Time Stepping

The first three inputs below do not take a prefix. Note that the first two are both specified, both criteria are used and the simulation still stop when the first criterion is hit. In the case of unsteady flow, the simulation will stop when either the number of steps reaches max_step or time reaches stop_time. In the case of steady flow, the simulation will stop when either the tolerance (difference between subsequent steps) is reached or the number of iterations reaches the maximum number specified.

	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?	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	Real	0.5
dt_change_max	maximum percentage dt can increase	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 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 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.