, the conditional spatiotemporal proper orthogonal decomposition (POD) analysis of Hack & Schimdt (J. Fluid Mech. , vol. 907, 2021, A9) is performed both in the perturbed and in the unperturbed flow, showing a clear agreement between the two cases and with the reference study. Thus, the optimal perturbation at initial time can be considered as a precursor of extreme events. [ABSTRACT FROM AUTHOR]
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- 2023
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14. Global Stability Analyses Unraveling Roughness-induced Transition Mechanisms
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Loiseau, J.-Ch., Robinet, J.-Ch., Cherubini, S., and Leriche, E.
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- 2015
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15. Sensitivity analysis and passive control of flows around NACA 4412 swept wings
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Nastro, G, Robinet, J.-C, Loiseau, J.-C, Passaggia, P.-Y, Mazellier, N, Laboratoire pluridisciplinaire de recherche en ingénierie des systèmes, mécanique et énergétique (PRISME), Université d'Orléans (UO)-Institut National des Sciences Appliquées - Centre Val de Loire (INSA CVL), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA), Laboratoire de Dynamique des Fluides (DynFluid), Conservatoire National des Arts et Métiers [CNAM] (CNAM), HESAM Université - Communauté d'universités et d'établissements Hautes écoles Sorbonne Arts et métiers université (HESAM)-HESAM Université - Communauté d'universités et d'établissements Hautes écoles Sorbonne Arts et métiers université (HESAM)-Arts et Métiers Sciences et Technologies, HESAM Université - Communauté d'universités et d'établissements Hautes écoles Sorbonne Arts et métiers université (HESAM), Europe H2020 CleanSky, and European Project: 887010,H2020 CleanSky 2,H2020-CS2-CFP10-2019-01,PERSEUS(2020)
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[PHYS.PHYS.PHYS-FLU-DYN]Physics [physics]/Physics [physics]/Fluid Dynamics [physics.flu-dyn] - Abstract
International audience
- Published
- 2022
16. Radiation safety in orthopedic operating theaters: What is the current situation?
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Torres-Torres, M., Mingo-Robinet, J., Moreno Barrero, M., Rivas Laso, J.Á., Burón Álvarez, I., and González Salvador, M.
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- 2014
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17. Effect of intramedullary reaming and nailing on the production of growth factors in the femur fracture callus in rats
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Mingo-Robinet, J., Valle-Cruz, J.A., Ortega-Medina, L., Fuentes-Ferrer, M., and López-Durán Stern, L.
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- 2013
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18. Global stability, sensitivity and passive control of low-Reynolds-number flows around NACA 4412 swept wings.
- Author
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Nastro, G., Robinet, J.-C., Loiseau, J.-C., Passaggia, P.-Y., and Mazellier, N.
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DOPPLER effect ,REYNOLDS number ,BOUNDARY layer separation ,LAMINAR flow ,HOPF bifurcations - Abstract
The stability and sensitivity of two- and three-dimensional global modes developing on steady spanwise-homogeneous laminar separated flows around NACA 4412 swept wings are numerically investigated for different Reynolds numbers ${\textit {Re}}$ and angles of attack $\alpha$. The wake dynamics is driven by the two-dimensional von Kármán mode whose emergence threshold in the $\alpha \unicode{x2013}{\textit {Re}}$ plane is computed with that of the three-dimensional centrifugal mode. At the critical Reynolds number, the Strouhal number, the streamwise wavenumber of the von Kármán mode and the spanwise wavenumber of the leading three-dimensional centrifugal mode scale as a power law of $\alpha$. The introduction of a sweep angle attenuates the growth of all unstable modes and entails a Doppler effect in the leading modes' dynamics and a shift towards non-zero frequencies of the three-dimensional centrifugal modes. These are found to be non-dispersive as opposed to the von Kármán modes. The sensitivity of the leading global modes is investigated in the vicinity of the critical conditions through adjoint-based methods. The growth-rate sensitivity map displays a region on the suction side of the wing, wherein a streamwise-oriented force has a net stabilising effect, comparable to what could have been obtained inside the recirculation bubble. In agreement with the predictions of the sensitivity analysis, a spanwise-homogeneous force suppresses the Hopf bifurcation and stabilises the entire branch of von Kármán modes. In the limit of small amplitudes, passive control via spanwise-wavy forcing produces a stabilising effect similar to that of a spanwise-homogeneous control and is more effective than localised spherical forces. [ABSTRACT FROM AUTHOR]
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- 2023
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19. Posterolateral approach in trimalleolar ankle fractures. Surgical technique
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Mingo-Robinet, J., Abril Larrainzar, J.M., and Valle Cruz, J.A.
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- 2012
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20. Open synovectomy of the ankle joint in young haemophiliacs: mid-term to long- term results of a single-centre series of 32 procedures
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Mingo-Robinet, J., Odent, T., Elie, C., Torchet, M.-F., Glorion, C., Padovani, J.-P., and Rothschild, C.
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- 2015
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21. Comparison of Subgrid-scale Viscosity Models and Selective Filtering Strategy for Large-eddy Simulations
- Author
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Aubard, G., Stefanin Volpiani, P., Gloerfelt, X., and Robinet, J. -C.
