Learning Forum

[karimi]

I have used ANSYS CFD Fluent and LS-DYNA ICFD to model the exact same fluid path, with the same boundary conditions, mesh resolution, and fluid properies. However, while the velocity look the same the pressure and shear contours look SIGNIFICANTLY different with CFD fluent giving us better results. I was wondering what is the problem here? I am pretty sure LS-DYNA ICFD does something wrong here either in calculation or in presenting the results. Appreciate any help ...

LS-DYNA ICFD

CFD Fluent

[Reno Genest]

Hello Karimi,

Could you describe the problem in more details? This is a 2D flow? Could you describe the inlet, outlet, and wall boundary conditions?

What is the fluid? What are the fluid properties? Note that the ICFD solver assumes incompressibility. This assumption may cause a change in the results compared with Fluent.

Also, did you use a boundary layer in Fluent? What about ICFD? 

With the ICFD solver, the mesh is generated by the solver based on the surface mesh. Make sure to review the volume mesh (tet mesh) generated by the solver for size and element quality.

 

Reno.

[karimi]

Hi Reno,

It is a simple cylindrical fluid with the left as inlet and right as outlet. No-slip BC and everything is the same between teh two models, The fluid is incompressible for both solvers and I paid attanetion to that. 
I defined inflation layer in CFD and just a no slip in ICFD.
Teh mesh was exactly the same between two models

Best

Ali

[Reno Genest]

Hello Ali,

I would have to look at the 2 models. Unfortunately Ansys employees are not allowed to upload and download files on the Ansys Forum. 

If you are a commercial customer, you can create a support case on ACSS (Ansys Customer Support Space) and we will have a look at your models:

customer.ansys.com

 

You can still post your models on the Ansys Forum and other users may be able to help.

 

Reno.

[Reno Genest]

Hello Ali,

Have you tried with no inflation layer in both Fluent and ICFD? Make sure all the conditions are exactly the same. Do you have a typo in your input? Units problem?

 

Reno.

[karimi]

Hi Reno,

I can upload the fluent CAS file and ls-dyna K file for you if you want to check that?
My confusion is that the velocity in these two software is exactly the same and only shera stress and pressure magnitudes and contours are different. Seems like ICFD reads the results wrong in LS-Prepost. But then I checked different Pre-Post versions and the resultts are the same

Do you think one simple boundary layer would change everything here? then why the velocity is the same?

best

Ali

[Reno Genest]

Hello Ali,

To compare apples to apples, it is best to have the exact same conditions, mesh, etc. in both software.

You can upload the models on the Ansys Forum, but I won't look at it because Ansys employees cannot download files on the Forum.

 

Reno.

[karimi]

Hi Reno,

Sure I will run one on ANSYS without infalation boundary, however, we know Ansys results are correct and match the litartre and physiology. My main question is why LS-DYNA ICFD results are wrong? This is not my first experince with LS-DYNA and I ran several other models that basically I have used exact examples from LSdyna example website and the shear stresses and resultant pressure contours are all wrong.

Best

Ali