For what type applications is filament modeling beneficial?
In many engineering applications, different components of a model may have length scales that vary significantly. While modeling such problems, the user has to decide to either increase the computational cost significantly (by increasing the total number of cells/elements to resolve the smaller length scale components) or compromise on accuracy by under-resolving/approximating the small length scale components. Similarly, the topology of different components in a model may vary significantly and complicate the mesh generation process (for example, heating elements of different shapes in an essentially cubic domain).
The filament model in CFD-ACE+ is specifically designed to allow such components to be included in the model without explicitly resolving the underlying mesh, thus reducing the computational cost and incorporating an accurate version of the physics. Filaments are objects that are predominantly one-dimensional: the transverse length scales of the filament are much smaller than the isotropic length scales of the full computational domain. Some examples include micro-channels, optical or electrical leads, resistive electric micro-heaters, or conducting paths in micro-chips.
In CFD-ACE+, filaments can be meshed independently from the full computational domain without any constraints on the location, alignment or resolution of the meshes. The different meshes communicate with each other during simulation through the exchange of appropriate source terms.
Filaments can be easily created within CFD-GEOM. To create a filament:
- Create an edge from a set of lines/curves.
- Select Mesh → Filament Options → Create Filament.
- Select the previously created edge(s), which will be used as the filament extrusion guide.
- Specify the default radius and the number of sides (to get the correct shape and cross-sectional area).
- Click "Apply" to create the filament.
Figure 1. Filament creation tool in CFD-GEOM
Once you have the filament, it can be copied to a model that contains the background mesh. Alternatively, the filament could be created in the same model (if the model is complex, it may be easier to create the filament on a different layer). If you have multiple edges and would like to apply different properties on the different sections of the filament, make sure that the Multiple Volume Condition option is ON. An essential assumption of the filament model is that the filament occupies a significantly smaller cell volume. A good rule of thumb is that the background cell cross-sectional area should be four times larger than the filament cell cross-sectional area.
Two examples of filament usage are shown below. Figure 2 shows a heating element in the shape of the ESI logo modeled as a filament, and demonstrates heat transfer from the filament to the solid domain. Figure 3 shows an electric coil modeled as a filament in an ICP reactor simulation.
ESI CFD Support Team
Figure 2. Heating elements modeled as
Figure 3. Coils modeled as filaments in
an ICP reactor simulation
Tested with V2011.0
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12838/18%Last update: 2012-03-13 12:37
Author: ESI-CFD Support Team
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