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» Conférences d’après mars 2011 : nouveau site

 

Journée Visualization of High-Resolution 3D Turbulent Flows

Organisé par : Marie Farge (CNRS)

Journée d’études enregistrée avec le soutien du GDR Dynamo
The goal is to address and discuss together the problems encountered when visualizing high-resolution 3D turbulent flows, either computed by direct numerical simulation (DNS), or measured by particle image velocimetry (PIV). Progresses made recently by both techniques lead to the production of large datasets (typically 3D vector fields, up to 40963 for DNS and up to 1283 for PIV, this at each time step). The analysis of such high-resolution 3D turbulent flows requires advanced visualization tools, in particular to study the formation and evolution of coherent structures which emerge from random fluctuations. We consider important that numerical experimentalists, using DNS, and laboratory experimentalists, using PIV, apply the same visualization tools and graphic representations in order to compare their results. This should enhance the mutual validation and interpretation of DNS and PIV results in order to better understand 3D turbulence.
The National Center for Atmospheric Research (NCAR, Boulder, USA) is presently developing a new graphic package, called VAPOR (http://www.vapor.ucar.edu). It is based on orthogonal wavelets which allow to efficiently visualize high-resolution 3D flows on work stations. The authors of this package, John Clyne and Alan Norton, will present VAPOR and discuss with us the graphic needs of our community. The other invited speakers will address the visualization of different types of 3D turbulent flows encountered in fluid mechanics and astrophysics, together with the methods currently used for identifying coherent structures and understanding their dynamical properties.
The aim of this workshop is to assess the present state of the art and propose future developments for visualizing high-resolution 3D turbulent flows.
We are very grateful for financial support to:
CNRS-Sciences et Technologies de l’Information et de l’ingénierie (ST2I)
CNRS-Formation Entreprises
Institut Pierre Simon Laplace (IPSL)
European GDR Mechanics of Numerical Fluids
and GDR Dynamo

