simulation around an hydrofoil using simpleFoam - SA model
I am trying to simulate a steady-state turbulent flow around a chord-normalized hydrofoil. The Reynolds number is Re = 10^6 and the angle of attack is set to 2deg.
I am using simpleFoam with the Spalart-Allmaras model. For the initial & boundary conditions, we need to define the eddy viscosity (nut) and the viscosity-like variable (nuTilda). My assumption is that the flow is laminar in the farfield, so I set the turbulent viscosity to zero at the inlet, outlet and on the top/bottom (symmetryPlane).
I also make the assumption that in the viscous sub-layer, the flow can be considered as laminar, and so, the eddy viscosity is set to zero.
To avoid refining the mesh so much, I also use a wall function "nutUSpaldingWallFunction".
My first question is: from which value of y+ do I have to use a wall function?
My convergence criteria are set to 10^-5 (see fvSolution file attached). However, the convergence is never reached. When I am plotting the drag and lift coefficients over the iterations, I have a lot of oscillations (see attached file). Even when I am refining the mesh, these oscillations are still here. Moreover, the convergence history looks very poor; my pressure residual is around 0.1 (see attached file).
Plotting the vorticity field, it looks like it is not well resolved (see attached file).
My second question: what is the best solver solution for the pressure for high Reynolds?
If you have any advice to give me, that will be very helpful!
Thank you very much.
1) SA is not really good for that flow regime, you will need more advanced turbulence models to have realistic results,
2) i'ts been a while since i used it but i don't think SA cope well with wall functions. you shuld fully define the viscous sublayer and have a y+ less than 1
3) check your mesh, i bet you have something horrible going on with the BL at approx 60-80% of the chord, on both sides of the foil
4) increase the residuals tolerance. for the pressure try GAMG
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