Hello,
I needed some help with incompressible flow simulations for basic front wing designs for a model F1 in schools car. I set up a simulation with one of the wings using the Ahmed Body Tutorial and managed to obtain a successful simulation but I have several doubts regarding Run 1 of my simulation:
The drag coefficient is negative - I couldn’t understand why.
The simulation took a lot of time (568 minutes) - I was completely unaware of what settings to use, so I’m concerned I may have used settings that are too ‘high quality’ for my purposes. I also noticed that the results of the simulation seemed to have stabilised within the very early stages of the simulation run.
This is the link to the project:
I am a 16 y/o newbie to CFD, and this is my first attempt at using simscale. I would appreciate any reference to the best guide/instructional video so I can understand how to utilise it properly for further model car simulations in the future.
Thank you!
Very cool to have someone that young on our platform experimenting with CFD 
Keep up the spirit!
Regarding the setup, the BC’s look quite good to me.
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Make sure to explicitly add a no-slip wall boundary condition to your wing structure
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For the Drag Direction I would go with (0,0,-1) instead of your current setting
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Lift is correct so far
CFD Squad, can you counter-check here and see if I missed something? 
Cheers,
Jousef
Hello,
I made the changes suggested, and that has fixed the issue related to the negative drag coefficient. (Thank you!) However, the drag coefficient seems to be a bit high - over 5 - on all the simulation runs. Is this just how it is as a genuine result or is there a fault in my simulation settings for forces and moments coefficient result control? I’m confused as for the geometry I’m using, a front wing, it doesn’t seem right.
According to the drag coefficient formula, if I’m not wrong, it depends on the reference area I’m using. How do I determine what the best value for this is? The current one is based on the approximate total surface area of one of the 5 wings, and perhaps I have set it too low, resulting in a higher dc. (reference area could have possibly been miscalculated)
My main objective is to compare all the wings and choose the one that can push air upward or to the side by a reasonable extent (around the wheel behind it) while causing the least drag or slowing down the car the least. I could just compare the current drag coefficients and choose the one with the lowest, but is looking at the pressure force in the z-axis an appropriate alternative for this purpose?
Sorry for the lengthy questions
Hey!
It does depend on the area of reference but it’s not the surface area.
For car airfoils, Aref is the projection of the airfoil area onto a plane (in a frontal view). So it would be this area highlighted in red.
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