[sr71blackbird]

Hi Everyone,

At present I am trying to simulate the case of flow past a square cylinder at Re=10 using simpleFoam (v20.12). As I am trying to run a steady laminar flow case, I have changed the simulationType from default RAS to "laminar" in the constant/turbulenceProperties file and all other input data are left untouched.

However, when I look at the drag coefficients value after running it for t_end=100000, it seems like the code has diverged as I get Cd value of the order 1.0e+9. I am sure grid & timestep doesn't have any issues at all. I would truly appreciate any kind of suggestions by the community.

Regards,
Smruti

[dlahaye]

Looking into residual norm using e.g. foamLog ?

[sr71blackbird]

Thanks for your reply.

I could open the log file where I am saving all the output residuals, but if I could print those residuals (of Ux, Uy and p) vs the iteration counter then that would be great. Any ideas or suggestions?

I would also like to know why did you suggest to look into residual norms?

Thanks,
Smruti

[dlahaye]

Residual norms are likely more informative than drag coefficient.

Plotting the residual norm of various fields vs. iteration number

* write residual norms of the various fields to file instead of to screen. Do so using so-called unix pipe command, e.g., simpleFoam >& log.simpleFoam or use the runApplication utility instead (typically inside of Allrun);
* use foamLog utility to generate the the logs-directory in the case directory; foamLog runs a bunch of scripting commands to read data from the log-file and reorders the information in separate files;
* use gnuplot to load and plot the data in the logs-directory: in separate terminal run ./myplot. See sample myplot file below

Sample myplot file to plot residual norm vs. iteration number

#!/bin/bash

# Requires running foamLog <log-file> first!!

gnuplot -persist >/dev/null 2>&2 << EOF
set logscale y
plot "logs/UxFinalRes_0" with lines, \
"logs/UyFinalRes_0" with lines, \
"logs/UzFinalRes_0" with lines, \
"logs/pFinalRes_0" with lines, \
"logs/kFinalRes_0" with lines, \
"logs/epsilonFinalRes_0" with lines