[Nek5000-users] Variable density flows

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

OK. I tried clipping and it seems to run atleast. I need to see the results
tomorrow in office.

There is an option to do filtering in nek. If I understood it correctly, on
each element, you first interpolate solution to lower degree polynomial and
then interpolate it back to higher degree. This kills highly oscillatory
components in the solution. Is this implemented for passive scalars also if
I enable the filtering in rea file ?

I implemented clipping passive scalar like this in userchk but is there a
better way to do the loops

      do e=1,nelv
      do k=1,nz1
      do j=1,ny1
      do i=1,nx1
         t(i,j,k,e,2) = max(0.0, t(i,j,k,e,2))
         t(i,j,k,e,2) = min(1.0, t(i,j,k,e,2))
      enddo
      enddo
      enddo
      enddo

Thanks
praveen


On Sun, Oct 13, 2013 at 7:38 PM, <nek5000-users at lists.mcs.anl.gov> wrote:

>
> With such a small diffusion coefficient you typically
> are going to need very fine resolution in space.
>
> Maintaining monotonicity (i.e., no over- / undershoots) in
> an under-resolved scenario is a current research topic.
> For the time being, I typically simply clip when monotonicity
> is critical.
>
> Paul
>
>
>
> On Sun, 13 Oct 2013, nek5000-users at lists.mcs.anl.**gov<nek5000-users at lists.mcs.anl.gov>wrote:
>
>  I am not sure that what you are solving for  c  is a normalized scalar
>> like a mass fraction Y for example
>> If c is not normalized May be the formulation is equivalent to
>> C= rho* Y where y is a normalized scalar and rho is the total density..
>>
>> Finally check mass conservation
>> By integrating over the volume of the channel, the density equation
>> d/dt integral(rho) + integral (u. Grad rho) =error
>> And see how error changes over time
>>
>> Ammar
>>
>> Sent from my iPhone
>>
>>  On Oct 13, 2013, at 1:46 AM, nek5000-users at lists.mcs.anl.**gov<nek5000-users at lists.mcs.anl.gov>wrote:
>>>
>>>
>>>  On Sun, Oct 13, 2013 at 10:35 AM, <nek5000-users at lists.mcs.anl.**gov<nek5000-users at lists.mcs.anl.gov>>
>>>> wrote:
>>>> You can also try error function like profile with 0 value at the inlet
>>>> and increases to a peak somewhere and stays constant up to the exit so
>>>> gradient is0 at the exit
>>>> Insulation normally refers to the diffusive flux (first form)
>>>> Ammar
>>>>
>>>
>>> Thanks for the tips. I am using a smoothed initial condition for scalar
>>> now. However after some time the scalar does not stay within [0,1] which is
>>> important. My time step is already small with cfl ~= 0.1. What can I do to
>>> get better behaviour of the scalar ?
>>>
>>> The diffusion coefficient for my scalar is quite small, D = 5*10^(-5).
>>>
>>> Regards
>>> praveen
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