Hi Syavash,

I'm not exactly familiar with computing viscous dissipation but I think that it could be computed with the enstrophy with the "energy" filter. 

There's a tutorial on Taylor Green's vortex on this, https://doc.nektar.info/tutorials/latest/incns/taylor-green-vortex/incns-taylor-green-vortex.pdf

Hope this helps.

Cheers,
Chi Hin

From: Ehsan Asgari <eh.asgari@gmail.com>
Sent: 18 June 2023 11:56
To: Chan, Chi Hin <chi.chan19@imperial.ac.uk>
Cc: nektar-users <nektar-users@imperial.ac.uk>
Subject: Re: [Nektar-users] Time-average of a gradient
 
Hi Chi Hin

Thanks. You are right about the velocity gradient alone. Sorry, I didn't ask the right question. 
What can be done when we have a product of velocity gradients? 
More precisely, I need to calculate the TKE viscous dissipation term:
nu*<s_ij s_ij>,
where s_ij refers to the fluctuation strain rate tensor. I need this quantity to subsecuently calculate the Kolmogorov length scale.
I see it calculated in a paper that has utilized Nektar++, but I have not a clear idea how it was done.

Kind regards
syavash

On Sun, Jun 18, 2023, 14:03 Chan, Chi Hin <chi.chan19@imperial.ac.uk> wrote:
Hi Syavash,

You could use FieldConvert -m gradient on the time-averaged fields.

Regards,
Chi Hin

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Sent: Saturday, June 17, 2023 8:20:29 PM
To: nektar-users <nektar-users@imperial.ac.uk>
Subject: [Nektar-users] Time-average of a gradient
 

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Dear All,

How may I calculate the time-average of a gradient, for example velocity gradient?

Kind regards
syavash