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rave July 6, 2007 00:55

external flow meshing for a Sedan in pro*am
I'm stuck.

I want to create volume mesh around a sedan geometry for external flow analysis. I tried pro-am for tht but I always endup with an internal mesh.

I even tried inverting the cell orientation and creating subsurface outside the original geometry, but after tht i don't know how can i input the extent of mesh creation outside the car-body.

also in the manual its given tht for external flow analysis a box has to be created outside the geometry, which wd create flow volume outside the body(external flow).Can sm1 tell me how can i attach the symmetry plane of the car with one of the faces of the box so tht external flow mesh cd be generated.

i wd be very thankful for any help.

ravi July 10, 2007 06:45

Re: external flow meshing for a Sedan in pro*am
Please smbdy help me..............I'm stuck.

thnks for any help

mahesh July 10, 2007 12:47

Re: external flow meshing for a Sedan in pro*am
did u uncheck: .disable -ve vol prevention .disable convex cell prevention .flipped normal prevention .disable surface check

and check: .flip shell orientation

also for smoothing option: select "preserve angle"

check these aspects and see how it goes. mahesh

mahesh July 10, 2007 12:50

Re: external flow meshing for a Sedan in pro*am
also do a sche for free edges,inter,mani,needles and sharp

try removing them b4 submitting for subsurface


Peter July 10, 2007 14:51

Re: external flow meshing for a Sedan in pro*am
The reason why you have an internal mesh is because your surface model is not closed. There are a very large number of reasons for this. It could be anything from some part(s) are missing from the model, or something more subtle such as the hole where the gear lever enters the cabin, for example.

There is no point in further volume meshing until you have traced the problem(s).

If this is a real car and you started from "body in white" CAD parts then closing the surface is not a trivial job. Consider breaking the model up into smaller parts, front siderails + front cross members together in a sub model. Work on the sub model to get it surface wrapped without holes. Use prosurf before pro-am. Proceeding this way will give you a BIW structure in 6 to 9 parts, which are hole free before you assemble the vehicle into one piece. A BIW for a real car is too complex to mesh from nothing in one hit. If you need other parts in the vehicle such as powertrain, then assemble them as a surface mesh to make an additional sub model. When you bring all the sub models together, if an internal mesh is generated then there is a limited number of locations where the problem is located and therefore it is easier to find and resolve.

This is a case where before you reach for the CFD tool, you must first think of a strategy to create the model first, and then think about how easy is it to modify the model if design changes are required.

On large complex models, you should expect to have some problems with the mesh. Plan ahead to make you life easier.

Finally, any reason why you are not talking to CD-adapco support? Or arranging to take a professional training course?


rave July 11, 2007 23:49

Re: external flow meshing for a Sedan in pro*am
thnks peter for the reply.

as far as my geometry is concern there is no holes in it, and before importing it to pro-am i repair and triangulate it in pro-surf. I have only the half body (symmetric) and thr is no face in the original geometry at the symmetry plane. so after repairing it in pro-surf, i get only edges attached to this symmetry plane of the half car body as free edges.beside tht thr r no other free edges or non-manifold or any holes in the geomtry. the free edges and the "hole"(the entire symmetry face of the car geometry) at the symmetry plane is removed while resurfacing in the pro-am. so after tht i have a complete close surface without any holes as my geometry.

upto this point i don't have any prob..........after it i orient all the surface cells and create the subsurface (with flip orientation 'on' so tht it wd cr8 SS outside the geometry) and then get stuck ......... i try to mesh it, never get a external flow volume. even i cr8 a box arnd the body,then i don't know how can i attach the geomtry with the box face.

Is my approach correct, or at wat point i'm making the mistake.

thnks for further help.

*i'm going to attend a training on 22nd of this month in bangalore.

ravi July 17, 2007 00:23

Re: external flow meshing for a Sedan in pro*am
Finally, I called the STAR-CD support for this prob.

they told that,the box has to be created b4 importing it to pro-surf or pro*am. that means box should be created as the part of ur geometry, and then treat ur geometry as if u r doing internal flow analysis. then i cdn't understand y they have provided the features like "INVERTING THE CELL ORIENTATION" & "GENERATING THE BOX", also they have mentioned in the user guide that"for external flow u need to generate the box arnd the geomtry, a feature in pro*am".

so this is really not very user friendly, bcoz geometries r provided without the box, and thr's no feature in STAR-CD for doing tht and attaching the box to the geometry.

but they r telling tht new star-design have sm features to do things like tht. lets see.


David Baker July 17, 2007 09:48

Re: external flow meshing for a Sedan in pro*am
use es-aero.

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