Turbulent cylinder flow simulation errors
******************* 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. ******************* Hello Nektar++ users, I have been experiencing unusual results while simulating cylinder flow with the incompressible Navier-Stokes Solver. When running the simulation at higher Reynolds numbers such as Re = 3900, the flow does not appear as would be expected. The early wake looks too unsymmetric, with one of the first vortex growing to an unusually large size before shedding. After running the simulation for a long period of time the vortices still look quite unusual, lacking the symmetry that would be expected in the vortex street. In trying to solve this issue I have checked the turbulent length scale and ensured I have enough mesh resolution. I also have used a small time scale of 0.0001. I was wondering whether anyone had advice on what I might be doing wrong or how I may attempt to fix the issue. I have included some of the results of the vorticity contours and the .xml conditions in hopes someone recognizes why the simulation is not behaving as expected. Thank you, Matt Duran PhD student University of Central Florida
Hi Matt, The vortices certainly look odd. But I wouldn't expect that much of symmetry at this Re either. Nevertheless, I noticed in your condition file no expansions are set. This means you are using the default expansion in the mesh file? I would explicitly set the expansion in the condition file. Also, I would suggest using high order out flow for the outlet boundary
From your plots, the inlet and sides are also too close. Particularly the side walls can affect your vortex structure
After your 2D is sorted out, you also might want to try 3DH1D too We have a tutorial for flow over cylinder (https://www.nektar.info/notebooks//tutorials/basics-incns-solver/) that might be helpful. It is quite through, and you might find it helpful Hope this helped Cheers Mohsen Mohsen Lahooti Lecturer in Fluid-Structure Interaction Mechanical Engineering Newcastle University School of Engineering Stephenson Building Newcastle upon Tyne NE1 7RU UK ________________________________ From: nektar-users-bounces@imperial.ac.uk <nektar-users-bounces@imperial.ac.uk> on behalf of Matt Duran <matt.duran60@gmail.com> Sent: Tuesday, May 9, 2023 1:24:44 AM To: nektar-users <nektar-users@imperial.ac.uk> Subject: [Nektar-users] Turbulent cylinder flow simulation errors 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. Hello Nektar++ users, I have been experiencing unusual results while simulating cylinder flow with the incompressible Navier-Stokes Solver. When running the simulation at higher Reynolds numbers such as Re = 3900, the flow does not appear as would be expected. The early wake looks too unsymmetric, with one of the first vortex growing to an unusually large size before shedding. After running the simulation for a long period of time the vortices still look quite unusual, lacking the symmetry that would be expected in the vortex street. In trying to solve this issue I have checked the turbulent length scale and ensured I have enough mesh resolution. I also have used a small time scale of 0.0001. I was wondering whether anyone had advice on what I might be doing wrong or how I may attempt to fix the issue. I have included some of the results of the vorticity contours and the .xml conditions in hopes someone recognizes why the simulation is not behaving as expected. Thank you, Matt Duran PhD student University of Central Florida
Hi Matt I noticed you are simulating the benchmark cylindrical flow at Re=3900. As you may see in literature, the flow and the wake at this Re are highly 3-D and 2-D representative will lead to overprediction of drag, as high as 60%. So, I would not expect to have a physical vortex shedding with this 2-D setup. Kind regards syavash On Tue, May 9, 2023, 04:09 Lahooti, Mohsen <m.lahooti@imperial.ac.uk> wrote:
Hi Matt,
The vortices certainly look odd. But I wouldn't expect that much of symmetry at this Re either.
Nevertheless, I noticed in your condition file no expansions are set. This means you are using the default expansion in the mesh file? I would explicitly set the expansion in the condition file. Also, I would suggest using high order out flow for the outlet boundary
From your plots, the inlet and sides are also too close. Particularly the side walls can affect your vortex structure
After your 2D is sorted out, you also might want to try 3DH1D too
We have a tutorial for flow over cylinder ( https://www.nektar.info/notebooks//tutorials/basics-incns-solver/) that might be helpful. It is quite through, and you might find it helpful
Hope this helped
Cheers Mohsen
Mohsen Lahooti Lecturer in Fluid-Structure Interaction Mechanical Engineering
Newcastle University School of Engineering Stephenson Building Newcastle upon Tyne NE1 7RU UK
------------------------------ *From:* nektar-users-bounces@imperial.ac.uk < nektar-users-bounces@imperial.ac.uk> on behalf of Matt Duran < matt.duran60@gmail.com> *Sent:* Tuesday, May 9, 2023 1:24:44 AM *To:* nektar-users <nektar-users@imperial.ac.uk> *Subject:* [Nektar-users] Turbulent cylinder flow simulation errors
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.
