To contribute to the existing knowledge of the hydrodynamic force exerted on a spherical particle placed in the axis of a cylinder, at small Reynolds numbers, the influence of the uniform and Poiseuille flows on the w...
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To contribute to the existing knowledge of the hydrodynamic force exerted on a spherical particle placed in the axis of a cylinder, at small Reynolds numbers, the influence of the uniform and Poiseuille flows on the wall correction factor are numerically and asymptotically investigated. The Stokes and continuity equations are expressed in the stream function and vorticity formulation and are rewritten in an orthogonal system of curvilinear coordinates. These equations are solved using a finite differences method. The generation of the grid was carried out by the singularities method. The accuracy of the numerical code is tested through comparison with theoretical and experimental results. In both cases we numerically calculated the separate contributions of the pressure and viscosity forces. In concentrated regime these numerical calculations are in very good agreement with those obtained by asymptotic expansions. This analysis allowed us to show the prevalence of the pressure term over the viscosity one in the lubrication regime contrary to what happened for the dilute regime. All our numerical and asymptotical results compared with those of Bungay et al. (Int. J. Multiphase Flow 1, 25-56 (1973)) seem to give a response to this problem argued for a long time.
We derive minimal discrete models of the Boltzmann equation consistent with equilibrium thermodynamics, and which recover correct hydrodynamics in arbitrary dimensions. A new discrete velocity model is proposed for th...
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We derive minimal discrete models of the Boltzmann equation consistent with equilibrium thermodynamics, and which recover correct hydrodynamics in arbitrary dimensions. A new discrete velocity model is proposed for the simulation of the Navier-Stokes-Fourier equation and is tested in the setup of Taylor vortex flow. A simple analytical procedure for constructing the equilibrium for thermal hydrodynamics is established. For the lattice Boltzmann method of isothermal hydrodynamics, the explicit analytical form of the equilibrium distribution is presented. This results in an entropic version of the isothermal lattice Boltzmann method with the simplicity and computational efficiency of the standard lattice Boltzmann model.
The method of dissipative particle dynamics (DPD) was introduced by Hoogerbrugge and Koelman (Europhys. Lett., 19 ( 1992) 155) to study meso-scale material processes. The theoretical investigation of the DPD method wa...
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The method of dissipative particle dynamics (DPD) was introduced by Hoogerbrugge and Koelman (Europhys. Lett., 19 ( 1992) 155) to study meso-scale material processes. The theoretical investigation of the DPD method was initiated by Espanol (Phys. Rev. E, 52 ( 1995) 1734) who used a Fokker-Planck formulation of the DPD method and applied the Mori-Zwanzig projection operator calculus to obtain the equations of hydrodynamics for DPD. A current limitation of DPD is that it requires a clear separation of scales between the resolved and unresolved processes. In this letter, we suggest a simple extension of DPD that allows for inclusion of unresolved stochastic processes with exponentially decaying variance for any value of the decay rate, and give an application of this algorithm to the simulation of the shallow-water equations using the Hamiltonian particle-mesh method. The proposed extension is as easy to implement as the standard DPD methods.
We present an advected-field model of fluid interfaces at low Reynolds numbers and apply it to the fundamental problem of drop dynamics in an external flow. We focus on the ability of the numerical method to account f...
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We present an advected-field model of fluid interfaces at low Reynolds numbers and apply it to the fundamental problem of drop dynamics in an external flow. We focus on the ability of the numerical method to account for topology changes such as breakup, and compare the results obtained with this method to experimental data and theoretical predictions.
Solving the Navier-Stokes equation for incompressible fluids is greatly simplified by the solution of the vorticity equation. To accomplished this for three-dimensional flows requires vector potentials. These potentia...
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Solving the Navier-Stokes equation for incompressible fluids is greatly simplified by the solution of the vorticity equation. To accomplished this for three-dimensional flows requires vector potentials. These potentials are not only useful to take care of the incompressibility. Their modes are suitable also as test functions since the familiar Galerkin procedure does not work. The new method is checked by examples with known results and its relation to the classical approach with the stream function is clarified. The principle, demonstration, however, concerns the transition to turbulence in plane shear flows. A simple layer of long rolls with axes parallel to the basic flow incites the transition.
We study a gas of inelastic rough spheres confined on a 2D plane, driven on the rotational degrees of freedom. Event-driven molecular dynamics (MD) simulations are compared to mean-field (MF) predictions with surprisi...
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We study a gas of inelastic rough spheres confined on a 2D plane, driven on the rotational degrees of freedom. Event-driven molecular dynamics (MD) simulations are compared to mean-field (MF) predictions with surprisingly good agreement for strong coupling of rotational and translational degrees of freedom even for very strong dissipation in the translational degrees. Although the system is spatially homogeneous, the rotational velocity distribution is essentially Maxwellian. Surprisingly, the distribution of tangential velocities is strongly deviating from a Maxwellian. An interpretation of these results is proposed, as well as a setup for an experiment.
A previously proposed thermohydrodynamic lattice BGK scheme using non-perturbative, or non-polynomial, equilibria is found to simulate continuum equations that differ from the Euler equations of gas dynamics at leadin...
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A previously proposed thermohydrodynamic lattice BGK scheme using non-perturbative, or non-polynomial, equilibria is found to simulate continuum equations that differ from the Euler equations of gas dynamics at leading order. Shock tube simulations with this BGK scheme coincide with solutions obtained by solving these different continuum equations with conventional methods. Both sets of solutions contain unphysical compound waves, shocks attached to rarefactions, where the Euler equations contain contact discontinuities.
A Lattice Boltzmann model is developed to account for the competition between surface tension and dipolar interaction in magnetic fluids. The description of the interactions was kept as simple as possible to identify ...
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A Lattice Boltzmann model is developed to account for the competition between surface tension and dipolar interaction in magnetic fluids. The description of the interactions was kept as simple as possible to identify and isolate the nature of the essential interactions in the examined situations. The model is used thereafter in order to simulate the deformation of a magnetic fluid drop under the action of an external magnetic field, as well as the onset of the normal field instability in magnetic fluids. The success of the model, and easily identified deviations, demonstrate that the model is a powerful and versatile tool for the study of magnetic and nonmagnetic fluid systems with interfaces.
We investigate the effects of geometrical micro-irregularities on the conversion efficiency of reactive flows in narrow channels of millimetric size. Three-dimensional simulations, based upon a Lattice-Boltzmann-Lax-W...
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We investigate the effects of geometrical micro-irregularities on the conversion efficiency of reactive flows in narrow channels of millimetric size. Three-dimensional simulations, based upon a Lattice-Boltzmann-Lax-Wendroff code, indicate that periodic micro-barriers may have an appreciable effect on the effective reaction efficiency of the device. Once extrapolated to macroscopic scales, these effects can result in a sizeable increase of the overall reaction efficiency.
Analogies between dissipative particle dynamics ( DPD) and stochastic dynamics are exploited to derive new algorithm for DPD with an improved temperature control, without recursion or tuneable parameters.
Analogies between dissipative particle dynamics ( DPD) and stochastic dynamics are exploited to derive new algorithm for DPD with an improved temperature control, without recursion or tuneable parameters.
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