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چكيده انگليسي :

Numerical Simulation of Buoyant Drops Suspended in a Shear Flow Sina Goodarzi s goodarzi@me iut ac ir Date of Submission 2011 06 12 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Saeed Mortazavi saeedm@cc iut ac irAbstractThe motion of drops suspended in another fluid has a wide variety of practical applications These includethe flow of oil and water through pipelines the recovery of oil through porous rock the flow of slurries andpolymer processing The lateral migration of deformable particles in shear flows has been the subject ofmany investigations The lateral migration of immersed objects in carrier fluids becomes very important intransport processes where mass momentum and energy are exchanged Removal of the vapor bubbles fromthe walls of pipes enhances the heat and mass transfer rates Lateral dispersion of a group of droplets inshear flow improves the mixing of fuel and air and results in higher rate and more efficient combustion Thehigher shear of the flow close to the bottom of rivers impedes the sedimentation process and underfavorable conditions causes resuspension of older sediment The lateral migration of a buoyant drop in simple shear flow is studied numerically in two dimensions Fora slightly buoyant drop the drop migrates to an equilibrium position which is close to the walls dependingon whether the drop leads or lags the flow If the drop is relatively more buoyant the equilibrium positionmoves back to the centerline The equilibrium position of the drop depends on the Froude number of theflow The behavior has been investigated for various Froude numbers The equilibrium position alsodepends on the drop deformation When the Capillary number is raised the equilibrium position movesaway from the wall At relatively large Capillary numbers the drop shape is not stable and the equilibriumposition shows small oscillation due to an unstable drop shape The effect of the Reynolds number on theequilibrium position has also been studied by a few simulations It is found that at a relatively largeReynolds number Reb 80 and a moderate Froude number Fr 160 the drop oscillates with a finiteamplitude inside the channel The equilibrium position of the drop agrees qualitatively with perturbationtheories and numerical results available for solid particles Suspensions of buoyant drops at low and moderate and areal fractions are studied at non zero Reynoldsnumbers in simple shear flow The flow is studied as a function of the Capillary number the Reynoldsnumber the Froude number and the density ratio It is found that the effective viscosity decreases withCapillary number The normal stress difference increases with Capillary number The effective viscosityand normal stress difference also depend on the Reynolds number In the dilute limit 0 22 thenormal stress difference decreases with Froude number and becomes negative at large Froude numbers Ata moderate areal fraction 0 44 the behavior of the suspension is nearly similar to the dilute case except that the normal stress difference is always positive Also the flow weakly depends on the Froudenumber at moderate areal fraction The density distribution of buoyant drops across the channel is non uniform Keywords Neutrally and non neutrally buoyant drop Shear flow Density ratio Capillary number Froude number Reynolds number suspensions of buoyant drops

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شبيه سازي عددي قطرات شناور در جريان برشي

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