- Published
- 2013
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22. Meandering dynamics of streamwise vortex pairs in afterbody wakes
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Ranjan, Rajesh, Robinet, J. -Ch., and Gaitonde, Datta
- Subjects
Physics::Fluid Dynamics ,Fluid Dynamics (physics.flu-dyn) ,FOS: Mathematics ,FOS: Physical sciences ,Dynamical Systems (math.DS) ,Physics - Fluid Dynamics ,Mathematics - Dynamical Systems - Abstract
Wakes of upswept afterbodies are often characterized by a counter-rotating streamwise vortex pair. The unsteady dynamics of these vortices are examined with a spatio-temporally resolved Large-Eddy Simulation dataset on a representative configuration consisting of a cylinder with an upswept basal surface. Emphasis is placed on understanding the meandering motion of the vortices in the pair, including vortex core displacement, spectral content, stability mechanisms and overall rank-behavior. The first two energy-ranked modes obtained through Proper Orthogonal Decomposition(POD) of the time-resolved vorticity field reveals a pair of vortex dipoles aligned relatively perpendicularly to each other. The dynamics is successfully mapped to a matched Batchelor vortex pair whose spatial and temporal stability analyses indicate similar dipole structures associated with an |m|=1 elliptic mode pair. This short-wave elliptic instability dominates the meandering motion, with strain due to axial velocity playing a key role in breakdown. The low frequency of the unstable mode (Strouhal number StD =0.3 based on cylinder diameter) is consistent with spectral analysis of meandering in the LES. The wake is examined for its rank behavior; the number of modes required to reproduce the flow to given degree of accuracy diminishes rapidly outside of the immediate vicinity of the base. Beyond two diameters downstream, only two leading POD modes are required to reconstruct the dominant meandering motion and spatial structure in the LES data with < 15% performance loss, while ten modes nearly completely recover the flow field. This low-rank behavior may hold promise in constructing a reduced-order model for control purposes., 39 pages, 10 figures
- Published
- 2020
23. Low-frequency resolvent analysis of the laminar oblique shock wave/boundary layer interaction.
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Bugeat, B., Robinet, J.-Ch., Chassaing, J.-C., and Sagaut, P.
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BOUNDARY layer (Aerodynamics) ,SHOCK waves ,BOUNDARY layer separation ,MACH number ,REYNOLDS number ,SPEED - Abstract
Resolvent analysis is used to study the low-frequency behaviour of the laminar oblique shock wave/boundary layer interaction (SWBLI). It is shown that the computed optimal gain, which can be seen as a transfer function of the system, follows a first-order low-pass filter equation, recovering the results of Touber & Sandham (J. Fluid Mech., vol. 671, 2011, pp. 417-465). This behaviour is understood as proceeding from the excitation of a single stable, steady global mode whose damping rate sets the time scale of the filter. Different Mach and Reynolds numbers are studied, covering different recirculation lengths L. This damping rate is found to scale as 1/L, leading to a constant Strouhal number StL as observed in the literature. It is associated with a breathing motion of the recirculation bubble. This analysis furthermore supports the idea that the low-frequency dynamics of the SWBLI is a forced dynamics, in which background perturbations continuously excite the flow. The investigation is then carried out for three-dimensional perturbations for which two regimes are identified. At low wavenumbers of the order of L, a modal mechanism similar to that of two-dimensional perturbations is found and exhibits larger values of the optimal gain. At larger wavenumbers, of the order of the boundary layer thickness, the growth of streaks, which results from a non-modal mechanism, is detected. No interaction with the recirculation region is observed. Based on these results, the potential prevalence of three-dimensional effects in the low-frequency dynamics of the SWBLI is discussed. [ABSTRACT FROM AUTHOR]
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- 2022
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24. Minimal energy thresholds for sustained turbulent bands in channel flow.
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Parente, E., Robinet, J.-Ch., De Palma, P., and Cherubini, S.
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CHANNEL flow ,THRESHOLD energy ,REYNOLDS number ,CONTROLLED low-strength materials (Cement) ,TURBULENCE - Abstract
In this work, nonlinear variational optimization is used for obtaining minimal seeds for the formation of turbulent bands in channel flow. Using nonlinear optimization together with energy bisection, we have found that the minimal energy threshold for obtaining spatially patterned turbulence scales with Re
-8.5 for Re > 1000. The minimal seed, which is different to that found in a much smaller domain, is characterized by a spot-like structure surrounded by a low-amplitude large-scale quadrupolar flow filling the whole domain. This minimal-energy perturbation of the laminar flow has dominant wavelengths close to 4 in the streamwise direction and 1 in the spanwise direction, and is characterized by a spatial localization increasing with the Reynolds number. At Re ≲ 1200, the minimal seed evolves in time, creating an isolated oblique band, whereas for Re ≲ 1200, a quasi-spanwise-symmetric evolution is observed, giving rise to two distinct bands. A similar evolution is found also at low Re for non-minimal optimal perturbations. This highlights two different mechanisms of formation of turbulent bands in channel flow, depending on the Reynolds number and initial energy of the perturbation. The selection of one of these two mechanisms appears to be dependent on the probability of decay of the newly created stripe, which increases with time, but decreases with the Reynolds number. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
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25. Continuing invariant solutions towards the turbulent flow.
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Parente, E., Farano, M., Robinet, J.-Ch., De Palma, P., and Cherubini, S.
