When running a simulation, the Flacs simulator will produce several output files. These files contain the results of the computations. In this article, you learn about the different files and their content.

Overview of Flacs output file types

The following files may be created by Flacs when running a simulation with the job number 000000:

file name contents
tt000000 simulation log file, terminal output
rt000000.dat3 simulation log
r1000000.dat3 scalar-time output
r3000000.dat3 3D field output
rd000000.dat3 simulation dump
rx000000.dat3 temporary file

The following sections explain the type and content of these files.

Simulation log files (rt-file)

File name template: rt000000.dat3

Name: rt-file, log file


Flacs logs textual output about the simulation progress, warnings or errors to the rt-file. It is often useful to monitor this file during simulations.

Error messages are identified by three stars "***" at the beginning of the line. In the case of a simulation restart, Flacs overwrites the rt-file, so you should make a copy of the original before a load/rerun is performed. The information on the log file is also written to a connected terminal (standard output) during the simulation. On Linux, when using the run-script, this output is redirected to another file, the tt-file, which you can monitor in the shell with the command

> tail --f tt010100

Depending on the settings for your simulation, you may find additional log files with specific data, for example:

rt000000.CFL
CFL-numbers and time step log file
rt000000.FUEL
amount of fuel log file
rt000000.P
pressure log file

Scalar-time output file (r1-file)

File name template: r1000000.dat3

Name: r1-file, scalar-time output file


The r1-file contains the monitor point data, that is the values of the variables requested at each monitor point at the prescribed iteration interval. Typically monitor point data is written in every time step. The r1-file is written in binary format. It can be transformed to textual data with the help of the r1file tool. Mostly, r1-files are, however, used to create scalar-time plots in Flowvis.

In the case of a simulation restart the r1-file will by default be deleted (i.e. old results are lost). If you want to keep the old results at restart you must set KEEP_OUTPUT=.TRUE. using a job file. During a LOAD, an existing r1-file will be scanned up to the time recorded on the specified dump file before any new results are written. It is usually wise to make a copy of the original r1-file before a load/rerun is performed.

The r1-files generally require modest amounts of disk space. The number of bytes in one data record can be calculated from the following expression: RecordSize = 4 * (2 + SUM), where SUM is the total number of references made to monitor points and panels.

Field output file (r3-file)

File name template: r3000000.dat3

Name: r3-file, field output file


The r3-file contains the values of the parameters specified for 3D-output in in the cs-file in all grid cells. The r3-file is in binary format. You can convert it to textual data with the help of the r3file tool. But mostly, r3-files are used to create 3D plots in Flowvis.

The Flacs simulator writes data for each variable selected for field output to the r3-file whenever this is triggered by one of the following event types:

  • simulation start and stop,
  • passing certain fuel levels,
  • time values,
  • runtime-specified events.

Flacs issues a message on the log file(s) for each event that triggers output. If several events happen at the same time, this will generate just one instance of output.

In case of a simulation restart, Flacs by default overwrites the r3-file. If you want to keep the old results after a restart you must set KEEP_OUTPUT=.TRUE. using a job file. During a LOAD, Flacs scans an existing r3-file up to the time recorded in the specified dump file before new results are written. Take a copy of the original r3-file before continuing with a load/rerun.

r3-files often require large amounts of disk space. The number of bytes in one data record can be calculated from the following expression: RecordSize = 4 * (2 + NX * NY * NZ) * NVAR, where NVAR is the number of variables specified and NX, NY, NZ are the grid dimensions.

Simulation dump file (rd-file)

File name template: rd000000.n000, the index number in the file name extension identifies the dump.

Name: rd-file, dump file


A dump file is a snapshot of the simulation at a selected time defined in the runtime simulation control file (cc-file); it contains the information necessary to restart a simulation from a given time. Flacs can write several dump files during a simulation, numbering them with the extensions n000, n001 and so forth.

A typical use of the dump file is to start an explosion simulation using the resulting gas cloud from a dispersion simulation. It is possible to convert the dump file data to restart a simulation on a smaller grid by using the rdfile utility.

If you want to append new data to existing result files, do not change the output specification, the grid, or the geometry when using a dump file.

Creating and loading of dump files is explained in the article What are dump files?

Simulation save file

File name template: rx000000.n000

Name: rx-file, save file


The rx-files are temporary files generated by Flacs when you request certain output variables to be written that require time integrals, namely NP_IMP, NUDRAG_IMP, NVDRAG_IMP, NWDRAG_IMP, NDRAG_IMP, NRESID. The simulator deletes the rx-files when the simulation terminates normally. If the simulation does not finish correctly, these files will exist after program stop and you must delete them manually. Using rx-files allows Flacs to use less core memory than without these. On the other hand, accessing large files is slow compared to memory access. Therefore, you should avoid 3D output of the above variables.