Mesh generation for engine simulation is difficult and represents a significant bottleneck in the design flow. The typical engine CFD design project begins with a lengthy process to construct an adequate computational mesh of the engine geometry, which may include valves, spark plugs, ports, etc. The generated mesh must account for the fact that it must compress and stretch during the full engine cycle. The process of mesh creation can take up to weeks for a single design, making a design-of experiments that considers multiple geometries particularly challenging. The FORTÉ mesh generator is fully automated and created a Cartesian mesh to assure that all boundary conditions are accurately enforced at the real physical boundaries. The automatic mesh generation capability works from the inside-out, removing issues that might occur when the CAD (e.g., STL) file contains small holes or discontinuities and eliminates the requirement for the imported surface-mesh files to be “water tight.” In addition, mesh refinement around exceptional features (like valves, etc) is accomplished automatically, with user control of the desired mesh size. Read more in this Application Note.

1. Application Note: FORTÉ Simulation Package
Automatic Mesh Generation with FORTÉ
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Overview
This application note provides a description of how to use the automatic mesh generation capabilities
with the FORTÉ Simulation Package. The automatic mesh generation begins by importing the engine
geometry, typically from a CAD program in the form of an STL file. The user then performs any splitting
or merging of surfaces to separate specific engine components, e.g. head, valves, piston, in the
FORTÉ Simulator. The mesh generated is based on the global minimum cell size specified by the
user. Optionally, the user can locally refine the mesh around important features, e.g. valves, piston,
etc. The mesh is automatically created at every crank angle during the simulation. Prior to running the
simulation, a preview of the mesh can be generated at different points during the cycle, i.e. different
crank angles, to determine the quality of the mesh is at different locations.
Automatic Mesh Generation Overview
Mesh generation for engine simulation is difficult and represents a significant bottleneck in the design
flow. The typical engine CFD design project begins with a lengthy process to construct an adequate
computational mesh of the engine geometry, which may include valves, spark plugs, ports, etc. The
generated mesh must account for the fact that it must compress and stretch during the full engine
cycle. The process of mesh creation can take up to weeks for a single design, making a design-of-
experiments that considers multiple geometries particularly challenging.
The FORTÉ mesh generator is fully automated and created a Cartesian mesh to assure that all
boundary conditions are accurately enforced at the real physical boundaries. The automatic mesh
generation capability works from the inside-out, removing issues that might occur when the CAD (e.g.,
STL) file contains small holes or discontinuities and eliminates the requirement for the imported
surface-mesh files to be “water tight.” In addition, mesh refinement around exceptional features (like
valves, etc) is accomplished automatically, with user control of the desired mesh size.
FORTÉ Automatic Mesh Generation Set Up
The first step in generating a mesh is to import the engine geometry, typically from a CAD STL file. The
FORTÉ package can also read-in geometry in CGNS and KIVA-3V file formats. After importing the
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2. Automatic Mesh Generation with FORTÉ
geometry, the FORTÉ simulator will display the geometry as shown in Figure 1. In this screen, the
geometry features are listed in the visualization section on the right side of the window. You can turn
on and off geometric surfaces as needed.
The work tree is listed on the upper left portion of the screen and shows all of the geometry elements.
You have the ability to split the geometry and remove areas that are not of interest. You can also
merge geometry elements.
Figure 1: FORTE's automatic mesh generation screen layout
Setting Mesh Sizes
Once you have completed any splitting or merging of elements, you are ready to set the global mesh
size through the Mesh Controls work tree element, as shown in Figure 2.
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3. Automatic Mesh Generation with FORTÉ
Once the global mesh sizes are set, you can optionally specify local mesh refinement for the piston
head and around the valves. You do this by selecting the elements that are associated with the piston
face and valves as show in Figure 3.
Figure 2: Setting the global mesh size in FORTÉ
Now, you are ready to begin your simulation. No other set up is required.
The FORTÉ simulator will automatically build the mesh at each crank angle during the solution process.
You can get a preview of the mesh construction by selecting Preview Mesh and specifying a cut plane
where you enter the location of the plane and the crank angle you would like to see, as shown in Figure
4. By creating a preview of the mesh, it provides feedback on how the mesh will look during the actual
simulation.
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4. Automatic Mesh Generation with FORTÉ
Figure 3: Setting the mesh size on the piston face and around the valves
Figure 4: Preview the mesh to see detail around the valves and the piston
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5. Automatic Mesh Generation with FORTÉ
Summary
In this application note, we used the automatic mesh generation feature in the FORTÉ Simulation
Package to automatically create a Cartesian mesh for the full cylinder with moving valves. An STL
CAD file is imported and geometry features that are not relevant are split from the domain. Once the
mesh sizes have been input, the FORTÉ package automatically creates the mesh during the CFD
simulation. It is also possible to preview the mesh to verify that the treatment around valves and the
piston are appropriate. The FORTÉ automatic mesh generation feature in is an important
advancement that significantly reduces the overall time-to-solution for combustion CFD analysis of
internal combustion engines.
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