Abstract
AbstractTwo different methods for closure modeling of the unresolved terms appearing in the filtered two‐fluid model are discussed and compared. The spatially averaged two‐fluid model is based on generalizing the concepts of large eddy simulation to gas‐particle flows. In the approximate deconvolution method‐two‐fluid model approach, the unresolved terms are modeled by an approximate deconvolution method, where an approximation of the unfiltered solution is obtained by repeated filtering. Finally, these models are applied to a lab‐scale and a pilot‐scale fluidized bed. Both approaches yield fairly good agreement with a highly resolved reference simulation as well as with experimental data. Additionally, both methods deliver reasonable grid‐independent solutions up to a grid resolution of 2 cm in the case of Geldart type A particles.
Highlights
Fluidized beds are widely used in a variety of industrially important processes
For the group A particles employed in the pilot-scale fluidized bed, the characteristic length scale is 265 mm, which is by factor 40–80 smaller than the coarse grid spacing
A previous study [17] indicates that for coarse grid spacings of about 8Lch, the contribution stemming from the interparticle collisions is insignificant compared to the ‘‘turbulent’’ Reynolds stress
Summary
Fluidized beds are widely used in a variety of industrially important processes. During the last decades, the analysis of the hydrodynamics or the efficiency of fluidized beds through numerical simulations has become increasingly common [1,2,3,4,5,6,7,8,9,10], where the two-fluid model (TFM) approach has proven to provide fairly good predictions of the hydrodynamics of gassolid flows [1]. Closure models are commonly deduced from highly resolved simulations, either Euler-Euler or EulerLagrange [25, 26], which are filtered using filters of different sizes Various markers, such as solids volume fraction and slip velocity, are employed to classify the sub-filter scale state and averaged to obtain statistics of the filtered quantities. Based on these markers, functional fits are provided that the fTFM can be applied in coarse-grid simulations [12, 15,16,17,18,19, 22]. The latter fluidized bed is operated in bubbling and turbulent regimes
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