Ressources en ligne

  • Introduction - Visualization of high-resolution 3D turbulent flows (le 8 juin 2007) — Marie Farge
    Journée d’études enregistrée avec le soutien du GDR Dynamo
  • The peril of the petascale: emerging challenges in large scale computational Sciences (le 8 juin 2007) — John Clyne
    Thanks to over 40 years of steady advancement in microprocessor chip design and fabrication we are now poised to enter an era of petascale computing. Yet unsolved problems exist for computational scientists in the current period of terascale computing that will only become further exasperated as we move forward. High resolution numerical simulations can lead to vast volumes of data that may be impenetrable with the analysis and visualization resources available to many scientists today. The result is often a significantly reduced scientific return on our largest computational efforts. This talk will explore the challenges associated with large scale data analysis and will discuss fundamental changes in computational science that we feel are increasingly necessary to ensure full return on our scientific investments as we approach the era of the petascale.
    Journée d’études enregistrée avec le soutien du GDR Dynamo
  • Visualization and analysis of massive turbulent data sets (le 8 juin 2007) — Alan Norton
    A desktop suite of analysis and visualization tools (“VAPOR”) has been developed at NCAR for interactive analysis of huge datasets. VAPOR is intended to enable turbulence researchers to interactively understand the results of simulation. Simulation data on very large grids are analyzed and visualized directly from a wavelet representation, enabling interactive isolation of high-resolution details, such as current sheets and vortices, allowing analysis of their time-evolution. Flow integration and volume rendering can be applied on local regions in the grid, combined with numerical analyses to characterize the geometric structures that result. VAPOR is a desktop visualization and analysis application, running on Linux, Irix, Windows and Mac OSX. VAPOR is tightly coupled with IDL, enabling turbulence scientists to easily perform analysis and visualization on large datasets. This presentation will demonstrate the latest capabilities, showing how VAPOR can be used to interactively visualize small structures in time-varying data (e.g. an MHD simulation of resolution 15363), and demonstrating the use of field-line advection to track the motion of magnetic field lines in a velocity field.
    Journée d’études enregistrée avec le soutien du GDR Dynamo
  • Open questions in stellar MHD (le 8 juin 2007) — Allan Sacha Brun
    Many stars display intense turbulence and magnetism. Understanding how this comes about is very challenging given the complexity of describing the dynamical behaviour of a rotating turbulent magnetic star. It is currently thought that dynamo action plays a central role in generating and maintaining the observed field. In this talk we intend to make a brief overview of the current status of stellar MHD, what have been the most recent progresses, how, depending of the spectral type of star, magnetism can either be irregular or cyclic, and what are the future development in this field of research, such as developping a new code for petascale machines or high hand 3-D rendering softwares to visualize MHD turbulence and magnetic field lines.
    Journée d’études enregistrée avec le soutien du GDR Dynamo
  • Interactive visualization of astrophysical plasma simulation with SDVision (le 8 juin 2007) — Daniel Pomarède
    SDvision is a graphical interface developed in the framework of IDL Object Graphics and designed for the interactive and immersive visualization of astrophysical plasma simulations. Three-dimensional scalar and vector fields distributed over regular mesh grids or more complex structures such as adaptive mesh refinement data or multiple embedded grids, as well as N-body systems, can be visualized in a number of different, complementary ways. Various implementations of the visualization of the data are simultaneously proposed, such as 3D isosurfaces, volume projections, hedgehog and streamline displays, surface and image of 2D subsets, profile plots, particle clouds. The SDvision widget allows to visualize complex, composite scenes both from outside and from within the simulated volume. This tool is used to visualize data from RAMSES, a hybrid N-body and hydrodynamical code which solves the interplay of dark matter and the baryon gas in the study of cosmological structures formation, from HERACLES, a radiation hydrodynamics code used in particular to study turbulences in interstellar molecular clouds, from the ASH code dedicated to the study of stellar magnetohydrodynamics, and from the JUPITER multi-resolution code used in the study of protoplanetary disks formation.
    Journée d’études enregistrée avec le soutien du GDR Dynamo
  • Numerical simulation of oceanic mesoscale turbulence on the Japanese Earth Simulator (le 8 juin 2007) — Patrice Klein
    High resolution simulations of the mesoscale oceanic eddy turbulence have been performed on the Earth Simulator in Japan. They involve 3000x1000x200 grid points in a domain of 3000km x1000km x 4000m. Results reveal an efficient communication between the surface and the ocean interior due to the vertical velocity field induced by the mesoscale and submesoscale structures. New visualization technics are highly needed to understand and further quantify this communication.
    Journée d’études enregistrée avec le soutien du GDR Dynamo
  • Quantitative visualization of coherent structures in 3D tomographic-PIV measurements (le 8 juin 2007) — Gerrit Elsinga
    The talk will present the visualization of coherent motion in turbulent flows measured with 3D (time-resolved) tomographic-PIV. We will show results for cylinder wake flow, turbulent boundary layers and a shock wave turbulent boundary layer interaction and discuss the tispatial resolution as well as how to obtain velocity gradients from the measured velocity.
    Journée d’études enregistrée avec le soutien du GDR Dynamo
  • Direct numerical simulation of vortical flows using vortex methods: simulation and visualization (le 8 juin 2007) — Philippe Chatelain et Diego Rossellini
    We present the Direct Numerical Simulations of high Reynolds numbers vortical flows employing a vortex particle method. The method relies on the Lagrangian discretization of the Navier-Stokes equations in vorticity-velocity form, along with a remeshing of the particles in order to ensure convergence. Our implementation is scalable and efficient for massively parallel architectures (tested up to 16K IBM BlueGene/L CPUS). The visualization of the resulting data is a challenge in itself. To that effect, we developed our own volume rendering code. The algorithm combines the CPU and GPU in a master-slave paradigm: the master, in this case the CPU, is responsible for managing the data and the tasks of the slave. The slave, the GPU, handles the numerical computations necessary for the rendering. The algorithm is parallelizable (multiple pairs of CPU-GPU), and can be optimized for interactive applications.
