# momentum coefficients in collocated grid SIMPLE

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January 12, 2022, 21:44
momentum coefficients in collocated grid SIMPLE
#1
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Gao Shangya
Join Date: Oct 2021
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Hello everyone,
I am simulating lid driven cavity in Matlab using collocated grid SIMPLE. Now I have a code that runs well. But I am a little confused about the momentum coefficients in this code. As you can see in the pic, top wall gives A_n(i,j) = 2*D_n+max(0.0,-F_n), why the D_n mulipy by 2?
If I add v-velocity on the top,should I change the coefficients?

Could anyone help me ?
Many thanks
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February 4, 2022, 05:05
#2
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Join Date: Jan 2022
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Quote:
 Originally Posted by Harlotte Hello everyone, I am simulating lid driven cavity in Matlab using collocated grid SIMPLE. Now I have a code that runs well. But I am a little confused about the momentum coefficients in this code. As you can see in the pic, top wall gives A_n(i,j) = 2*D_n+max(0.0,-F_n), why the D_n mulipy by 2? If I add v-velocity on the top,should I change the coefficients? Could anyone help me ? Many thanks
I am guessing this is because the distance is half at the wall. Inside the domain, to calculate the D we consider the difference between two cell center. At boundaries, in this code, I think D is calculated between the cell center and the face value. this makes the distance half.

 Tags cfd, collocated grid, matlab, simple