| 1. |
- Benavides, Aldo, 1978, et al.
(författare)
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Comparison of experimental and simulation results for turbulent gas-solid riser flow
- 2008
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Ingår i: Circulating Fluidized Bed Technology IX. Proceedings of the 9th International Conference on Circulating Fluidized Beds, CFB-9. May 13-16, 2008. Hamburg, Germany..
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Konferensbidrag (refereegranskat)abstract
- This paper compares measurements of the radial solids concentration in a riser with CFD simulations. An Eulerian model based upon the kinetic theory for granular flow, extended with models describing turbulence modulation and dispersion, is used to treat the particulate phase. Coupling between momentum equations of the gas and particulate phases is taken into account via a mean drag force formulation. Solids distribution profiles over three horizontal planes are measured by the use of optical probes. The pressure drop is used to estimate an average solids concentration profile along the riser. The comparison is reported for a single superficial gas velocity and solids mass flux.
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| 2. |
- Benavides, Aldo, 1978, et al.
(författare)
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Numerical computation of turbulent gas-particle flow in a backward-facing step
- 2008
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Ingår i: Proceedings 7th International Symposium on Engineering Turbulence Modelling and Measurements - ETMM7. Limassol, Cyprus, 4-6 June 2008.. ; 1, s. 144-149
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In the present article, a numerical study of turbulent gas-particle flow in a vertically oriented backward-facing step is compared with literature data. The dispersed phase is simulated by an Eulerian approach based upon the kinetic theory for granular flow, including interaction with the continuous phase. The modeling of turbulent motion within the dispersed phase as well as the correlation between gas and particle velocity fluctuations are discussed. This work demonstrates that treatment of such quantities is essential to correctly describe the particulate phase distribution and turbulence modulation in the gas phase. In addition, closure relations for the dispersed phase are extended to incorporate the influence of the continuous fluid. The derived models are validated with benchmark experimental results of a planar sudden expansion turbulent flow including particles. In general, good agreement is found between model predictions and experimental data.
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| 3. |
- Benavides, Aldo, 1978, et al.
(författare)
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Numerical computation of turbulent gas-particle flow in a backward-facing step. Model comparison with experimental data
- 2008
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Ingår i: Proceedings 11th International Conference on Multiphase Flow in Industrial Plants, MFIP 2008. September 7-10, Palermo, Italy.. - 888819813X ; , s. 63-70
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Konferensbidrag (refereegranskat)abstract
- In the present article, the predictions of two models describing turbulent gas-particle flow in a vertically oriented backward-facing step are compared to each other and with literature data. The first model is an Eulerian approach based upon the kinetic theory of granular flow, including turbulence modulation and interaction with the continuous phase. The gas-phase turbulence is predicted by use of a k-epsilon dispersed turbulence model, including inter-phase energy transfer between gas and particle fluctuating motions. The second model also uses an Eulerian approach coupled to a k-omega turbulence model. The latter model considers the transport of particles to the near-wall region due to turbulence intensity gradients, and particulate phase influences on the gas flow. It is shown that the combined effect has an impact on the two-phase flow. The derived models are validated with benchmark experimental results of a planar sudden expansion turbulent flow including particles.
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| 4. |
- Benavides, Aldo, 1978, et al.
(författare)
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Numerical simulation and validation of dilute turbulent gas-particle flow with inelastic collisions and turbulence modulation
- 2008
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Ingår i: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 182:2, s. 294-306
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Tidskriftsartikel (refereegranskat)abstract
- This work describes a theoretical and numerical study of turbulent gas-particle flows in the Eulerian framework. The equations describing the flow are derived employing Favre averaging. The closures required for the equations describing the particulate phase are derived from the kinetic theory of granular flow. The kinetic theory proposed originally is extended to incorporate the effects of the continuous fluid on the particulate phase behavior. Models describing the coupling between the continuous phase kinetic energy and particulate phase granular temperature are derived, discussed, and their effect on the flow predictions is shown.The derived models are validated with benchmark experimental results of a fully developed turbulent gas-solid flow in a vertical pipe. The effect of the models describing the influence of turbulence on the particle motion as well as the turbulence modulation due to the presence of particles is analyzed and discussed.
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| 5. |
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| 6. |
- Gopala, Vinay, 1979, et al.
(författare)
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Volume of fluid methods for immiscible-fluid and free-surface flows
- 2008
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 141:1-3, s. 204-221
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Tidskriftsartikel (refereegranskat)abstract
- This article reviews and analyzes a number of numerical methods to track interfaces in multiphase flows. Several interface tracking methods can be found in literature: the level-set method, the marker particle method, the front tracking method and the volume of fluid method (VOF) to name a few. The volume of fluid method has an advantage of being conceptually simple, reasonably accurate and phenomena such as interface breakup and coalescence are inherently included. Over the years a number of different techniques to implement the VOF method have been devised. This article gives a basic introduction to the VOF method and focuses on four VOF methods: flux-corrected transport (FCT) by Boris et al. [J.P. Boris, D.L. Book, Flux-corrected transport. I: SHASTA, a fluid transport algorithm that works, J. Comput. Phys. 11 (1973) 38-69], Lagrangian piecewise linear interface construction (L-PLIC) by van Wachem and Schouten [B.G.M. van Wachem, J.C. Schouten, Experimental validation of 3-d Lagrangian VOF model: bubble shape and rise velocity, AIChE 48 (12) (2002) 2744-2753], Compressive interface capturing scheme for arbitrary meshes (CICSAM) by Ubbink [O. Ubbink, Numerical prediction of two fluid systems with sharp interfaces, Ph.D. Thesis, Imperial College of Science, Technology and Medicine, 1997] and inter-gamma scheme by Jasak and Weller [H. Jasak, H.G. Weller, Interface-tracking capabilities of the InterGamma differencing scheme, Technical Report, Imperial College, University of London, 1995]. A detailed description of these schemes is given and implemented into an in-house fully coupled solver. Further, the performance of these schemes is examined employing a number of tests to analyze their strengths and weaknesses. Their advantages and limitations are discussed. (C) 2008 Elsevier B.V. All rights reserved.
