How to calculate the gradient along the boundaries from a known volScalarFiled?
 

Hi,

I first obtained a volScalarField in a calculation domain, and then I want to calculate the gradient along the domain boundaries.

Does anyone know how to obtain the gradient along domain boundaries from a known volScalarField?

Thank you very much!

hi shddx1:
I have the same problem with you ! I define a volScalrField first and the value is fixed for all the cells, but I want to caculate the gradient. Do you solve the problem, can you tell me? Thank you!

You can obtain the surface normal gradient at each boundary using snGrad function.

p.boundaryField()[patchI].snGrad();

This will give you the surface normal gradient without any non-orthogonality or skewness corrections. If you need these corrections, use fvc::snGrad().

surfaceScalarField snGradP = fvc::snGrad(p);
Then access the value at the boundary with snGradP.boundaryField()[patchI].

If you are looking for a full gradient vector at the boundary, this is a little tricker. Here you will have to interpolate the field gradient (fvc::grad(p)) to the faces and then replace the surface normal component of this with the value coming from fvc::snGrad(p).

Hope this helps
Ivor