Need some help
 

Just a little brief of my project. I'm currently simulating winglet (a device attached to the tip of a wing) in order to determine the coefficient of lift and drag. One of my design is a triangular winglet.

When I run the simulation, my residual graph have this thing call "nut" (I think it means turbulent dynamic viscosity) and it's fluctuating. It doesn't converge. At the console in Fluent, it keeps mentioning something about reverse flow. I think it might be due to the sharp end of the triangular winglet and the flow around that region is very turbulent around that area.


The coefficient of lift and drag for this triangular winglet is very large (sometimes about 0.6 sometimes 66 *depends on what number of iteration used, too high the solution diverge instead of converge*), as compared to my other rectangular and trapezoidal shaped design (at 0 degree angle of attack is only about 0.00XXX for trapezoidal and rectangular).

May I know is it possible for aerodynamics expert here to enlighten me how can I fix this issue?

Hello! I think it's a good idea to pay attention to the sharp edge. Try a blunt edge instead of the sharp one. Also please show the mesh

Hi,

Thanks for your advice ...

I wanted to but that computer is currently running on this simulation ...

But the mesh is just a regular 3D C-shaped mesh ...

Edit:
I tried to avoid the sharp edge design by cutting it away. The "reverse flow" no longer shows up in the console. The residual graph also smoothens out alot. But at times when it converges about 1e-3, divergence is showed in the console. The whole thing then jumped back up to 0 again.

# Divergence detected in AMG for pressure coupled: protective actions enabled!
# Divergence detected in AMG for pressure coupled, temporarily solve with BCGSTAB!

Are you sure you distributed the elements on the surface properly (that's why I wanted to see the mesh)? Do you obtain the boundary layer in the solution? Did you try laminar regime?

Okay ...

The mesh are here ...

I'm sorry don't really get your point for the last 2 questions ...

use goole and youtube to find examples, how the mesh for simulation flow over an Airfoil should looks like.

key words: airfoil, mesh, prism layer, boundary layer

you can find good example in ansys fluent tutorials as well

Best regards