[Nek5000-users] Marangoni effect

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

Hi Frank,

There should be a way to impose the shear, which corresponds to an
inhomogeneous Neumann condition in the stress-formulation.

The precise values would be supplied by the user through userbc --
generally it's a good idea to compute the quantity in userchk and
save this to an array, then de-reference the array values in userbc(),
which is called once per gridpoint per timestep (as opposed to
once per timestep, like userchk).

I'll check to see if I can determine the correct bc flag to enable
this condition.   To be sure, you will need to use the Pn-Pn-2
formulation, with the stress condition turned on.

Unit normal and unit tangent vectors are available for each element
surface, and routines that allow computations with volume-based and
surface-based arrays abound (e.g., compute dot-product of grad T with
unit normal, where former array is volume-based and latter is surface
based).



Note that Nek supporst an ALE free-surface formulation - just fyi
if this is relevant to your problem.

Paul


On Tue, 6 Apr 2010, nek5000-users at lists.mcs.anl.gov wrote:

> Hello all,

Is there a boundary condition that allows one to specify the shear
stress vector in terms of the temperature gradient along the boundary?
The boundary in question is a curved surface in 3D.

If not, do y'all think that is this something that could be done without
extreme difficulty?

Cheers,
Frank

-- 
Frank Herbert Muldoon, Ph.D. Mechanical Engineering
Technische Universität Wien (Technical University of Vienna)
Inst. f. Strömungsmechanik und Wärmeübertragung (Institute of Fluid
Mechanics and Heat Transfer)
Resselgasse 3
1040 Wien
Tel: +4315880132232
Fax: +4315880132299 
Cell:+436765203470
fmuldoo (skype)
http://tetra.fluid.tuwien.ac.at/fmuldoo/public_html/webpage/frank-muldoon.html

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