Filtering options in .par

[Harry]

Hello Neks,

I am having some stability problems with a simulation and would like to run with a filter to see if filtering resolves the issue.  I am very new to CFD and numerical methods and was wondering if anybody has any documentation on the explicit and hpfrt filtering options available in the .par file.  I am trying to pick good values for the filterCurtoffRatio and filterWeight parameters, which would be easier if I understood how the filter options work.  I am guessing that Nek supplies default values if I don't specify these parameters, however in future runs I would like to optimize the filter and use an appropriate filter for my task.

My simulation is a 2D dynamic stall/unsteady aero simulation with user-specified mesh rotation in a circular domain at Re = 6,000.  The entire domain rotates and there is no mesh deformation.  I am solving the incompressible navier-stokes equations.

Kind regards,

-Harry

Harry E. Werner IV

Graduate Research Assistant

Clarkson University

Potsdam, New York, USA

[Robert Steele II]

I haven't see anyone else answer Harry's question, but I too was wondering something similar.  If I wanted to see how Nek5000 mathematically implements LES filtering, where can I find that (at a minimum, where is the routine coded)?

Thanks!

Rob Steele

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[Stefan Kerkemeier]

You'll find the code of the two filter options in
- q_filter()
- make_hpf()

References:
J.S. Mullen and P.F. Fischer, "Filtering techniques for complex geometry fluid flows" Comm. in Num. Meth. in Eng. 15 pp. 9-18 (1999).
Schlatter, P., Stolz, S. & Kleiser, L. 2004 LES of transitional flows using the approximate deconvolution model. Int. J. Heat Fluid Flow 25, 549–558.


-----Original message-----
> From:Robert Steele II <stee...@isu.edu>
> Sent: Saturday 13th July 2019 2:51
> Cc: Nek5000 <nek...@googlegroups.com>
> Subject: Re: [nek5000] Filtering options in .par
>
> I havent see anyone else answer Harrys question, but I too was wondering something similar.  If I wanted to see how Nek5000 mathematically implements LES filtering, where can I find that (at a minimum, where is the routine coded)?
>
> Thanks!
> Rob Steele

>
> On Wed, Jul 10, 2019 at 4:13 AM Harry <wern...@clarkson.edu <mailto:wern...@clarkson.edu>> wrote:
> Hello Neks,
>

> I am having some stability problems with a simulation and would like to run with a filter to see if filtering resolves the issue.  I am very new to CFD and numerical methods and was wondering if anybody has any documentation on the explicit and hpfrt filtering options available in the .par file.  I am trying to pick good values for the filterCurtoffRatio and filterWeight parameters, which would be easier if I understood how the filter options work.  I am guessing that Nek supplies default values if I dont specify these parameters, however in future runs I would like to optimize the filter and use an appropriate filter for my task.

>
> My simulation is a 2D dynamic stall/unsteady aero simulation with user-specified mesh rotation in a circular domain at Re = 6,000.  The entire domain rotates and there is no mesh deformation.  I am solving the incompressible navier-stokes equations.
>
> Kind regards,
> -Harry
>
> Harry E. Werner IV
> Graduate Research Assistant
> Clarkson University
> Potsdam, New York, USA
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