CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)
-   FLUENT (https://www.cfd-online.com/Forums/fluent/)

 Emma66 December 23, 2009 04:32

How to compute UDS fourth order gradient

Hi! Guys!
I computate fourth order derivative with UDS through Gauss's divergence theorem.

We can obtain second order derivative of Φ through integrating Laplacian of Φ at cell c0.
For computing fourth order derivative, the idea is that using Gauss's divergence theorem again and let the second order derivative to be the UDS.

i was confusing that seconder order gradient is a vector here, and not like the original Φ, which is a scalar.

how to solve this problem?

I directly use C_face_loop to present second order derivative first.
c_face_loop(c,t,n)
{

At = NV_MAG(A);
Aterm = At/C_VOLUME(c,t);

}

For computing fourth order derivative, I use magnitude of second order gradient to define a UDS.

The fourth gradient is then be,
c_face_loop(c,t,n)
{
At = NV_MAG(A);
Aterm = At/C_VOLUME(c,t);

}

I was wondering if this is correct to slove it.

Many thanks,

 Ronnfors April 27, 2010 05:44

Hi Emma,

I program a UDF and I need the second order gradient of temperature or any UDSI. I see that you caluculate it by: "integrating Laplacian of Φ at cell c0" The code is:

"c_face_loop(c,t,n)
{
At = NV_MAG(A);
Aterm = At/C_VOLUME(c,t);