Understanding output files

Restart files

In order to restart a simulation, STREAmS needs at least two files, rst.bin and field_info.dat.

The file rst.bin contains the flow field in terms of conserved variables. For a single-species, ideal gas, these are \(\rho\), \(\rho\,u\), \(\rho\,v\), \(\rho\,w\), and \(\rho\,E\), where \(\rho\) is the density, \(u,v,w\) are the streamwise, wall-normal and spanwise velocity components, and \(E\) is the total energy.

The file field_info.dat contains the following information needed for restart:

• current step number

• current time

• running index for runtime averaging

• time interval from when last restart file was written

• time interval from when last statistics file was written

• time interval from when last slices where written

• number of flow samples that have been stored in VTK or Plot3D format

The frequency with which rst.bin and field_info.dat are written is controlled by the input parameter dtsave_restart. At each restart, after reading the two files, STREAmS automatically renames them into rst.bak and field_info.bak.

Flow fields

Flow fields can be stored in standard VTK and/or Plot3D formats. Plot3D files are made of the mesh, stored in plot3dgrid.xyz, and the flow fields, stored in files flow_nnnn.q. VTK files are stored in flow_nnnn.vtr, which contains both the mesh and the solution. nnnn is the file number. Both Plot3d and VTK files contain the same primitive variables, namely \(\rho\), \(u\), \(v\), \(w\) and \(T\).

Solutions in VTK format are printed only if the input flag enable_vtk=1, whereas Plot3D files are printed only if enable_plot3d=1. The frequency with which these solutions are stored is controlled by the variable dtsave in the input file.

Mean flow statistics

Flow statistics are collected at runtime and stored in stat.bin and stat3d.bin.

The file stat.bin contains statistics averaged in time and in the spanwise direction, for a total of 68 variables:

Mean flow statistics

\(\overline{\rho}\quad\quad\)	\(\overline{\nu}\quad\quad\)	\(\overline{p u}\quad\quad\)	\(\overline{pu_x}\)
\(\overline{u}\quad\quad\)	\(\overline{\omega_x^2}\quad\quad\)	\(\overline{p v}\quad\quad\)	\(\overline{pv_y}\)
\(\overline{v}\quad\quad\)	\(\overline{\omega_y^2}\quad\quad\)	\(\overline{\sigma_{11}}\quad\quad\)	\(\overline{pw_z}\)
\(\overline{w}\quad\quad\)	\(\overline{\omega_z^2}\quad\quad\)	\(\overline{\sigma_{12}}\quad\quad\)	\(\overline{u_y+v_x}\)
\(\overline{p}\quad\quad\)	\(\overline{\rho T}\quad\quad\)	\(\overline{\sigma_{13}}\quad\quad\)	\(\overline{(\boldsymbol\nabla\cdot\mathbf{U})^2}\)
\(\overline{T}\quad\quad\)	\(\overline{\rho T^2}\quad\quad\)	\(\overline{\sigma_{22}}\quad\quad\)	\(\overline{\rho T^3}\)
\(\overline{\rho^2}\quad\quad\)	\(\overline{\rho^2}\quad\quad\)	\(\overline{\sigma_{23}}\quad\quad\)	\(\overline{\rho T^4}\)
\(\overline{u^2}\quad\quad\)	\(\overline{T_0}\quad\quad\)	\(\overline{\sigma_{33}}\quad\quad\)	\(\overline{\rho u^4}\)
\(\overline{v^2}\quad\quad\)	\(\overline{\rho T_0}\quad\quad\)	\(\overline{\sigma_{11}u}\quad\quad\)	\(\overline{C_p}\)
\(\overline{w^2}\quad\quad\)	\(\overline{\rho u T}\quad\quad\)	\(\overline{\sigma_{12}u}\quad\quad\)	\(\overline{\gamma}\)
\(\overline{p^2}\quad\quad\)	\(\overline{\rho v T}\quad\quad\)	\(\overline{\sigma_{21}v}\)
\(\overline{T^2}\quad\quad\)	\(\overline{\rho w T}\quad\quad\)	\(\overline{\sigma_{22}v}\)
\(\overline{\rho u}\quad\quad\)	\(\overline{M}\quad\quad\)	\(\overline{\sigma_{31}w}\)
\(\overline{\rho v}\quad\quad\)	\(\overline{M^2}\quad\quad\)	\(\overline{\sigma_{32}w}\)
\(\overline{\rho w}\quad\quad\)	\(\overline{\rho u^3}\quad\quad\)	\(\overline{\sigma_{11}v+\sigma_{21}u}\)
\(\overline{\rho u^2}\quad\quad\)	\(\overline{\rho v u^2}\quad\quad\)	\(\overline{\sigma_{12}v+\sigma_{22}u}\)
\(\overline{\rho v^2}\quad\quad\)	\(\overline{\rho u v^2}\quad\quad\)	\(\overline{\sigma_{11}u_x+\sigma_{12}u_y + \sigma_{13}u_z}\)
\(\overline{\rho w^2}\quad\quad\)	\(\overline{\rho v^3}\quad\quad\)	\(\overline{\sigma_{21}v_x+\sigma_{22}v_y + \sigma_{23}v_z}\)
\(\overline{\rho uv}\quad\quad\)	\(\overline{\rho u w^2}\quad\quad\)	\(\overline{\sigma_{31}w_x+\sigma_{32}w_y + \sigma_{33}w_z}\)
\(\overline{\mu}\quad\quad\)	\(\overline{\rho v w^2}\quad\quad\)	\(\overline{\sigma_{31}v_x+\sigma_{12}(u_x+v_y) + \sigma_{22}u_y+\sigma_{13}v_z+\sigma_{23}u_z}\)

The symbol \(\overline{(\cdot)}\) indicates averaging in time and spanwise direction.

The file stat3d.bin contains 3D flow statistics averaged in time, for a total of 14 variables:

1. \(\langle\rho\rangle\quad\quad\)

2. \(\langle\rho u\rangle\quad\quad\)

3. \(\langle\rho v\rangle\quad\quad\)

4. \(\langle\rho w\rangle\quad\quad\)

5. \(\langle p\rangle\quad\quad\)

6. \(\langle\rho^2\rangle\quad\quad\)

7. \(\langle\rho u^2\rangle\quad\quad\)

8. \(\langle\rho v^2\rangle\quad\quad\)

9. \(\langle\rho w^2\rangle\quad\quad\)

10. \(\langle\rho u v\rangle\quad\quad\)

11. \(\langle\rho u w\rangle\quad\quad\)

12. \(\langle\rho v w\rangle\quad\quad\)

13. \(\langle\rho T^2\rangle\quad\quad\)

14. \(\langle p^2\rangle\quad\quad\)

The output frequency of the statistics files is controlled by the input parameter dtsave_restart. If restart_type=2, stat.bin and stat3d.bin are read and renamed as stat.bak and stat3d.bak.

progress.out

The file progress.out is written and updated at runtime and contains different quantities depending on the initial flow condition.

For channel flow cases, it contains the following quantities:

• step number

• time step

• time

• residual of :math: rho u

• pressure gradient :math:Pi

• bulk density

• bulk velocity

• bulk temperature

For boundary layer and shock wave/boundary layer interaction flow cases, it contains the following quantities:

• step number

• time step

• time

• residual of \(\rho u\)

The same variables printed in progress.out are also printed on screen while the solver is running.