FSAE - CFD Webinar - homework 2

[dwagner]

Hi guys,

I had some problems with the Simulation of homework 2. Following error accured:
The job execution was aborted, possibly due to a numerical instability. Review the log to identify reasons: unphysically large field values, extremely small time step size, etc. Modifying numerical settings and time step size could resolve the issue.

I checked all the values in numerics and some other parts (rotating wheels and porous media), but couldn´t find mistakes. The step by step tutorial had some differences of values shown in decription and pictures. One of these was rad/s at boundary conditions with 90.9 and in advanced concepts of 90.91 …

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Another question is what exatly we have to do for homework 2. In the webinar they told of more than one simulation and in the step by step tutorial i can find some indications for 3 simulations (model name with config 1-2 and simulation run config 3). The step by step tutorial leads just to one simulation …

Thx for your help

[AnnaFless]

@dwagner,

Just took a quick look - it seems you have assigned extra boundary conditions

Regarding what you need to submit: you have to only perform the simulation shown in this homework post. i.e. with all rotaing BC, porous media and MRF zones. One mesh one simulation, please ignore configuration 3 as stated in the tutorial.

Best,
Anna

[dwagner]

Thx for your reply!

In the step by step tutorial (page 1) are the last 2 steps for rotating wheels.
link here:

Step-by-Step Tutorial: Homework of Session 2

Recording [Formula Student / Formula SAE Workshop: Complete Car Aerodynamics] Homework Submission Submitting all four homework assignments will qualify you for a free Professional Training (value of 500€) as well as a SimScale Certificate of Completion. Homework 2 - Deadline: Date, 15th of December, 11:59 pm Homework Submission Form Introduction Your task is to investigate the Full car model Model-Conf-1-2 with a radiator using the porous media approach, rotating wheels using th…

When I dont need these boundary conditions, I can simply delete them …

Greetings
David

[AnnaFless]

Hi @dwagner.

You are correct in fact in the set up -I did not read deeply enough into the tutorial.

My colleague Ali has written an update that might be relevant to your case:

Step-by-Step Tutorial: Homework of Session 2

Hello Everyone, @varunsura , @PhilippB94, @durgesh786 , @agupta , @fhnx ,@LoganZundel , @slibbi , @kianz89 IMPORTANT NOTE: for all who are facing issue of strange simulation results e.g the figure below [image] What was causing this ? The reason for this was a lot of illegal cells ( bad quality ) in the mesh. You can check that by clicking the meshing log as shown in the figure below: [image] In most cases, the number was around approx 200 illegal cells which then requires more iterations …

[shivansh0]

Hi,
I am facing the same issue as above “The job execution was aborted, possibly due to a numerical instability. Review the log to identify reasons: unphysically large field values, extremely small time step size, etc. Modifying numerical settings and time step size could resolve the issue.” tried removing the extra boundary conditions. still gives the same result.
here is the link to my project https://www.simscale.com/workbench?publiclink=013d48fc-3687-438a-be6d-3bbf2b942832

thanks in advance
-Shivansh

[pfernandez]

Hi @shivansh0,

You have an extra mesh refinement that might be messing with the mesh creating a ton o illegal cells. Remove the extra refinement, generate the mesh again and run the case.