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We present a combination of laboratory experiments and numerical simulations modelling a geophysically relevant mechanical forcing: libration. Longitudinal libration corresponds to the periodic oscillation of a body's rotation and is, along with precessional and tidal forcings, a possible source of turbulence in the fluid interior of satellites...
conference paper 2015
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The emergence of fluid instabilities in the relevant limit of vanishing fluid inertia (i.e., arbitrarily close to zero Reynolds number) has been investigated for the well-known Kolmogorov flow. The time-lagged viscosity change from lower to higher values due to shear changes is the crucial ingredient for the instabilities to emerge. This...
conference paper 2015
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The Direct Numerical Simulation (DNS) of an incompressible open channel flow over a layer of rigid spherical roughness elements fixed on the wall in well-packed square arrangement has been performed which shows values of the Reynolds number Rb ~ 6900 (ks+ ~ 100) and produces a mean velocity defect ∆U+ ~ 7 in the range of the fully-rough regime....
conference paper 2015
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We report new experimental results that use tools from braid theory to characterize two-dimensional turbulent flows driven by Faraday waves. The average topological length of the material fluid lines is found to grow exponentially with time. It allows us to compute the braid’s topological entropy SBraid. We show that SBraid increases as the...
conference paper 2015
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The recent discovery of rare backflow events in turbulent boundary layer flows based on the analysis of DNS data has raised again the need of experimental visualizations of wall-shear stress (WSS) fields in such unsteady flows. Of importance is the localization of critical points which are thought to strongly correlate with large-scale events in...
conference paper 2015
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High area ratio rocket engines generate strong vibro-acoustic loads primarily during transient operations, like start-up and shut-down of the engine. These loads can adversely affect the launch vehicle and its payload. Thus, an accurate prediction of the loads produced during engine start-up is pertinent to the safety and reliability of the...
conference paper 2015
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With transient LES and DNS simulations, we investigate flow in melt pools driven by thermocapillary forces. The developing pool is at first axisymmetric as are the boundary conditions, but flow instabilities arise that lead to 3D oscillatory flow patterns. At higher laser powers a sign-change in the surface tension temperature coefficient occurs...
conference paper 2015
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Jacobitz, F. (author), Schneider, K. (author), Farge, M. (author)
Direct numerical simulation data of homogeneous turbulence with shear and stratification are analyzed to study the Lagrangian and Eulerian acceleration statistics. Richardson numbers from <em>Ri</em>=0, corresponding to unstratified shear flow, to <em>Ri</em>=1, corresponding to strongly stratified shear flow, are considered. The scale...
conference paper 2015
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Since direct simulations of the incompressible Navier-Stokes equations are limited to relatively low-Reynolds numbers, dynamically less complex mathematical formulations are necessary for coarse-grain simulations. Eddy-viscosity models for Large-Eddy Simulation is probably the most popular example thereof: they rely on differential operators...
conference paper 2015
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Jets are the most basic flow used in industrial field and are widely used for heating, cooling, mixing. Recently, the improvement of mixing efficiency is required in order to downsize many industrial equipments and upgrade their performance. In the case of jets, their characteristic, such as the diffusion, depends on the inlet condition....
conference paper 2015
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In linearly stable shear flows like pipe and plane Couette flows, the transition from the laminar to the turbulent regime occurs abruptly. To better understand this transition, the time evolution of turbulent patches, created by controlled finite amplitude perturbations, have been studied in the literature. These studies mostly focused on pipe flows...
conference paper 2015
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The hydrodynamic breakup of small inertial aggregates in homogenous and isotropic turbulence is studied through numerical simulations. Small inertial aggregates are subject to shear stress caused by the local velocity gradient and drag stress caused by the relative velocity of the aggregate and the fluid flow. In our simulations, we follow...
conference paper 2015
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The behavior of particles in compressible turbulence has been seldom investigated to date despite its importance in many natural and industrial flows. Direct numerical simulations of particle-laden compressible isotropic turbulence are performed to study the preferential concentration of particles and the underling mechanisms. It turns out that...
conference paper 2015
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While continuous free jets have been investigated and optimised during the last 60 years, the impulsively started jet is still relatively unexplored. We focus here upon the very first stage of a compressible free round jet, when the flow is only few diameters long and the vortex ring generated by the sudden expansion interacts with the shock...
conference paper 2015
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We investigate the effect of temperature dependent thermal conductivity λ and isobaric specific heat c_P on the transient amplification of perturbations in a thermally stratified laminar plane Poiseuille flow. It is shown that for decreasing thermal conductivity the maximum transient energy growth is amplified with respect to the λ=1 case, while...
conference paper 2015
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Nguyen, M.Q. (author), Simöens, S. (author), Delache, A. (author), El Hajem, M. (author), Bos, W. (author), Poole, R. (author)
The comparison of the results of direct numerical simulations of isotropic turbulence of Newtonian and viscoelastic fluid, based on the FENE-P model, provide evidence that viscoelasticity modifies qualitatively the behavior of the smallest scales: we observe a k<sup>−6</sup> law in the far dissipation range of the energy spectrum and we show...
conference paper 2015
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This abstract examines the evolution of perturbations generated by various trips in a turbulent boundary layer. Measurements taken using hot wire anemometry show that the evolution towards the natural state is strongly dependent on the formation mechanisms of the boundary layer, this being different for different wall normal distribution of the...
conference paper 2015
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Turbulent patches are localized events of turbulence, typically characterized by sharp differences between the flow characteristics across their interfaces. These localized events might add to the global mixing, heat exchange and mass transfer, playing a non-negligible role in the total energy balance in lakes or the ocean. This study takes a...
conference paper 2015
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The fluid dynamics process leading to laminar-turbulent transition behind an isolated roughness element is investigated in the incompressible regime using particle image velocimetry. The study covers the effect of roughness size and geometry on the promotion of transition. The measurement domain covers a large streamwise range from the near wake...
conference paper 2015
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Effects of high-Prandtl number density-stratifying scalar, i.e., active scalar, on decaying and forced turbulence in stratified fluids are investigated by numerical simulations. In decaying turbulence, potential energy spectrum of the high-Prandtl number active scalar (Pr=6) agrees with the kinetic energy spectrum even at small scales. In forced...
conference paper 2015
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