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TURBULENT flow ,TURBULENCE ,NAVIER-Stokes equations ,FLUID dynamics ,CHANNEL flow ,EDDY viscosity ,REYNOLDS stress - Abstract
A new mathematical framework is proposed for characterizing the coherent motion of fluctuations around a mean turbulent channel flow. We search for statistically invariant coherent solutions of the unsteady Reynolds-averaged Navier–Stokes equations written in a perturbative form with respect to the turbulent mean flow, using a suitable approximation of the Reynolds stress tensor. This is achieved by setting up a continuation procedure of known solutions of the perturbative Navier–Stokes equations, based on the continuous increase of the turbulent eddy viscosity towards its turbulent value. The recovered solutions, being sustained only in the presence of the Reynolds stress tensor, are representative of the statistically coherent motion of turbulent flows. For small friction Reynolds number and/or domain size, the statistically invariant motion is almost identical to the corresponding invariant solution of the Navier–Stokes equations. Whereas, for sufficiently large friction number and/or domain size, it considerably departs from the starting invariant solution of the Navier–Stokes equations, presenting spatial structures, main wavelengths and scaling very close to those characterizing both large- and small-scale motion of turbulent channel flows. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 2)'. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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26. Linear and nonlinear optimal growth mechanisms for generating turbulent bands.
- Author
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Parente, E., Robinet, J.-Ch., De Palma, P., and Cherubini, S.
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TURBULENT shear flow ,CHANNEL flow ,TRANSIENT analysis ,KINETIC energy ,TURBULENCE - Abstract
Recently, many authors have investigated the origin and growth of turbulent bands in shear flows, highlighting the role of streaks and their inflectional instability in the process of band generation and sustainment. Recalling that streaks are created by an optimal transient growth mechanism, and motivated by the observation of a strong increase of the disturbance kinetic energy corresponding to the creation of turbulent bands, we use linear and nonlinear energy optimisations in a tilted domain to unveil the main mechanisms allowing the creation of a turbulent band in a channel flow. Linear transient growth analysis shows an optimal growth for wavenumbers having an angle of approximately 35°, close to the peak values of the premultiplied energy spectra of direct numerical simulations. This linear optimal perturbation generates oblique streaks, which, for a sufficiently large initial energy, induce turbulence in the whole domain, due to the lack of spatial localisation. However, spatially localised perturbations obtained by adding nonlinear effects to the optimisation or by artificially confining the linear optimal to a localised region in the transverse direction are characterised by a large-scale flow and lead to the generation of a localised turbulent band. These results suggest that two main elements are needed for inducing turbulent bands in a tilted domain: (i) a linear energy growth mechanism, such as the lift-up, for generating large-amplitude flow structures, which produce inflection points; (ii) spatial localisation, linked to the presence or generation of large-scale vortices. We show that these elements alone generate isolated turbulent bands also in large non-tilted domains. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
27. 3D Steady and Unsteady Bifurcations in a Shock-wave/Laminar Boundary Layer Interaction: A Numerical Study
- Author
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Boin, J. -Ph., Robinet, J. Ch., Corre, Ch., and Deniau, H.
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- 2006
- Full Text
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28. Diffusion of organic anions in clay-rich mediaeffect of porosity exclusion on retardation
- Author
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Dagnelie, R.H., Rasamimanana, S., Blin, V., Radwan, J., Thory, E., Robinet, J-C., Lefevre, G., CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Agence Nationale pour la Gestion des Déchets Radioactifs (ANDRA), and Université Paris sciences et lettres (PSL)
- Subjects
[PHYS.NUCL]Physics [physics]/Nuclear Theory [nucl-th] ,adsorption ,diffusion ,transport ,Organic anions ,retardation factor ,anionic exclusion ,[PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex] - Abstract
International audience; The transport of emerging organic contaminants through the geosphere is often an environmental issue. The sorption of organic compounds slows their transport in soils and porous rocks and retardation is often assessed by extrapolation of batch experiments. However, transport experiments are preferable to strengthen migration data and modelling. In this context, we evaluated the adsorption of various organic acids by means of through-diffusion experiments in a sedimentary clay-rich rock (Callovo-Oxfordian, East of Paris Basin, France). A low diffusivity of organic anions was quantified with effective diffusion coefficients, De, ranged between 0.5 and 7 10$^{−12}$ m$^2$ s$^{−1}$. These values indicated an organic anion exclusion. As for chloride, the porosity accessible to organic anions was lower than that of water: $\varepsilon _a$(organic anions)
- Published
- 2018
29. Transport of Organic Molecules in environment insights from retardation in sedimentary rocks
- Author
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Dagnelie, R., Robinet, J.-C., CADARACHE, Bibliothèque, CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA), and Agence Nationale pour la Gestion des Déchets Radioactifs (ANDRA)
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organic molecules ,[PHYS.NUCL] Physics [physics]/Nuclear Theory [nucl-th] ,sorption ,[PHYS.NUCL]Physics [physics]/Nuclear Theory [nucl-th] ,[PHYS.NEXP] Physics [physics]/Nuclear Experiment [nucl-ex] ,transport ,geological barrier ,[PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex] ,retardation - Abstract
International audience; Organic molecules are widely studied in environmental sciences, marine chemistry, soil- and geosciences. Among them, anthropogenic organic matter (AOM) can be potentially released from hazardouswaste and migrate through geological rock formation or soils. AOM refers to a wide range of compounds,including both ionic and neutral molecules, polar and apolar molecules. The ionic polar molecules are highly soluble in water and more mobile in soils and rocks. The neutral (poly)aromatic compounds are less soluble, often absorbed by soil organic matter, but also more resistent against (bio)degradation. For all thesecompounds, adsorption or absorption processes can slow down their migration in environmental conditions. Consequently, understanding retardation phenomena of soluble organic matter in rocks and soils is crucial for safety assements of waste storage, decontamination processes, ore extraction and remediation of soils.
