[Nek5000-users] Neek5000 variable viscosity case

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

Dear Francesco,

For low Mach, if you want var. viscosity you must also set ifexplvis
to be true.   This will treat the remaining part of the stress tensor
explicitly, so that you do capture the physics of the full stress tensor.

Now, a couple of comments ---

The original explicit formulation, based on strong form developed by 
Stefan,
worked well with our dyn. smag. model, but was not in exact agreement
the PnPn-2 stress formulation until refined to convergence.

I modified this to a weak form in January and it does now agree w/ PnPn-2,
but the dyn. smag. tests that I've done do not work.

I've been so busy for the past months with travel and proposal writing
that I've not had a chance to understand why dyn. smag. appears to be
broken.  I'm hoping to resolve this shortly.

Cheers,

Paul


On Mon, 16 May 2011, Francesco Lucci wrote:

> Dear Paul,
>
> sorry to bother you but we need a clarification about the variable viscosity 
> simulations.
>
> We run a LowMach number case of an heated channel and we see a strong 
> variation
> changing the viscosity temperature dependence.
> (in pic we plot the square of the streamwise velocity fluctuation)
> This is not surprising but we would like to have more insight on how the code 
> treats
> the variable viscosity in order to valuate the possible assumptions or errors 
> we made.
>
> We assume that the code, instead of solving for div( mu S), solves mu div(S) 
> with mu that varies in space.
> Thus the term (grad muj) S is neglected.
>
> Is that correct? Is there anything else we have to know?Have anybody 
> evaluated the effect of this approximation?
>
> Thank you a lot for you help.
> francesco
>
>