
[Sponsors] 
July 22, 2008, 14:39 
Hello,
I've been working on c

#1 
New Member
Trevor Sherk
Join Date: Mar 2009
Location: Ontario, Canada
Posts: 10
Rep Power: 9 
Hello,
I've been working on creating a mesh for a cylindrical annulus, but have had no luck finding out how to extends the mesh points INSIDE the annulus so that there are grid points to solve the solution inside the cylinder rather than just on the outside. I can't seem to find out how to do this anywhere. Am I missing something? OpenFOAM wouldn't solve all the way through the cylinder if I only had grid points on the exteriors of the annulus would it? i.e., I believe the fluid flow would appear the same the entire way through the cylinder along the z direction as I have no mesh on the inside connecting the boundaries. Thanks for your help! Trevor 

July 22, 2008, 15:58 
Here is a picture of my mesh s

#2 
New Member
Trevor Sherk
Join Date: Mar 2009
Location: Ontario, Canada
Posts: 10
Rep Power: 9 
Here is a picture of my mesh so far


July 22, 2008, 16:07 
And here is my blockMesh file:

#3 
New Member
Trevor Sherk
Join Date: Mar 2009
Location: Ontario, Canada
Posts: 10
Rep Power: 9 

July 23, 2008, 02:57 
I Trevor,
just small questi

#4 
Senior Member
Cedric DUPRAT
Join Date: Mar 2009
Location: Belgium
Posts: 187
Rep Power: 9 
I Trevor,
just small questions, what do you want to do ?  solve NavierStokes equation inside the "internal"pipe ? (but no mesh ...)  solve NavierStokes inside the annulus part ? well, where is your fluid, ect ... Can you tell me a little bit more just for me to help you (if I can) because, if you need to solve a cylindrical annulus, I don't understand why you need solution in the internal pipe ... Cedric 

July 23, 2008, 06:47 
To make a cylinder, you need 1

#5 
Senior Member
Eugene de Villiers
Join Date: Mar 2009
Posts: 725
Rep Power: 13 
To make a cylinder, you need 12 blocks. 4 for the core region and 8 around the outside.
When joined together, the 4 core blocks will expose 8 facets in the radial direction. Seen end on, you will distort them to look like an octagon. To each of these 8 facets you then attach one of the 8 outer blocks to interface with the outer cylinder. 

July 23, 2008, 08:44 
Hello Cedric,
The fluid is

#6 
New Member
Trevor Sherk
Join Date: Mar 2009
Location: Ontario, Canada
Posts: 10
Rep Power: 9 
Hello Cedric,
The fluid is inside the annulus, so between the inner wall and the outer wall. I wish to solve NavierStokes inside the annulus part which is empty of mesh points. My understanding of simulation and modeling is that when solving these equations, the solution is iterated over the mesh points. Therefore, to model the fluid inside the annulus I must have grid points inside the annulus and not just on the walls. Is this correct? If so, I am wondering how to connect the inner and outer walls with a grid inside the annulus. The problem is the differentially heated rotating annulus problem. Perhaps you've heard of this classic experiment. Thanks! Trevor 

July 23, 2008, 10:46 
Hi, Trevor,
It does look li

#7 
Senior Member
PeiYing Hsieh
Join Date: Mar 2009
Posts: 317
Rep Power: 10 
Hi, Trevor,
It does look like you have grid points inside domain you are interested. I run your blockMeshDict and plotted the mesh and a clip of the mesh. Pei 

July 23, 2008, 10:52 
Hi, Trevor,
It does look li

#8 
Senior Member
PeiYing Hsieh
Join Date: Mar 2009
Posts: 317
Rep Power: 10 
Hi, Trevor,
It does look like you have grid points inside domain you are interested. I run your blockMeshDict and plotted the mesh and a clip of the mesh. Pei 

July 23, 2008, 11:03 
Hi trevor,
As pei show us,

#9 
Senior Member
Cedric DUPRAT
Join Date: Mar 2009
Location: Belgium
Posts: 187
Rep Power: 9 
Hi trevor,
As pei show us, it seems that you aldready have some points inside the annulus region. These points correspond to the line : hex (0 1 2 3 16 17 18 19) (10 10 10) simpleGrading (1 1 1) of the blockMeshDict. For exemple here, the (10 10 10) is the number of points in each direction (x, y z) for the first block. The same for the other. If you are still not sure (I hope you are now) you can still do a checkMesh of your case and you should see the number of nodes, cells, ect ... of your geometry 

July 23, 2008, 12:43 
Sorry, I'm not convinced still

#10 
New Member
Trevor Sherk
Join Date: Mar 2009
Location: Ontario, Canada
Posts: 10
Rep Power: 9 
Sorry, I'm not convinced still. Paraview must fill in those lines so that it appears to have mesh points inside. I have done the clip filter with a simple box too and it shows the same effect  making it appear to have grid points all the way through, but they don't. Try doing the clip filter at, say, a 45 degree angle and you will see what I mean. Those lines you see in Pei's picture are created by ParaView for some reason.
Thanks, Trevor 

