How to set adaptive time step in Nek5000

In the Nek5000 documentation, variableDT in GENERAL keys in .par file is used to control whether the step size will be adjusted to match the targetCFL.

In Snek5000, you can enable this feature by setting params.nek.general.variable_dt to True.

For example, in the script below, we set variable_dt as True, which subsequently leads to an adaptive time step based on the target_cfl:

from snek5000_tgv.solver import Simul

params = Simul.create_default_params()
params.output.sub_directory = "examples_snek/tuto"

params.oper.nx = params.oper.ny = params.oper.nz = 8
params.oper.elem.order = params.oper.elem.order_out = 8
params.oper.nproc_min = 2

params.nek.velocity.residual_tol = 1e-07
params.nek.pressure.residual_tol = 1e-05

params.nek.general.write_control = "runTime"
params.nek.general.write_interval = 2.0

params.output.spatial_means.write_interval = 0.5

params.nek.general.end_time = 10
params.nek.general.dt = 1
params.nek.general.target_cfl = 1.4
params.nek.general.variable_dt = True
params.nek.general.extrapolation = "OIFS"

sim = Simul(params)
sim.make.exec("run_fg", nproc=2)