Time Stepping

The first three inputs below do not take a prefix. Note that if the first two are both specified, both criteria are used and the simulation will stop when the first criterion is hit, i.e. when either the number of steps reaches max_step or time reaches stop_time.

	Description	Type	Default
max_step	Maximum number of time steps to take	Int	-1
stop_time	Maximum time to reach	Real	-1.0
steady_state	Is this a steady state problem? Not yet implemented: setting it to true aborts when the inputs are read	Bool	False

The inputs below must be preceded by “incflo.”

	Description	Type	Default
fixed_dt	Value of fixed dt if > 0	Real	-1.
cfl	CFL constraint (dt < cfl * dx / u) if fixed_dt not > 0; at most 0.5 for MOL and 1.0 for Godunov and BDS	Real	0.5
dt_change_max	Maximum factor by which dt can increase from one step to the next; must be between 1.0 and 1.1	Real	1.1
init_shrink	reduce the initial time step by this safety factor	Real	0.1

Setting the Time Step

• If you want to fix the dt, simply set incflo.fixed_dt = XXX and the fluid time step will always be that number.

• If you want to let the code determine the appropriate time step using the advective CFL condition, then set incflo.cfl = 0.7 for example, and (in the absence of forcing terms and of explicit diffusion, which further restrict it) the fluid time step will be computed to be dt = 0.7 * dx / max(vel).

• Note that the cfl defaults to 0.5 so it does not have to be set in the inputs file. If neither incflo.cfl nor incflo.fixed_dt is set, then default value of cfl will be used. If incflo.fixed_dt is set, then it will override the cfl option whether incflo.cfl is set or not.