How about I write U by reconstruct(phi)?

sharonyue · September 3, 2013, 21:14

Hi Foamers!

Wonderful day!

lol, AFAWK, in the algorithm, we can get the U after solving possion equation via this equation: U = HbyA - rAU*fvc::grad(p);

In OpenFOAM, We all know that phi is divergence free indtead of U, Well, how about writing U by myU = fvc::reconstruct(phi)? Shouldn't it be more precise?

I made a test on cavity, there is a little difference but not much.

sharonyue · September 5, 2013, 05:21

Hello guys??

sharonyue · September 11, 2013, 04:49

Any ideas?

derkermit · September 17, 2013, 09:55

Shouldn't reconstruct just (linear) interpolate the face centered values of (in this case) phi to the cell centers?
Do you get the same dimensions for myU and U?

sharonyue · September 22, 2013, 21:30

Quote:

Originally Posted by derkermit

Shouldn't reconstruct just (linear) interpolate the face centered values of (in this case) phi to the cell centers?
Do you get the same dimensions for myU and U?

Yep, its the same. And it surely interpolate the phi to the cell centers. Just as OpenFOAM make sure phi is divergence free. So I think myU would be more precise than U. but as of the algorithm, U can be get by another equation. So I'm wondering which method would be more precise.

derkermit · September 23, 2013, 06:28

How can they both have the same dimensions?
As an example: reconstruct(T) would give me the linear interpolated cell centered temperature values from face centered values. That will not affect the units or am I wrong with this?
If not, why would you get the same dimensions for myU and U?

sharonyue · September 23, 2013, 20:41

Quote:

Originally Posted by derkermit

How can they both have the same dimensions?
As an example: reconstruct(T) would give me the linear interpolated cell centered temperature values from face centered values. That will not affect the units or am I wrong with this?
If not, why would you get the same dimensions for myU and U?

I dont know if you can do reconstruct(t), but you can do reconstruct(phi) then you would get U at the cell center. more details see here and welcome comments: http://www.cfd-online.com/Forums/ope...-two-same.html. so myU 's unit,which is get by reconstructing, would be the same with U.

Actually, I have to make a new file in time file. I just copy U and rename it by myU.

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September 5, 2013, 05:21		#2
sharonyue Senior Member Dongyue Li Join Date: Jun 2012 Location: Beijing, China Posts: 838 Rep Power: 17	Hello guys??

September 11, 2013, 04:49		#3
sharonyue Senior Member Dongyue Li Join Date: Jun 2012 Location: Beijing, China Posts: 838 Rep Power: 17	Any ideas?

September 17, 2013, 09:55		#4
derkermit Member A. Bernath Join Date: Jun 2011 Location: Karlsruhe, Germany Posts: 39 Rep Power: 14	Shouldn't reconstruct just (linear) interpolate the face centered values of (in this case) phi to the cell centers? Do you get the same dimensions for myU and U?

September 23, 2013, 06:28		#6
derkermit Member A. Bernath Join Date: Jun 2011 Location: Karlsruhe, Germany Posts: 39 Rep Power: 14	How can they both have the same dimensions? As an example: reconstruct(T) would give me the linear interpolated cell centered temperature values from face centered values. That will not affect the units or am I wrong with this? If not, why would you get the same dimensions for myU and U?