Hello Nektar++ users,
I have been experiencing unusual results while simulating cylinder flow with the incompressible Navier-Stokes Solver. When running the simulation at higher Reynolds numbers such as Re = 3900, the flow does not appear as would be expected. The early wake looks too unsymmetric, with one of the first vortex growing to an unusually large size before shedding. After running the simulation for a long period of time the vortices still look quite unusual, lacking the symmetry that would be expected in the vortex street.
In trying to solve this issue I have checked the turbulent length scale and ensured I have enough mesh resolution. I also have used a small time scale of 0.0001.
I was wondering whether anyone had advice on what I might be doing wrong or how I may attempt to fix the issue. I have included some of the results of the vorticity contours and the .xml conditions in hopes someone recognizes why the simulation is not behaving as expected.
Thank you,
Matt Duran
PhD student
University of Central Florida
_______________________________________________ Nektar-users mailing list Nektar-users@imperial.ac.uk https://mailman.ic.ac.uk/mailman/listinfo/nektar-users
And I forgot to mention that this configuration has already a Nektar simulation by Jiang et al. You can look into their works on POF and JFM journals. A blog post is also available on Nektar website that presents their results On Tue, May 9, 2023, 10:20 Ehsan Asgari <eh.asgari@gmail.com> wrote:
Hi Matt
I noticed you are simulating the benchmark cylindrical flow at Re=3900. As you may see in literature, the flow and the wake at this Re are highly 3-D and 2-D representative will lead to overprediction of drag, as high as 60%. So, I would not expect to have a physical vortex shedding with this 2-D setup.
Kind regards syavash
On Tue, May 9, 2023, 04:09 Lahooti, Mohsen <m.lahooti@imperial.ac.uk> wrote:
Hi Matt,
The vortices certainly look odd. But I wouldn't expect that much of symmetry at this Re either.
Nevertheless, I noticed in your condition file no expansions are set. This means you are using the default expansion in the mesh file? I would explicitly set the expansion in the condition file. Also, I would suggest using high order out flow for the outlet boundary
From your plots, the inlet and sides are also too close. Particularly the side walls can affect your vortex structure
After your 2D is sorted out, you also might want to try 3DH1D too
We have a tutorial for flow over cylinder ( https://www.nektar.info/notebooks//tutorials/basics-incns-solver/) that might be helpful. It is quite through, and you might find it helpful
Hope this helped
Cheers Mohsen
Mohsen Lahooti Lecturer in Fluid-Structure Interaction Mechanical Engineering
Newcastle University School of Engineering Stephenson Building Newcastle upon Tyne NE1 7RU UK
------------------------------ *From:* nektar-users-bounces@imperial.ac.uk < nektar-users-bounces@imperial.ac.uk> on behalf of Matt Duran < matt.duran60@gmail.com> *Sent:* Tuesday, May 9, 2023 1:24:44 AM *To:* nektar-users <nektar-users@imperial.ac.uk> *Subject:* [Nektar-users] Turbulent cylinder flow simulation errors
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.
Hello Nektar++ users,
I have been experiencing unusual results while simulating cylinder flow with the incompressible Navier-Stokes Solver. When running the simulation at higher Reynolds numbers such as Re = 3900, the flow does not appear as would be expected. The early wake looks too unsymmetric, with one of the first vortex growing to an unusually large size before shedding. After running the simulation for a long period of time the vortices still look quite unusual, lacking the symmetry that would be expected in the vortex street.
In trying to solve this issue I have checked the turbulent length scale and ensured I have enough mesh resolution. I also have used a small time scale of 0.0001.
I was wondering whether anyone had advice on what I might be doing wrong or how I may attempt to fix the issue. I have included some of the results of the vorticity contours and the .xml conditions in hopes someone recognizes why the simulation is not behaving as expected.
Thank you,
Matt Duran
PhD student
University of Central Florida
_______________________________________________ Nektar-users mailing list Nektar-users@imperial.ac.uk https://mailman.ic.ac.uk/mailman/listinfo/nektar-users
participants (3)
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Ehsan Asgari
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Lahooti, Mohsen
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Matt Duran