[Nek5000-users] Compute the derivatives
nek5000-users at lists.mcs.anl.gov
nek5000-users at lists.mcs.anl.gov
Mon Jul 12 20:39:05 CDT 2010
Hi Fred,
It looks like the delta is coming from the forcing function, ffz=.035.
For periodic flows, pressure is not periodic, but grad p is a periodic
function. The true pressure for the computation is:
p = pr - ffz*z - ffy*y -ffx*x
where pr is the quantity computed by Nek. For your analysis below,
use p as defined above and all should be ok. Note that computation
of drag over an object must acount for this --- I've done this in the
past and some of the infrastructure is in place in navier5.f (dpdx_mean,
etc.) --- but there are difficulties if the object is cut by the
periodic plane and so it does not generalize to every possible case.
Hope this helps.
Paul
>
> On Thu, 8 Jul 2010, nek5000-users at lists.mcs.anl.gov wrote:
>
>> Thanks a lot for you answer. But if I compute all my derivates in this way,
>> I have deviation in my momentum equations...
>> In the stagnation point of my sphere (u=v=w=0) I get the following:
>>
>> -1/rho dp/dx = 0.4125
>> nu (d2u/dx2 + d2u/dy2 + d2u/dz2) = 0.3775
>>
>> --> delta = 3.5e-2
>>
>> Do you have an idea from where this delta might result??
>>
>> Best, Fred
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