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- 저자 : Kahouadji, Lyes (검색결과 4 건)
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Kahouadji, Lyes,Nowak, Emilia,Kovalchuk, Nina,Chergui, Jalel,Juric, Damir,Shin, Seungwon,Simmons, Mark J. H.,Craster, Richard V.,Matar, Omar K. Springer Berlin Heidelberg 2018 MICROFLUIDICS AND NANOFLUIDICS Vol.22 No.11
<P>The three-dimensional two-phase flow dynamics inside a microfluidic device of complex geometry is simulated using a parallel, hybrid front-tracking/level-set solver. The numerical framework employed circumvents numerous meshing issues normally associated with constructing complex geometries within typical computational fluid dynamics packages. The device considered in the present work is constructed via a module that defines solid objects by means of a static distance function. The construction combines primitive objects, such as a cylinder, a plane, and a torus, for instance, using simple geometrical operations. The numerical solutions predicted encompass dripping and jetting, and transitions in flow patterns are observed featuring the formation of drops, ‘pancakes’, plugs, and jets, over a wide range of flow rate ratios. We demonstrate the fact that vortex formation accompanies the development of certain flow patterns, and elucidate its role in their underlying mechanisms. Experimental visualisation with a high-speed imaging are also carried out. The numerical predictions are in excellent agreement with the experimental data.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1007/s10404-018-2149-y) contains supplementary material, which is available to authorized users.</P>
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Numerical simulation of supersquare patterns in Faraday waves
Kahouadji, L.,Pé,rinet, N.,Tuckerman, L. S.,Shin, S.,Chergui, J.,Juric, D. Cambridge University Press 2015 Journal of fluid mechanics Vol.772 No.-
<P>We report the first simulations of the Faraday instability using the full three-dimensional Navier–Stokes equations in domains much larger than the characteristic wavelength of the pattern. We use a massively parallel code based on a hybrid front-tracking/level-set algorithm for Lagrangian tracking of arbitrarily deformable phase interfaces. Simulations performed in square and cylindrical domains yield complex patterns. In particular, a superlattice-like pattern similar to those of Douady & Fauve (<I>Europhys. Lett.</I>, vol. 6, 1988, pp. 221–226) and Douady (<I>J. Fluid Mech.</I>, vol. 221, 1990, pp. 383–409) is observed. The pattern consists of the superposition of two square superlattices. We conjecture that such patterns are widespread if the square container is large compared with the critical wavelength. In the cylinder, pentagonal cells near the outer wall allow a square-wave pattern to be accommodated in the centre.</P>
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Intra- and inter-configurational luminescence spectroscopy of Pr3+ -doped YPO4 nanophosphors
B. Kahouadji,L. Guerbous,A. Boukerika,Slobodan D. Dolic,Dragana J. Jovanovic,Miroslav D. Dramicanin 한국물리학회 2018 Current Applied Physics Vol.18 No.4
Nanopowders of YPO4 phosphors with different Pr3+doping were successfully prepared by a sol gel method under different synthesis conditions. The crystallite size and strain show a strong dependence on the Pr3+ doping concentration and on the annealing temperature. By annealing at 300 °C one can obtain the xenotime structure of the pure YPO4. The crystallite size can be controlled by controlling the annealing temperature and it increases with increasing the annealing temperature. The room temperature inter-configurational 4f2 ↔ 4f5d and intra-configurational 4f2↔ 4f2 emission-excitation transitions spectra are measured and investigated. Upon 4f2 → 4f5d excitation transition, all the samples present broad intense emission bands attributed to 4f5d → 4f2 emission transitions and peaks in red region assigned to 1D2→3H4 transition as photon cascade emission phenomena (PCE). The presence of only 1D2→3H4 transition is discussed. In addition, the 1D2 energy level lifetimes as well as the refractive indexes were determined and discussed.
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A hybrid interface tracking – level set technique for multiphase flow with soluble surfactant
Shin, Seungwon,Chergui, Jalel,Juric, Damir,Kahouadji, Lyes,Matar, Omar K.,Craster, Richard V. Elsevier 2018 Journal of computational physics Vol.359 No.-
<P><B>Abstract</B></P> <P>A formulation for soluble surfactant transport in multiphase flows recently presented by Muradoglu and Tryggvason (JCP 274 (2014) 737–757) is adapted to the context of the Level Contour Reconstruction Method, LCRM, (Shin et al. IJNMF 60 (2009) 753–778, ) which is a hybrid method that combines the advantages of the Front-tracking and Level Set methods. Particularly close attention is paid to the formulation and numerical implementation of the surface gradients of surfactant concentration and surface tension. Various benchmark tests are performed to demonstrate the accuracy of different elements of the algorithm. To verify surfactant mass conservation, values for surfactant diffusion along the interface are compared with the exact solution for the problem of uniform expansion of a sphere. The numerical implementation of the discontinuous boundary condition for the source term in the bulk concentration is compared with the approximate solution. Surface tension forces are tested for Marangoni drop translation. Our numerical results for drop deformation in simple shear are compared with experiments and results from previous simulations. All benchmarking tests compare well with existing data thus providing confidence that the adapted LCRM formulation for surfactant advection and diffusion is accurate and effective in three-dimensional multiphase flows with a structured mesh. We also demonstrate that this approach applies easily to massively parallel simulations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Extension of the LCRM Front-tracking method (Shin et al. IJNMF 60 (2009) 753–778) to flows with surfactant. </LI> <LI> Following Muradoglu and Tryggvason (JCP 274 (2014) 737–757) surfactant transport is solved on the interface and in the bulk. </LI> <LI> Accuracy demonstrated for mass conservation, surface advection and diffusion, bulk transport and Marangoni stresses. </LI> <LI> Large scale parallel calculations of two-phase annular film flow in the counter-current flow regime. </LI> </UL> </P>
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