Outlet patch with a hole inside

osol · September 6, 2011, 07:44

Hi there
I am using openfoam to model the interface between 2 fluids. I have a .stl model, and used snappyhexmesh to create my mesh. I defined a bounding box around this model, so that one of the faces would be the inlet and others would be the outlet. I succeeded, but the time steps were too small. (That is a problem I would also like to ask) The problem: Now, I want to create the inlet so that it would be on one of the faces of the cube, however smaller than the face. The small patch on the face of the cube would be the inlet, and the rest of the face would be the outlet. The outlet therefore has a hole inside, and I could not find a way to model it. Is there any way to construct a polygon, and subtract a smaller polygon from that?

The other problem is that the time steps are too small. I am guessing the reasons may be:

the boundary conditions
absence of the atmosphere. I have created this case using a previous tutorial in which there was an atmosphere patch. I have reconstructed my case from that case. At first, I tried with the atmosphere being one face of the cube; that also had very small time steps. I now removed the atmosphere and it has no difference.
my mesh has 80000 cells. I don't think this would pose a problem.

I have created my mesh using blockMesh and snappyHexMesh, so if you could just briefly check if there is an apparent reason for the small timesteps, I would really appreciate it. The link to my case is below, I have uploaded it to 2shared.
Thanks in advance

http://www.2shared.com/file/C_we4D7D/trial1tar.html

osol · September 7, 2011, 07:53

I have dealt with the small time step issue by decreasing the number of cells. Now, I only want to know if there is a way to create a perforated patch.
I would appreciate the smallest clue, I am on a tight schedule now.

niklas · September 7, 2011, 08:08

If I have understood you correctly, you want openfoam to guess where the hole is?

You need to have a properly defined stl, where the hole-patch is defined as a separate part.

osol · September 7, 2011, 11:10

I have the coordinates for the hole, I just don't know how to implement the hole, in this case a square hole on a square plate. I think I managed to do it by dividing the blocks into four pieces, but that was easy because of the geometry. For example, what could we do if we were to define a ring (circular hole on a circular plate) as a patch?

September 6, 2011, 07:44	Outlet patch with a hole inside	#1
osol New Member Join Date: Sep 2011 Posts: 4 Rep Power: 15	Hi there I am using openfoam to model the interface between 2 fluids. I have a .stl model, and used snappyhexmesh to create my mesh. I defined a bounding box around this model, so that one of the faces would be the inlet and others would be the outlet. I succeeded, but the time steps were too small. (That is a problem I would also like to ask) The problem: Now, I want to create the inlet so that it would be on one of the faces of the cube, however smaller than the face. The small patch on the face of the cube would be the inlet, and the rest of the face would be the outlet. The outlet therefore has a hole inside, and I could not find a way to model it. Is there any way to construct a polygon, and subtract a smaller polygon from that? The other problem is that the time steps are too small. I am guessing the reasons may be: the boundary conditions absence of the atmosphere. I have created this case using a previous tutorial in which there was an atmosphere patch. I have reconstructed my case from that case. At first, I tried with the atmosphere being one face of the cube; that also had very small time steps. I now removed the atmosphere and it has no difference. my mesh has 80000 cells. I don't think this would pose a problem. I have created my mesh using blockMesh and snappyHexMesh, so if you could just briefly check if there is an apparent reason for the small timesteps, I would really appreciate it. The link to my case is below, I have uploaded it to 2shared. Thanks in advance http://www.2shared.com/file/C_we4D7D/trial1tar.html

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September 7, 2011, 07:53		#2
osol New Member Join Date: Sep 2011 Posts: 4 Rep Power: 15	I have dealt with the small time step issue by decreasing the number of cells. Now, I only want to know if there is a way to create a perforated patch. I would appreciate the smallest clue, I am on a tight schedule now.

September 7, 2011, 08:08		#3
niklas Super Moderator Niklas Nordin Join Date: Mar 2009 Location: Stockholm, Sweden Posts: 693 Rep Power: 29	If I have understood you correctly, you want openfoam to guess where the hole is? You need to have a properly defined stl, where the hole-patch is defined as a separate part.

September 7, 2011, 11:10		#4
osol New Member Join Date: Sep 2011 Posts: 4 Rep Power: 15	I have the coordinates for the hole, I just don't know how to implement the hole, in this case a square hole on a square plate. I think I managed to do it by dividing the blocks into four pieces, but that was easy because of the geometry. For example, what could we do if we were to define a ring (circular hole on a circular plate) as a patch?