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Simple Shear Flow (simple + shear_flow)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

VOF-Simulation of the Lift Force for Single Bubbles in a Simple Shear Flow

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2006
D. Bothe
Abstract Bubbles in shear flows experience a lift force, causing them to migrate sideways while they are rising. This lateral migration is investigated in numerical simulations, which are carried out with an extended version of the highly parallelized code FS3D, employing an advanced Volume-of-Fluid method. The movement of single bubbles in linear shear flows is simulated to obtain the magnitude of the lift force , expressed by the lift force coefficient CL , for various bubble diameters and material data. Simulation results are in good agreement with experiments for medium liquid phase viscosities. An investigation of the dynamic pressure on the bubble surface explains why large bubbles migrate in the opposite direction compared to small bubbles. [source]

Coarse-Grained Simulations of Elongational Viscosities, Superposition Rheology and Shear Banding in Model Core,Shell Systems

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 8 2007
A. van den Noort
Abstract A recently developed coarse-grain model is used to investigate nonlinear rheological properties of model core,shell systems. The influence of several model parameters on the stresses and shear rates is investigated. Continuous planar elongational flow and superposition rheology are studied and compared to simple shear flow results. With particular values of the model parameters, an initially linear velocity profile splits into many bands with different shear rates and different densities, which finally merge into just two bands stacked along the gradient direction. With the box sizes used in our simulations, stick and Lees,Edwards boundary conditions lead to qualitatively similar results, with the stick boundary simulations showing better quantitative agreement with experiments. [source]

Direct meso-scale simulations of fibres in turbulent liquid flow

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010
J. J. Derksen
Abstract A procedure for direct, meso-scale simulations of flexible fibres immersed in liquid flow is introduced. The fibres are composed of chains of spherical particles connected through ball joints with the bending stiffness of the joints as a variable. The motion of the fibres and the liquid is two-way coupled with full resolution of the solid,liquid interface. First the simulation procedure is validated by means of an analytical solution for sphere doublets in zero-Reynolds simple shear flow. Subsequently we use the numerical method to study inertial flows with fibres, more specifically the interaction of a fibre with isotropic turbulence. Une procédure pour des simulations directes à la méso-échelle de fibres souples immergées dans la circulation de liquide est présentée. Les fibres sont composées de chaînes de particules sphériques reliées par des joints à rotule avec la rigidité à la flexion des joints comme variable. Le mouvement des fibres et du liquide est bidirectionnel avec une résolution intégrale de l'interface solide-liquide. D'abord, la procédure de simulation est validée au moyen d'une solution analytique pour les doublets de sphère dans un écoulement de cisaillement simple à nombre de Reynolds nul. Par la suite, nous utilisons la méthode numérique pour étudier les flux inertiels avec les fibres, plus précisément l'interaction d'une fibre avec la turbulence isotrope. [source]

Do mean-field dynamos in nonrotating turbulent shear-flows exist?

ASTRONOMISCHE NACHRICHTEN, Issue 4 2006
G. Rüdiger
Abstract A plane-shear flow in a fluid with forced turbulence is considered. If the fluid is electrically-conducting then a mean electromotive force (EMF) results even without basic rotation and the magnetic diffusivity becomes a highly anisotropic tensor. It is checked whether in this case self-excitation of a large-scale magnetic field is possible (so-called W, × J, -dynamo) and the answer is NO. The calculations reveal the cross-stream components of the EMF perpendicular to the mean current having the wrong signs, at least for small magnetic Prandtl numbers. After our results numerical simulations with magnetic Prandtl number of about unity have only a restricted meaning as the Prandtl number dependence of the diffusivity tensor is rather strong. If, on the other hand, the turbulence field is strati.ed in the vertical direction then a dynamo-active , -effect is produced. The critical magnetic Reynolds number for such a self-excitation in a simple shear flow is slightly above 10 like for the other , but much more complicated , flow patterns used in existing dynamo experiments with liquid sodium or gallium. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]