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amrbekhit December 31, 2010 21:28

How to model a pipe with obstructions in it
Hi all,

I'm trying to model the flow inside a pipe with obstacles in it in order to determine the forces exerted on the obstacles due to the flow. I've looked through the tutorials and they seem to use the solid geometry to represent the cavity that the fluid flows through. So a simple pipe would be modelled using a solid cylinder. However, if I want obstacles in the pipe, I either have to model them as solids inside the pipe solid (which doesn't work as ANSYS considers it as just one solid), or I have to cut out the obstructions from the pipe solid. I've tried this and although it seems to work, but I can't view the faces inside the solid when I create a Stress map of the model. Am I doing this right? (I'm using ANSYS 13 Workbench).

Happy 2011!


PSYMN January 1, 2011 13:00

You can create an enclosure or fill to create a fluid body out of the region between the solids.

You only need the one fluid body to get the forces exerted on the solids (just pressure over area).

However, if you want stresses, then you are talking about 1 way FSI (Fluid Structure Interaction). This is pretty easy to do in WB, you just need to drop a structural system onto the results of the fluid system and then link the pressures from the CFD as input loads into the Structural. It can use the same intial model but can use a separate mesh for the structural portion, etc. WB usually takes care of all the details.

I suggest finding one of the tutorials about one way FSI on the customer portal.

amrbekhit January 2, 2011 20:32

Thanks for your reply Simon,

I'll play some more with the simulation and if I continue to run into problems, I'll post again.


Saima January 14, 2011 10:23


I want to analyze the flow inside the pipe. I made a solid cylinder in Design modeler and mesh it. But the problem is that how can i define inside as a fluid domain?

I solved this solid in CFX but it gave me very low mass flow rate, that means it is not treating as a hollow.

Kindly hel me out how can i treat it as a fluid or is there any tutorila in design modeler for flow inside pipe pls let me know.

PSYMN January 14, 2011 11:39

What's in a name?
If it meshed the region, then the solver can treat it as Fluid or Solid regardless of the name... However, if you want to control the name, this movie on named selections may help... I get to volumes at the very end.

You can also click on a body and change it from a solid to a fluid in DM (look at the bottom of the details panel when the body is selected). I suppose this is worth doing if you are using Workbench to setup a real FSI because it can automatically break up where each body is solved, but it doesn't really matter if you are just sending the mesh to a CFD solver... Of course you mean for the mesh to be a fluid... The solver won't care about the name. Just apply fluid properties to the "SOLID" part.

You low mass flow issue is due to your boundary conditions... not weather the geometry is labeled as a fluid or solid...

PSYMN January 14, 2011 11:56

Details of Body
In DM, use the body selection tool (Green Cube in the top row of icons) and select the body in the screen or tree. At the bottom of the details panel (bottom left) there is a pull down to change it from Solid (default) to Fluid...

PSYMN January 14, 2011 11:57

Details of Body
1 Attachment(s)
In DM, use the body selection tool (Green Cube in the top row of icons) and select the body in the screen or tree. At the bottom of the details panel (bottom left) there is a pull down to change it from Solid (default) to Fluid...
Attachment 6058

Saima January 14, 2011 12:15

Thank you very much. It works.


Saima January 14, 2011 14:24


I have one more question,

I did an airfoil in iCEM CFD and want to solve in CFX but when i trandformed it in CFX it takes automatically thickness, and consider the outer side as a solid instead of fluid.

Is there any other way to solve this ICEM 2D geometry in CFX?

Anyother format of importing file inorder todon't chnage nature of geometry.

Beast Regards,

PSYMN January 14, 2011 16:43

Which one is different, can't we all just get along
CFX always represents a 2D model as a thin layer of 3D hexas... Basically it is really a 2.5D model.

I usually just export the mesh from ICEM CFD as a 2D Fluent mesh (*.msh) and read that into CFX. While reading in the *.msh file, CFX automatically extrudes it into a format that it can use.

Don't worry about it, the solution will be similar to what Fluent would give on a 2D model. Both are just representative slices of the real problem expressed in different ways.

amjadfirst December 7, 2014 19:34

4 Attachment(s)
Hello everyone,

I'm stuck on a problem for a while and I can't find a solution to it yet. I hope some of the experts here can help :)
I'm trying to mesh a pipe with an obstacle in it, however I'm meshing only 1/8 of the pipe (45 degrees radially). and the obstacle is a solid button attached to the wall (I'm not sure how to attach it other than just have it overlap the wall).
I created a block and split (i have an entrance region with no heat then flow region with heat from the wall). I set the part mesh parameters then meshed the whole thing. In boundary conditions I set the volumes to fluid and solid, then exported the mesh to FLUENT. In FLUENT it solves and converges but then in post processing I see no button and it seems like the flow is continuous with no obstruction.

I'm not sure how to "subtract" the solid from the fluid. I know ICEM doesn't have Boolean operations but I can't seem to find a working alternative.

Any help would be much appreciated.


diamondx December 8, 2014 09:59

When you do your split, associate the face to your wall. when you export your mesh, define it as wall

amjadfirst December 8, 2014 10:39

Thank you for the reply. associate one face to one wall? The button has 6 faces, so do I need to split another time and associate one full (small) block to the button?



myaccount December 31, 2014 03:10

flow through a 3d duct
I have a 3d duct and want to simulate flow through it.
I have created all the faces,closed all the edges.Iam now confused how to create the fluid inside and mesh the fluid to analyse the flow.:confused:

PSYMN December 31, 2014 10:45

That is the sort of very basic thing that trying a single tutorial or watching a video on youtube would cover... you need to put in a little effort.

Assuming you mean ICEM CFD tetra...

spz January 31, 2017 15:30

I have a basic question about simulating fluid flow in the pipe with obstacle, i would be grateful if any body could help me
i want to model pipe flow with obstacle(Re=600) but i dont know the flow regime, thus which moldel (laminar, turbulent) i can use in fluent?

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