...
First, the region that will be simulated must be determined. This is known as the Background Mesh Box (Also commonly called the bounding box or domain). Typical guidelines are to use 2-8 times the car’s dimensions as the dimensions of the domain. Less space is needed on the sides, moderate space is needed in front of the car, and the majority of space should be behind the car. So for MSXIV (Approximately 5 m long, 2 m wide, 1 m tall), the domain should extend about 15 m (= 5 m * 3) in front of the car, 35 m (= 5 m * 7) behind the car, and 5 m above and on either side. Now, it is important to note that there is a plane of symmetry running down the center of the car. This means that we only need to simulate half of the car. The resulting drag (and other forces) can be doubled when post-processing, since each half of the car should have identical drags. This can drastically reduce the number of elements in your mesh, without sacrificing resolution, and is something that was not taken advantage of for the design of MSXIV. The end result is a domain that is still 50 m long and , 5 m tall, but only and 5 m wide, offset to one side of the car.
...
Distance [m] | Level [-] |
|---|---|
0.75 | 4 |
1.255 | 3 |
2.5 | 2 |
Assign this refinement to the car geometry by clicking the car in the geometry viewer (you may need to click inside the box that says Pick Volumes first so that the program knows you’re ready to select the geometry, ensure the box is blue). Add 2 more geometry refinements, this time leave the modes as Inside. Set the level of the first one to 2, and assign it to the larger Cartesian box geometry primitive that was created earlier by clicking the sliding switch to the left of the label at the bottom of the panel. Then set the level of the second one to 3 and assign it to the smaller Cartesian box geometry primitive that was created earlier. The next refinement is called a Surface refinement. I started using it because I find it helps with the step afterwards (forming the boundary layers). Set the Min level and Max level to 5 and assign it to the car entity. We don’t need cell zones for this type of simulation.
...
| Expand | ||
|---|---|---|
| ||
| ||
| Info | ||
On meshes with around 8M elements or more, mesh clips will start failing
|
You may also have noticed a section called Meshing log, this can be used to see what the mesh generation algorithm is doing while the mesh is being generated. This can be difficult to read at first, but it does provide a lot of information about the mesh.
If the mesh is an appropriate size, with an appropriate number of boundary layer cells, and no obvious defects you can continue to the actual simulation.