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Abstract
Resolved simulation of disperse multiphase flows is often used as fundamental tool to derive closures for homogenized models like twofluid models, or socalled discrete particle models [1]. However, it is often not possible to produce high quality numerical grids (especially in the case of moving bodies) due to the complex topology of the fluid domain. Therefore, immersedboundary methods are often used to model the presence of a dispersed solid phase within a simply connected fluid domain. Another issue of particleresolved simulations is the large amount of produced data and their processing, especially in the case of transient phenomena.
In our contribution, we first describe a method to impose general boundary conditions (Dirichlet, Neumann or Robin) at immersed surfaces by means of appropriate source terms in the governing equations. This method can be seen as a generalization of our Hybrid Fictitious Domain Immersed Boundary (HFDIB) method [2] that uses second order interpolation to impose a Dirichlet boundary condition at the particle surface. As the HFDIB, our generalized method is coupled with the CFDDEM library CFDEM® [3] to allow simulation of moving bodies. Unlike the HFDIB that was based on a polynomial reconstruction of the boundary layer, the new method consists in expanding Eulerian fields in Taylor series (up to second order) along the direction normal to the immersed surfaces. These terms are evaluated using field values interpolated at multiple fluid points along the normal direction, as well as by considering the desired boundary condition. Subsequently, the Taylor series expansion is used to evaluate the field values at a surface cell (i.e., a cell intersected by the immersed surface), and this value is then imposed using a directforcing approach. In this work, we demonstrate the accuracy and convergence of the proposed method and we show its application to particleresolved direct numerical simulation of momentum, heat and mass transfer in dense particle beds (Figure 1).
Second, we show how the opensource parallel data processing library CPPPO [4] can be used in conjunction with the new immersed boundary method. CPPPO is a filtering tool capable of performing filtering, sampling and binning operations onthefly, i.e. while the solver is running, that features advanced filtering algorithms to reduce the number of parallel communications and increase flexibility (for example, computing covariances, or customizing filtering kernels). Specifically, we show how CPPPO can be used to track the particlebased drag coefficient and Nusselt number in gassolid suspensions. We show that our results are in agreement with existing literature and that more insight can be obtained using the advanced capabilities of CPPPO: for example, we highlight that closures developed for discrete particle models (i.e., closures for particlebased quantities) are significantly different from those used in twofluid models (in which ensemble averaged quantities are considered).
In our contribution, we first describe a method to impose general boundary conditions (Dirichlet, Neumann or Robin) at immersed surfaces by means of appropriate source terms in the governing equations. This method can be seen as a generalization of our Hybrid Fictitious Domain Immersed Boundary (HFDIB) method [2] that uses second order interpolation to impose a Dirichlet boundary condition at the particle surface. As the HFDIB, our generalized method is coupled with the CFDDEM library CFDEM® [3] to allow simulation of moving bodies. Unlike the HFDIB that was based on a polynomial reconstruction of the boundary layer, the new method consists in expanding Eulerian fields in Taylor series (up to second order) along the direction normal to the immersed surfaces. These terms are evaluated using field values interpolated at multiple fluid points along the normal direction, as well as by considering the desired boundary condition. Subsequently, the Taylor series expansion is used to evaluate the field values at a surface cell (i.e., a cell intersected by the immersed surface), and this value is then imposed using a directforcing approach. In this work, we demonstrate the accuracy and convergence of the proposed method and we show its application to particleresolved direct numerical simulation of momentum, heat and mass transfer in dense particle beds (Figure 1).
Second, we show how the opensource parallel data processing library CPPPO [4] can be used in conjunction with the new immersed boundary method. CPPPO is a filtering tool capable of performing filtering, sampling and binning operations onthefly, i.e. while the solver is running, that features advanced filtering algorithms to reduce the number of parallel communications and increase flexibility (for example, computing covariances, or customizing filtering kernels). Specifically, we show how CPPPO can be used to track the particlebased drag coefficient and Nusselt number in gassolid suspensions. We show that our results are in agreement with existing literature and that more insight can be obtained using the advanced capabilities of CPPPO: for example, we highlight that closures developed for discrete particle models (i.e., closures for particlebased quantities) are significantly different from those used in twofluid models (in which ensemble averaged quantities are considered).
Originalsprache  englisch 

Publikationsstatus  Veröffentlicht  27 Aug 2017 
Veranstaltung  International Conference on Numerical Methods in Multiphase Flows III  The University of Tokyo, Institute of Industrial Science, (KomabaII campus), Tokyo, Japan Dauer: 26 Jul 2017 → 29 Jul 2017 http://www.jsmf.gr.jp/icnmmf2017/ 
Konferenz
Konferenz  International Conference on Numerical Methods in Multiphase Flows III 

Kurztitel  ICNMMFIII 
Land  Japan 
Ort  Tokyo 
Zeitraum  26/07/17 → 29/07/17 
Internetadresse 
ASJC Scopus subject areas
 !!Fluid Flow and Transfer Processes
 Numerische Mathematik
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Projekt: Foschungsprojekt