Fluent doesn't interact with box?

jppilot · March 30, 2016, 06:16

Hello,

I'am Jurriën from the Netherlands. At the moment i'am following a course in fluid dynamics. I have to calculate the drag coefficient of a box. First I used the autodesk CFD programs, but I also want to understand Ansys Fluent (16.0).

I modelled a 'windtunnel' and a box. Herefore I used the primitive geometries. I named one of the sides of the windtunnel 'symmetry'. The box dimensions are for this: x=1 [m], y=1 [m], z=0.5 [m].

During the meshing I did some refinement at the box. After solving the model it looks like ansys doesn't interact with the box. The monitor also gives me a drag coefficent Cd=0. What's going on? Please find attached some helpfull screenshots about the setup and contourplot of the velocity.

CeesH · March 30, 2016, 06:20

Hi,
Did you remove the box geometry from the domain (using boolean subtract in the design modeler), or are there also grid cells in the box?

If the latter is true, do the box walls show up in FLUENT? At first glance, it looks like the fluid is just flowing through.

Cheers,
Cees

jppilot · March 30, 2016, 06:30

No I didn't remove the box geometry from the domain... I can't find the option boolean subtract (I only see create -> boolean). I'll take a further look.

edit: found it, lets see how this will work out...

CeesH · March 30, 2016, 06:41

that's the one I mean indeed

now subtract the small box from the big one so that there is a 'hole' in your geometry. Then it should work!

jppilot · March 30, 2016, 10:04

Thanks, i got it working. the velocity plot at the symmetry plane looks ok

The Cd still is a bit low... around 0.5. it has to be around 1.0 for Re <10^5...

CeesH · March 30, 2016, 11:48

Great you got it working!

Cd may be sensitive to your numerical settings; your mesh density will be of importance but also discretization scheme, turbulence model and wall function use may play a role. Good luck on getting that working!

C

March 30, 2016, 06:16	Fluent doesn't interact with box?	#1
jppilot New Member Join Date: Mar 2016 Posts: 10 Rep Power: 10	Hello, I'am Jurriën from the Netherlands. At the moment i'am following a course in fluid dynamics. I have to calculate the drag coefficient of a box. First I used the autodesk CFD programs, but I also want to understand Ansys Fluent (16.0). I modelled a 'windtunnel' and a box. Herefore I used the primitive geometries. I named one of the sides of the windtunnel 'symmetry'. The box dimensions are for this: x=1 [m], y=1 [m], z=0.5 [m]. During the meshing I did some refinement at the box. After solving the model it looks like ansys doesn't interact with the box. The monitor also gives me a drag coefficent Cd=0. What's going on? Please find attached some helpfull screenshots about the setup and contourplot of the velocity.

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March 30, 2016, 06:20		#2
CeesH Senior Member Cees Haringa Join Date: May 2013 Location: Delft Posts: 607 Rep Power: 0	Hi, Did you remove the box geometry from the domain (using boolean subtract in the design modeler), or are there also grid cells in the box? If the latter is true, do the box walls show up in FLUENT? At first glance, it looks like the fluid is just flowing through. Cheers, Cees

March 30, 2016, 06:30		#3
jppilot New Member Join Date: Mar 2016 Posts: 10 Rep Power: 10	No I didn't remove the box geometry from the domain... I can't find the option boolean subtract (I only see create -> boolean). I'll take a further look. edit: found it, lets see how this will work out...

March 30, 2016, 06:41		#4
CeesH Senior Member Cees Haringa Join Date: May 2013 Location: Delft Posts: 607 Rep Power: 0	that's the one I mean indeed now subtract the small box from the big one so that there is a 'hole' in your geometry. Then it should work!

March 30, 2016, 10:04		#5
jppilot New Member Join Date: Mar 2016 Posts: 10 Rep Power: 10	Thanks, i got it working. the velocity plot at the symmetry plane looks ok The Cd still is a bit low... around 0.5. it has to be around 1.0 for Re <10^5...

March 30, 2016, 11:48		#6
CeesH Senior Member Cees Haringa Join Date: May 2013 Location: Delft Posts: 607 Rep Power: 0	Great you got it working! Cd may be sensitive to your numerical settings; your mesh density will be of importance but also discretization scheme, turbulence model and wall function use may play a role. Good luck on getting that working! C