time settings
Physical time layout (steady, global or dual timestepping)
Whether the run is time-accurate. 'steady' converges a single steady state in pseudo-time; 'unsteady' marches in physical time over total_time in steps of time_step.
| Value | What it does | When to use it |
|---|---|---|
| steady | Converges one steady state by marching in pseudo-time, with a local time step in each cell and no physical time derivative. | For flows that settle to a steady state. |
| unsteady | Marches the solution in physical time to | For flows that vary in time. Dual time stepping converges each physical step in pseudo-time, so |
How each physical time step is taken: global timestepping advances in physical time alone, dual time stepping converges a pseudo-time loop within every step.
| Value | What it does |
|---|---|
| global timestepping | Advances the solution in physical time only, using the same physical time step in every cell — there is no pseudo-time convergence loop. |
| dual time stepping | Advances the solution in physical time, with an inner pseudo-time convergence loop run at each physical time step to converge that step before advancing. |
Total physical simulation time
Physical time step size
Time integration order
| Value | What it does | When to use it |
|---|---|---|
| first | First-order backward difference (BDF1, implicit Euler) for the physical time derivative. | More dissipative in time than |
| second default | Second-order backward difference (BDF2) for the physical time derivative. Until two earlier time levels are held, the step is taken at first order. | The default, for time-accurate results. |
| 1 | The same as | |
| 2 | The same as |
Steady pseudo cycles run at real-time cycle 0 before time-accurate stepping begins; the same solve as a steady run of that length. A settling phase for an impulsive start. 0 (the default) runs none, so real-time cycle 0 is itself time-accurate and a supplied initial condition is marched from as given