CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   FLUENT (http://www.cfd-online.com/Forums/fluent/)
-   -   2D and 3D results completely different (http://www.cfd-online.com/Forums/fluent/108250-2d-3d-results-completely-different.html)

2D and 3D results completely different

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 ?

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

 Marion October 18, 2012 04:39

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.

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. :confused:.

Have you done the comparison for turbulent jets ???

Regards
Ameya

 Marion October 18, 2012 07:29

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.

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

 Marion October 18, 2012 08:58

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.

 All times are GMT -4. The time now is 18:31.