- Published
- 2018
30. Laminar supersonic sphere wake unstable bifurcations.
- Author
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Sansica, A., Ohmichi, Y., Robinet, J.-Ch., and Hashimoto, A.
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MACH number ,AXIAL flow ,VORTEX shedding ,SYMMETRY breaking ,STOCHASTIC dominance ,BIFURCATION diagrams - Abstract
The laminar sphere unstable bifurcations are sought at a Mach number of M
∞ = 1.2. Global stability performed on steady axisymmetric base flows determines the regular bifurcation critical Reynolds number at R e c r r e g = 650 , identifying a steady planar-symmetric mode to cause the loss of the wake axisymmetry. When global stability is performed on steady planar-symmetric base flows, a Hopf bifurcation is found at R e c r H o p f = 875 and an oscillatory planar-symmetric mode is temporally amplified. Despite some differences due to highly compressible effects, the supersonic unstable bifurcations present remarkably similar characteristics to their incompressible counterparts, indicating a robust laminar wake behavior over a large range of flow speeds. A new bifurcation for steady planar-symmetric base flow solutions is found above Re > 1000, caused by an anti-symmetric mode consisting of a 90° rotation of the dominant mode. To investigate this reflectional symmetry breaking bifurcation in the nonlinear framework, unsteady nonlinear calculations are carried out up to Re = 1300 and dynamic mode decomposition (DMD) based on the combination of input data low-dimensionalization and compressive sensing is used. While the DMD analysis confirms dominance and correspondence in terms of modal spatial distribution with respect to the global stability mode responsible for the Hopf bifurcation, no reflectional symmetry breaking DMD modes were found, asserting that the reflectional symmetry breaking instability is not observable in the nonlinear dynamics. The increased complexity of the wake dynamics at Re = 1300 can be instead explained by nonlinear interactions that suggest the low-frequency unsteadiness to be linked to the destabilization of the hairpin vortex shedding limit cycle. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
31. Weathering profile in a near-surface aquitard : example of the teguline Clay, East Paris Basin, France
- Author
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Lerouge, Catherine, Robinet, J. C., Debure, Mathieu, Henry, Benoît, Maubec, Nicolas, Madé, Benoit, Tournassat, Christophe, Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), ANDRA, Chatenay Malabry, France, Institut des Sciences de la Terre d'Orléans - UMR7327 (ISTO), Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), BRGM/ANDRA, Nagra, and collaboration BRGM/ANDRA
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pore waters ,[SDE]Environmental Sciences ,weathering ,tégulines clay ,mineralogy - Abstract
International audience; Near-surface aquitards are targeted for the containment of low-level radioactive waste (LLW) in near-surface environments because they could act as natural low-permeability protective barriers for underlying groundwater resources. Few detailed mineralogical and geochemical studies have been dedicated to surficial clay formations (Hendry and Wassenaar, 2000), compared to the abundance of data made available for reduced clay formations foreseen for deep nuclear repository systems. Their study is however of primary interest for the near-surface waste storage. The objectives of this study were (1) to describe the distribution of major ions in pore waters of a 80 m-thick clay-rich aquitard near the surface, and (2) to identify geochemical processes controlling the distribution of these ions. These objectives were completed by measurements of several parameters which are currently used to model pore water chemistry in deep reduced aquitards: (1) mineralogy and diagenetic sequence, (2) water content and porosity, (3) cation exchange capacity and cation distribution on the clay exchanger as well as the determination of anion concentrations (Cl and SO4) through milliQ leaching, (4) partial pressure of CO2, O2, and N2.
- Published
- 2017
32. Near-field perturbations in mudstone studied by large-scale laboratory experiments
- Author
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Arnoux, P., Radwan, J., Robinet, J.-C., Dagnelie, R., amplexor, amplexor, CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)
- Subjects
[PHYS.NUCL] Physics [physics]/Nuclear Theory [nucl-th] ,[PHYS.NUCL]Physics [physics]/Nuclear Theory [nucl-th] ,[PHYS.NEXP] Physics [physics]/Nuclear Experiment [nucl-ex] ,[PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex] ,ComputingMilieux_MISCELLANEOUS - Abstract
International audience
- Published
- 2017
33. Adsorption of anthropogenic organic molecules past and forthcoming challenges on cox and tegulines mudstones
- Author
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Dagnelie, R., Robinet, J.-C., amplexor, amplexor, CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)
- Subjects
[PHYS.NUCL] Physics [physics]/Nuclear Theory [nucl-th] ,[PHYS.NUCL]Physics [physics]/Nuclear Theory [nucl-th] ,[PHYS.NEXP] Physics [physics]/Nuclear Experiment [nucl-ex] ,[PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex] ,ComputingMilieux_MISCELLANEOUS - Abstract
International audience
- Published
- 2017
34. On the influence of the modelling of superhydrophobic surfaces on laminar–turbulent transition.
- Author
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Picella, F., Robinet, J.-Ch., and Cherubini, S.
