[Nek5000-users] Synthetic jet with outflow boundary condition

[nek5000-users at lists.mcs.anl.gov]

Hi,

I am working on a 3-D simulation of a synthetic jet. The synthetic jet exits a nozzle and expands in a box that has an outflow boundary condition. After one or two cycles, the solution returns NaN because of the reverse flow that occurs at the outflow boundary condone. I am aware of the trick that consists in locally accelerating the fluid near the outflow but I am not sure this could be useful to me since I do not have an inlet condition.

My next step will be to increase the computational domain, i.e. the box where the jet expands, and hope that the jet does not reach the outflow boundary condition. The only drawback of this option is that it will require more CPU time.

Before I move forward, I would like to know if someone else has experienced the same problem and came up with a solution that could be useful to me. I also though of increasing the viscosity near the outflow boundary condition.

Any help will be appreciated.

Thanks,
Marco