Export Flow Simulation (Voxel)
To generate a journal file and mesh for a flow computation with Fluent, select Export Flow Simulation (Voxel) from the pull-down menu in the ExportGeo-Fluent section.
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Important! The same results can be achieved with the FlowDict module directly in GeoDict.
In general, this is the recommended way if FlowDict is in your GeoDict license, since the GeoDict solvers are optimized for voxel structures and therefore faster and more memory efficient for this use case.
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Click the Options’ Edit… button to define the settings for the export to Fluent. After entering all parameters, click Export to export the simulation settings for Fluent.
In the ExportGeo-Fluent - Export Flow Simulation dialog, choose a Result File Name (*.gdr) according to the current project. The result file contains all information about the current export. The corresponding result folder contains the mesh and journal files for Fluent and the chosen structure saved as GDT file.
The options for ExportGeo-Fluent are organized under the tabs Constituent Materials, Solver, and Grid.
Constituent Materials
The fluid parameters of all constituent materials in the structure are defined in the corresponding fields under the Constituent Materials tab.
The structure already contains a fluid
If one fluid is present in the structure, this fluid is chosen automatically. If the structure contains more than one fluid, the fluid used for the flow simulation must be selected through the Use pull-down menu. Then, the other fluids in the structure are treated as solid in the simulation.
Alternatively, all fluids in the structure can be set to one specific material with Set all Fluids to….
The parameters of the selected fluid (Density, Dynamic Viscosity, and Kinematic Viscosity) are then used in the Fluent simulation.
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The structure does not contain a fluid
If the structure does not contain a fluid, assign one to a material of a given material ID. For this, click on the material button to open the Material Selector. Then, choose a fluid from the material database. To enter the fluid parameters manually, set the material to Fluid → Manual.
The parameters of the selected fluid (Density, Dynamic Viscosity, and Kinematic Viscosity) are then used in the Fluent simulation.
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Solver
All settings for the Fluent solver and the simulation parameters are defined under the Solver tab.
Accuracy
The value in Accuracy defines the convergence criterion for the Fluent simulation. Therefore, it controls the precision of the computed solution and should be adapted to the simulation task. When there is doubt about the quality of the solution, increase the accuracy by setting a smaller value for that solver.
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Maximal Iterations
The number of iterations for the flow solver can be limited with Maximal Iterations. When the solver stops because the number of Maximal Iterations is reached, the quality of the solution might be doubtful since the requested Accuracy is not reached. Therefore, it is recommended to choose a large value here and adapt it only if there are strong constraints on the allowed runtime.
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Fluent Version
From the pull-down menu, select your Fluent Version. Currently Fluent 6.2, Fluent 6.3, Fluent 12, Fluent 18 and Fluent 2022 are supported.
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Mesh Format
The desired mesh format (*.msh or *.neu) can be selected from the pull-down menu Mesh Format. The check box Write Binary Files determines if the created mesh file (*.msh) is stored in binary or ASCII format.
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Know how! In binary format file sizes are smaller, whereas ASCII files are human readable.
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Solver Type
From the Solver Type pull-down menu, select the available implementations of the Fluent solver: SIMPLE, SIMPLEC, PISO, and Coupled.
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Direction
Choose the direction of the flow, available are Flow in X-, Y-, or Z-Direction.
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Inflow and Outflow
The size of the necessary Inflow and Outflow region depends on the structure and on the specific simulation task. Choose the number of Voxels that are added at the Inflow and at the Outflow before export.
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Boundary Conditions in Tangential Direction
Choose the Boundary Conditions in Tangential Direction. For the Periodic boundary conditions, Fluent requires the first and last layer of voxels to be identical on opposite boundaries. This is not necessary for Symmetric boundary conditions. Therefore, the exported mesh is slightly larger if Periodic is selected.
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Input file
In the Input file panel, choose between the permeability journal file (Fluent computes the permeability in the flow direction) or to use your own journal body file.
The Fluent manuals explain how to create Fluent journal body files (*.jbf). Several journal body files (pressureDrop_X.jbf, pressureDrop_Y.jbf, pressureDrop_Z.jbf, and massFlux.jbf) are included as examples in the ExportGeoFluent folder in the GeoDict installation directory (e.g. C:\Program Files\Math2Market GmbH\GeoDict2025\ExportGeoFluent).
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Experiment Input/Output
As Experiment Input, either the Pressure Drop, the Mean Velocity, or the Flow Rate (for a given Flow Area) can be defined.
For a given Pressure Drop as experiment input, the output is the Mean Velocity and vice versa. The Pressure Drop is the difference between the inflow and outflow pressures, and the Mean Velocity is the average speed of the flow in the flow-direction.
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Grid
Structures in GeoDict are always based on voxels. With Voxels with side length …, the voxel structure from GeoDict is exported as-is to Fluent.
If the simulation in Fluent should be done on a boxel grid, the size of these boxels can be entered with Boxels with…. With this option, every voxel in GeoDict is mapped on a boxel with the given size.
