Software: PFC: Pre-Release 4.0
CCFD Add-on: Couple PFC3D with CFD
The CCFD documentation (see link on right side of page) provides a detailed overview of the PFC3D 4.0 add-on, provides two verification problems, and gives two step-by-step tutorial example problems. The following description – intended to provide an overview of the new add-on – is a summary of the steps illustrated in the tutorials.
Overview
The CFD (computational fluid dynamics) solver, CCFD, is called from within an application called GID. GID is a universal, adaptive, and user-friendly graphical user interface for geometrical modeling. The geometrical description of the fluid container, the fluid properties, and the initial and boundary conditions of the flow problem are specified in GID and saved as a GID project file (extension .gid). In addition, the coupled analysis is initiated in GID. The initial location, size and properties of the particles are specified in a PFC3D data file. The interaction of the components that are used for a CFD analysis is shown below.
The tutorials present two examples: 1) A spherical particle dropping in a vertical cylinder filled with liquid, and 2) particles conveyed with the flow along a curved pipe.
Geometry Definition
In both examples, the first step is to use GID and its geometrical modeling tools to create the problem volumes. These are saved as .gid files and result in output shown below.
Left: the vertical cylinder in the first tutorial as created in GID.
Right: creating the curved section of the curved pipe in the second tutorial.
Assignment of Boundary Conditions and Material Properties
The next step is the fluid flow model setup. The .gid files from the first step are opened in GID and materials are defined and assigned to the model volumes. When complete, the material assignment state may be rendered to verify the right materials have been assigned to the right volumes, as in the figures below.
Left: specifying water and its properties as the material contained by the volume.
Right: specifying air and its properties as the material contained in the curved pipe.
In the next step, CFD problem data is specified. Controls are provided to set a range of problem parameters, including general (such as sweep, turbulence relax factor, relax factor P, and others), whether to restart the problem, how to monitor the model, scalar definition, VOF, and coupling attributes. Problem data also controls the rate of communication between CCFD and PFC3D, and the duration, of the coupled model run. Next, the initial conditions are specified for the fluid in the model volume and boundary conditions are provided.
CFD meshing and PFC3D wall generation
At this stage, the volume is meshed. CCFD will accept both hexahedral and tetrahedral meshes. Controls are provided for mesh refinement, depending on the type of mesh to be created. In both tutorials, hexahedral meshes are created, with results shown below.
In the curved pipe example the initial volume is created in three sections. In order to provide a description of the walls of the domain for PFC3D, the next step in this problem is to use a copy of the .gid file to remove internal volumes and surfaces and to export the resulting outer surface of the volume to an STL file that may be read into PFC3D. In the first tutorial, this step is avoided by using a built-in primitive in PFC3D to create the walls.
Once the steps for setting up the CCFD model are completed, the PFC3D portion of the simulation is prepared by creating a data file that describes the location, size, and properties of the particles in the model.
Calculation
With both the CCFD and the PFC3D sides of the model completely set up, the simulation is ready to be run. To do so, the CCFD project (the .gid file) is loaded into GID, then the PFC3D data file is also specified. Calculations are initiated and the rate of information exchange between CCFD and PFC3D, as well as the duration of the simulation, are determined by the settings provided when the problem data was specified. Using the FISH language the user has read/write access to the internal state of the code during the calculation. The feature allows for great flexibility and for customization of the coupling for specific applications. During the calculation the properties of both the fluid and the particles can be observed with the PFC3D plot-items.
PFC plot items during a coupled calculation. In this example we observe the behavior of a fluidized bed. PFC3D particles are plotted in yellow. The red and black vectors plotted at the ball centers are the drag force applied by the fluid and the ball velocity respectively. The light gray mesh represents the CFD elements and the blue vectors show the fluid velocity.
Post-processing
After the calculation has completed GID provides an extensive post-processing environment for viewing and interpreting the model results.
Contours of fluid velocity and streamlines for a cyclone separator example.
Contours of fluid pressure, porosity and drag force for a pneumatic conveying flow in a bent pipe.
