Unsteady solver¶
Commands of the unsteady_solver chapter of the database, 9 entries. The status words are defined once, on the compatibility matrix, which says what each rests on and what the script builder does with it. Read it before this page: broken and removed are refusals, so a row here can be telling you the emitter will not write that command for that version.
NEW_UNSTEADY_SOLVER_SURFACE_PROBE¶
Phase setup, layout inline. Manual: SRC-740 p.350.
Samples one surface property per solver time step at a fixed vertex, the surface counterpart of UNSTEADY_SOLVER_NEW_FLUID_PLOT. New in the 26.121 manual edition, and it is where the six boundary-layer parameters enter the unsteady vocabulary: displacement, momentum and total thickness, shape factor, skin friction and the transition marker. CSYS is 1-based, index 1 being the reference frame; the coordinates are inline here, unlike the fluid plot's preformatted VERTEX line.
| Argument | Specification |
|---|---|
name |
str |
parameter |
enum in |
csys |
int |
x |
float [length units of the named coordinate system] |
y |
float [length units of the named coordinate system] |
z |
float [length units of the named coordinate system] |
| Version | Status | Evidence |
|---|---|---|
| 26.121 | documented | SRC-740 p.350 |
| 26.122 | documented | SRC-750 p.352, same grammar as 26.121 |
| 26.123 | documented | SRC-751 p.352, unchanged from SRC-750 p.352 |
| 26.124 | documented | SRC-752 p.352, the SRC-751 file, carried from 26.123; not run on 26.124 |
SET_NEW_UNSTEADY_SOLVER_ACTION¶
Phase init, layout inline. Manual: SRC-750 p.353.
Registers an action the solver runs after each unsteady time step, either a FlightStream script or a shell command. First documented by the 26.122 edition. The path goes on the line after the command, which is what the printed sample shows. COMMAND_LINE RUNS A SHELL COMMAND FROM INSIDE THE SOLVER, once per time step. That is a capability worth naming rather than leaving for a reader to infer from the value list: an unsteady run of a thousand steps runs it a thousand times, and the emitter validates the grammar of the line and nothing about what the line does. NO EDITION SAYS WHAT THE ACTION RECEIVES, and the silence is recorded so the next reader does not open the same pages again. Four things a step-aware action would need were looked for: any arguments appended to the script or the shell command, the working directory the command is run from, whether the time-step index or the physical time is reachable from inside it, and any environment the solver sets. The scripting pages, SRC-750 p.353 and SRC-751 p.353, describe TYPE, NAME and FILENAME and stop. The user-interface pages, SRC-750 p.212 and SRC-751 p.212, are the only other place the feature is described at all; they say the actions run after each time step, that several may be registered, that they execute in creation order and that the order cannot be changed afterwards, and they say nothing about context either. The two editions are word for word identical on all four pages. The consequence is worth stating because it is what a caller hits: an action that has to behave differently on different steps cannot learn which step it is on from anything documented, so it needs state of its own, and the correctness of that route rests on the invocation count being exactly the step count, which is also unstated. Settling it needs one licensed unsteady run rather than another reading; the reading is reports/RPT-030_what-an-unsteady-action-receives_2026-08-19.md and it names the probe that would answer it. THAT RUN WAS MADE ON 26.123 ON 2026-09-08 (reports/RPT-041_script-action-reread-on-26123_2026-09-08.md), and it answers the five things, on that build alone. A SCRIPT action's file is re-read on every invocation, so a program run by an earlier COMMAND_LINE action may rewrite it between steps. The invocation count equals the time-step count exactly and nothing fires before the first step. The action receives no arguments and no solver-named environment variable, and runs from the directory the solver was started in, which is the simulation folder. The solver appends _iteration=
| Argument | Specification |
|---|---|
type |
enum in |
name |
str |
filename |
path |
| Version | Status | Evidence |
|---|---|---|
| 26.122 | documented | SRC-750 p.353, the first edition to document it |
| 26.123 | documented | SRC-751 p.353, unchanged from SRC-750 p.353. Run on 2026-09-08 as tests/tier3_licensed/matriz_actions.fs row 6001, eight time steps (reports/RPT-041_script-action-reread-on-26123_2026-09-08.md): SCRIPT action file re-read on every invocation: YES; eight invocations for eight steps, none before the first; no arguments, no solver-named environment, working directory the simulation folder; exports from an action script are stamped _iteration=N. |
| 26.124 | documented | SRC-752 p.353, the SRC-751 file, carried from 26.123; not run on 26.124 |
SET_UNSTEADY_VISCOUS_COUPLING_ITERATION¶
Phase init, layout inline. Manual: SRC-747 p.321.