- Subjects
SUPERHYDROPHOBIC surfaces ,INTERFACE dynamics ,CHANNEL flow ,GAS-liquid interfaces ,TRANSITION flow ,DRAG reduction - Abstract
Superhydrophobic surfaces dramatically reduce the skin friction of overlying liquid flows, providing a lubricating layer of gas bubbles trapped within their surface nano-sculptures. Under wetting-stable conditions, different models can be used to numerically simulate their effect on the overlying flow, ranging from spatially homogeneous slip conditions at the wall, to spatially heterogeneous slip–no-slip conditions taking into account or not the displacement of the gas–water interfaces. These models provide similar results in both laminar and turbulent regimes, but their effect on transitional flows has not been investigated yet. In this work we study, by means of numerical simulations and global stability analyses, the influence of the modelling of superhydrophobic surfaces on laminar–turbulent transition in a channel flow. For the K-type scenario, a strong transition delay is found using spatially homogeneous or heterogeneous slippery boundaries with flat, rigid liquid–gas interfaces. Whereas, when the interface dynamics is taken into account, the time to transition is reduced, approaching that of a no-slip channel flow. It is found that the interface deformation promotes ejection events creating hairpin heads that are prone to breakdown, reducing the transition delay effect with respect to flat slippery surfaces. Thus, in the case of modal transition, the interface dynamics must be taken into account for accurately estimating transition delay. Contrariwise, non-modal transition triggered by a broadband forcing is unaffected by the presence of these surfaces, no matter the surface modelling. Thus, superhydrophobic surfaces may or not influence transition to turbulence depending on the interface dynamics and on the considered transition process. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
35. Dense-gas effects on compressible boundary-layer stability.
- Author
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Gloerfelt, X., Robinet, J.-C., Sciacovelli, L., Cinnella, P., and Grasso, F.
- Subjects
SPECIFIC heat ,RELATIVE velocity ,SOUND waves ,WORKING fluids ,NATURE - Abstract
A study of dense-gas effects on the stability of compressible boundary-layer flows is conducted. From the laminar similarity solution, the temperature variations are small due to the high specific heat of dense gases, leading to velocity profiles close to the incompressible ones. Concurrently, the complex thermodynamic properties of dense gases can lead to unconventional compressibility effects. In the subsonic regime, the Tollmien–Schlichting viscous mode is attenuated by compressibility effects and becomes preferentially skewed in line with the results based on the ideal-gas assumption. However, the absence of a generalized inflection point precludes the sustainability of the first mode by inviscid mechanisms. On the contrary, the viscous mode can be completely stable at supersonic speeds. At very high speeds, we have found instances of radiating supersonic instabilities with substantial amplification rates, i.e. waves that travel supersonically relative to the free-stream velocity. This acoustic mode has qualitatively similar features for various thermodynamic conditions and for different working fluids. This shows that the leading parameters governing the boundary-layer behaviour for the dense gas are the constant-pressure specific heat and, to a minor extent, the density-dependent viscosity. A satisfactory scaling of the mode characteristics is found to be proportional to the height of the layer near the wall that acts as a waveguide where acoustic waves may become trapped. This means that the supersonic mode has the same nature as Mack's modes, even if its frequency for maximal amplification is greater. Direct numerical simulation accurately reproduces the development of the supersonic mode and emphasizes the radiation of the instability waves. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
36. Large scale dynamics of a high Reynolds number axisymmetric separating/reattaching flow.
- Author
-
Pain, R., Weiss, P.-E., Deck, S., and Robinet, J.-C.
- Subjects
KELVIN-Helmholtz instability ,REYNOLDS number ,VORTEX shedding ,FLUID dynamics ,HELICAL structure ,FOURIER analysis ,DISTRIBUTION (Probability theory) - Abstract
A numerical study is conducted to unveil the large scale dynamics of a high Reynolds number axisymmetric separating/reattaching flow at M
∞ = 0.7. The numerical simulation allows us to acquire a high rate sampled unsteady volumetric dataset. This huge amount of spatial and temporal information is exploited in the Fourier space to visualize for the first time in physical space and at such a high Reynolds number (ReD = 1.2 × 106 ) the statistical signature of the helical structure related to the antisymmetric mode (m = 1) at StD = 0.18. The main hydrodynamic mechanisms are identified through the spatial distribution of the most energetic frequencies, i.e., StD = 0.18 and StD ≥ 3.0 corresponding to the vortex-shedding and Kelvin-Helmholtz instability phenomena, respectively. In particular, the dynamics related to the dimensionless shedding frequency is shown to become dominant for 0.35 ≤ x/D ≤ 0.75 in the whole radial direction as it passes through the shear layer. The spatial distribution of the coherence function for the most significant modes as well as a three-dimensional Fourier decomposition suggests the global features of the flow mechanisms. More specifically, the novelty of this study lies in the evidence of the flow dynamics through the use of cross-correlation maps plotted with a frequency selection guided by the characteristic Strouhal number formerly identified in a local manner in the flow field or at the wall. Moreover and for the first time, the understanding of the scales at stake is supported both by a Fourier analysis and a dynamic mode decomposition in the complete three-dimensional space surrounding the afterbody zone. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
37. Processes of cation migration in clayrocks: Final Scientific Report of the CatClay EuropeanProject
- Author
-
