lift/drag forces on car

[fishbowl38]

Hi,

I'm still a newbie at this program so please bare with me.

In flow design, the wind tunnel cannot render the object properly without the polygons bugging out. (I'm importing from inventor). It also does not allow the calculation of lift and downforce. Is there anyway in which I can recreate simulations, like flow design's but in simulation CFD instead?.

A video tutorial or a simple set of instructions would be appriciated. Also, how do you rotate an object in CFD. The orientation of my car is always the wrong direction.

thanks

[Jon.Wilde]

Hi,

Is this is the same as the other thread? Wondering if we could just use that?

http://forums.autodesk.com/t5/simulation-cfd/need-help-with-car-aerodynamics-cfd/m-p/5334377#M5802

We should be able to do this in Sim CFD, yes. Although it would need an excellent mesh. Check out the NACA post on this forum and the video here for a good idea of how to set up an external aero model: NACA Airfoil Build Your IQ session

The model cannot be rotated in Sim CFD. Draw it as you need it in CAD, or just rotate the view?

I would have thought it would be wise to draw the air volume in CAD too - the airbox in CFD cannot touch the geomtry but you will want it to. Overlap it with the wheels a little to avoid a zero angle in the air where the wheels meet the grounf.

I would also think you would at least want to run a 1/2 symmetry model here too, saves on mesh (you are going to need quite a bit!).

Keep posting as you progress and we can assist.

Thanks,

Jon

[Jon.Wilde]

Also - you need a flat surface inside where the rocket sits if you want to apply another velocity condition there 🙂

Make sure your CAD is really clean, nice smooth edges where surfaces meet etc, it looks like it might fail to mesh at present. There are overlapping surfaces here.

[fishbowl38]

Thanks for the advice. So from what I understand, another surface is needed to simulate thrust behind the car. Do I just extrude out a box to simulate the boundaries of the airflow for the car then set one of the surfaces as the inlet for the fluid and the other side as out. That makes sense in that case. I'm not quite sure what you mean by overlapping surfaces. I've done fillets all around the sharp corners to smooth it out a bit. And also, the first link to the NACA airfoil doesn't work.

[Jon.Wilde]

A few steps

1. Suppress the car from the mesh
2. Apply an additional velocity condition to a recessed surface within where the rocket will reside (if you still wish to add the jet). This must be applied to a suppressed volume
3. Air box will have v on inlet, P=0 at outlet and slip/symmetry on the side walls (not the floor)
4. I didn't share a link, thought you could find it with a quick search. No probs though, it's here
5. The geom issue is to do with how some of the surfaces overlap I think, just be sure everything is tidy before you launch into CFD and it should mesh OK

Your airbox ought to look something like this, just 1/2 the model as we don't need to run the full thing.