Good night, i need help with how can i trust my results. The mesh we made for our FSAE car is really close in the meshing parameters with the tutorial of a fsae car that you guys sent me a while ago. Even so, the results that we had on our simulation is not real, during the past years our team used another software to obtain the lift and drag results and they all came to a convergence of results. The results we had with this simulation is really off reality and i have watched every tutorial you guys have available, and also had a look really close on the tutorial for fsae car that you gave me and still, i believe we made a equal mesh in quality overall but the results just doesnt match reality.
I need assitance on what can i do to make results more accurate.
Can you please make your project public so we can take a look at your simulation?
Okay, just did it. Thank you
I have a couple suggestions to help you increase the accuracy of your results.
Starting at the beginning…
- Your enclosure size is much to small for an FSAE car. You dont want to have any interference of forces induced by the walls so a good measure is 10 X the size of your geometry. So a total tunnel length of 30 meters is good. About 10 in front of the car, 20 behind, and about 6-7 to the side and top.
- Based on the size of your wind tunnel you need to calculate these two numbers (K and W). They are for how energy is dispersed into the free stream but are not so important. From the tutorial they use for K = 0.06 and W = 44.7. These are fine to use for a 30m long bounding box.
- Your simulation has only run for 500 timesteps. Normally a sim should be 1000-3000 based on how complex the simulation. I would let this run longer to see if convergence is met, but do so after the making the changes i stated in 1 and 2.
- I was unable to check your mesh because you are running another simulation. You can easily copy or start a new mesh and dont have to delete or overwrite the old one. It is easier to see other problems that could arise with your sim if the mesh is still there.
For this i mean you need to change the geometry of the wing profile in CAD. You have two options.
- You can make a sharp trailing edge where there are mesh cells on both top and bottom surfaces. ( pic 1)
- You can increase the size of the trailing edge face so that a mesh cell will fit well → no jagged edges (pic 2)
PIC 1 … Sharp
PIC 2 … Trailing edge large face to fit cells (red cells)
I recommend option 1 because its more realistic. Depending on how small the cells are you can make the trailing edge face 2-3mm thick but it will add more overall cells to the mesh.