July 23, 2008, 15:31 
Hi, Trevor,
OK, this is a c

#11 
Senior Member
PeiYing Hsieh
Join Date: Mar 2009
Posts: 317
Rep Power: 10 
Hi, Trevor,
OK, this is a cut out of the original mesh. It will hard to believe that there are no nodes inside the domain. Pei 

July 23, 2008, 15:39 
Hi, Trevor,
Forgot to menti

#12 
Senior Member
PeiYing Hsieh
Join Date: Mar 2009
Posts: 317
Rep Power: 10 
Hi, Trevor,
Forgot to mention this: Look in constant/polyMesh/Points file, it lists 9680 points. This is 11*11*80  matches the number of points you specified. Pei 

July 23, 2008, 16:54 
Hello Pei,
Well, after seei

#13 
New Member
Trevor Sherk
Join Date: Mar 2009
Location: Ontario, Canada
Posts: 10
Rep Power: 9 
Hello Pei,
Well, after seeing that picture I now believe you are right. Thanks! I will now try my simulation. I just assumed the points weren't inside because of Paraview actually. When I would look at the mesh in Paraview and zoom inside, there was no inside grid. Also, when I would run the tutorial cases, the fluid flow would appear the same through all slices of the geometry. I guess they must not have been intended to be 3D cases. This is great! I hope you are right. Thank you very much for your time and assistance. Trevor 

July 24, 2008, 02:48 
Hi Trevor and Pei
"I hope y

#14 
Senior Member
Cedric DUPRAT
Join Date: Mar 2009
Location: Belgium
Posts: 187
Rep Power: 9 
Hi Trevor and Pei
"I hope you are right" .... no doubt, we are :o) Pei, nice picture the last one, I'm really curious to know how you managed to get that with paraView ? Did you decompose the mesh for parallel run and it correspond to one processor mesh ? Thanks, Cedric 

July 24, 2008, 07:43 
Hi, Cedic,
In paraview 3.2.

#15 
Senior Member
PeiYing Hsieh
Join Date: Mar 2009
Posts: 317
Rep Power: 10 
Hi, Cedic,
In paraview 3.2.1, 1. click "Edit", select "Select Cells Through" 2. select the area of mesh you are interested using the mouse. 3. Click "Filter", then, "Alphabetical", then, select "Extract Selection". 4. click "Copy Active Selection". 5. click "Apply" 6. click "Display" 7. under "Style", select "Surface With Edges" under Representation. Pei PS: hope I did not miss anything. 

July 25, 2008, 03:31 
Hi Pei,
Thank you, I'll try

#16 
Senior Member
Cedric DUPRAT
Join Date: Mar 2009
Location: Belgium
Posts: 187
Rep Power: 9 
Hi Pei,
Thank you, I'll try with the old version of paraView first. And maybe with the new one in a couple of weeks. Cedric 

July 31, 2008, 17:28 
Hello again!
I am having some

#17 
New Member
Trevor Sherk
Join Date: Mar 2009
Location: Ontario, Canada
Posts: 10
Rep Power: 9 
Hello again!
I am having some trouble inputting the equations for the model into OpenFOAM. Specifically, for dU/dt (U is the vector fluid velocity), I need to calculate r, the radius ((x^2+y^2)^(1/2)), and the cylindrical unit vector r, i_r, which, when expressed in terms of cartesian coordintes, I THINK is cos(arctan(y/x))*i_x + sin(arctan(y/x))*i_y, where x and y are the usual cartesian coordinates. I think I can use mag(U) to calculate r (?), but from my reading I believe OpenFOAM treats tensors as a unit, and does not look at individual components, such as x and y... anyhow, I am not sure how to do handle finding x and y. I tried U.component(0) and U. component(1) for x and y, and get a floating point exception. So I gather my other problem is that U.y is sometimes 0... Any suggestions would be greatly appreciated!! Thanks, Trevor 

August 1, 2008, 09:57 
Never mind! I think I figured

#18 
New Member
Trevor Sherk
Join Date: Mar 2009
Location: Ontario, Canada
Posts: 10
Rep Power: 9 
Never mind! I think I figured out another way to do the problem.


September 15, 2010, 11:50 

#19 
Senior Member
Join Date: Sep 2010
Location: France
Posts: 224
Rep Power: 9 
Hi Guys, i am new in openfoam, my question is that: if i want to the solve the navier stokes eqns in cylindrical coordinates, i must just define my coordinates system to cylindrical one (r, theta,z)? if so, what about the operators like "laplacian","divergence", for example: div(phi), they will be automatically used in cylindrical coordinates? or we must write new definitions for them in cylind. coord.?
thanks a lot 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Create fine mesh that grows to coarse mesh (Urgent  CZ  FLUENT  1  January 3, 2009 11:36 
Oscillatory mesh motion setup mesh flux ERROR  jaswi  OpenFOAM Running, Solving & CFD  5  August 23, 2007 04:41 
Icemcfd 11: Loss of mesh from surface mesh option?  Joe  CFX  2  March 26, 2007 18:10 
dynamic mesh  structured or cooper mesh  Manoj Kumar  FLUENT  2  November 11, 2005 02:18 
How to convert STAR mesh into FLUENT mesh ?  Jihwan  CDadapco  8  November 10, 2004 05:11 