# Boundary Conditions Problem

 Register Blogs Members List Search Today's Posts Mark Forums Read

February 11, 2013, 09:32
Unresolved problem and Queries
#21
Senior Member

Himanshu Sharma
Join Date: Jul 2012
Posts: 101
Rep Power: 7
Quote:
Hi,
From other post on the forums (http://www.cfd-online.com/Forums/ope...rintstack.html) i came across checking the mesh by "checkMesh" i did that thing and found few things about my mesh bold ones.
Code:
```Overall number of cells of each type:
hexahedra:     223866
prisms:        0
wedges:        0
pyramids:      0
tet wedges:    0
tetrahedra:    0
polyhedra:     0

Checking topology...
Boundary definition OK.
Point usage OK.
Upper triangular ordering OK.
Face vertices OK.
Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces ...
Patch               Faces    Points   Surface topology
wall                21803    21858    ok (non-closed singly connected)
inlet               278      300      ok (non-closed singly connected)
outlet              493      528      ok (non-closed singly connected)

Checking geometry...
Overall domain bounding box (-0.0199212 -4.33681e-19 -0.0008) (-0.00992118 0.01 0.0108)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (-2.29843e-15 2.69037e-17 -4.91973e-18) OK.
Max cell openness = 3.26926e-16 OK.
Max aspect ratio = 21.2719 OK.
Minumum face area = 1.27927e-10. Maximum face area = 1.16148e-07.  Face area magnitudes OK.
Min volume = 1.28223e-14. Max volume = 2.27969e-11.  Total volume = 1.00065e-06.  Cell volumes OK.
Mesh non-orthogonality Max: 43.6834 average: 7.57081
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 1.12467 OK.
Coupled point location match (average 0) OK.```
you can see my cells are very small is it the reason of my Courant number getting raised very high?? i have another doubt that as the flow inside develops in ,since my outlet sections is way small comparative to the wall,are my boundary conditions right to make the flow patterns in side the box ?? what i want as a result is after providing a pressure outlet condition i should get a velocity at the outlet patch since there is no other outlet present in the domain.Is my approach right in setting the boundary conditions since this is the common approach for seeing boundary conditions in the commercial softwares. Do open foam work in same way? i.e. if we provide zeroGradient condition in the 0/p at the outlet then the solver will extrapolate values from inside for the velocity.These are some basic doubts regarding the software if you can throw some light on it.

 February 12, 2013, 09:08 #22 Member   Ali Khalifesoltani Join Date: Mar 2011 Location: Esfahan, Iran Posts: 53 Rep Power: 8 Hi, According to CFL condition, your dt should be less than 1.2e-14 sec, so you should make a coarser mesh. I am not an expert on openFoam but as much as I know if you don't overconstrain the B.Cs there should be no problem in the boundary conditions you defined. I ran your case and worked a little bit on it but no success was observed. I thought that the problem is probably for your Initial Pressure Condition in the domain and it will cause some math. error in the solution but there was no success. I think the first step to solve your problem is to obey the CFL condition(by decreasing dt or making a coarser mesh) and then investigate on the B.Cs. Regards. Ali

February 13, 2013, 00:43
#23
Senior Member

Himanshu Sharma
Join Date: Jul 2012
Posts: 101
Rep Power: 7
Quote:
 Originally Posted by asoltoon Hi, According to CFL condition, your dt should be less than 1.2e-14 sec, so you should make a coarser mesh. I am not an expert on openFoam but as much as I know if you don't overconstrain the B.Cs there should be no problem in the boundary conditions you defined. I ran your case and worked a little bit on it but no success was observed. I thought that the problem is probably for your Initial Pressure Condition in the domain and it will cause some math. error in the solution but there was no success. I think the first step to solve your problem is to obey the CFL condition(by decreasing dt or making a coarser mesh) and then investigate on the B.Cs. Regards. Ali
Hi,
I also think that it necessary for defining an interior pressure conditions in side the box since i don't think wit the given velocity inlet the solver is developing the interior pressure field. but then if i specify some interior pressure inside the domain then it will start affecting my inlet boundary conditions hence i am totally in a mess how to make this problem as this is on of my projects in the university.And i will now try to coarse my mesh and then try to implement the boundary condition how it might work.if you find some ways than please do share.

Regards
Himanshu sharma

 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 volo87 CFX 5 June 14, 2013 17:44 moomba Main CFD Forum 2 February 17, 2010 04:37 saii CFX 2 September 18, 2009 08:07 Mahiboobswamulu Main CFD Forum 10 August 26, 2003 13:24 reinaldo kuhn Phoenics 1 March 27, 2003 12:46

All times are GMT -4. The time now is 09:23.