[arunsmec]

I am performing LES of a roundjet using OpenFOAM. SGS model is smagorinsky.
Upto around 12500 time steps my courant number was well below 1 (0.5-0.7). After that it has been increasing and, now at 13750 iterations, it is ~14. Is the solution right? I am using a time step 5e-5. Why is this sudden increase in courant number happening?

[FMDenaro]

Originally Posted by arunsmec

I am performing LES of a roundjet using OpenFOAM. SGS model is smagorinsky.
Upto around 12500 time steps my courant number was well below 1 (0.5-0.7). After that it has been increasing and, now at 13750 iterations, it is ~14. Is the solution right? I am using a time step 5e-5. Why is this sudden increase in courant number happening?

if your time-step is fixed then you have an increasing of the velocities, that can indicate a numerical instability

[arunsmec]

I am surprised why this instability has come up after these many timesteps

[FMDenaro]

Originally Posted by arunsmec

I am surprised why this instability has come up after these many timesteps

why not? numerical instability can be a slow process ...

[Tushar@cfd]

Originally Posted by arunsmec

I am surprised why this instability has come up after these many timesteps

I agree with "FMDenaro",

@Arun...

The error usually builds up during iterations, try to add under-relaxation factor to the variables. Also, re-check your mesh.