Sets the unsteady time-stepping iteration at which the viscous coupling switches on, so the early steps run inviscid and the boundary-layer coupling starts once the wake has developed. Documented by the three pre-26.100 editions and by none after. Measured unrecognized on 26.124 (RPT-068, 2026-09-24); 26.123 carries no record. The setup key unsteady_viscous_coupling_iteration emits it on 25.100 and 26.000, the builds that document it and render an unsteady script, and is refused at plan on every other.
| Argument | Specification |
|---|---|
num_iteration |
int |
| Version | Status | Evidence |
|---|---|---|
| 25.000 | documented | SRC-749 p.309, this edition documents it |
| 25.100 | documented | SRC-748 p.322, this edition documents it |
| 26.000 | documented | SRC-747 p.321, this edition documents it |
| 26.100 | removed | SRC-741 pp.275-369, the whole scripting reference of the 26.100 edition, does not print this command. That is a fact about the document rather than a measurement of the solver, which is the weakest of the three ways a removal is recorded here; no probe has asked this build whether it still answers the name. |
| 26.101 | removed | SRC-725 pp.280-375, the whole scripting reference of the 26.101 edition, does not print this command. That is a fact about the document rather than a measurement of the solver, which is the weakest of the three ways a removal is recorded here; no probe has asked this build whether it still answers the name. |
| 26.120 | removed | SRC-003 pp.281-376, the whole scripting reference of the 26.120 edition, does not print this command. That is a fact about the document rather than a measurement of the solver, which is the weakest of the three ways a removal is recorded here; no probe has asked this build whether it still answers the name. |
| 26.121 | removed | SRC-740 pp.284-379, the whole scripting reference of the 26.121 edition, does not print this command. That is a fact about the document rather than a measurement of the solver, which is the weakest of the three ways a removal is recorded here; no probe has asked this build whether it still answers the name. |
| 26.124 | removed | reports/RPT-068_two-documented-setup-commands-are-unrecognized-on-26124_2026-09-24.md; Measured 2026-09-24: the 26.124 solver answers SET_UNSTEADY_VISCOUS_COUPLING_ITERATION 5 as an unrecognized command and the script stops at that line, the same answer and the same stopped script it gives a name no edition documents. Its edition does not print the command either |
SOLVER_TIME_AVERAGING¶
Phase init, layout inline. Manual: SRC-750 p.353.
Averages the surface flow properties over a window of unsteady time iterations, given as the first and last iteration to include. First documented by the 26.122 edition. UNVERIFIED: SRC-750 p.353 names each bound an unsteady time iteration without explicitly distinguishing time steps from inner iterations. The pproc conversion uses inclusive time steps; the C01 hang on 2026-09-19 prevented verification of the bounds. The export header iteration counter counts inner iterations and is not used to derive them. The window is in ITERATIONS and not in seconds, so it moves with the time-step size: halving the step doubles the iteration numbers that bound the same physical interval. No edition says what a DISABLE call does with the two bounds, and both are required here because the signature and the sample both carry all three.
| Argument | Specification |
|---|---|
mode |
enum in |
starting_iteration |
int |
ending_iteration |
int |
| Version | Status | Evidence |
|---|---|---|
| 26.122 | verified | reports/compat/CMP-26122_2026-09-25_time-averaging.yaml; SRC-750 p.353 documents the command. Measured 2026-09-25 on FlightStream 26.122 (build 8092026) by the licensed probe T21 (RPT-079): ENABLE 7 12, just before INITIALIZE_SOLVER on a 12-step unsteady point, ran and made the final surface the uniform mean of the run's per-step surfaces over TIME STEPS 7 to 12 inclusive, to 1e-13 in Cp, Vx and speed; the skin friction is not averaged (the last step's). Folded in by hand: the promotion cannot rewrite a block that carries a note. |
| 26.123 | removed | reports/compat/CMP-26123_2026-09-25_time-averaging.yaml; SRC-751 p.353 documents the command; MEASURED REMOVED 2026-09-25 on FlightStream 26.123 (build 8112026) by the licensed probe T21 (RPT-079): the line SOLVER_TIME_AVERAGING ENABLE 7 12 was refused as an unrecognized command and the script stopped there, while the same line, byte for byte, ran on 26.122. The edition documents a command the build does not carry. |
| 26.124 | broken | reports/compat/CMP-26124_2026-09-19_time-averaging.yaml; Measured 2026-09-19 on FlightStream 26.124: SOLVER_TIME_AVERAGING ENABLE hangs the solver both in INIT before INITIALIZE_SOLVER and [...] |
UNSTEADY_SOLVER_ANIMATION¶
Phase init, layout keyword_block. Manual: SRC-003 pp.347-348.
