# Normal vector issue

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 October 21, 2013, 02:34 Normal vector issue #1 Member   Tayo Join Date: Aug 2012 Posts: 94 Rep Power: 6 Hello all, I have two quick questions. I want to implement heat conduction equation in my phaseChange solver. 1.) How to get a normal vector, n in OF? 2.) How to obtain area A, of the cell face? Here is what I've tried so far: Code: ```volVectorField gradT = fvc::grad(T); volVectorField n = T.mesh().Sf()/T.mesh().magSf(); ;) volScalarField A = T.mesh().magSf(); ;) volScalarField q = A*(gradT & n);``` I keep getting errors in the form of: "conversion from GeometricField, fvsPatchField, SurfaceMesh> to non-scalar type requested". I guess I'm not doing something right. Thank you for your help.

 October 21, 2013, 06:37 #2 Senior Member     Tobias Holzmann Join Date: Oct 2010 Location: Leoben (Austria) Posts: 1,622 Blog Entries: 6 Rep Power: 28 not correct post

October 21, 2013, 13:11
#3
Member

Tayo
Join Date: Aug 2012
Posts: 94
Rep Power: 6
Quote:
 Originally Posted by Tobi not correct post
Hi Tobi,

I don't understand what you mean; the gradient of a scalar field is a vector field, so grad(T) will give me a volVectorField. The code is actually works up to that point so I dont have a problem with gradT. Here is how I call my "T".

Code:
`const volScalarField& T = alpha1_.db().lookupObject<volScalarField>("T");`
My question is how do I compute the normal vector and facearea of the cell. Thanks

 October 21, 2013, 15:16 #4 Member   Tayo Join Date: Aug 2012 Posts: 94 Rep Power: 6 Never mind, problem fixed . I simply used the wrong syntax in defining the normal and face area. Here's the correction. Thanks Code: ```volVectorField gradT = fvc::grad(T); vectorField n = T.mesh().Sf()/T.mesh().magSf(); scalarField A = T.mesh().magSf(); scalarField q = A*(gradT & n);```

 October 22, 2013, 04:20 #5 Senior Member     Tobias Holzmann Join Date: Oct 2010 Location: Leoben (Austria) Posts: 1,622 Blog Entries: 6 Rep Power: 28 Hi, as I wrote later - I made a mistake because I had mixed up some Information. The Gradient of a scalar is a vector field with it s gradients of the components in x, y, z. So I was wrong in my first post. And your error was the following signs: Code: `;)` Regards Tobi

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