Reference : A Dual-Grid Multiscale Approach to CFD-DEM Couplings for Multiphase Flow
Dissertations and theses : Doctoral thesis
Engineering, computing & technology : Multidisciplinary, general & others
Computational Sciences
A Dual-Grid Multiscale Approach to CFD-DEM Couplings for Multiphase Flow
Pozzetti, Gabriele mailto [University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Engineering Research Unit >]
University of Luxembourg, ​​Luxembourg
Docteur en Sciences de l'Ingénieur
Peters, Bernhard mailto
Zilian, Andreas mailto
Bordas, Stéphane mailto
Mahmouidi, Amir
Useldinger, Ralph
Varrette, Sébastien mailto
[en] Multiscale ; CFD-DEM
[en] This thesis focuses on a novel dual-grid multiscale approach to CFD-
DEM1 couplings, proposes its advantages in terms of numerical proper-
ties and performance, and provides examples of engineering applications
that can benefit from it. In recent years, CFD-DEM couplings are be-
coming a more and more adopted solution for the numerical simulation
of particle-laden flows. In particular, couplings based on the volume av-
eraging technique have become a standard for numerical simulations in
chemical and process engineering. Furthermore, they are rapidly spread-
ing to civil, geotechnical and mechanical applications due to their ability
in dealing with arbitrarily complex mixtures of continuum and granular
Despite the several advantages that these Eulerian-Lagrangian cou-
plings provide, their rigorous application to complex scenarios is currently
limited by two main factors. First, the computational traceability of the
solutions can become problematic due to the lack of a general theory on
the subject. In particular, grid-convergence studies for the solution of the
continuous phases are often not feasible due to the averaging procedure
that imposes limitations on the grid structure and refinement. Second,
the parallel implementation of these numerical schemes holds important
disadvantages in terms of memory consumption and inter-physics com-
munication load. These disadvantages are significantly limiting the ex-
tension of these approaches to large-scale scenarios.
This thesis collects some of the most significant works published in
the last years on a novel approach that allows solving the two above-
mentioned problems, and, therefore, tackling more complex and expen-
sive scenarios. I refer to this approach as dual-grid multiscale approach
for CFD-DEM couplings. It consists in using two different computational
grids, one for the coupling between continuum and discrete entities and
one for the solution of the so-obtained continuum equations. The two
grids, i.e. the two problems, are in this way resolved on two different
scales. The first scale or “bulk” scale is chosen to optimize the averag-
ing operation. At this length-scale, the discrete entities are considered
as zero-dimensional, and interact with the fluid with local exchanges of
momentum, mass, and energy. The second scale or “fluid-fine” scale is
identified as the one at which a unique solution for the averaged equa-
tions can be provided. In practice, this is chosen as the one at which the
solution of the fluid equations becomes grid-independent. An inter-scale
communication is adopted by interpolating fields from the fluid-fine scale
to the bulk one and vice-versa.
The theoretical description of the method is first provided with par-
ticular reference to the DEM-VOF coupling. Even in its simplest version,
the multiscale approach is shown to generate grid-convergent solutions
and significantly higher accuracy than a standard CFD-DEM coupling.
This shows how the new approach is able to overcome the first main
limitation described above.
Then, an optimized parallel implementation of the method is pro-
posed to show how this multiscale approach can provide significant ben-
efits also for what concerns the execution time. Technically, this is made
possible by moving the communication cost of the coupling from the
inter-physics communication that characterized the standard CFD-DEM
couplings to an optimized inter-scale communication routine. This en-
ables the method to overcome a major bottleneck of the parallel execution
of CFD-DEM couplings and therefore the second main limitation of those
Finally, the dual-grid multiscale method is applied to approach in-
dustrially relevant problems that were till now out-of-reach for standard
CFD-DEM couplings, proving how this technique can have direct real-
case application and produce immediate benefits for practitioners willing
to adopt it.

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