[Nek5000-users] Variable density flows

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

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 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 wrote:
>>
>>
>>> On Sun, Oct 13, 2013 at 10:35 AM, <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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