Altmann, S., Aertsens, M., Appelo, T., Bruggeman, C., Gaboreau, Stéphane, Glaus, M., Jacquier, P., Kupcik, T., Maes, N., Montoya, V., Rabung, T., Robinet, J.-C., savoye, Sebastien, Schaefer, T., Tournassat, C., Van Laer, L., Van Loon, L., ANDRA, Chatenay Malabry, France, Centre d'Etude de l'Energie Nucléaire (SCK-CEN), Hydrochemical Consultant, Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), Paul Scherrer Institute (PSI), Laboratoire de Mesures et Modélisation de la Migration des Radionucléides (L3MR), Service d'Etudes du Comportement des Radionucléides (SECR), Département de Physico-Chimie (DPC), CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Département de Physico-Chimie (DPC), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, Karlsruhe Institute of Technology (KIT), and European Project: 249624,EC:FP7:Fission,FP7-Fission-2009,CATCLAY(2010)
- Subjects
sorption ,clay: claystones ,diffusion ,zinc ,[SDE]Environmental Sciences ,[CHIM]Chemical Sciences ,strontium ,cations ,europium - Abstract
International audience; In the framework of the feasibility studies on the radioactive waste disposal in deep argillaceous formations, it isnow well established that the transport properties of solutes in clay rocks, i.e. parameter values for Fick’s law, are mainlygoverned by the negatively charged clay mineral surface. While a good understanding of the diffusive behaviour of non-reactiveanionic and neutral species is now achieved, much effort has to be placed on improving understanding of coupledsorption/diffusion phenomena for sorbing cations. Indeed, several cations known to form highly stable surface complexes withsites on mineral surfaces migrate more deeply into clay rock than expected. Therefore, the overall objective of the EC CatClayproject is to address this issue, using a ‘bottom-up’ approach, in which simpler, analogous systems (here a compacted clay,‘pure’ illite) are experimentally studied and modelled, and then the transferability of these results to more complex materials, i.e.the clay rocks under consideration in France, Switzerland and Belgium for hosting radioactive waste disposal facilities, isverified. The cations of interest were chosen for covering a representative range of cations families: from a moderately sorbingcation, the strontium, to three strongly sorbing cations, Co(II), Zn(II) and Eu(III). For the 4 years of this project, much effort wasdevoted to developing and applying specific experimental methods needed for acquiring the high precision, reliable data neededto test the alternative hypotheses represented by different conceptual-numerical models. The enhanced diffusion of the sorbingcations of interest was confirmed both in the simpler analogous illite system for Sr2+, Co(II) and Zn(II), but also in the naturalclay rocks, except for Eu(III). First modelling approach including diffusion in the diffuse double layer (DDL) promisinglysucceeded in reproducing the experimental data under the various conditions both in illite and clay rocks, even though someassumptions made have to be verified. In parallel, actual 3D geometrical pore size distributions of compacted illite, and in lessextent, clay rock samples, were successfully determined by combining TEM and FIB-nt analyses on materials maintained in awater-like saturation state by means of an extensive impregnation step. Based on this spatial distribution of pores, first numericaldiffusion experiments were carried at the pore scale through virtual illite, enabling a better understanding of how transferpathways are organized in the porous media. Finally, the EC CatClay project allowed a better understanding of the migration ofstrongly sorbing tracers through low permeability ‘clay rock’ formations, increasing confidence in our capacity to demonstratethat the models used to predict radionuclide migration through these rocks are scientifically sound.
- Published
- 2015
38. A hairpin-shaped optimal perturbation in a plane Poiseuille flow
- Author
-
Farano, M, Cherubini, Stefania, Robinet, J. C., and DE PALMA, Pietro
- Published
- 2015
39. Investigation of the roughness-induced transition: linear and non-linear optimal perturbations
- Author
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Loiseau, J. C., Cherubini, Stefania, DE PALMA, Pietro, and Robinet, J. C.
- Published
- 2015
40. P-norm optimal 3D perturbations in the Poiseuille flow
- Author
-
Farano, M., Cherubini, Stefania, Robinet, J. C., and DE PALMA, Pietro
- Published
- 2015
41. Bifurcation analysis and frequency prediction in shear-driven cavity flow.
- Author
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Bengana, Y., Loiseau, J.-Ch., Robinet, J.-Ch., and Tuckerman, L. S.
- Subjects
FORECASTING ,LIMIT cycles ,INCOMPRESSIBLE flow ,HILBERT transform ,HOPF bifurcations ,BIFURCATION diagrams - Abstract
A comprehensive study of the two-dimensional incompressible shear-driven flow in an open square cavity is carried out. Two successive bifurcations lead to two limit cycles with different frequencies and different numbers of structures which propagate along the top of the cavity and circulate in its interior. A branch of quasi-periodic states produced by secondary Hopf bifurcations transfers the stability from one limit cycle to the other. A full analysis of this scenario is obtained by means of nonlinear simulations, linear stability analysis and Floquet analysis. We characterize the temporal behaviour of the limit cycles and quasi-periodic state via Fourier transforms and their spatial behaviour via the Hilbert transform. We address the relevance of linearization about the mean flow. Although here the nonlinear frequencies are not very far from those obtained by linearization about the base flow, the difference is substantially reduced when eigenvalues are obtained instead from linearization about the mean and in addition, the corresponding growth rate is small, a combination of properties called RZIF (real zero imaginary frequency). Moreover growth rates obtained by linearization about the mean of one limit cycle are correlated with relative stability to the other limit cycle. Finally, we show that the frequencies of the successive modes are separated by a constant increment. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
42. Attached cavitation in laminar separations within a transition to unsteadiness.
- Author
-
Croci, K., Ravelet, F., Danlos, A., Robinet, J.-C., and Barast, L.
