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Greg Carnie March 10, 2008 06:03

FSI, Fluent Ansys coupling
Hi all,

This is more of an Ansys question, but if any of you have ever done the following could you please advise. I use fluent 6.3.23 to export the pressure forces for a wing (generic). I then apply the forces to my Ansys model. I made the model myself as it has an internal structure. Therefore I just used the forces from the exported .cdb (through a bit of coding) and applied them to my wing. All good so far. Next is where my model goes wrong!

The lift force I get from Fluent is not enough to support the wing in flight. I did this on purpose to see if the wing would bend downwards under its own weight. I apply a gravity force in Ansys to take into account the weight of the wing. But instead of my wing bending downwards it actually deflected in the positive y-direction?

Now I think the problem could be the way I set the gravity model in Ansys. If you look at the user manual, you do something like,

g=9.81 MP,1,dens=2100/g


This according to the manual should mimic a gravity force on the structure.

What am I doing wrong?

Thanks in advance,


Syed Shabbar Raza March 11, 2008 03:52

Re: FSI, Fluent Ansys coupling
dude chk your material properties in ansys,

like density of material is important.

and also specity gravity in negative direction,its upward down.

change ur density value form +9.81 to -9.81

let me know your feedback

Greg Carnie March 11, 2008 10:37

Re: FSI, Fluent Ansys coupling
Hi, Thanks for your reply but gravity is not specified like that in Ansys:

From the Ansys users manual:

The ACEL command applies an acceleration field (not gravity) to a body. Therefore, to apply gravity to act in negative Y direction you should specify a positive Y acceleration.

Next it goes on to mention the difference in definition between "weight density, lb/in3 or kg/m3" and "mass density". Mass density is just weight density divide by acceleration due to gravity.

The manual says to use weight density in place of mass density only under these condtions:

1) The model will only be used in a static analysis. 2) No angular velocity or angular acceleration is applied 3) Gravitational acceleration is unity (g=1.0)

From section 2.5.9 in Ansys10 user manual.

I am doing a static analysis, and there are no angular velocity or accelerations. Not sure on third point, I should have g=9.81, so to me I must use mass density?


sabbasi_mr January 6, 2010 23:17

Interaction problem with Fluent
Hi every one.
I am using Fluent to solve a sloshing problem and I have to calculate the interaction between water and tank.
Is there any way to couple this with Ansys in real time? I mean is it possible to run Fluent from Ansys domain or vice versa?
Or is there any capability with Fluent to solve simple elasticity problems such as a simply supported beam or plate?

Bernhard January 7, 2010 04:14

Fluent has no support for elasticity problems as far as I know. In general it should be possible to implement it via an UDF, but another option is switching to ANSYS and CFX in Workbench, where two way coupled FSI is integrated.

sabbasi_mr January 7, 2010 20:15

Sorry, but I didn't understand! Do you mean I model the problem by ANSYS CFX? Workbench? what is that? Thanks in advance...

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