Can CFX run 2D problems
 

Hi I need to ask can I run 2 D mesh geometries within CFX?

Mariam Sara

HI

CFX has a 3D Space. if you want to have a 2D simulation, you have to draw a geometry in 2D and with a small thickness ( this geometry is in 3D but solved in 2D). define both side of thickness as symmetry. See tutorial 7 of CFX tutorial 11.0 (free surface flow over bump)

Did you mean I need to draw the geometry as 3D and give the third dimension as small thickness and give it symmetry boundary? I use Gambit for mesh is it suitable for CFX?

Hi
Yes.
I am using CFX-mesh for meshing. In CFX-mesh, you can meshing 2D geometry by " extruded 2D mesh" tools. I dont know Gambit.

CFX pre can import Gambit Mesh it work fine with it. You said in your reply I need to use small thickness for the third dimension I need to ask how much thickness I need to use ? for example I want to draw rectangular channel with 2 m length and 0.5 m height if I take the third dimension thickness as 0.1 m is this value suitable or should I reduce it more to solve it as 2 D problem in CFX?

Thanks a lot
Mariam

Hello talebzarei may you send me the steps of drawing the mesh in Bump tutorial in CFX-Mesh or Icem I am really new with both of these programs and need to follow your steps to create my channel with it?

Hi Mariam,
You just need two cells along thickness ( not sure about one, check the fact in tutorial). Just keep a small portion of thickness no need for too thick a mesh.

Thanks D.B for the reply. As I mentioned I am new with ICEM and CFX-Mesh so I need to ask if my channel length is 8 m and height is 0.1 m if I chose the third dimension as 0.001 m (i.e. 1 mm) is it sufficient or i need make it smaller?

Hi Mariam,
I think you just take a look at CFX tutorial, and see if their thickness is vaguely different from other dimensions. I had once done this for a cylindrical geometry and used only 1 degree of the sector for a diameter of approx 600 mm

This is covered in the FAQ, including the recommended thickness for the third dimension extrusion.

http://www.cfd-online.com/Wiki/Ansys..._simulation.3F

Thanks guys for the valuable information. I am wondered how I can view the mesh file for the bump tutorial (paratran file) within CFX-mesh?

for your help
 

yes, you should create one thick element body and this thick must be in Z direction. Aw well as, the thickness should be small ( less than other dimensions). use sweep mesh method and define the symmetry faces as target and source through mesh set up.
Ihope that help.

Regards

Thanks Happy for the reply. May you please illustrate me to how I can use sweep mesh method and define the symmetry faces as target and source through mesh set up which you mentioned in your last post? you mean I need to apply this in CFX-Pre or in ICEM? I use Gambit for mesh because I not have wide experience with ICEM and CFX-mesh is this can be done in Gambit?

Since CFX V13 (I think) CFX-Pre has been able to import gambit meshes, including 2D meshes. When CFX gets a 2D mesh it automatically extrudes it 1 element. So you cen generate your geometry in gambit as a 2D model and load it directly in CFX-Pre.

I was imported 2d mesh file from gambit into CFX-Pre I have CFX 12.1 release I think CFX make the mesh as 3D truly but the problem I not see the front and back faces which need to be set as symmetry as the guys mentioned I found the boundaries I define in gambit such as, inlet,outlet,downwall,upwall and CFX add unknown boundaries I not understood what they represents they are primitive 2D A and primitive 2D B are these boundaries the sides of the geometry that needed to be set as symmetry? here is a link for the mesh file in CFX-Pre attached at the link below.

http://www.2shared.com/file/1Aswm-4I/meshtwo.html

more explaining
 

To apply sweep method for mesh you should import the geometry or draw it via cfd design modeler and then automatically the model will processed to mesh and through the cfx mesher you can use sweep method. to identify where you should apply your back face and down face, first, you should know where your symmetry b.Cs, and actually, I want to aske what you are going to model?? By the way drawing the geometry via design modeler is too easy. I hope this help

Thanks I use Gambit now. Glenn may you have a look on the mesh I sent in my above post I import it from Gambit as 2D please let me know if there is any problem with it?

I do not have the time to look at your files.

CFX-Pre extrudes 2D meshes from Gambit, so if you cannot see it then it probably has only done a tiny extrusion. This is often bad as it means the aspect ratio of the resulting elements is terrible. Under the advanced mesh import options I think there is an option to define how far CFX-Pre extrudes the mesh. You need to increase that number.

I saw the third dimension in my mesh there is one element on it and when I press mesh statistics CFX give me the following about it:
min x ,max x: 0,25
min y,max y: 0,0.0985
min z,max z : -0.001,0
all dimension in meters. As seen the last dimension is the extruded one which it 1 mm so is it sufficient or i need to increase extrude factor (currently 1) at advance import options?

This is discussed in the FAQ

http://www.cfd-online.com/Wiki/Ansys..._simulation.3F