- Subjects
CAVITATION ,FLOW separation ,REYNOLDS number ,BOUNDARY layer separation ,LAMINAR flow ,TRANSITION flow - Abstract
Attached sheet cavitation is usually observed in turbulent water flows within small laminar separation bubbles which can provide favorable conditions for inception and attachment of cavities. In the present study, viscous silicone oils are used within a small scale Venturi geometry to investigate attached cavitation into laminar separated flows for Reynolds numbers from 346 to 2188. Numerical simulations about single phase flows are performed with steady simulations for a Reynolds number range Re ∈ [50; 1400] and with unsteady simulations for Re ∈ [1000; 2000]. They reveal the emergence of two large laminar boundary layer separations downstream of the Venturi throat in addition to low pressure zones which can possibly induce both degassing or cavitation features. Experiments are performed with high-speed photography, and several multiphase dynamics are observed in these viscous flows, which are considered as quasisteady flows at low Reynolds numbers Re ≤ 1400. Degassing phenomenon with air bubble recirculation has been first observed at pressures far above liquid vapor pressure whereas typical attached cavities have been identified for low pressure conditions as "band" and "tadpole" cavities into the different separations of the laminar flows. For higher Reynolds numbers, a flow regime transition can be noticed in the wake of well-developed gas structures, characterized by wake instabilities, causing vortex cavitation above a critical Reynolds number associated with the bubble width R e c b ≃ 616. This regime transition can possibly occur either quasicontinuously in the wake of an attached "band" vapor cavity or intermittently behind a recirculating air bubble generated with degassing. This last phenomenon is associated in our study to classical "patch" cavitation. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
43. Computing heteroclinic orbits using adjoint-based methods.
- Author
-
Farano, M., Cherubini, S., Robinet, J.-C., De Palma, P., and Schneider, T. M.
- Subjects
NONLINEAR dynamical systems ,SHEAR flow ,COUETTE flow - Abstract
Transitional turbulence in shear flows is supported by a network of unstable exact invariant solutions of the Navier–Stokes equations. The network is interconnected by heteroclinic connections along which the turbulent trajectories evolve between invariant solutions. While many invariant solutions in the form of equilibria, travelling waves and periodic orbits have been identified, computing heteroclinic connections remains a challenge. We propose a variational method for computing orbits dynamically connecting small neighbourhoods around equilibrium solutions. Using local information on the dynamics linearized around these equilibria, we demonstrate that we can choose neighbourhoods such that the connecting orbits shadow heteroclinic connections. The proposed method allows one to approximate heteroclinic connections originating from states with multi-dimensional unstable manifold and thereby provides access to heteroclinic connections that cannot easily be identified using alternative shooting methods. For plane Couette flow, we demonstrate the method by recomputing three known connections and identifying six additional previously unknown orbits. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
44. Optimal perturbation for two-dimensional vortex systems: route to non-axisymmetric state.
- Author
-
Johnson, H. G., Brion, V., Jacquin, L., Navrose, and Robinet, J. C.
- Subjects
FLUX flow ,VORTEX motion ,PERTURBATION theory - Abstract
We investigate perturbations that maximize the gain of disturbance energy in a two-dimensional isolated vortex and a counter-rotating vortex pair. The optimization is carried out using the method of Lagrange multipliers. For low initial energy of the perturbation (E.0/), the nonlinear optimal perturbation/gain is found to be the same as the linear optimal perturbation/gain. Beyond a certain threshold E.0/, the optimal perturbation/gain obtained from linear and nonlinear computations are different. There exists a range of E.0/ for which the nonlinear optimal gain is higher than the linear optimal gain. For an isolated vortex, the higher value of nonlinear optimal gain is attributed to interaction among different azimuthal components, which is otherwise absent in a linearized system. Spiral dislocations are found in the nonlinear optimal perturbation at the radial location where the most dominant wavenumber changes. Long-time nonlinear evolution of linear and nonlinear optimal perturbations is studied. The evolution shows that, after the initial increment of perturbation energy, the vortex attains a quasi-steady state where the mean perturbation energy decreases on a slow time scale. The quasi-steady vortex state is non-axisymmetric and its shape depends on the initial perturbation. It is observed that the lifetime of a quasi-steady vortex state obtained using the nonlinear optimal perturbation is longer than that obtained using the linear optimal perturbation. For a counter-rotating vortex pair, the mechanism that maximizes the energy gain is found to be similar to that of the isolated vortex. Within the linear framework, the optimal perturbation for a vortex pair can be either symmetric or antisymmetric, whereas the structure of the nonlinear optimal perturbation, beyond the threshold E.0/, is always asymmetric. No quasi-steady state for a counter-rotating vortex pair is observed. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
45. Three-dimensional instability of a flow past a sphere: Mach evolution of the regular and Hopf bifurcations.
- Author
-
Sansica, A., Robinet, J. Ch., Alizard, F., and Goncalves, E.
