SimScale CAE Forum

External simulation

I am doing a full car simulation of my fsae car. the simulation results came out to be perfect for the first simulation with a velocity of 11.5m/s. But when I did the next simulation by changing only the velocity to 27.7 m/s the results came out to be impractical. Why?

https://www.simscale.com/workbench/?pid=5347068172919700759&mi=spec%3A87c2fed6-5ef0-4302-8dda-6578f8fca16d%2Cservice%3ASIMULATION%2Cstrategy%3A2

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Hi there, thank you for using the forum!

I have a few comments.

  1. Initially, I noticed that the second simulation finished after 500 loops, and the solution was not converged yet. Maybe you want to consider continuing your run to let the solution converge. Can I Continue an Existing Simulation Run in SimScale?

  2. Did you make sure to add an inflate boundary layer according to the velocity inlet’s value for both of the cases? What is y+ (yplus)?

Best regards,
Fillia

  1. You can continue the simulation but the problem is the lift value is positive which is highly impractical comparing with the previous simulation. So even if the simulation converge the value would still be positive.
  2. the y+ value I have chosen is 30

https://www.simscale.com/workbench/?pid=8197990634517819716&mi=spec%3Af0fa5196-b937-49c0-96db-4c85328d951f%2Cservice%3ASIMULATION%2Cstrategy%3A2

Here is another situation where I get the same problem even after convergence

The thing is that in order to achieve this y + value, you must create your boundary layer appropriately, as described in the document I sent you.

Make sure you add ‘Turbulence’ under the ‘Field calculations’, so you can check the y+ values after the run is finished too.

Yes, I have taken the y+ to be 30 and calculated the first cell height from the point-wise website. I am sure there is not a problem with mesh as I re-meshed the mesh with different first cell heights for different velocities. Please take a look at my simulation for any errors.
I had good convergence for the first simulation but when I change the velocity the results are not practical(ex: drag in negative and lift in positive) and also poor convergence.

Hi!

I have already seen similar patterns in the results from other FSAE car simulations. Have you already tried activating potential flow initialization?

This usually helps a lot for external aerodynamic cases, by initializing the velocity field based on potential flow.

Cheers

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