[daenlol]

Hello everyone,

First of all thanks a lot for all your knowledge which helped me a lot during my studies. I am a student in cfd & fluid mechanics currently in my final year thesis in a windsurf company.

I am currently trying to optimize the trim angle of a surfboard for it to be able to lift exactly a weight of 95kg.

To do so, I used the VoF model of starccm+ with the VoF Flat Wave (U_wind=U_current=10m/s (same axis than the board)). The board is placed with a trim angle of 3° and has a wet surface of 1.15m long (the board is 2.25m long). This needs to stay constant for the whole simulation.

The problem is, while running the simulation, the contact line between the water and the board moves backwards from the nose to the tail of the board. However, I want the wet surface to stay constant so the lift can converge (currently it keeps decreasing!).

I'm using implicit unsteady kwSST model, DFBI without any degrees allowed just to take into account the gravity and fluid forces.

I noticed a divergence slightly above the contact line between the water and the board where the velocity is way too high. The CFL is also > 1. This is weird because the smallest cell is 5mm long & dt = 4.5E-4s (I tried 1E-4s also) so it's supposed to be <1).
The fluid is apparently correctly calculated in the rest of the domain.

I tried to refine the mesh at this location, to change the turbulence settings (intensity etc...), the sharp factor of the interface, but nothing works.

I think this divergence of velocity is the reason why (obviously) CFL >1 and thus the contact line moves due to (maybe I'm wrong) some numerical diffusion...

Do you have any idea where it comes from? Did I miss something in the VoF configuration?
How can I have a constant wet surface? I'm in a bit of a struggle with this since several days ...

Thanks a lot for your attention,

Regards,

Yohann


Courant2.jpg

mesh2.jpg

Water_fraction.jpg

U_vel_1.jpg

U_Vel_2.jpg

[daenlol]

problem solved