Contact

Dr. Fabian Schlegel

Research Assistant
Computational Fluid Dynamics
f.schlegelAthzdr.de
Phone: +49 351 260 3467

Within this project the main developments for the numerical simulation of multiphase flows at Helmholtz-Zentrum Dresden-Rossendorf are transferred to the C++ library OpenFOAM. The complete access to the source code, in contrast to commercial CFD software, give rise to much more possibilities concerning the development of new physical models and simulation methods.

Modelling of Multiphase Flows with OpenFOAM

To support a sustainable research and a broad application of the research results, the main developments in the field of numerical simulation of multiphase flows at Helmholtz-Zentrum Dresden-Rossendorf are implemented in the open source library OpenFOAM. Helmholtz-Zentrum Dresden-Rossendorf has signed the Contributors Agreement with the OpenFOAM Foundation in 2017 and is since than an active contributor to OpenFOAM in the field of multiphase flows. 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.


Current Work

Automation of Baseline Cases

Scientific workflow for Baseline automation ©Copyright: Hänsch, Susann

The baseline strategy requires the analysis and evaluation of a multitude of bubbly flow cases that are part of an extensive case repository established at the CFD department. For the efficient validation of new models an automated workflow environment is being developed that aims to allow the simulation of all ~400 cases and their joint evaluation in a single report. This enables the sustainable development and assessment of new baseline models.


Large-Eddy Simulations (LES) of Resolved Interfaces

Gas bubble rising in stagnant liquid with characteristic vortex structures in the wake flow. ©Copyright: Meller, Richard

Similarly to modelling of interfacial flows, turbulent eddies are separated into large and small, sub-filter scales. In LES, large scale structures are resolved in space and time, while the small turbulent structures need modelling. In the framework of multiphase flows in a two-fluid model, additionally to the "classical" turbulent stress, a number of sub-filter scale contributions is present, which describe the dynamics and interaction of interfaces and turbulence. For these sub-filter contributions, different models and their combinations are assessed in a-posteriori investigations for application to technically relevant simulations.


Population Balance Modelling Based on a Class Method

Sketch for binary breakup on non-uniform grids ©Copyright: Lehnigk, Ronald

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 code is available in the current OpenFOAM release (Commit).


Generalized CFD-Model for Multiphase Flows (Gentop)

Generation of dispersed air bubbles by an impinging jet ©Copyright: Couteau, Arthur

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.


Modelling of Horizontally Stratified Flows (AIAD)

Simulation of stratified air-water counter-current flow in WENKA channel ©Copyright: Dr. Tekavcic, Matej

One of our goals is to advance the capabilities of current two-fluid (Euler-Euler) based modelling tools towards simulation of industrially relevant turbulent two-phase flows. Present work is focused on the development, implementation and validation of improved two-phase heat and mass transfer models for stratified flows. Advancement includes improvements concerning the treatment of interaction between gas-liquid interfaces and turbulence.


Modelling of Bubble Dynamics under Pool Scrubbing Conditions

Numerical simulation of single bubbles for pool scrubbing applications ©Copyright: Dr. Liao, Yixiang

Pool scrubbing is an effective method for removing radioactive aerosol particles during severe nuclear accidents. Bubble dynamics including growth and detachment at the nozzle, oscillation and deformation as the bubble rising through the pool and even coalescence and breakup is a crucial factor affecting the decontamination factor. The work mainly focuses on the study of bubble dynamics under pool scrubbing conditions using the interface-tracking method in OpenFOAM. It is a part of the international project IPRESCA (Integration of Pool scrubbing Research to Enhance Source-term Calculations).


Publications

Y. Liao, K. Upadhyay, F. Schlegel.
Eulerian-Eulerian two-fluid model for laminar bubbly pipe flows: validation of the baseline model.
Computers & Fluids, under review.

R. Meller, F. Schlegel, and D. Lucas.
A Morphology Adaptive Multi-Field Two-Fluid Model.
International Journal for Numerical Methods in Fluids, under review.

Y. Liao, R. Oertel, S. Kriebitzsch, F. Schlegel, and D. Lucas.
A Discrete Population Balance Equation for Binary Breakage.
International Journal for Numerical Methods in Fluids, 2018, 1–14, 10.1002/fld.4491.


Contact

Dr. Fabian Schlegel

Research Assistant
Computational Fluid Dynamics
f.schlegelAthzdr.de
Phone: +49 351 260 3467