Residual calculation

Bdew8556 · March 23, 2021, 07:24

Hi all,

Just wondering how CFX calculates it's residuals.
I know what a residual is but when we see the line in the solver are we looking at some sort of averaged value over the whole domain?

Opaque · March 23, 2021, 07:41

The linear solver shows 2 different residuals:

RMS = Root Mean Square of the vector residual

MAX = Maximum of | residual vector component |

Bdew8556 · March 23, 2021, 07:43

thanks Opaque,

How are those calculated? specifically whether it's at a certain point or over the whole domain?

Opaque · March 23, 2021, 09:03

The residual vector includes every vertex (control volume) in the mesh.

The summation for the RMS is over all the control volumes, and the maximum is computed among all the control volumes

aero_head · March 23, 2021, 09:58

It's a kind of secretive thing. I looked into the inner mechanics for about three full weeks so far, so I know a bit more about how it works. They don't make it easy to find info on this, that's for sure. Makes sense though, as it is a 'secret sauce'. So if you are serious about finding out, you will have to really look into it.

March 23, 2021, 07:24	Residual calculation	#1
Bdew8556 Senior Member Brett Join Date: May 2013 Posts: 217 Rep Power: 14	Hi all, Just wondering how CFX calculates it's residuals. I know what a residual is but when we see the line in the solver are we looking at some sort of averaged value over the whole domain?

March 23, 2021, 07:41		#2
Opaque Senior Member Join Date: Jun 2009 Posts: 1,880 Rep Power: 33	The linear solver shows 2 different residuals: RMS = Root Mean Square of the vector residual MAX = Maximum of \| residual vector component \| aero_head likes this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

March 23, 2021, 09:03		#4
Opaque Senior Member Join Date: Jun 2009 Posts: 1,880 Rep Power: 33	The residual vector includes every vertex (control volume) in the mesh. The summation for the RMS is over all the control volumes, and the maximum is computed among all the control volumes aero_head likes this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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March 23, 2021, 07:43		#3
Bdew8556 Senior Member Brett Join Date: May 2013 Posts: 217 Rep Power: 14	thanks Opaque, How are those calculated? specifically whether it's at a certain point or over the whole domain?

March 23, 2021, 09:58		#5
aero_head Senior Member Kira Join Date: Nov 2020 Location: Canada Posts: 435 Rep Power: 9	It's a kind of secretive thing. I looked into the inner mechanics for about three full weeks so far, so I know a bit more about how it works. They don't make it easy to find info on this, that's for sure. Makes sense though, as it is a 'secret sauce'. So if you are serious about finding out, you will have to really look into it.