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25 results on '"Debliquy, Olivier"'

1. Local shell-to-shell energy transfer via nonlocal Interactions in fluid turbulence

Author

Verma, Mahendra K., Ayyer, Arvind, Debliquy, Olivier, Kumar, Shishir, and Chandra, Amar V.

Subjects
Nonlinear Sciences - Chaotic Dynamics, Condensed Matter
Abstract

In this paper we analytically compute the strength of nonlinear interactions in a triad, and the energy exchanges between wavenumber shells in incompressible fluid turbulence. The computation has been done using first-order perturbative field theory. In three dimension, magnitude of triad interactions is large for nonlocal triads, and small for local triads. However, the shell-to-shell energy transfer rate is found to be local and forward. This result is due to the fact that the nonlocal triads occupy much less Fourier space volume than the local ones. The analytical results on three-dimensional shell-to-shell energy transfer match with their numerical counterparts. In two-dimensional turbulence, the energy transfer rates to the near-by shells are forward, but to the distant shells are backward; the cumulative effect is an inverse cascade of energy., Comment: 10 pages, Revtex4

Published
2002
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3. Energy Fluxes and Shell-to-Shell Transfers in MHD Turbulence

Author

Carati, Daniele, Debliquy, Olivier, Knaepen, Bernard, Teaca, Bogdan, Verma, Mahendra, Barth, Timothy J., editor, Griebel, Michael, editor, Keyes, David E., editor, Nieminen, Risto M., editor, Roose, Dirk, editor, Schlick, Tamar, editor, Kassinos, Stavros C., editor, Langer, Carlos A., editor, Iaccarino, Gianluca, editor, and Moin, Parviz, editor

Published
2007
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6. Pseudo-spectral methods applied to hydrodynamic and magnetohydrodynamic turbulence

Author

Debliquy, Olivier, Carati, Daniele, Weyssow, Boris, Degrez, Gérard, Knaepen, Bernard, Mareschal, Michel, Sagaut, Pierre, Winckelmans, Grégoire, and Malek-Mansour, Mohammad-Ali

Subjects
Physique, Plasma dynamics, Plasmas, Dynamique des, DNS, Turbulence -- Computer simulation, Physics::Fluid Dynamics, Magnetohydrodynamics, Turbulence -- Simulation par ordinateur, Hydrodynamique, LES, Hydrodynamics, Numerical simulations, Magnétohydrodynamique, Sciences exactes et naturelles
Abstract

In our everyday life, turbulence is an omnipresent phenomenon and yet remains poorly understood. Its random and chaotic nature makes it a subject almost impossible to treat from the mathematical point of view and, at present, thereis no real prospect of a simple analytic theory. Scientists have therefore regarded the numerical simulation as an alternative to compute the relevant properties of turbulent flows. In this context, our thesis aims at developing and using accurate computational methods, namely pseudo-spectral methods, for studying hydrodynamic (1st part) and magnetohydrodynamic (2nd part) turbulence.In the hydrodynamic part, Chapter I introduces the governing equations of fluid mechanics as well as the main issues related to the numerical study of turbulent flows. In particular, the Direct Numerical Simulations (DNS) of turbulence, in which accurate numerical solutions of the Navier-Stokes equations are obtained, are shown to be limited to moderately turbulent flows.Chapter II introduces the Large Eddy Simulation (LES) technique which aims at simulating highly turbulent flows and which is based on a separation of scales.In practice, it consists of simulating the large - resolved - scales of the flow explicitly while modelling the small - unresolved - scales. Two different approaches for modelling the kinetic energy of the unresolved scales are proposed and their respective advantages and drawbacks are discussed.Chapter III is devoted the study of the mixing-layer using both DNS and LES. It consists of an inhomogeneous turbulent flow which has been studied experimentally and for which well-documented measurements are available. A highly accurate DNS mimicking the same experiment has been produced. It allows to study the inhomogeneity and anisotropy properties of this flow. Also, LES of the same flow, using different models, have been evaluated. In Chapter IV, we explore a pseudo-spectral method to investigate turbulence in a pipe. In this case, the method has to take into account two additional difficulties: i) the presence of the boundary and ii) the axis singularity. We detail how to circumvent these issues.The second part of the thesis is devoted to magnetohydrodynamic (MHD) turbulence. It concerns phenomena where electrically conducting flows interact with electromagnetism and for which governing equations are derived in Chapter V. In Chapter VI, a detailed analysis of the energy transfers between the magnetic and velocity fields is performed thanks to a high resolution database of homogeneous MHD turbulence. It provides some insights to understand the physics of the nonlinear interactions and is also a valuable diagnostic in the framework of LES modelling. Finally, the inhomogeneous configuration studied in Chapter III has been extended to MHD. Several statistics related to the kinetic and magnetic energies are measured and LES of this flow are performed and presented in Chapter VII., Doctorat en sciences, Spécialisation physique, info:eu-repo/semantics/nonPublished

Published
2004

8. Energy transfers in forced MHD turbulence

Author

Carati, Daniele, Debliquy, Olivier, Knaepen, Bernard, Teaca, Bogdan, Verma, Mahendra, Carati, Daniele, Debliquy, Olivier, Knaepen, Bernard, Teaca, Bogdan, and Verma, Mahendra

Abstract

SCOPUS: ar.j, info:eu-repo/semantics/published

Published
2006

10. Local shell-to-shell energy transfer via nonlocal interactions in fluid turbulence

Author

Verma, Mahendra, Ayyer, Arvind, Debliquy, Olivier, Kumar, Shishir, Chandra, Amar A.V., Verma, Mahendra, Ayyer, Arvind, Debliquy, Olivier, Kumar, Shishir, and Chandra, Amar A.V.

