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Boundary Conditions. fixedValue and fixedGradient

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Old   August 22, 2014, 04:46
Default Boundary Conditions. fixedValue and fixedGradient
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Pratik Nanavati
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Hello all,

I am very much confused between these two boundary conditions.

- fixedValue and fixedGradient

I have gone through the user guide but it just states that Value of phi and Gradient of phi are specified respectively.

can anyone please explain me in detail the difference between Value and Gradient ?

or If you know some good online links then please post. I need to study boundary conditions in much depth.
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Old   August 25, 2014, 11:09
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Hi nanavati,

FixedValue means a Dirichlet boundary condition:
http://en.wikipedia.org/wiki/Dirichl...dary_condition

Take for example the temperature T
If you give a boundary condition of your temperature field with a fixedValue at a wall
WALL
{
type fixedValue;
value uniform 300;
}
It means, that there is a temperature of exactly 300K at this wall.

fixedGradient means a Neumann boundary condition:
http://en.wikipedia.org/wiki/Neumann_boundary_condition

If you give a fixedGradient at the wall
WALL
{
type fixedGradient;
value uniform 0;
}
or with the same meaning
WALL
{
type zeroGradient;
}
Then the gradient of the Temperature dT/dx_i has this value.
In this example dT/dy=0, so it is an adiabatic wall.

Regards
squirrel
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Old   August 26, 2014, 03:30
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Pratik Nanavati
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Many thanks for the clear cut explanation with the Examples..
My Doubt is Solved now
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