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| 7. |
- Mark, Andreas, 1980, et al.
(författare)
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Derivation and Validation of a Novel Implicit Second-Order Accurate Immersed Boundary Method
- 2008
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Ingår i: Journal of Computational Physics. ; 227/13, s. 6660-6680
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Tidskriftsartikel (refereegranskat)abstract
- A novel implicit second-order accurate immersed boundary method (IBM) for simulating the flow around arbitrary stationary bodies is developed, implemented and validated in this paper.The IBM is used to efficiently take into account the existence of bodies within the fluid domain. The flow domain consist of simple Cartesian cells whereas the body can be arbitrary. At the triangulated interface of the body and the fluid, the immersed boundary, the coefficients obtained from discretizing the Navier–Stokes equations are closed with a second-order accurate interpolation arising from the immersed boundary condition employed at the interface. Two different conditions are developed in this paper and it is shown that for the mirroring method the resulting coefficients lead to a well-posed and diagonally dominant system which can be efficiently solved with a preconditioned Krylov sub-space solver. The immersed boundary condition generates a fictitious reversed velocity field inside the immersed boundary, which is excluded from the continuity equation to account for the presence of the IB in the pressure correction equation, resulting in no mass flux over the IB. The force acting on the object from the fluid is determined by integrating the pressure and the viscous forces over the object.The method is validated by simulating the flow around a sphere for a range of Re numbers. It is shown that the drag is very well in agreement with experimental data. Accuracy and convergence studies are employed, proving the second-order accuracy of the method and showing the superiority in convergence rate compared to other IBM. Finally the drag force of a cluster of non-spherical particles is employed to show the generality and potential of the method.
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| 8. |
- Sasic, Srdjan, 1968, et al.
(författare)
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Individual fibre in an arbitrary flow field - true direct numerical simulation (DNS) using an implicit immersed boundary method
- 2008
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Ingår i: 11th International Conference on Multiphase Flow in Industrial Plants.
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Konferensbidrag (refereegranskat)abstract
- A novel immersed boundary method for three-dimensional, time-dependent flows is presented in this work and applied to simulating the behaviour of an individual fibre in various flow regimes. The fibre is placed in a periodic box and has either a fixed position or is allowed to move freely (including translation and rotation) through the domain. The immersed boundary method mirrors the velocity field along the normal of the local triangulated immersed boundary segment to guarantee that the fluid takes into account the immersed body accurately. As a result of the procedure, there is a fictitious velocity field inside the immersed boundary, mirroring the boundary layer. Care is taken to solve the velocity field in such a way that the mass is conserved in the cells containing the immersed boundary. The method applied is second-order accurate and is intended to be used for fully resolving the flow field around arbitrary moving bodies immersed in a fluid. The immersed boundary method is employed on a selection of different fibre shapes, aiming at predicting the behaviour of real fibres in realistic flow situations. The force exerted by the fluid is directly calculated by integrating the pressure and viscous forces over the objects immersed. The resulting coarse-grained drag and lift force functions can be employed in larger scale calculations of fluid-fibre flows.
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| 9. |
- van Wachem, Berend, 1972, et al.
(författare)
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Derivation, Simulation and Validation of a Cohesive Particle Flow CFD Model
- 2008
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Ingår i: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 54:1, s. 9-19
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensive physical model describing the agglomeration behavior present during fluidization of fine powders is still missing in literature. In this work, a model of balance of forces acting on a single solid particle is introduced, aiming at predicting and locally estimating the size of the agglomerates created in the bed. Computational Fluid Dynamics (CFD) have been used to investigate the hydrodynamics of a gas-solid fluidized bed operated with particles belonging to group A of Geldart classification(Geldart, 1973). The key issue is that, in the gas and particle flow field, both hydrodynamic and inter-particle forces are of importance. The model is incorporated into simulations based on an Eulerian approach and using the kinetic theory of granular flow. In the simulations, the closure models describing the hydrodynamics of the solids phase are directly affected by the behavior of the agglomerates. No empirical data or parameters were used to close the model. The simulations are compared with experiments of an independent research group, through the time-averaged solids volume fraction in a fluidized bed operated at different gas velocities. The agreement obtained between the simulation results and data from the literature is very good. Also, it is shown that, under flow conditions treated in the present work, agglomerates of size of several single particle diameters are present in the fluidized bed.
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