    Journée d’études enregistrée avec le soutien du GDR Dynamo
  • Ingredients for a Virtual Topology Lab: feature extraction and visualization of flow fields (le 8 juin 2007) — Tino Weinkauf
    We introduce a virtual flow topology lab that combines several algorithms in order to analyze and visualize the topology of vector fields. While we explain the topological features of 2D steady and time-dependent as well as 3D steady vector fields, we present efficient algorithms to capture them.
    These include Feature Flow Fields and Saddle Connectors. Due to the strong correlation between the different topological features, a combination of several algorithms often leads to a new technique: as an example, a combination of Feature Flow Fields and Saddle Connectors can be used to find and track closed stream lines in 2D vector fields. Furthermore, we show that most techniques for extracting topological features can be built up from the following three core algorithms:
    - finding zeros in a 2D/3D field
    - integrating stream objects (streamlines, stream surfaces, etc.)
    - intersecting stream objects
    Those are the core ingredients for our virtual topology lab, which we implemented in our visualization suite Amira. We give an interactive demo where we analyze the topology of real-life data sets.
    Journée d’études enregistrée avec le soutien du GDR Dynamo
  • Visualizing vortices in turbulent flows: short review and practical considerations (le 8 juin 2007) — Lionel Larchevêque
    For the past two decades, numerous methods have been proposed for educing coherent structures. The most popular ones will be briefly described, including discussion on the mathematical and physical assumptions behind them. The second part of the talk will be dedicated to some practical issues in visualizing coherent structures using these methods, with applications to various turbulent flowfields coming from direct or large-eddy simulations.
    Journée d’études enregistrée avec le soutien du GDR Dynamo
  • Automated topology classification method for instantaneous velocity fields (le 8 juin 2007) — Sébastien Depardon
    Topological concepts provide highly comprehensible representations of the main features of a flow with a limited number of elements. This talk presents an automated classification method of instantaneous velocity fields based on the analysis of their critical points distribution and feature flow fields. It uses the fact that topological changes of a velocity field are continuous in time to extract large scale periodic phenomena from insufficiently time-resolved datasets. This method is applied to two test-cases : an analytical flow field and PIV plamounted cube. [Depardon et al., Exp. Fluids (2007) 42: 697-710]
    Journée d’études enregistrée avec le soutien du GDR Dynamo
  • 3D feature recognition of an unsteady flow: 2D PIV, direct simulation and Virtual Reality (le 8 juin 2007) — François Lusseyran et Jean-Marc Vézien
    As metrology and numerical simulation capabilities get perfected, one needs an increasingly clearer understanding of three-dimensional flow fields. However the analysis of unsteady velocity fields encounters various difficulties from a fundamental point of view (mathematical criteria of 3D vortex identification) as well as from the point of view of space localization and time characterisation. We illustrate this problem using the unsteady 3D flow generated by an open cavity observed via 2D experimental data and with validated 3D direct numerical simulation. In parallel, Virtual Reality (VR) researchers of the VENISE team investigate the interactive visualization of the massive data sets, such as the ones produced by Computer Fluid Dynamics (CFD). The design of truely effective VR software is hindered by the fact that the exploration of a CFD simulation is a « free » task i.e. it doesn’t follow a predetermined, formalized action sequence. Nevertheless, cognitive and ergonomic tools exist so that an activity analysis can be performed, out of the live observation of scientists and subsequent interviews. The CORSAIRE project aims at proposing innovative tools for data exploration in Virtual Reality environment, such as the CAVE-like set-up available at LIMSI, given the result of such an analysis. It also proposes to CFD researchers new rendering modalities, such as sound and haptics, so that data exploration is more intuitive, faster and possibly reveals new phenomena within the simulations.
    Journée d’études enregistrée avec le soutien du GDR Dynamo
  • Coherent structures in the separated shear layer on the side of a square cylinder : a multi-scale problem (le 8 juin 2007) — Christophe Brun
    The scope of the present contribution is related to the design of proper signal processing tools to identify, visualise and understand, from both experimental and numerical data, the main coherent structures present in a turbulent flow. We will consider the multiscale problem of the separated shear layer on the side of a square cylinder for a Reynolds number ranging from Re=1000 to Re=200000. Unsteady analysis based on LES at intermediate Reynolds numbers and LDV/PIV at high Reynolds numbers are carried out. For numerics, 2D and 3D visualisations are performed based on iso-vorticity contours and isovalues of the Q-criterion (2nd invariant of the velocity gradient tensor). The storage of huge time data bank allows for building time dependent movies for the main coherent structures. For experiments, smoke visualisations provide a qualitative description of the flow which can be viewed as the behaviour of a passive scalar. A special care was taken to obtain very high sampling frequency for LDV in order to capture properly the smallest coherent structures related to the present multiscale problem, based on a time 1D wavelet analysis. This procedure should be improved and extended to space-time analysis based on PIV data.
    Journée d’études enregistrée avec le soutien du GDR Dynamo
  • Interactive simulation and visualization for reaction-diffusion equations (le 8 juin 2007) — Dwight Barkley
    I will present simulations of reaction-diffusion equations in two and three space dimensions. Solutions to these equations have certain features in common with vortices found in fluid flows. I will demonsvisualization.
    Journée d’études enregistrée avec le soutien du GDR Dynamo
  • Numerical simulation of star formation (le 8 juin 2007) — Patrick Hennebelle
    I will present the context of star formation and interstellar medium within galaxies, showing various examples of numerical simulations relevant for various stages of the condensation process.
    Journée d’études enregistrée avec le soutien du GDR Dynamo

Organisateurs

Marie_Farge

Marie Farge (CNRS)

Directeur de recherche CNRS
LMD-IPSL-CNRS

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