Dear Reda,

Attached is a session file with the numerical setup I would suggest to use (obviously change the expansion order to as you see fit).

I would keep SVV turned on, and if the simulation still blows up increase diffusion coefficient and decrease cutoff ratio for the homogeneous direction.

As Spencer was saying, you also have to be careful about the outflow - possibly coarsening the mesh in this region might help.

As a diagnostic tool, I would suggest using the IO_CFLWriteFld parameter to understand where the instability is arising, which may give you hints on how to tackle the problem.

Kind regards,

Andrea Cassinelli
PhD candidate
Department of Aeronautics
Imperial College London
London SW7 2AZ
Mob.: +44 (0)7956957642

On 14 Jun 2020, at 21:46, Sherwin, Spencer J <s.sherwin@imperial.ac.uk> wrote:

HI Reda,

I would definitely try Dealiasing, at least in the Spectral Element plane. Also you need to make sure the outflow boundary condition is not causing problems and possibly require HOUTFLOW conditions at the outflow?

The IMEXOrder2 is BDF2 on the linear viscous solve but we do not have a scheme to make the advection term implicit currently.

It should certainly run at Re=2000. We have a number of runs for a circular cylinder at Re=3900. @Andrea: Could you forward a session file for that?

Thanks,

Spencer.

Spencer Sherwin FREng, FRAeS
Head of Aerodynamics Section,
Director of Research Computing Service,
Professor of Computational Fluid Mechanics,
Department of Aeronautics,
s.sherwin@imperial.ac.uk South Kensington Campus,
Phone: +44 (0)20 7594 5052 Imperial College London,
Fax: +44 (0)20 7594 1974 London, SW7 2AZ, UK
http://www.imperial.ac.uk/people/s.sherwin/

On 14 Jun 2020, at 07:15, sgepner@meil.pw.edu.pl wrote:

Hi Reda,

Have you tried using Dealliasing?

Pozdrawiam,
Stanisław Gepner

14 cze 2020 01:32 Moto Light <redamansyhh@gmail.com> napisał(a):

This email from redamansyhh@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 to disable email stamping for this address.

Hi All,

I wish all of you are fine these days, I am running a 3D homogeneous case for a square cylinder, when I run the case at high Reynolds 2000 it keeps crashing, I tried "SpectralVanishingViscosity" it is working but it is filtering my field, what about using a different time integration method "BDFImplicitOrder2" instead of using "IMEXOrder2", I think the two of them are 2nd order but using Implicit instead of Implicit explicit will not crash, but also I will keep CFL under 1 to be sure it is fine, even with this method i can go for higher CFL, my Reynolds is 2000 turbulent flow.

Regards,

Reda

UPC Barcelona

+34 632 675 853

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