[Nek5000-users] turbChannel example

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

Hi Marco,

Yes, the gradient model should be added as a forcing term in userf()
subroutine.

Best Regards,
Tanmoy

On Fri, Mar 24, 2017 at 10:40 AM, <nek5000-users at lists.mcs.anl.gov> wrote:

> Hi Tanmoy,
>
> thank you for your reply. I did find the correlation in the reference you
> provided.
>
> I have one more question regarding the implementation of the gradient
> model:
> the gradient model consists of computing \tau defined as proportional to
> the tensor product \grad u \dot \grad u. Then, once \tau is computed, \grad
> \tau is added to the momentum equation as a source term. Should I add \grad
> \tau to the momentum equation using userf function in the user file?
>
> Thanks,
> Marco
>
>
> On Mar 21, 2017, at 9:07 PM, nek5000-users at lists.mcs.anl.gov wrote:
>
> Hi Marco,
>
> For the gradient model, you can use gradm1() subroutine to calculate the
> gradient of vx, vy, and vz individually and then the implementation is
> straightforward.
> For the turbChannel example check for the grid (genbox) and the Reynolds
> number used, such that it matches the paper., param(2) in negative is
> basically the inverse of dynamic viscosity. So, a properly defined scale,
> to generate the Reynolds number relationship for you. Eg, if your bulk flow
> streamwise velocity is 1, and the channel half width is 1, then Re_Delta =
> param(2), (Reynolds number based on half channel width). The relationship
> between Re_tau and Re_delta, can be found from Dean's correlation, that is
> provided in the seminal paper of Kim and Moin (1987) for DNS of Re_tau =
> 180.
>
> Best Regards,
> Tanmoy
>
> On Tue, Mar 21, 2017 at 12:25 PM, <nek5000-users at lists.mcs.anl.gov> wrote:
>
>> Hello,
>>
>> I am trying to reproduce some of the turbChannel results that were
>> published with Nek5000 in the paper that can be found in the following link:
>> https://arxiv.org/pdf/math/0205264.pdf
>>
>> In this paper, two turbulent models are tested: the gradient model and
>> the static Smagorinsky model. The paper also shows results from a coarse
>> DNS for comparison.
>>
>> The implementation of the static Smagorinsky model is easily done when
>> starting from the turbChannel example but I am not sure how to implement
>> the gradient model since it involves a tensor product \grad u \dot \grad u.
>> Can anyone point me to an example that has a similar implementation or
>> explain how to implement the gradient model in Nek5000?
>>
>> Is it correct to assume that the current setup of the turbChannel example
>> in Nek5000 should allow to reproduce the coarse DNS results presented in
>> the paper?
>>
>> What is the relationship between Re_tau and the Reynolds number
>> (param(2)) set in the rea file?
>>
>> Any help will be appreciated.
>>
>> Thanks,
>> Marco
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