ETC13 Invited Speakers
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Experimental investigations of turbulent transport of inertial particlesThis presentation will be devoted to recent experimental work investigating the inertial dynamics of material particles transported by a turbulent flow. In a first step, the case of isolated particles will be considered, focusing on the influence of particles size and density on their Lagrangian dynamics. To this scope a close statistical analysis of particles velocity and acceleration is particularly enlightening to better understand the forcing exerted by the carrier turbulence on the particle. While some features do exhibit specific size and density effects, others are found to preserve an extremely robust signature regardless of particles inertia, in contrast with usual point particle models predictions. In a second step the multi-particles problem will be addressed with a main focus on the preferential concentration phenomenon. A novel analysis technique, based on Voronoï tesselation, allows to carefully characterize particles concentration field and to investigate clustering properties. One important aim of this study is the identification of collective effects, where the dynamics of multiple particles cannot be simply derived from isolated particles considerations, as subtler coupling between the particles may occur. |
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On turbulence modulation by dispersed inertial particlesTurbulent flows laden with inertial particles are ubiquitous in nature (e.g. aerosols in clouds, and dust storms on Earth and Mars) and in industrial applications (e.g. liquid fuel and pulverized coal sprays in combustion chambers). Experimental and numerical studies of these flows are quite challenging due to the wide spectra of length- and time-scales of the dispersed particles in addition to the spectra of scales intrinsic to the carrier fluid turbulence. The two-way and and four-way nonlinear interactions between the dispersed particles and the turbulence result in complex multi-scale physical phenomena.The lecture focuses on the physical mechanisms of interactions between dispersed spherical particles and isotropic turbulence using Direct Numerical Simulation (DNS). Particles whose diameter is smaller than the Kolmogorov length scale are simulated as point particles. Larger particles with diameter of the order of Taylor microscale are fully resolved using the Immersed Boundary method. |
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Interaction of turbulence and mean flow in fluid layersI will briefly review recent theoretical and experimental results on turbulence in thin and thick layers. I describe spectral condensation i.e. appearance of a system-size coherent vortex flow. Interaction of the vortex and turbulence will be described in much detail. Implications for geophysical and industrial applications will be briefly discussed. |
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Regularization of turbulence - a comprehensive modeling approachTurbulence readily arises in numerous flows in nature and technology. The large number of degrees of freedom of turbulence poses serious challenges to numerical approaches aimed at simulating and controlling such flows. While the Navier-Stokes equations are commonly accepted to precisely describe fluid turbulence, alternative coarsened descriptions need to be developed to cope with the wide range of length and time scales. These coarsened descriptions are known as large-eddy simulations in which one aims to capture only the primary features of a flow, at considerably reduced computational effort. Such coarsening introduces a closure problem that requires additional phenomenological modeling. A systematic approach to the closure problem, know as regularization modeling, will be reviewed. Its application to multiphase turbulent will be illustrated in which a basic regularization principle is enforced to physically consistently approximate momentum and scalar transport. Examples of Leray and LANS-alpha regularization are discussed in some detail, as are compatible numerical strategies. We illustrate regularization modeling to turbulence under the influence of rotation and buoyancy and investigate the accuracy with which particle-laden flow can be represented. A discussion of the numerical and modeling errors incurred will be given on the basis of homogeneous isotropic turbulence. |
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High Reynolds number wall turbulenceThe study of wall-bounded turbulent flows has received considerable attention over the past few years as a result of high Reynolds number experiments conducted in purpose-built high-Reynolds number facilities, and using direct methods to obtain the wall-shear stress (such as oil-film interferometry). Some of these experiments have brought into question the fundamental scaling laws of the turbulence and mean flow quantities as well as revealed high Reynolds number phenomena, which make extrapolation of low Reynolds number results highly questionable.In this talk we will focus on findings related to the region traditionally referred to as the logarithmic region, and consider its dominant coherent structures and how they interact across the boundary layer. These findings lead to a new consideration of so-called “inner-outer” interactions and form the basis of a new predictive model for the near-wall inner region. |
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Heat transport in dry and moist Rayleigh-Benard convectionWe discuss and compare turbulent heat transport of thermal convection with and without phase changes in three-dimensional direct numerical simulations. They are referred to as moist and dry convection respectively. In both cases we restrict the studies to the well-known and simplest case of Rayleigh-Benard convection in the Boussinesq approximation. Our focus is on a better understanding of the detailed local mechanisms of heat transfer such as the dynamics in the boundary layers close to the isothermal walls in the dry or the impact of the latent heat release due to condensation of liquid water in the moist convection case. |
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Turbulence in atmospheric cloudsTurbulence is tightly coupled with cloud physical processes, and its role in thermodynamic phase changes and in the mechanics of particle interactions will be the focus of this talk. Atmospheric clouds are at the heart of the climate problem, and therefore represent an applied turbulence problem of great societal relevance. Cloud properties on all scales are related to the mixing of cloudy and clear air, and the nature of that mixing process depends on relative rates of mixing, which is scale dependent, and thermodynamic response of the condensed phase. New insights into the problem of homogeneous versus inhomogeneous mixing will be given. Cloud optical properties and the efficiency of precipitation depend on the mechanics of cloud particle interactions through collisions, coalescence, aggregation, and breakup. Under certain conditions, these processes also can be strongly influenced by turbulence. |
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Quantum TurbulenceWe review physical properties of quantum fluids He II and 3He-B, where quantum turbulence (QT) has been studied experimentally. Basic properties of QT in these working fluids are discussed within the phenomenological two-fluid model introduced by Landau. Experimental techniques such as second sound attenuation, Andreev reflection, NMR, ion propagation are introduced and results of various experiments on so-called Vinen QT and Kolmogorov QT both in He II and 3He discussed, emphasizing similarities and differences between classical and quantum turbulence. |
