[Werne]

Hello,

I'm looking for a way to calculate the local residuals of the velocity-field. I know that there is a utility (namely simpleFoamResiduals) to do this for a simpleFoam setup, however it doesn't work with a rhoSimpleFoam case.
Is there a way to calculate the residual field of a rhoSimpleFoam simulation in a way that allows me to view it in Paraview?

I'm glad for any help.

[PanPeter]

Hi Werne,

There's no residual field. What you probably want is to plot the residual of some field. For the rhoSimpleFoam solver you can plot the residuals for p and U simply by executing the residuals function object: Add this to your controlDict file:

functions
{
	#includeFunc  residuals
}

You'll then need to copy the residuals dictionary from

 $WM_PROJECT_DIR/etc/caseDicts/postProcessing/numerical/residuals

to your system folder. The residuals for your case are then monitored and written to your postProcessing folder. You can then monitor the development of the residuals through:

foamMonitor -l postProcessing/residuals/0/residuals.dat

There's more options to it, so here's the documentation to the above said:

https://cfd.direct/openfoam/user-guide/graphs-monitoring/

What I would really like to know in that regard is why it is not possible to use the residuals function object for monitoring the rho field. Any ideas?

cheers,
Fynn

[enginpower]

Hello,
me too I'm using rhoSimpleFoam in this case " solver for supersonic flow butane close to condensation" and I'd like to plot residuals. I do that, but I have the problem that U, Ux, Uv, etc.. are not plotted. Is the above description useful to solve this issue? Or is it independent?

Thanks

[PanPeter]

Hi enginpower,

First, note that I corrected an error in my post above. Does that already fix your problem?

If not:

I have the problem that U, Ux, Uv, etc.. are not plotted

Does that mean that you get an empty gnuPlot window and the residuals are simply not plotted? Then I would test the above procedure on the squareBend example case for rhoSimpleFoam. If that is plotting your residuals you have a working example that you can compare you case with.

Or is there not even an empty gnuPlot window appearing? Then foamMonitor should give you an error message.

cheers,
Fynn

[enginpower]

Hi,
thanks for reply

Actually, I'm using this script:

set logscale y
set title "Residuals"
set ylabel 'Residual'
set xlabel 'Iteration'
plot "< cat log.rhoSimpleFoam | grep 'Solving for Ux' | cut -d' ' -f9 | tr -d ','" title 'Ux' with lines,\
     "< cat log.rhoSimpleFoam | grep 'Solving for Uy' | cut -d' ' -f9 | tr -d ','" title 'Uy' with lines,\
     "< cat log.rhoSimpleFoam | grep 'Solving for Uz' | cut -d' ' -f9 | tr -d ','" title 'Uz' with lines,\
     "< cat log.rhoSimpleFoam | grep 'Solving for U' | cut -d' ' -f9 | tr -d ','" title 'U' with lines,\
     "< cat log.rhoSimpleFoam | grep 'Solving for omega' | cut -d' ' -f9 | tr -d ','" title 'omega' with lines,\
     "< cat log.rhoSimpleFoam | grep 'Solving for epsilon' | cut -d' ' -f9 | tr -d ','" title 'epsilon' with lines,\
     "< cat log.rhoSimpleFoam | grep 'Solving for k' | cut -d' ' -f9 | tr -d ','" title 'k' with lines,\
     "< cat log.rhoSimpleFoam | grep 'Solving for nut' | cut -d' ' -f9 | tr -d ','" title 'nut' with lines,\
     "< cat log.rhoSimpleFoam | grep 'Solving for T' | cut -d' ' -f9 | tr -d ','" title 'T' with lines,\
     "< cat log.rhoSimpleFoam | grep 'Solving for e' | cut -d' ' -f9 | tr -d ','" title 'e' with lines,\
     "< cat log.rhoSimpleFoam | grep 'Solving for rho' | cut -d' ' -f9 | tr -d ','" title 'rho' with lines,\
     "< cat log.rhoSimpleFoam | grep 'Solving for alphat' | cut -d' ' -f9 | tr -d ','" title 'alphat' with lines,\
     "< cat log.rhoSimpleFoam | grep 'Solving for p' | cut -d' ' -f9 | tr -d ','" title 'p' with lines
pause 1
reset
reread

It works for tutorial cases.

As I explained in this post, the problem is not plotting in general, but plotting some variables like Ux, Uy, etc...
As you can see in this image, the residuals of other variables are plotted, what is not plotted is the velocity residuals.
A concern to help to understand this is that Ux information is not in the log file. What I mean is this:

• part of the log file of the tutorial case is the following:

  Starting time loop
  
  Time = 1
  
  smoothSolver:  Solving for Ux, Initial residual = 1, Final residual = 0.0673067, No Iterations 4
  smoothSolver:  Solving for Uy, Initial residual = 1, Final residual = 0.0519002, No Iterations 4
  smoothSolver:  Solving for Uz, Initial residual = 1, Final residual = 0.0564047, No Iterations 4
  smoothSolver:  Solving for e, Initial residual = 0.00130693, Final residual = 1.34285e-05, No Iterations 2
  GAMG:  Solving for p, Initial residual = 1, Final residual = 0.0490362, No Iterations 8
  time step continuity errors : sum local = 6.68145, global = -1.46266, cumulative = -1.46266
  rho max/min : 1.20199 1.17693
  smoothSolver:  Solving for epsilon, Initial residual = 0.0857374, Final residual = 0.000364367, No Iterations 2

  and it has Ux value residual
• part of the log file of my case is the following:

  Starting time loop
  
  Time = 1
  
  smoothSolver:  Solving for e, Initial residual = 0.999872, Final residual = 0.0742461, No Iterations 1
  GAMG:  Solving for p, Initial residual = 1, Final residual = 0.000128453, No Iterations 1
  time step continuity errors : sum local = 1.08951, global = 0.335102, cumulative = 0.335102
  rho max/min : 51.2989 1.86835
  smoothSolver:  Solving for epsilon, Initial residual = 0.169512, Final residual = 0.00942059, No Iterations 2
  smoothSolver:  Solving for k, Initial residual = 1, Final residual = 0.0520951, No Iterations 2
  ExecutionTime = 40.51 s  ClockTime = 40 s
  
  Time = 2

  It has not any ux information. Why? I believe there is some problem with the setting, but I can't solve alone. I don't catch where is the problem.

I hope to solve very soon with your help.



Thanks to who wants to help me