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Abstract: A boundary element method based solver for particle motion simulation in dilute suspensions under the influence of hydrodynamic and magnetic forces was applied. The Euler-Lagrangian formulation for simulation of dilute two-phase flow was applied. The algorithm solves the incompressible Navier-Stokes equations written in velocity-vorticity formulation. The non uniform magnetic field was defined analytically for the case of a set of long thin wires. The particle trajectories were computed by applying the 4th order Runge-Kutta method. The computed test case consisted of a narrow channel under the influence of a nonuniform magnetic field, where magnetite and aluminium particles were suspended in water. The results of computations show the distributions of particles along the channel and confirms the suitability of the proposed configuration as a separation device under ideal conditions.
Keywords: boundary element method, laminar flow, magnetic particles, viscous fluids
Published in DKUM: 01.06.2012; Views: 2650; Downloads: 59
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Abstract: V prispevku je predstavljen sklopljenega primera naravne in prisilne konvekcije v toku mikropolarnih tekočin preko kotanje. Glede na tok klasinih tekoćčin, kjer je zajeto le translatorno gibanje delov tekočine, se v primeru mikropolarnih tekočin k translatornemu gibanju prišteva tudi gibanje tekočine zaradi rotacije togih nedeformabilnih delcev okrog srediišča določenega majhnega volumna, kar je opisano s pomočjo vektorja mikrorotacije. Numerično modeliranje dodatnih mikro vplivov se izvede z modificiranjem klasičnega sistema Navier-Stokesovih enačb, ki predstavljajo osnovo orodja za numerično simulacijo toka tekočine. Prispevek poda rezultate tokovnega, temperaturnega in mikrorotacijskega polja izračunanega z računskim algoritmom za reševanje modificiranih Navier-Stokesovih enačb s pomočjo metode robnih elementov (MRE), natančneje z Robno-območno integralsko metodo.
Keywords: mikropolarne tekočine, naravna konvekcija, prisilna konvekcija, dinamika tekočin, vektor mikrorotacije
Published in DKUM: 31.05.2012; Views: 2133; Downloads: 43
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Abstract: The contribution deals with numerical simulation of natural convection in micropolar fluids, describing flow of suspensions with rigid and underformable particles with own rotation. The micropolar fluid flow theory is incorporated into the framework of a velocity-vorticity formulation of Navier-Stokes equations. The governing equations are derived in differential and integral form, resulting from the application of a boundary element method (BEM). In integral transformations, the diffusion-convection fundamental solution for flow kinetics, including vorticity transport, heat transport and microrotation transport, is implemented. The natural convection test case is the benchmark case of natural convection in a square cavity, and computations are performed for Rayleigh number values up to 107. The results show, which microrotation of particles in suspension in general decreases overall heat transfer from the heated wall and should not therefore be neglected when computing heat and fluid flow of micropolar fluids.
Keywords: natural convection, micropolar fluid, boundary element method
Published in DKUM: 31.05.2012; Views: 2573; Downloads: 114
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Abstract: This paper presents simulation of rotating impeller in a mixing vessel by means of Computational Fluid Dynamics (CFD). A special emphasis is devoted to the study of influence of the choice of numerical model for simulation of rotation of impeller when mixing a Newtonian fluid in a vessel equipped with Rushton impeller, and operating under turbulent flow conditions. In order to determine the best simulation approach experimental validation of the selected problem is done by means of Particle Image Velocimetry (PIV) system. When using the rotating frame of reference approach, the stirring vessel geometry has to be split into a stationary and rotating part, and the questionarises where to position the interface between both regions in order to avoid numerical errors, originating in numerical approximations at the interface. To answer this question, a comparison between the CFD based numerical results and experimental results, was made.
Keywords: fluid mechanics, turbulent flow, Computational Fluid Dynamics, Particle Image Velocimetry, rotating frame of reference
Published in DKUM: 31.05.2012; Views: 2093; Downloads: 88
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Abstract: A large eddy simulation using the velocity-vorticity formulation of the incompressible Navier-Stokes equations in combination with the turbulent heat transfer equation is proposed for the solution of the turbulent natural convection drive flow in a 1:4 enclosure. The system of equations is closed by an enthropy-based subgrid scale model.The Prandtl turbulent number is used to estimate turbulent diffusion in the heat transfer equation. The boundary element method is used to solve the kinematics equation and estimate the boundary vorticity values. The vorticity transport equation is solved by FEM. The numerical example studied in this paper is the onset of a turbulent flow regime occuring at high Rayleigh number values ▫$(Ra=10^7-10^10)$▫. The formation of vortices in the boundary layer is observed, along with buoyancy driven diffusive convective transport. Quantitative comparison with the laminar flow model and the worh of other authors is also presented in terms of Nusselt number value oscillations.
Keywords: fluid mechanics, incompressible viscous fluid, turbulent flow, velocity vorticity formulation, finite element method, large eddy simulation
Published in DKUM: 31.05.2012; Views: 2363; Downloads: 44
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