ICE Strömungsforschung

Filtration Solver

For more than 3 years ICE has developed a large, Lagrangian particle model within the OpenSource Computational Fluid Dynamics ( CFD) software environment OpenFOAM. The original purpose of the project was the creation of a novel tool to simulate the micro-scale dirt particle’s hydrodynamics and deposition behaviour within the vicinity of realistically reconstructed fluid filter fibre geometries.
The present model is capable of handling spherical and non-spherical particles that span and affect multiple fluid calculation cells. A digitally reconstructed, deformable filter fibre, paper or garment structure gives the framework for all particle interactions with their surroundings. Two-way fluid-particle coupling, particle-particle impacts as well as particle-solid interactions can be handled. Using the software it is possible to determine decisive process parameters like filter fibre efficiencies and particle penetration depth values for any filter fibre material on a purely computational basis.
Over the past year a number of additional features have been added to the software tool. The Lagrangian objects are now capable of performing highly detailed collision interaction within large, dense particle collectives. A realistic simulation of e.g. various settling phenomena is thus enabled. In addition to that an electro-static module has been included. It allows the particles to bear charges and to interact with any surrounding, electric potential field, which is an essential ability to consider dominant phenomena in air filtration. Furthermore deformation of particles due to wall interaction effects can be taken into account. This opens a wide range of other possible application areas, e.g. in the Health, Cleaning, Automotive, Chemical, Paper, Household Appliances and Cleaning Industry.


The main innovations integrated within the software can be summarized as follows:

• Based on the geometrically versatile shape of ellipsoids, large particles, that feature six degrees of motional freedom, can be modelled. A wide variety of particle shapes, - anything from plates to sticks to simple spheres -, can be approximated by this concept.
• An explicit, force- and torque vector model which reduces the modelling to the mere formulation of single force effects.
• An efficient adaptive time stepping scheme for explicit Euler discretization of the Particle Momentum Equations (PME).
• A surface help point scheme to account for large particle effects in terms of fluid–particle, particle–wall and particle–particle interaction is implemented.
• Application of a drag force implementation that uses a combination of non-spherical, semi-empirical drag force formulas, a panel method to consider free flow swirling effects, a plugging method to include inter particle and particle–wall hydrodynamics and a simple adaptation of basic concepts known from the immersed boundary method.
• Implementation and description of an efficient particle–fluid, two–way coupling method.

The available computational tool enables the virtual, purely digital pre-design of materials. Since material structure characterization is based on statistical functions, it is possible to upload artificially created material samples, conduct the CFD analysis and to use the results as a good estimate on the expected performance of the newly designed material.


Main advantages

Existing spherical particle models do not take into account the rotational degrees of freedom encountered by non-spherical particles and hence the significant effects on particle drag and lift forces encountered by real particle shapes.

Also it has been found that particle shape-effects play an important role in e.g. filtration applications. With the newly developed software they can be assessed in detail solely on a theoretical basis.

The software includes an easy to use Windows based Graphical User Interface ( GUI) which encompasses all steps required for performing a complete simulation run:

• Set-up of micro-structural material models based on Computer Tomography ( CT) data or statistical functions
• Specification of boundary conditions, run time parameters and solution monitoring
• Main fluid flow, particle motion and material deformation computation
• Data base storage of simulation data
• Post-processing of results based on the OpenSource software ParaVIEW