Gradient at face center of a scalar volume field

praveen · June 28, 2011, 12:33

Hello

How do I get the gradient vector at the face centers, given a scalar volume field ?

santiagomarquezd · June 28, 2011, 12:49

Praveen, it's usually achieved by a linear interpolation of fvc::grad(field) at faces. The following is an example taken from:

src/transportModels/interfaceProperties/interfaceProperties.C

Code:

00113     // Cell gradient of alpha
00114     const volVectorField gradAlpha(fvc::grad(alpha1_));
00115 
00116     // Interpolated face-gradient of alpha
00117     surfaceVectorField gradAlphaf(fvc::interpolate(gradAlpha));

Regards.

praveen · June 29, 2011, 00:02

Thanks. So I guess there is no available scheme to directly obtain face gradients by applying a green-gauss or least-squares scheme centered at the face-center.

Bernhard · June 29, 2011, 02:20

What do you mean by directly? You set the discretization of grad(alpha) and interpolate(gradAlpha) in fvSchemes as you're used to.

praveen · June 29, 2011, 02:23

Without interpolation. Define a volume around the face center and apply green-gauss theorem. Or least squares method.

Bernhard · June 30, 2011, 08:00

If you're referring to a staggered kind of mesh, I don't think such a thing is possible in OpenFOAM

June 28, 2011, 12:33	Gradient at face center of a scalar volume field	#1
praveen Super Moderator Praveen. C Join Date: Mar 2009 Location: Bangalore Posts: 342 Blog Entries: 6 Rep Power: 18	Hello How do I get the gradient vector at the face centers, given a scalar volume field ?

June 28, 2011, 12:49		#2
santiagomarquezd Senior Member Santiago Marquez Damian Join Date: Aug 2009 Location: Santa Fe, Santa Fe, Argentina Posts: 452 Rep Power: 23	Praveen, it's usually achieved by a linear interpolation of fvc::grad(field) at faces. The following is an example taken from: src/transportModels/interfaceProperties/interfaceProperties.C Code: 00113 // Cell gradient of alpha 00114 const volVectorField gradAlpha(fvc::grad(alpha1_)); 00115 00116 // Interpolated face-gradient of alpha 00117 surfaceVectorField gradAlphaf(fvc::interpolate(gradAlpha)); Regards. __________________ Santiago MÁRQUEZ DAMIÁN, Ph.D. Research Scientist Research Center for Computational Methods (CIMEC) - CONICET/UNL Tel: 54-342-4511594 Int. 7032 Colectora Ruta Nac. 168 / Paraje El Pozo (3000) Santa Fe - Argentina. http://www.cimec.org.ar

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June 29, 2011, 00:02		#3
praveen Super Moderator Praveen. C Join Date: Mar 2009 Location: Bangalore Posts: 342 Blog Entries: 6 Rep Power: 18	Thanks. So I guess there is no available scheme to directly obtain face gradients by applying a green-gauss or least-squares scheme centered at the face-center.

June 29, 2011, 02:20		#4
Bernhard Senior Member Bernhard Join Date: Sep 2009 Location: Delft Posts: 790 Rep Power: 21	What do you mean by directly? You set the discretization of grad(alpha) and interpolate(gradAlpha) in fvSchemes as you're used to.

June 29, 2011, 02:23		#5
praveen Super Moderator Praveen. C Join Date: Mar 2009 Location: Bangalore Posts: 342 Blog Entries: 6 Rep Power: 18	Without interpolation. Define a volume around the face center and apply green-gauss theorem. Or least squares method.

June 30, 2011, 08:00		#6
Bernhard Senior Member Bernhard Join Date: Sep 2009 Location: Delft Posts: 790 Rep Power: 21	If you're referring to a staggered kind of mesh, I don't think such a thing is possible in OpenFOAM