[Nek5000-users] Synthetic jet with outflow boundary condition

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

Hi Paul,

I simulate a synthetic jet that is produced by a membrane that I model with a moving boundary. The membrane vibrates inside a cavity that is connected to a nozzle and then to a box. The box has an outflow boundary condition and all other boundaries are wall boundaries.

Because of the moving membrane, the fluid enters and exits the nozzle, and the same fluid motions are observed in the box near the outflow boundary, i.e., I have reverse flow.

Hope this helps to understand my problem.

Thanks for your time,

Marco

On Aug 15, 2017, at 6:36 PM, nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov> wrote:


Hi Marco,

I'm not certain of your bcs... is flow leaving the domain? If so, is any flow
coming in?  How does this happen?  Can you give a bit more of a description?
Thanks.

Best,
Paul

________________________________
From: Nek5000-users <nek5000-users-bounces at lists.mcs.anl.gov<mailto:nek5000-users-bounces at lists.mcs.anl.gov>> on behalf of nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov> <nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov>>
Sent: Tuesday, August 15, 2017 9:28:47 AM
To: nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov>
Subject: [Nek5000-users] Synthetic jet with outflow boundary condition

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
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