# Question about cyclic bc

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

July 8, 2014, 04:59
Question about cyclic bc
#1
New Member

Andre Weiner
Join Date: Aug 2012
Posts: 27
Rep Power: 5
Hello FOAMers!

I try to connect inlet and outlet of my flow domain with a cyclic/cyclicAMI bc. (picture attached)

When I define the bc as follows, the patches point in the opposite direction.
Code:
```    inlet
{
type cyclicAMI;
neighbourPatch outlet;
transform        rotational;
rotationAxis     (0 0 1);
rotationCentre   (11.25e-3 11.25e-3 0.5e-3); // center of domain
//rotationAngle    180;
faces
(
(0 10 12 2)
(2 12 14 4)
);
}```
A possible solution would be to transform two times (one as above and one to flip the direction), but when I define another transform type, the first one gets overwritten.
Another solution would be to extend the domain, what I want to avoid.

Maybe there is a very simple way to fix this and I just don't want to see it

Thanks in advance for any ideas!

Best regards!
Attached Images
 mesh.jpg (98.2 KB, 49 views)

 July 8, 2014, 09:48 #2 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,133 Rep Power: 16 Hi, I don't really get the picture... Are inlet and outlet "around the corner"? Thus, everything that leaves on the lower horizontal line comes back through the top and everything that leaves on the lower vertical (right) line comes back trough the upper horizontal (left) line? __________________ The skeleton ran out of shampoo in the shower.

 July 8, 2014, 10:15 #3 New Member   Andre Weiner Join Date: Aug 2012 Posts: 27 Rep Power: 5 I try to simulate flow through staggered tube bundle form the ERCOFTAC database. (Case C.78) The main flow direction is x (as in the picture) with an average velocity of 1.06m/s. The sides y-max and y-min are symmetry planes. I could extend the flow domain in x direction (imagine the complete mesh mirrored on the outlet), then inlet and oulet could be connected with a cyclic bc. The smallest possible flow domain, when the flow is assumed to be fully periodic and steady, is what you see in the picture. The oulet-velocity corresponds to the inlet-velocity mirrored on the x-z-plane through the center of the domain. I hope this helps to understand the case better. Thanks!

 July 8, 2014, 10:39 #4 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,133 Rep Power: 16 Ok, looks like you would need to tell openfoam the "direction" for a regular cyclic patch (not cyclicAMI). I don't know how this can be done. Would it be sufficient to let the outlet "line" have a direction from bottom to top in you meshing tool? But anyway: Why this crazy blocking? Don't you have distorted cells in the upper left and lower right corner? This doesn't look right... Edit: It looks like there is a way to set the transformation tensor, so it must be something like 1 0 0 0 -1 0 0 0 1 __________________ The skeleton ran out of shampoo in the shower.

 July 8, 2014, 11:37 #5 New Member   Andre Weiner Join Date: Aug 2012 Posts: 27 Rep Power: 5 When using cyclic bc I always get the following error: (I tried many different transformations and changed the order of the vertices) Code: ```face 0 area does not match neighbour by 120% -- possible face ordering problem. patch:inlet_1 my area:6.87521e-08 neighbour area:2.75008e-07 matching tolerance:0.0001 Mesh face:11028 fc:(0 0.0108844 0.0005) Neighbour fc:(0.0225 0.0087875 0.0005)``` cyclicAMI is not necessary as the blocking is conform. I was just playing around to see if there were any improvements. For the mesh generation I used blockMesh. The cells you pointed out are not optimal but ok. Any idea how to devide this geometry in different blocks? There is still the opportunity to switch to an unstructured mesh but it wont solve the bc problem. Best regards Andre

 July 9, 2014, 02:16 #6 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,133 Rep Power: 16 You get this error when something doesn't match 100%. I make the grids with ICEM (ansys) and if I have one point at 1.210000 and the other one at 1.210004 I get these kinds of errors in OpenFoam. Here you go: mesh.jpg __________________ The skeleton ran out of shampoo in the shower.

July 9, 2014, 07:14
#7
New Member

Andre Weiner
Join Date: Aug 2012
Posts: 27
Rep Power: 5
Many thanks for the hint to the blocking! It looks indeed much better

Regrading to the cyclic bc I ran blockMesh in debug mode. In the attached picture you can see how cell-faces are connected. The picture shows a mesh without grading. When I use grading, of course an error is thrown as the wrong cell-faces are coupled.

I couldn't figure out how to change this. Extending the flow domain is probably the easiest solution.

Thanks again for your help!
Attached Images
 cyclic.jpg (32.1 KB, 21 views)

 Tags cyclic, cyclicami

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post fs82 OpenFOAM 37 January 7, 2015 01:31 sebastian OpenFOAM Bugs 4 October 31, 2012 11:24 gregdB Main CFD Forum 0 January 25, 2012 10:08 maverick OpenFOAM Other Meshers: ICEM, Star, Ansys, Pointwise, GridPro, Ansa, ... 2 June 18, 2011 04:36 askjak OpenFOAM Bugs 18 October 27, 2010 03:35

All times are GMT -4. The time now is 14:20.

 Contact Us - CFD Online - Top