[Nek5000-users] Convergence problem in 2D square cylinder

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

Hi Victor,

Do you get any improvement by decreasing dt (.i.e. timstep) in the .rea
file or playing around with the order of temporal scheme (TORDER) ?.
You can introduce some filtering, through parameters 101 and 103, which
would mimic the effects of artificial viscosity. You can read more about
the filtering by carefully reading the subroutine  q_filter(wght) from the
file navier5.f. If you really want to go through the artificial viscosity
procedure in its literal sense, you can modify the subroutine uservp() (You
can go through the example in turbChannel to see how to make modifications)
and set param(30) = 1.

Best Regards,
Tanmoy
On Fri, Jan 13, 2017 at 4:48 AM, <nek5000-users at lists.mcs.anl.gov> wrote:

> Dear Nek users,
>
> I am a PhD student at School of Aeronautics and Astronautics, Technical
> University of Madrid, Spain.
> I am really interested in using Nek5000 in order to generate a flow field
> database. After that, I will apply reduced order modelling techniques. The
> final goal is to study the reduced order models and to investigate possible
> ways to speed up the calculations.
>
> My first run in Nek5000 is bidimensional flow over a square cylinder for
> low Reynolds numbers (Re = 100). Sadly, I am getting some convergence
> problems, Courant number grows up and explodes in a few iterations.
> Plotting the velocity fields, I have noticed that the velocity near the
> square cylinder corners is very big compared to what should be expected.
>
> Anyone has any recommendation? Is there any way to introduce artificial
> viscosity or to increment dissipation?
>
> Regards,
>
> VBeltranM
>
> --
> Víctor Beltrán Martínez
> Ph.D. Student in Applied Mathematics
> Escuela Técnica Superior de Ingeniería Aeronáutica y del Espacio
> Universidad Politécnica de Madrid
>
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