- Subjects
HOPF bifurcations ,COMPRESSIBLE flow ,REYNOLDS number - Abstract
A fully three-dimensional linear stability analysis is carried out to investigate the unstable bifurcations of a compressible viscous fluid past a sphere. A time-stepper technique is used to compute both equilibrium states and leading eigenmodes. In agreement with previous studies, the numerical results reveal a regular bifurcation under the action of a steady mode and a supercritical Hopf bifurcation that causes the onset of unsteadiness but also illustrate the limitations of previous linear approaches, based on parallel and axisymmetric base flow assumptions, or weakly nonlinear theories. The evolution of the unstable bifurcations is investigated up to low-supersonic speeds. For increasing Mach numbers, the thresholds move towards higher Reynolds numbers. The unsteady fluctuations are weakened and an axisymmetrization of the base flow occurs. For a sufficiently high Reynolds number, the regular bifurcation disappears and the flow directly passes from an unsteady planar-symmetric solution to a stationary axisymmetric stable one when the Mach number is increased. A stability map is drawn by tracking the bifurcation boundaries for different Reynolds and Mach numbers. When supersonic conditions are reached, the flow becomes globally stable and switches to a noise-amplifier system. A continuous Gaussian white noise forcing is applied in front of the shock to examine the convective nature of the flow. A Fourier analysis and a dynamic mode decomposition show a modal response that recalls that of the incompressible unsteady cases. Although transition in the wake does not occur for the chosen Reynolds number and forcing amplitude, this suggests a link between subsonic and supersonic dynamics. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
46. Successive bifurcations in a fully three-dimensional open cavity flow.
- Author
-
Picella, F., Loiseau, J.-Ch., Robinet, J.-Ch., Lusseyran, F., Cherubini, S., and Pastur, L.
- Subjects
THREE-dimensional flow ,BIFURCATION theory ,CAVITY walls - Abstract
The transition to unsteadiness of a three-dimensional open cavity flow is investigated using the joint application of direct numerical simulations and fully three-dimensional linear stability analyses, providing a clear understanding of the first two bifurcations occurring in the flow. The first bifurcation is characterized by the emergence of Taylor-Görtler-like vortices resulting from a centrifugal instability of the primary vortex core. Further increasing the Reynolds number eventually triggers self-sustained periodic oscillations of the flow in the vicinity of the spanwise end walls of the cavity. This secondary instability causes the emergence of a new set of Taylor-Görtler vortices experiencing a spanwise drift directed toward the spanwise end walls of the cavity. While a two-dimensional stability analysis would fail to capture this secondary instability due to the neglect of the lateral walls, it is the first time to our knowledge that this drifting of the vortices can be entirely characterized by a three-dimensional linear stability analysis of the flow. Good agreements with experimental observations and measurements strongly support our claim that the initial stages of the transition to turbulence of three-dimensional open cavity flows are solely governed by modal instabilities. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
47. Roughness-induced transition by quasi-resonance of a varicose global mode.
- Author
-
Bucci, M. A., Puckert, D. K., Andriano, C., Loiseau, J.-ch., Cherubini, S., Robinet, J.-ch., and Rist, U.
- Subjects
REYNOLDS number ,STABILITY of linear systems ,PSEUDOSPECTRUM ,FLOW coefficient ,DYNAMICS - Abstract
The onset of unsteadiness in a boundary-layer flow past a cylindrical roughness element is investigated for three flow configurations at subcritical Reynolds numbers, both experimentally and numerically. On the one hand, a quasi-periodic shedding of hairpin vortices is observed for all configurations in the experiment. On the other hand, global stability analyses have revealed the existence of a varicose isolated mode, as well as of a sinuous one, both being linearly stable. Nonetheless, the isolated stable varicose modes are highly sensitive, as ascertained by pseudospectrum analysis. To investigate how these modes might influence the dynamics of the flow, an optimal forcing analysis is performed. The optimal response consists of a varicose perturbation closely related to the least stable varicose isolated eigenmode and induces dynamics similar to that observed experimentally. The quasi-resonance of such a global mode to external forcing might thus be responsible for the onset of unsteadiness at subcritical Reynolds numbers, hence providing a simple explanation for the experimental observations. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
48. Mechanical forces-induced human osteoblasts differentiation involves MMP-2/MMP-13/MT1-MMP proteolytic cascade
- Author
-
Barthelemi, S., Robinet, J., Garnotel, R., Antonicelli, F., Schittly, E., Hornebeck, W., Lorimier, S., Matrice extracellulaire et dynamique cellulaire - UMR 7369 (MEDyC), Université de Reims Champagne-Ardenne (URCA)-SFR CAP Santé (Champagne-Ardenne Picardie Santé), and Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
ComputingMilieux_MISCELLANEOUS - Abstract
International audience
- Published
- 2012
49. A transition scenario induced by high- intensity freestream turbulence in a boundary layer
- Author
-
Cherubini, Stefania, Robinet, J. C., and DE PALMA, Pietro
- Published
- 2012
50. Tracking the edge of chaos in a boundary-layer flow
- Author
-
Cherubini, Stefania, DE PALMA, Pietro, Robinet, J. C., and Bottaro, A.
- Published
- 2011
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