Outlet flow causing simulations to crash
******************* This email originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list https://spam.ic.ac.uk/SpamConsole/Senders.aspx to disable email stamping for this address. ******************* Dear Nektar++ users, I have been experiencing issues related to flow in the outlet region of my simulations. I have been running flow past a cylinder at Reynolds number Re = 3900, on some occasions when the vortexes being shed reach the outlet, they cause my simulation to crash. This problem persists for 2D and 3D simulations. I have tried several fixes such as a finer time step of 5E-5 and making the mesh very high resolution. I have also tried increasing the distance from the cylinder to the outlet, with the outlet being located 40 cylinder diameters downstream from the cylinder. And I have also tried using a higher resolution 'buffer zone' near the outlet and also making the mesh unstructured near the outlet but I still experience crashing. The issue seems to be that the vortexes get stuck in the outlet boundary and then begin sending pressure and velocity backwards upstream into the flow causing the simulation to crash. I would greatly appreciate it if anyone had a potential solution or work around to this. I can provide my simulation files if it would help. Thanks, Matt Duran
Hi Matt, What are your boundary conditions? I presume it is a zero gradient outlet condition. Are you using the higher-order outflow boundary condition, namely <REGION REF="1"> <!-- outlet !--> <N VAR="u" USERDEFINEDTYPE="HOutflow" VALUE="0" /> <N VAR="v" USERDEFINEDTYPE="HOutflow" VALUE="0" /> <D VAR="p" USERDEFINEDTYPE="HOutflow" VALUE="0" /> </REGION> This should prevent reflections from the boundary into the flow domain. Cheers, Ilteber -- İlteber R. Özdemir On Tue, 5 Sept 2023 at 13:01, Matt Duran <matt.duran60@gmail.com> wrote:
This email from matt.duran60@gmail.com originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list <https://spam.ic.ac.uk/SpamConsole/Senders.aspx> to disable email stamping for this address.
Dear Nektar++ users,
I have been experiencing issues related to flow in the outlet region of my simulations. I have been running flow past a cylinder at Reynolds number Re = 3900, on some occasions when the vortexes being shed reach the outlet, they cause my simulation to crash. This problem persists for 2D and 3D simulations.
I have tried several fixes such as a finer time step of 5E-5 and making the mesh very high resolution. I have also tried increasing the distance from the cylinder to the outlet, with the outlet being located 40 cylinder diameters downstream from the cylinder. And I have also tried using a higher resolution 'buffer zone' near the outlet and also making the mesh unstructured near the outlet but I still experience crashing.
The issue seems to be that the vortexes get stuck in the outlet boundary and then begin sending pressure and velocity backwards upstream into the flow causing the simulation to crash.
I would greatly appreciate it if anyone had a potential solution or work around to this. I can provide my simulation files if it would help.
Thanks,
Matt Duran _______________________________________________ Nektar-users mailing list Nektar-users@imperial.ac.uk https://mailman.ic.ac.uk/mailman/listinfo/nektar-users
******************* This email originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list https://spam.ic.ac.uk/SpamConsole/Senders.aspx to disable email stamping for this address. ******************* I can confirm now after running my simulation for many vortex shedding cycles, the fixes suggested to me worked. Using the higher-order outflow boundary condition <REGION REF="1"> <!-- outlet !--> <N VAR="u" USERDEFINEDTYPE="HOutflow" VALUE="0" /> <N VAR="v" USERDEFINEDTYPE="HOutflow" VALUE="0" /> <D VAR="p" USERDEFINEDTYPE="HOutflow" VALUE="0" /> </REGION> along with keeping the distance downstream from the outlet to the cylinder at L = 40D. Implementing both of these conditions prevents my simulations from crashing and reduces those instabilities in the flow from vortexes passing through the outlet. Thanks to Ilteber and Henrik for the assistance! Matt On Tue, Sep 5, 2023 at 7:00 AM Matt Duran <matt.duran60@gmail.com> wrote:
Dear Nektar++ users,
I have been experiencing issues related to flow in the outlet region of my simulations. I have been running flow past a cylinder at Reynolds number Re = 3900, on some occasions when the vortexes being shed reach the outlet, they cause my simulation to crash. This problem persists for 2D and 3D simulations.
I have tried several fixes such as a finer time step of 5E-5 and making the mesh very high resolution. I have also tried increasing the distance from the cylinder to the outlet, with the outlet being located 40 cylinder diameters downstream from the cylinder. And I have also tried using a higher resolution 'buffer zone' near the outlet and also making the mesh unstructured near the outlet but I still experience crashing.
The issue seems to be that the vortexes get stuck in the outlet boundary and then begin sending pressure and velocity backwards upstream into the flow causing the simulation to crash.
I would greatly appreciate it if anyone had a potential solution or work around to this. I can provide my simulation files if it would help.
Thanks,
Matt Duran
participants (2)
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İlteber Özdemir
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Matt Duran