Effects of heterogeneity on the drag force in random arrays of spheres


Kriebitzsch, S.H.L. and Hoef, M.A. van der and Kuipers, J.A.M. (2008) Effects of heterogeneity on the drag force in random arrays of spheres. In: 6th International Conference on Computational Fluid Dynamics in the Oil & Gas, Metallurgical and Process Industries, CFD 2008, 10-12 June 2008, Trondheim, Norway.

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Abstract:The modelling of the gas-solid interaction is a prerequisite in order
to accurately predict fluidized bed behaviour using models
such as the Discrete Particle Model (DPM) or the Two Fluid
Model (TFM). Currently, the drag force is usually modelled
purely based on porosity and slip velocity, which are averaged
with respect to the grid size used to solve the model equations.
Interfaces at heterogenous structures such as bubbles or free
board are not accounted for. As recently pointed out by Xu
et al. (2007), sub-grid information for the particle position is
available in DPM simulations, thus the local porosity is known
and can be used when calculating the drag.
Direct Numerical Simulation of flow in particulate systems
were done using the lattice Boltzmann method. These simulations
were carried out with random arrays of spheres which
only have a slight degree of heterogeneity and the gas-solid interaction
force on each particle was measured. First we compared
these results, which can be considered as the “true drag
force, with the drag force one would predict from a correlation
typically used in larger scale models (such as the relation of
van der Hoef et al. (2005)). Even for the random arrays, the
drag on some individual particles differed considerably (up to
40%) from the predicted drag. Then we evaluate the effectiveness
of improved drag models, that use information on local
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Link to this item:http://purl.utwente.nl/publications/68591
Organisation URL:http://www.sintef.no/Projectweb/CFD2008
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