[andyru]

Hello,

I looked at fixedGradientFvPatchField.C and
zeroGradientFvPatchField.C and for me

type fixedGradient;
value uniform (0 0 0);

behaves like using:

type zeroGradient;

So why do we have zeroGradient? fixedGradient type would be enough?!
Or do I draw the wrong conclusion?

Best regards,

Andy

[Bernhard]

They are not the same. zeroGradient only garantuees the wall-normal derivative to be zero, not the complete gradient.

[andyru]

Thank you for the fast answer. I got it.

Next little question:
A given fixedGradient value (a b c) will specify the gradient of for example U in the standard Coordinate-System(x,y,z) on a patch

http://foam.sourceforge.net/docs/cpp/a00671.html#details

This boundary condition supplies a fixed gradient condition, such that the patch values are calculated using:


where
= patch values
= internal field values
= gradient (user-specified)
= inverse distance from patch face centre to cell centre

Hence, x_p is independent from the normal patch face vector?

Thanks for the answer in advance,

Andy