Divergence of a scalarField in two forms

RaghavendraRohith · August 23, 2016, 08:17

Hi All,

I am a little enthusiastic to know about the difference between these convective terms

Code:

cp*fvm::(phi, T)

Code:

fvm::(phi, cp*T)

Using pen and paper the product seems to be equal

In the first case the divergence of a surfaceScalarField, phi and a volScalarField, T is a scalarField which is multiplied by a ScalarField cp resulting in a ScalarField.

In the second case the product of two scalarFields cp and T is a volScalarfield. The divergence of the volScalarField obtained through product and a surfaceScalarField phi is a ScalarField.

Can somebody tell me the strong difference between these two notations.

Thanking you in Advance,
Best Regards,
Rohith

Bloerb · August 23, 2016, 10:34

You should check that again

For a scalar s and a vector v:
div(s*v) = s*div(v)+v & grad(s)

Hence it is only equal if cp is a constant scalar.

August 23, 2016, 08:17	Divergence of a scalarField in two forms	#1
RaghavendraRohith Member Rohith Join Date: Oct 2012 Location: Germany Posts: 57 Rep Power: 13	Hi All, I am a little enthusiastic to know about the difference between these convective terms Code: cpfvm::(phi, T) Code: fvm::(phi, cpT) Using pen and paper the product seems to be equal In the first case the divergence of a surfaceScalarField, phi and a volScalarField, T is a scalarField which is multiplied by a ScalarField cp resulting in a ScalarField. In the second case the product of two scalarFields cp and T is a volScalarfield. The divergence of the volScalarField obtained through product and a surfaceScalarField phi is a ScalarField. Can somebody tell me the strong difference between these two notations. Thanking you in Advance, Best Regards, Rohith Last edited by RaghavendraRohith; August 23, 2016 at 10:45.

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August 23, 2016, 10:34		#2
Bloerb Senior Member Join Date: Sep 2013 Posts: 353 Rep Power: 20	You should check that again For a scalar s and a vector v: div(sv) = sdiv(v)+v & grad(s) Hence it is only equal if cp is a constant scalar.