[Nek5000-users] Reynolds number setting in the turbChannel example

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

One additional comment ---


I generally find PnPn to do a better job of LES than PnPn-2, presumably because of the better accuracy for pressure.


Also, interestingly, you can look both at integrated tau_wall and at mean dp/dx for the LES.  Generally, these are in better agreement for PnPn (based on my past experience...)


If you are running constant flow rate (p54/55 nonzero)  then


grep volf logfile > t.t


and plot col 3 of t.t vs col 1 of t.t will show the mean pressure drop, assuming that the body force set in userf is == 0.


I apologize that the volf line does not also show the time, but only the time step number.


(We should correct that...)


Paul


________________________________
From: Nek5000-users <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: Friday, December 22, 2017 8:59:52 AM
To: nek5000-users at lists.mcs.anl.gov
Subject: Re: [Nek5000-users] Reynolds number setting in the turbChannel example

Hi,
the formula mentioned by Paul can be found in Pope's book (Dean's
correlation). Indeed, if Re_tau is off by more than a few percent (say
10) then the quality of the LES is probably not good. Typically, I would
expect a dynamic Smagorinsky model to lead to an underprediction of the
shear.

Philipp

On 2017-12-22 15:19, nek5000-users at lists.mcs.anl.gov wrote:
>
> Yes -- but presumably if the LES is at all accurate then the mean wall
> shear should be reasonably close to DNS or it has otherwise missed an
> important quantity of interest?
>
>
> Paul
>
>
> ------------------------------------------------------------------------
> *From:* Nek5000-users <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:* Friday, December 22, 2017 7:40:46 AM
> *To:* nek5000-users at lists.mcs.anl.gov
> *Subject:* Re: [Nek5000-users] Reynolds number setting in the
> turbChannel example
> Re_tau is a simulation result and not known a-priori i.e. the number
> below holds for a DNS but not for an LES.
>
>
> -----Original message-----
>> From:nek5000-users at lists.mcs.anl.gov <nek5000-users at lists.mcs.anl.gov>
>> Sent: Friday 22nd December 2017 14:33
>> To: nek5000-users at lists.mcs.anl.gov
>> Subject: Re: [Nek5000-users] Reynolds number setting in the turbChannel example
>>
>> Hi Zhenrong,
>>
>> I used 2800 for shear Reynolds number 180 in channel flow and got a good agreement with Kim et al. (1987).
>>
>> Hope it work to you.
>>
>>
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