[Nek5000-users] Variable density flows

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

Hello Ammar
The initial c lies between 0 and 1 and I want it to stay in this range. The
problem is that there are narrow interfaces in which c changes from 0 to 1
and the change will not be monotone causing c to takes values outside [0,1].
Thanks
praveen


On Sun, Oct 13, 2013 at 7:42 PM, <nek5000-users at lists.mcs.anl.gov> wrote:

> I may have misunderstood your Q
> Did you mean that c initially has a max = 1 and that mixing will only
> cause it to go down?
> In this case check mass conservation
> And make sure the initial density is accurately specified and that it gets
> updated correctly
> Ammar
>
> Sent from my iPhone
>
> On Oct 13, 2013, at 9:01 AM, 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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