Modelling of Multiphase Flows with OpenFOAM
OpenFOAM is a C++ library, which is licensed free and open source under the GNU General Public Licence, and dedicated to solve partial differential equations with the focus on numerical simulation (CFD) of turbulent single and multiphase flows. The source code is published and maintained by the OpenFOAM Foundation. Within this field of application OpenFOAM becomes more and more important in the scientific community as well as in the industry. Hence, the main developments for the numerical simulation of multiphase flows at Helmholtz-Zentrum Dresden-Rossendorf, e.g., Gentop, AIAD and iMUSIG, are currently transferred to the OpenFOAM library. To account for sustainable research and a broad application Helmholtz-Zentrum Dresden-Rossendorf has signed the Contributors Agreement with the OpenFOAM Foundation in 2017. Furthermore, the complete access to the source code, in contrast to commercial CFD software like Ansys CFX, gives rise to much more possibilities concerning the development of new physical models and simulation methods, e.g., own solvers or implementation of the most recent numerical methods. As a member of the OpenFOAM Process Engineering Consortium Helmholtz-Zentrum Dresden-Rossendorf has established a strong cooperation with the chemical and process engineering industry to ensure that the research done on multiphase flows fits industrial needs.
Population Balance Modelling Based on a Class Method
Multiphase flows, or more in detail bubbly flows, which occur in industrial applications are typically polydisperse, and characterized by bubbles at different sizes and velocities. This influences the mass and heat transfer between the phases and has to be taken into account by numerical simulations. A common method to estimate the bubble size distribution is the so called class method (Kumar & Ramkrishna, Chemical Engineering Science 51, 1311-1342, 1996). This method was extended at Helmholtz-Zentrum Dresden-Rossendorf in the past and subdivides the bubbles into different size and velocity groups. The OpenFOAM library was equipped with such a class method and the corresponding code is going to be published together with the OpenFOAM Foundation and CFD Direct.
Population Balance Modelling with Method of Moments
As an attractive alternative for modelling the population balance serves quadrature bases method of moments (QMOM) due to their efficiency. In cooperation with the Institute of Energy Process Engineering and Chemical Engineering at TU Bergakademie Freiberg Helmholz-Zentrum Dresden-Rossendorf currently develops a method to include the bubble velocity as an internal coordinate into the solution of the population balance. This allows the description of the spatial separation process with fewer assumptions.
Modelling of Polydispersed Flows (Baseline)
The improvement of the predictive capability of numerical simulations for polydispersed flows is the idea of the baseline modelling strategy. Key aspects are the implementation of new models and the validation of existing models for, e.g., momentum transfer, bubble induced turbulence and wall functions in OpenFoam. An important work package is the comparison of results obtained with OpenFoam and other commercial CFD software, like Ansys CFX.
Modelling of Horizontal Stratified Flows (AIAD)
This development is focused on the modelling of the free surface for horizontal stratified flows within the two-fluid model (Euler-Euler). The essential part is the momentum transfer between the continuous phases at the interface and the detection of the local flow morphology (Porombka & Hoehne, Chemical Engineering Science 134, 348 - 359, 2015). more ...
Generalized CFD-Model for Multiphase Flows (Gentop)
The two-fluid model (Euler-Euler) will be modified in a way that it allows for the numerical simulation of co-existing resolved (continuous) and small-scale (polydisperse) gas structures. To achieve this it is necessary to adopt the solution procedure in OpenFOAM to the most recent developments (Cubero et al., Computers & Chemical Engineering 62, 96 - 107, 2014) and to derive new, generalized models for the resolved interface, e.g., an anisotropic interface drag formulation, models for the interaction between turbulent eddies and the interface, mass transfer between the adjacent phases, and the entrainment of dispersed gas due to interface deformation. more ...
Phase Field Model for a Rising Bubble
The phase field method has its origin in metallurgy and is based on the assumption of a diffuse interface. This is in contrast to state-of-the-art methods assuming a sharp interface, e.g., Level-Set or Volume-of-Fluid. However, it is applicable for the numerical simulation of multiphase flows and some preliminary tests for a single rising bubble in a stagnant water column according to Hysing et al., International Journal for Numerical Methods in Fluids 60, 1259-1288, 2009 are promising.
Y. Liao, R. Oertel, F. Schlegel, D. Lucas.
An efficient discrete formulation of the birth by breakup term for application in CFD.
R. Oertel, D. Lucas and F. Schlegel.
A generalized multi-field two-fluid concept for numerical simulation of two-phase flows.
4th OpenFOAM User Conference, Cologne, 2016.
F. Schlegel, F. Gauß, E. Krepper and D. Lucas.
Evaluation of Gentop Concept for the Buoyancy-Driven Motion of a Single Bubble.
International Conference on Multiphase Flow, Firenze, 2016.