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-   -   zeroGradient BC (http://www.cfd-online.com/Forums/openfoam-solving/121029-zerogradient-bc.html)

jaason July 19, 2013 09:59

zeroGradient BC
 
Hi all,
after reviewing a number of forums it seems to me that the zeroGradient BC is often used as a filler conditions, when often the boundary condition should be extrapolated from the internal flow (supersonic outlets) or some other BC would better describe the actual physics.
I feel silly asking this but I take zeroGradient to mean d/dt of the field is zero at the boundary. So for velocity the acceleration would be zero, or in the case of T zero thermal conductive heat transfer etc.

Why is zeroGradient used in many cases were the gradient of the field is not actual zero?
Is it because there is not a readily available substitute?

It seem zeroGradient is one of the more stable BC (Ive been using rhoCentralFoam for microNozzle simulations that include some of the plume)

I looked at the source code and had trouble decyphering how the actual code works I just started teaching myself C++

and help is greatly appreciated
cheers

alexeym July 19, 2013 10:02

Hi,

zeroGradient is actually not time derivative (dF/dt = 0) but spatial derivative (dF/dx = 0).


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