topic Re: Reduce nodes for CFD in Fusion Design, Validate & Document Forum

Reduce nodes for CFD

Anonymous — Wed, 21 Apr 2021 20:06:18 GMT

Hello!

My name is Alexander Holmberg and I have some questions concerning importing files from Fusion 360 into various CFD software for aerodynamic evaluation. I have tried running simulations on Simflow and Ansys Fluent student edition.

The problem I am having with both of the simulation programs is the limited amount of nodes. The car models in the link below exceeds this number many times over. I have tried scaling the models down using Meshmixer to try to reduce the amounts of nodes.

The scaling of the models has made very little difference. I am therefore wondering if there is any way of reducing the amount of nodes in each model.

Please reply!

Greatest regards Alex!

Link to GrabCad

Re: Reduce nodes for CFD

TrippyLighting — Wed, 21 Apr 2021 20:15:40 GMT

This is mesh based geometry and that almost never works in conjunction with CFD software.
CFD usually requires native CAD geometry (BRep and NURBS).

I've not looked at the STEP or Fusion 360 files but I assume based on their size that they contain highly faceted geometry.

Re: Reduce nodes for CFD

Anonymous — Wed, 21 Apr 2021 20:28:47 GMT

The step and Fusion 360 are all based on a surface. I have however managed to convert the complex surfaces into solids, by first importing them into Meshmixer.

I tried to trick the CFD software by first importing a model into Meshmixer, then bringing it back into Fusion 360 as a solid stl. Then I converted the stl into brep. I then scaled the models and reduced the amount of triangles. This sadly did not work.

Is it possible to reduce the nodes any other way? Or do I have to scale the models more?

Re: Reduce nodes for CFD

TrippyLighting — Wed, 21 Apr 2021 23:45:57 GMT

Perhaps before responding you should have read some of what I wrote and googled terms you did not understand.

Meshmixer, if the name isn't already a dead giveaway, deals exclusively with meshes, not CAD surfaces.

The solid Meshmixer creates aren't CAD solids, they are simply "watertight" meshes.

Anything coming out of meshmixer will be a mesh. If you convert it to a BRep in Fusion 360 it is highly faceted and while it then is a BRep it is still likely unusable for CFD.

CAD solids are BRep, stitched together from analytical geometry and NURBS surfaces.

NOw on to the native Fusion 360 models. The body of the vehicle in these files was crated as a T-Spline. Unfortunately, the author of these designs did not have the necessary skills to design with T-Spline s and the quality of the models is terrible. Trying to create a CAD solid from this stuff will be an uphill battle.

My recommendation would be to look for a better model created with Surfacing tools to perhaps by someone who actually knows how to model with T-Splines.