## Fluids

Topics relate to Fluent, CFX, Turbogrid and more

#### How to do 2 way fsi of a soft flapping foil?

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• yuanyangq
Subscriber

Hi everyone,

I have a 3d foil geometry and I want to run a FSI simulation with foil moving under pre-described motion law to calculate the hydrodynamic forces acting on the foil.

Now I know how to make it flap as a rigid body in fluent, and do 2 way FSI simulation with a stationary foil, but I don't know how to do both at the same time. Can anyone tell me how to do it or any recommended references/tutorials? Thanks!

• Rob
Ansys Employee
If you're not bending the foil I'd look at just setting the motion up in Fluent. Is the foil rotating above an axis or flapping?
• yuanyangq
Subscriber
It flaps. The material is soft, so it is supposed to deform while it flaps in incompressible flow. The problem is I dont know how to set up the system coupling of Fluent and Mechanical, while also make it flap using UDF. I can do these two things separately though.
• Rob
Ansys Employee
OK, probably one for You may find the Fluent intrinsic FSI to be better for this depending on how floppy/bendy the flap is.
• yuanyangq
Subscriber
Thank you, I havent paid attention to the fluent intrinsic FSI
• Steve
Ansys Employee
There are a few options here to prescribe the motion of the foil.
Use System Coupling to couple Fluent and Mechanical in a 1-way FSI where displacement is passed from Mechanical to Fluent. The motion is prescribed in Mechanical. For this you could use an applied force, pressure, or displacement. An example of a force applied on the Mechanical side is shown in this tutorial: https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v221/en/sysc_tut/sysc_tut_oscplate_export_cfx.html
Use Fluent only and specify the shape of the foil with the following UDF. This may be more https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v221/en/flu_udf/flu_udf_sec_define_grid_motion.html
Steve