Multi-element rear wing for racecar - Failed: Front advance failed

Submitted by rickyj on April 11, 2012 - 01:06

Questions

Hello!

I have created a multi element rear wing for a racecar, simply made of two upside-down NACA 4415 airfoils that comes from the 'Flow Over an Airfoil' tutorial (www.symscape.com/node/561).

I want to eventually get some velocity and downforce data by following the 'Flow over a CO2 Dragster' tutorial (www.symscape.com/node/1082), except by using the wing I've created in place of the dragster model and adjusting accordingly. However I'm having a problem when I try to apply the Vector Fields->U to the wing, as I get the following message:

"Tetulator: End: 2675 tetrahedra
Warning:
flow-volume [www.1289.5] Tetulator: Failed: Front advance failed: 568 faces remain"

I'm assuming this means there's something wrong with the meshing. I have attempted the 'Mesh Diagnostics' guide (www.symscape.com/node/995#comment-758) over the course of the past 3 hours but I have to admit I don't understand it very well as I'm new to CFD so I haven't gotten anywhere with regards to fixing the mesh or even finding out what the problem is.

I've tried and tried so posting here really is a last resort, could someone please give me some detailed instructions on what the problem is and how to correct it? It would be much appreciated! I can upload the file or something if that would help. Thanks again!
Ricky

Single flow volume

Submitted by symscape on April 11, 2012 - 08:03.

Are you sure you have a single flow volume? I.e., did you subtract your airfoils from a large box?

Where you able to view your mesh both on the faces and in the volume?

Did you try using the Accuracy tool to improve your mesh?

For a more complete mesh diagnostics routine see "How do I fix mesh and solver failures?".

Yes I subtracted them from

Submitted by rickyj on April 11, 2012 - 09:52.

Yes I subtracted them from the box to get a single flow volume, I was also able to view it on both the faces and the volume.
I had an issue with that however, as when I used the Booleans->Subtract to form the single flow volume roughly half of the length of the leading and trailing edges disappeared, despite having been a full volume previously. After messing with the Unite tool they 'reappeared' again and I continued with the tutorial.

Could this be the root of the problem?

I attempted to follow the "How do I fix mesh and solver failures?" diagnostics and the accuracy tool but it was a little beyond me :/. Thanks for the reply :)

Geometry corrupt

Submitted by symscape on April 11, 2012 - 10:22.

Based on your description it sounds like your geometry is corrupt, i.e., the Booleans->Subtract did not succeed. I don't see how using Booleans->Unite would help.

For Subtract to work you need to ensure that there are no coincident faces or edges. Also are you sure the airfoils are volumes (not just faces) - you extruded faces to form volumes right?

So make sure your airfoil volumes extend beyond the bounds of your box and perform the Subtract. Then check the File->Log for warnings or errors.

Do you have access to a CAD system? If so why not generate the flow volume in it? Then you could exchange the geometry using STEP (.stp).

So I started again from

Submitted by rickyj on April 11, 2012 - 11:48.

So I started again from scratch and still had the same problem after the Booleans->Subtract; half of the leading/trailing edges disappeared. They were definitely volumes before this happened (not just faces).

I used the Geometry->Others->Fix tool (not sure why but it looked like it might work) and lo and behold it "fixed" the edges :) So, all's well... but then when I advance to the next step of applying a substance (air) to the volume, the volume is no longer there in the Select dialog - it's just Sim,Faces,Edges,&Vertices with no 'Volume' available for selection.

It seems as if the Fix tool somehow fixed the missing edges but erased the Volume? Haha. Any ideas? Maybe a bug of some kind?
ps: Sadly I don't have any CAD as I'm working from home at the moment.
Thanks again

Fix the volume, not the faces

Submitted by symscape on April 11, 2012 - 12:47.

If you want to preserve the volume then you need to use Others->Fix on the volume, not the faces. Alternatively you can keep your fixed faces and then use the Volumes->Stitch tool to stitch the faces into a volume. After each operation check File->Log for warnings or errors.

Thank you for your

Submitted by rickyj on April 11, 2012 - 13:47.

Thank you for your perseverance in helping me with this :)

I'm having no luck with it so I was wondering if it would be possible to somehow isolate/cut-out the rear-wing from the 'Open Wheel Race Car' geometry (http://www.symscape.com/node/130) and maybe copy/paste it into a new simulation and use that rear wing instead of my own airfoil?

Caedium Professional Subscription Purchase

Submitted by symscape on April 11, 2012 - 14:42.

It seems you require dedicated email support to pursue this project, so I think it's time to consider a Caedium Professional 1 year subscription purchase.

I would if I wasn't a student

Submitted by rickyj on April 11, 2012 - 14:52.

I would if I wasn't a student who only needs to perform a single simulation. Thanks for the help thus far anyway :)

Symscape