[Lookid]

Hello,

the norvegian hydropower centre realized experiments on an hydrofoil:
- https://www.ntnu.edu/nvks/f99-test-case3
- https://www.jstage.jst.go.jp/article.../_pdf/-char/en

At V=11m/s, the hydrofoil should vibrate with a frequency of 630Hz.
The vibration of the foil is due a von karman vortex appearing behind the trailing edge.

So far, I consider only the fluid zone, and try to have the proper frequency for the vortex. So I fix V = 11 m/s, let things run and check the frequency of the vortex. But I have a much lower value, about 480Hz instead of 630Hz.

Here are the known problems:
- The turbulence is not fully developed, making URANS difficult to use.
- URANS does not even predict the vortex.

After trying some 2D cases, with different models, I tried 3D with LES (first LES case I do).
I have a proper y+ on the hydrofoil, but my x+ and z+ are way too coarse for a proper LES (both about 1000 instead of [15-100]).

- Smagorinsky gives about 480Hz. I joined a picture to show some information.
- I read about Smagorinsky model problems and tried dynSmagorinsky and locOneEqEddy, but they crash after some time. My guess is that my mesh is too coarse for LES.
- Now also running kOmegaSSTSAS, starting from the Smagorinsky solution, but it seems to damp completely the vortex.

My BC is simply V = 11m/s.
I tried turbulentInlet, but it doubles the computation time and I failed to use directMapped in parallel.

So my questions are:
- What could be the cause of the low frequency?
- Any turbulence model recommended for this type of case? I use foam-extend 4.0.
Ideally I don't have to multiply by 10 my number of cells
Any comment appreciated.


EDIT: The quality of the joined picture is terrible sorry, here it is better on google drive https://drive.google.com/file/d/1SFE...ew?usp=sharing

Lilian