Writes an output file every so many time steps of an unsteady run, which is how an animation is produced. THE MODE SITS ON THE COMMAND LINE AND EVERYTHING ELSE IS A KEYWORD LINE, the second command in the database to need
on_command_lineafter WRAPPER_EDIT_LOCAL_CONTROL. Every keyword is optional because the manual prints TWO samples: the enabling one carries four keyword lines and the disabling one is a single line with none. VOLUME_SECTIONS TAKES TWO VALUES ON ONE LINE, a toggle and a format, which is why the format joins the previous line rather than taking its own keyword. The manual states the pair in one parameter row. FREQUENCY IS IN SOLVER TIME STEPS AND NOT IN SECONDS: 1 writes every step, 2 every second step. Combined with PARAVIEW_VTK on a long run this is the fastest way in the package to fill a disk, and no edition says so.
| Argument | Specification |
|---|---|
mode |
enum in |
folder |
path (optional) |
filetype |
enum in {SOLVER_BITMAP, PLOTS_BITMAP, TECPLOT_DATA, PARAVIEW_VTK} (optional) |
frequency |
int (optional) |
volume_sections |
enum in {ENABLE, DISABLE} (optional) |
volume_sections_format |
enum in {VTK, DAT, VTK2D} (optional) |
| Version | Status | Evidence |
|---|---|---|
| 25.000 | documented | SRC-749 p.309, same grammar as 26.120 |
| 25.100 | documented | SRC-748 p.321, same grammar as 26.120 |
| 26.000 | documented | SRC-747 p.320, same grammar as 26.120 |
| 26.100 | documented | SRC-741 pp.343-344, same grammar as 26.120 |
| 26.101 | documented | SRC-725 pp.346-347, same grammar as 26.120 |
| 26.120 | documented | SRC-003 pp.347-348 |
| 26.121 | documented | SRC-740 pp.351-352, same grammar as 26.120 |
| 26.123 | documented | SRC-751 p.353, unchanged from SRC-750 p.353 |
| 26.124 | documented | SRC-752 p.353, the SRC-751 file, carried from 26.123; not run on 26.124 |
UNSTEADY_SOLVER_DELETE_ALL_PLOTS¶
Phase setup, layout bare. Manual: SRC-003 p.347.
Removes every unsteady solver plot, force and fluid alike, in one call; there is no documented per-plot delete. Found missing from this chapter while diffing the 26.121 manual against the database (PFS-8): it is documented in the 26.12 manual too, so its absence was a gap in the original ingestion rather than a version change.
| Version | Status | Evidence |
|---|---|---|
| 25.000 | documented | SRC-749 p.308, same grammar as 26.120 |
| 25.100 | documented | SRC-748 p.321, same grammar as 26.120 |
| 26.000 | documented | SRC-747 p.320, same grammar as 26.120 |
| 26.100 | documented | SRC-741 p.343, same grammar as 26.120 |
| 26.101 | documented | SRC-725 p.346, same grammar as 26.120 |
| 26.120 | documented | SRC-003 p.347 |
| 26.121 | documented | SRC-740 p.351, same grammar as 26.120 |
| 26.123 | documented | SRC-751 p.353, unchanged from SRC-750 p.353 |
| 26.124 | documented | SRC-752 p.353, the SRC-751 file, carried from 26.123; not run on 26.124 |
UNSTEADY_SOLVER_EXPORT_PLOTS¶
Phase export, layout param_lines. Manual: SRC-003 p.347.
