the calculation of gradient

zakir hussain · March 26, 2012, 01:45

hello everybody
From 10.1.1.3 Control Volume Gradients of the CFX-Sover Theory Guide ,I know that:
$\nabla$ ( $\varphi$ )= $\frac{1}{V}$ * $\sum$ ( $\varphi$ $\Delta$ n) $_{ip}$

where $\Delta$ n is the outward surface vector at ip,V is the volume of the control volume.
We can use the utility name USER_GETVAR to obtain the gradient we interest.what I want to know is how it calculate the gradient.What kind of algorithm does it use?Is it as the formulation above?

I have a source term like this:
source=- $\frac{1}{V}$ $\sum$ ( $\varphi_{f}$ A $_{f}$ )

where $\varphi$ $_{f}$ is the value of the variable at the cell faces f, and A $_{f}$ is the face area vectors

How can I implement it with fortran or something else?

Thank you very much!

zakir

zakir hussain · April 1, 2012, 00:34

hello everyone
I hope I can get help from you.
I have a source term like this:
source=- $\frac{1}{V}$ $\sum$ ( $\varphi_{f}$ A $_{f}$ )

where $\varphi$ $_{f}$ is the value of the variable at the cell faces f, and A $_{f}$ is the face area vectors

How can I implement it with fortran or something else?

Thank you very much!

zakir

ghorrocks · April 1, 2012, 07:53

What is the sum over? All the faces of the conttrol volume?

What is the purpose of the source term? I cannot see its physical significance.

zakir hussain · April 2, 2012, 10:33

yes,the sum over represents all the faces of the control volume.Considering the conservation I should solve the divergence of phi what I use as an source term of poisson equation through Gauss's law ,like
$\nabla$ $\cdot$ $\varphi$ = $\frac{1}{V}$ $\sum$ ( $\varphi_{f}$ A $_{f}$ )

Thank you for your help!

zakir

March 26, 2012, 01:45	the calculation of gradient	#1
zakir hussain Member zakir Join Date: Nov 2011 Posts: 44 Rep Power: 15	hello everybody From 10.1.1.3 Control Volume Gradients of the CFX-Sover Theory Guide ,I know that: $\nabla$ ( $\varphi$ )= $\frac{1}{V}$ * $\sum$ ( $\varphi$ $\Delta$ n) $_{ip}$ where $\Delta$ n is the outward surface vector at ip,V is the volume of the control volume. We can use the utility name USER_GETVAR to obtain the gradient we interest.what I want to know is how it calculate the gradient.What kind of algorithm does it use?Is it as the formulation above? I have a source term like this: source=- $\frac{1}{V}$ $\sum$ ( $\varphi_{f}$ A $_{f}$ ) where $\varphi$ $_{f}$ is the value of the variable at the cell faces f, and A $_{f}$ is the face area vectors How can I implement it with fortran or something else? Thank you very much! zakir Last edited by zakir hussain; March 26, 2012 at 02:21.

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April 1, 2012, 00:34		#2
zakir hussain Member zakir Join Date: Nov 2011 Posts: 44 Rep Power: 15	hello everyone I hope I can get help from you. I have a source term like this: source=- $\frac{1}{V}$ $\sum$ ( $\varphi_{f}$ A $_{f}$ ) where $\varphi$ $_{f}$ is the value of the variable at the cell faces f, and A $_{f}$ is the face area vectors How can I implement it with fortran or something else? Thank you very much! zakir

April 1, 2012, 07:53		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	What is the sum over? All the faces of the conttrol volume? What is the purpose of the source term? I cannot see its physical significance.

April 2, 2012, 10:33		#4
zakir hussain Member zakir Join Date: Nov 2011 Posts: 44 Rep Power: 15	yes,the sum over represents all the faces of the control volume.Considering the conservation I should solve the divergence of phi what I use as an source term of poisson equation through Gauss's law ,like $\nabla$ $\cdot$ $\varphi$ = $\frac{1}{V}$ $\sum$ ( $\varphi_{f}$ A $_{f}$ ) Thank you for your help! zakir