CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

2D and 3D results completely different

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 18, 2012, 02:30
Question 2D and 3D results completely different
  #1
New Member
 
Ameya Durve
Join Date: Jun 2009
Location: Mumbai
Posts: 8
Rep Power: 8
ameyadurve is on a distinguished road
I am simulating a Jet Loop Reactor.
The tank dimensions are: 1m height and 1 m diameter. The jet diameter is 0.0156 m and is located 0.5 m from the tank bottom. The jet velocity is 12.5 m/s. Fluid is water.

My problem is, when I float the simulations in 2D (k-epsilon Model) I can see the jet impinging on the tank bottom and recirculation zones created in the tank. However, when I float the simulation in 3D using same solution strategy, the jet loses all its momentum the moment it hits the bottom and there are no recirculation zones in the tank.

I do not understand why such a discrepancy exists in the 2D and 3D simulations. I can understand if there is difference in the accuracy of predictions but getting totally different flow patterns is not expected.

Can anyone help me understand why this is happening ?

Please note:
1) The mesh is not an issue. I have a best possible mesh for the domain. Skewness less than 0.4

2) Experimental observations show that 2D results represent the system more accurately
ameyadurve is offline   Reply With Quote

Old   October 18, 2012, 04:39
Default
  #2
Senior Member
 
Marion
Join Date: Jul 2012
Location: France
Posts: 122
Rep Power: 5
Marion is on a distinguished road
Hi,
Are you talking about 2D-Axisymmetric? Is your jet axis the same axis as the tank?
Are you sure that the geometry in 3D is the same as in 2D?
I've done the comparison previously, and between a 2D-axi and a 3D (just revolving the 2D surface around the axis) I had no difference at all. That is why I think there may be an issue with the set up of one of the models.
Marion.
Marion is offline   Reply With Quote

Old   October 18, 2012, 06:00
Default
  #3
New Member
 
Ameya Durve
Join Date: Jun 2009
Location: Mumbai
Posts: 8
Rep Power: 8
ameyadurve is on a distinguished road
Hello Marion,

It is 2D and not 2D axisymmetric. The geometries are exactly the same, as mentioned above. I have checked and double checked that part. .

Have you done the comparison for turbulent jets ???

Regards
Ameya
ameyadurve is offline   Reply With Quote

Old   October 18, 2012, 07:29
Default
  #4
Senior Member
 
Marion
Join Date: Jul 2012
Location: France
Posts: 122
Rep Power: 5
Marion is on a distinguished road
It's not jets, but I work with high pressure fluids, cavitation, turbulence.

Why are you modelling a cylindrical tank with 2D and not 2D-axi?

Standard 2D is used for when you have 1 of the dimensions very large compared to the others. 2D-axi is used when your geometry and boundary conditions hava an axis of revolution.

Therefore if you are modelling in standard 2D it is normal that it won't correlate with a 3D model of a cylinder.
Marion is offline   Reply With Quote

Old   October 18, 2012, 08:38
Default
  #5
New Member
 
Ameya Durve
Join Date: Jun 2009
Location: Mumbai
Posts: 8
Rep Power: 8
ameyadurve is on a distinguished road
Well, the tank has an outlet situated at 0.5 m from the bottom and hence 2D axisymmetry is not an option.

Thanks for the input regarding use of 2D flows.

I will now simulate a similar system, in which I have some good quantitative experimental data, in both 2D and 3D. I will keep you posted about the results of the study

Thanks again
ameyadurve is offline   Reply With Quote

Old   October 18, 2012, 08:58
Default
  #6
Senior Member
 
Marion
Join Date: Jul 2012
Location: France
Posts: 122
Rep Power: 5
Marion is on a distinguished road
I understand the geometry better now (I think!).
In my opinion, you can neither use standard 2D nor axisymmetric 2D, both are wrong since you want to model a diameter of 0.0156 m for the opening in a cylindrical tank.
Marion is offline   Reply With Quote

Reply

Tags
2d model, 3d modelling, jet mixing

Thread Tools
Display Modes

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 Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -4. The time now is 06:52.