Airfoil sim using LES

Andrew

Hi everyone,

I am running simulations for flow over a NACA0012 airfoil and are trying different turbulence models.

I have noticed that when running a RNG turbulence model at zero angle of attack, the solution converges quite soon in flow time and the lift coefficient settles to a constant value near zero.

However, when I run the same simulation using LES, the solution does not converge as soon and the lift coefficient does settle, but fluctuates slightly around zero.

For LES simulations, how long does it take for the solution to converge? I know it is a higher order scheme, which does require more computational time, but even after 10 seconds flow time, there is no sign of improving convergence.

Are there any special tricks that I must be looking out for to get convergence with LES, or is this the natural expectations of a LES simulation?

Thanks

Andrew