How to accurately measure the wall-clock time for a Fluent simulation?

This article will inform the reader on how to use the wall timer to record wall clock time.  When using the built-in timer (parallel->timer>usage) to compute the wall-clock time of a simulation, the output can be much lower than the actual elapsed time.  This article shows how to accurately measure the wall-clock time using the benchmark command. 

Discrepancies between the built-in timer in Ansys Fluent and the actual elapsed time could be due to several factors. The built-in timer, accessed via the command `/parallel/timer/usage`, only includes the solver time and does not account for time spent in collecting and reporting residuals, or in calculating and reporting monitors like force, surface, and volume. This could lead to a lower reported time compared to the actual elapsed time. To accurately measure the wall-clock time, one can use the `benchmark` command.  

For steady runs, one can use the following Text User Interface (TUI) command to print the elapsed time for, say, 200 iterations. 

(benchmark '(iterate 200)) 

For unsteady runs, use the following command to print the elapsed time for, say, 10 time steps with 20 iterations.  

(benchmark '(ti-menu-load-string "/solve/dual-time-iterate 10 20 ")) 

The result appears in the console as text.  The cpu-time and the elapsed-time are provided. 

In conclusion, the benchmark approach provides a more comprehensive measure of the wall-clock time.