2D Axisymmetric & 3D cylinder
 

Hai

I want to know the difference between 2D Axisymmetric (cylinder) problem and a 3D cylinder problem.

I modelled both for a heat transfer problem and analysed in FLUENT. But the results are not matching.

The problem is

Cylinder length = 500 mm Flowing fluid = Air Inlet temperature = 300 K Wall surface temperature = 400 K Inlet velocity = 0.05 m/s

The result i.e., outlet temperature is varying for both the cases.

Is there any difference in solving both the cases by FLUENT. How to get the same results from both cases.

Kindly suggest me some solution

Regards Raj.

Re: 2D Axisymmetric & 3D cylinder
 

It is interesting. Before I know your result, I also believe that the results of both case should be the same if the geomerey and boundary condition are axisymmetric. I just want to reminder you that the boundary type for the centerline of cyliner in 2D case should be axis, not symmetry. If all of your setting up is correct, I suggest running a case only with flow, then considering heat transfer.

Hope it help.

Re: 2D Axisymmetric & 3D cylinder
 

Thanks for your immediate reply Mr. Jiuan

The geometry and Boundary conditions are given the same. The geometry is 50 mm dia. pipe with 500 mm length. For 2D-Axisymmetric case, axis boundary condition was given in x-axis.

Flowing fluid is air.Flow is laminar. Velocity inlet (0.05 m/s)and pressure outlet (0) BC given.

First, I checked for without heat transfer.The results such as skin friction coeffcient at the wall and pressure at the inlet are not matching with that of the 3D case.

Then I included heat transfer i.e., wall is kept at constant temperature of 400 K. The inlet air temperature is given as 300 K.

The result i.e., the area weighted average of air temperature at the outlet doesnot match with that of the 3D case.

If you have already checked some benchmark problems of this kind, kindly suggest them for checking the results.

Thanks & Regards Raj.

Re: 2D Axisymmetric & 3D cylinder
 

Hi!

have you checked the reference values? Are they the same for both?

Maybe it is about the are calculation....

Is the grid the same for both cases??

Ralf

Re: 2D Axisymmetric & 3D cylinder
 

Thanks for your reply Mr. Ralf

I checked the reference values for the cases and they are same. The geometry is same for both cases. The grid is generated is approximately same for both the cases.

Wall is kept at constant temperature of 400 K. The inlet air temperature is given as 300 K.

The area weighted average of temperature at outlet for 1. 2D axisymmetric case : 383 K 2. 3D cylinder case : 399 K

I donot know why this difference is occuring?

Kindly suggest me some solution.

Thanks & Regards Raj.

Is it possible when dealing with 2d axisymmetric, to post-processing the results in a 3d view? How does it work?

Thanks
jpinho

Check for grid independence!
 

Hi,

This is very interesting problem. I was wondering if you had done any grid independence on both the 2D and 3D cases. If you find that the 3D model requires more refined grid and you make certain that results are good (within certain confidence interval) then try to use these the settings (i.e. grid pattern etc) on the 2D case.

If you do find the reason/solution for this mismatch of results, please let us know. I'm very curious about it.

Regards,

PawnPace

Dear Jiuan

what does it mean axis and axisymmetric?

When you model in axisymmetric mode, for example for a cylinder you just model a square that an edge would be the axis of the cylinder. Got it?

In fluent can I simulation the dispersion problem. If yes how ? In my problem the highly compressed liquid in comes out from the pipeline.

Hi ,

Is it possible when dealing with 2d axisymmetric, to post-processing the results in a 3d view? How does it work?

2D axisymmetric and 3D mismatch
 

Hi.. I am also solving a different problem but i also see that the results are varying. I'm modelling a flow around a hemispherical canopy with a vent hole to determine the drag force it experiences. I modeled the canopy geometry as a simple hemispherical shell will a vent hole in it. But the drag forces are varying by 16% when comparing the results of axisymmetric model and complete 3D model.

Hi ,
I am simulation a cylinder. I used 2Daxisymmetric model and normal 2D which looks like a rectangular. the comparison of the results by experimental values showed that normal 2D simulation produces less relative error than 2D axisymmetric model. While all the setup is the same in both simulation. the relative error of the the former is 26% while the latter is 40%.

Thanks

2D axisymmetric model
 

Hi,
I would like to ask if it is possible to view the results of a simulation using a 2D axisymmetric model in 3D?