Exports every unsteady solver plot (force and fluid) with one column per plot and one row per time step.
| Argument | Specification |
|---|---|
filename |
path |
| Version | Status | Evidence |
|---|---|---|
| 25.000 | documented | SRC-749 p.308, same grammar as 26.120 |
| 25.100 | documented | SRC-748 p.321, same grammar as 26.120 |
| 26.000 | documented | SRC-747 p.320, same grammar as 26.120 |
| 26.100 | documented | SRC-741 p.343, same grammar as 26.120 |
| 26.101 | documented | SRC-725 p.346, same grammar as 26.120 |
| 26.120 | documented | SRC-003 p.347 |
| 26.121 | documented | SRC-740 p.350, same grammar as 26.120 |
| 26.123 | documented | SRC-751 p.352, unchanged from SRC-750 p.352 |
| 26.124 | verified | reports/compat/CMP-26124_2026-09-14_full-sim.yaml; SRC-752 p.352, the SRC-751 file, carried from 26.123 |
UNSTEADY_SOLVER_NEW_FLUID_PLOT¶
Phase setup, layout keyword_block. Manual: SRC-003 p.347.
Samples one fluid property per solver time step at a fixed vertex. VERTEX takes the three coordinates preformatted on one line (X, then Y, then Z). The manual documents FRAME as the system the plot's VALUES are computed in and says nothing about which frame the vertex is read in (SRC-003 p.347), so this entry does not say either; the 26.121 surface probe states it and this command does not. The typed triple validation lives in the caller, the same preformatted-token convention as the per-surface lines of INITIALIZE_SOLVER.
| Argument | Specification |
|---|---|
frame |
int |
parameter |
enum in |
name |
str |
vertex |
str |
| Version | Status | Evidence |
|---|---|---|
| 25.000 | documented | SRC-749 p.308, same grammar as 26.120 |
| 25.100 | documented | SRC-748 p.321, same grammar as 26.120 |
| 26.000 | documented | SRC-747 p.320, same grammar as 26.120 |
| 26.100 | documented | SRC-741 p.343, same grammar as 26.120 |
| 26.101 | documented | SRC-725 p.346, same grammar as 26.120 |
| 26.120 | documented | SRC-003 p.347 |
| 26.121 | documented | SRC-740 p.350 extends PARAMETER with the six boundary-layer values, so the 26.121 grammar differs from the 26.120 one in its enum alone; the args override below carries it. |
| 26.122 | documented | SRC-750 p.352 lists the six BL parameters as in SRC-740 p.350. |
| 26.123 | documented | SRC-751 p.352 lists the six BL parameters as in SRC-740 p.350. |
| 26.124 | verified | reports/compat/CMP-26124_2026-09-14_full-sim.yaml; SRC-752 p.352, the SRC-751 file, carried from 26.123. The six BL parameters are documented there; the report does not verify each parameter. |
UNSTEADY_SOLVER_NEW_FORCE_PLOT¶
Phase setup, layout keyword_block. Manual: SRC-003 p.347.
Samples one force or moment parameter per solver time step, in FRAME and UNITS, over the listed boundaries. BOUNDARIES -1 selects every boundary and takes no index line; a positive count is followed by the comma-separated boundary indices on the next line. Plots must exist before the solver runs to record its steps.
| Argument | Specification |
|---|---|
frame |
int |
units |
enum in |
parameter |
enum in |
name |
str |
boundaries |
int |
boundary_indices |
int_list (optional) |
| Version | Status | Evidence |
|---|---|---|
| 25.000 | documented | SRC-749 p.308, same grammar as 26.120 |
| 25.100 | documented | SRC-748 p.321, same grammar as 26.120 |
| 26.000 | documented | SRC-747 p.320, same grammar as 26.120 |
| 26.100 | documented | SRC-741 p.343, same grammar as 26.120 |
| 26.101 | documented | SRC-725 p.346, same grammar as 26.120 |
| 26.120 | documented | SRC-003 p.347 |
| 26.121 | documented | SRC-740 p.350, same grammar as 26.120 |
| 26.123 | documented | SRC-751 p.352, unchanged from SRC-750 p.352 |
| 26.124 | verified | reports/compat/CMP-26124_2026-09-14_full-sim.yaml; SRC-752 p.352, the SRC-751 file, carried from 26.123 |