[Nek5000-users] Heat/passive scalar solver - Helmholtz

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

Dear Paul,

The Peclet and Reynolds number based on the Taylor-microscale and rms velocity are Pe = 33.9 and Re = 48.5.
The periodic box of edge legnth 2*pi is discretized with 20^3 spectral elements of polynomial order 7.
The grid Peclet number based on the mean grid spacing 2*pi/(20*7) and the rms velocity is Pe_grid = 6.69.

We increased the polynomial order from 7 to 11 and 17 and reduced dt accordingly (CFL < 0.4). However, the volumetric scalar means are still not constant. Is there a stability criterion for the solution of the passive scalar equations in Nek? Are there other possible reasons for our numerical errors?

Best, Philipp
________________________________________
Von: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov]" im Auftrag von "nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov]
Gesendet: Sonntag, 20. März 2016 23:01
An: nek5000-users at lists.mcs.anl.gov
Betreff: Re: [Nek5000-users] Heat/passive scalar solver - Helmholtz

Dear Philipp,

The usual way to cure the problem is to increase the spatial resolution.
This can be done by changing lx1 in the SIZE file (and, typically, reducing dt).

What is your Peclet or Reynolds number?

What is your grid resolution?

What is your grid Peclet number?

Best,

Paul

________________________________________
From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov]
Sent: Sunday, March 20, 2016 12:33 PM
To: nek5000-users at lists.mcs.anl.gov
Subject: [Nek5000-users] Heat/passive scalar solver - Helmholtz

Hi Neks,

We simulated the turbulent mixing of passive scalars with the Helmholtz solver. Parameter p22 in the .rea file is set to 10E-09. Our scalar fields show numerical errors, e.g. the scalar volumetric means are not constant but oscillate in time.

Is there a way to reduce the numerical errors / increase the accuracy of the Helmholtz solver?

Best, Philipp Weiss
_______________________________________________
Nek5000-users mailing list
Nek5000-users at lists.mcs.anl.gov
https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
_______________________________________________
Nek5000-users mailing list
Nek5000-users at lists.mcs.anl.gov
https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users