Restart File

Saving files for restarts or adjoint runs

The restart files are used to restart the code from a previous solution and also to run the adjoint simulations, which require a flow solution as input. To save a restart file, the user needs to add the option RESTART to the keyword OUTPUT_FILES in the configuration file:

OUTPUT_FILES= RESTART

The SU2 binary restart format has the extension .dat, but it is also possible to write out restart files in a simple ASCII file format with extension .csv. Have a look at the Output section to learn how to change output file formats.

A restart file with the name given by the keyword RESTART_FILENAME is then saved at the end of the simulation, or after every number of iterations given by the keyword OUTPUT_WRT_FREQ. For instance,

RESTART_FILENAME= restart_flow
OUTPUT_WRT_FREQ= 100

will write the file restart_flow.dat every 100 iterations when the total number of iterations is larger than 100, or only once at the end of the simulation when the total number of iterations is smaller than 100. Note that the file extension (the suffix) is automatic and can be left out. If you would like to keep copies of previously saved restart files, this is possible by setting

WRT_RESTART_OVERWRITE= NO

Additional to the regular restart file, a restart file with the current iteration appended to the filename will then be written every OUTPUT_WRT_FREQ iterations. Note that this option is available only for steady simulations. In unsteady simulations, the number of timesteps is appended to the filename automatically.

Starting a simulation from a saved solution

When restarting the primal or starting an adjoint, the filename given by the keyword SOLUTION_FILENAME will be used. In order to restart the primal or start the run of an adjoint simulation, the user must therefore first change the name of the saved file, e.g. restart_flow.dat (or restart_flow.csv if ASCII format) to the filename solution_flow.dat (or solution_flow.csv) in the execution directory. It is important to note that the adjoint solver will create a different adjoint restart file for each objective function, e.g. restart_adj_cd.dat. To restart a simulation the RESTART_SOL flag should be set to YES in the configuration file.

RESTART_SOL= YES
SOLUTION_FILENAME= solution_flow

If performing an unsteady restart the RESTART_ITER needs to be set to the iteration number which you want to restart from. For instance if we want to restart at iteration 100 and run the unsteady solver with 2nd-order dual time stepping method, we will need to specify RESTART_ITER = 100 and have the restart files solution_flow_00098.dat and solution_flow_00099.dat.