Abstract

In this paper we analytically compute the strength of nonlinear interactions in a triad, and the energy exchanges between wave-number shells in incompressible fluid turbulence. The computation has been done using first-order perturbative field theory. In three dimensions, magnitude of triad interactions is large for nonlocal triads, and small for local triads. However, the shell-to-shell energy transfer rate is found to be local and forward. This result is due to the fact that the nonlocal triads occupy much less Fourier space volume than the local ones. The analytical results on three-dimensional shell-to-shell energy transfer match with their numerical counterparts. In two-dimensional turbulence, the energy transfer rates to the nearby shells are forward, but to the distant shells are backward; the cumulative effect is an inverse cascade of energy. © 2005 Indian Academy of Sciences., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
2005

12. Pseudo-spectral methods applied to hydrodynamic and magnetohydrodynamic turbulence

Author

Carati, Daniele, Weyssow, Boris, Degrez, Gérard, Knaepen, Bernard, Mareschal, Michel, Sagaut, Pierre, Winckelmans, Grégoire, Malek-Mansour, Mohammad-Ali, Debliquy, Olivier, Carati, Daniele, Weyssow, Boris, Degrez, Gérard, Knaepen, Bernard, Mareschal, Michel, Sagaut, Pierre, Winckelmans, Grégoire, Malek-Mansour, Mohammad-Ali, and Debliquy, Olivier

Abstract

In our everyday life, turbulence is an omnipresent phenomenon and yet remains poorly understood. Its random and chaotic nature makes it a subject almost impossible to treat from the mathematical point of view and, at present, thereis no real prospect of a simple analytic theory. Scientists have therefore regarded the numerical simulation as an alternative to compute the relevant properties of turbulent flows. In this context, our thesis aims at developing and using accurate computational methods, namely pseudo-spectral methods, for studying hydrodynamic (1st part) and magnetohydrodynamic (2nd part) turbulence.In the hydrodynamic part, Chapter I introduces the governing equations of fluid mechanics as well as the main issues related to the numerical study of turbulent flows. In particular, the Direct Numerical Simulations (DNS) of turbulence, in which accurate numerical solutions of the Navier-Stokes equations are obtained, are shown to be limited to moderately turbulent flows.Chapter II introduces the Large Eddy Simulation (LES) technique which aims at simulating highly turbulent flows and which is based on a separation of scales.In practice, it consists of simulating the large - resolved - scales of the flow explicitly while modelling the small - unresolved - scales. Two different approaches for modelling the kinetic energy of the unresolved scales are proposed and their respective advantages and drawbacks are discussed.Chapter III is devoted the study of the mixing-layer using both DNS and LES. It consists of an inhomogeneous turbulent flow which has been studied experimentally and for which well-documented measurements are available. A highly accurate DNS mimicking the same experiment has been produced. It allows to study the inhomogeneity and anisotropy properties of this flow. Also, LES of the same flow, using different models, have been evaluated. In Chapter IV, we explore a pseudo-spectral method to investigate turbulence in a pipe. In this, Doctorat en sciences, Spécialisation physique, info:eu-repo/semantics/nonPublished

Published
2004

13. Samplings versus filters in large-eddy simulations

Author

Debliquy, Olivier, Knaepen, Bernard, Carati, Daniele, Wray, A., Debliquy, Olivier, Knaepen, Bernard, Carati, Daniele, and Wray, A.

Abstract

info:eu-repo/semantics/published

Published
2004

15. DNS and LES of a shear-free mixing layer

Author

Knaepen, Bernard, Debliquy, Olivier, Carati, Daniele, Knaepen, Bernard, Debliquy, Olivier, and Carati, Daniele

Abstract

info:eu-repo/semantics/published

Published
2003

24. Modelling of MHD Turbulence.

Author

Molokov, Sergei, Moreau, René, Moffatt, Keith, Knaepen, Bernard, Debliquy, Olivier, and Carati, Daniele

Abstract

Numerical simulations of turbulent phenomena in fluids have made considerable progress with the emergence of large parallel computers. For simple geometries, very efficient numerical methods have been developed to provide accurate numerical solutions to the equations of fluid dynamics. These approaches are referred to as direct numerical simulation (DNS) and their predictions are often regarded as almost as reliable as the experimental data. [ABSTRACT FROM AUTHOR]

Published
2007
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25. Energy Fluxes and Shell-to-Shell Transfers in MHD Turbulence.

Author

Barth, Timothy J., Griebel, Michael, Keyes, David E., Nieminen, Risto M., Roose, Dirk, Schlick, Tamar, Kassinos, Stavros C., Langer, Carlos A., Iaccarino, Gianluca, Moin, Parviz, Carati, Daniele, Debliquy, Olivier, Knaepen, Bernard, Teaca, Bogdan, and Verma, Mahendra

Abstract

A spectral analysis of the energy cascade in magnetohydrodynamics (MHD) is presented using high resolution direct numerical simulations of both forced and decaying isotropic turbulence. The triad interactions between velocity and magnetic field modes are averaged into shell interactions between similar length scales phenomena. This is achieved by combining all the velocity Fourier modes that correspond to wave vectors with similar amplitude into a shell velocity variable. The same procedure is adopted for the magnetic field. The analysis of the interactions between these shell variables gives a global picture of the energy transfers between different length scales, as well as between the velocity and the magnetic fields. Also, two different attempts to separate the shell-to-shell interactions into forward and backward energy transfers are proposed. They provide diagnostics that can be used in order to assess subgrid-scale modelling in large-eddy simulation for turbulent MHD systems. [ABSTRACT FROM AUTHOR]

Published
2007
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