The time step adjustment now starts from the minimum of the deltaT
calculated from Courant condition (and other physical limits), and the
deltaT specified in the system/controlDict.
This means that a small deltaT setting in system/controlDict results in
a gradual increase up to the Courant number limited value. This can be
useful in maintaining stability at the start of a simulation.
This functionality is an accidental side-effect at best. It is being
reinstated as existing cases are reliant upon it. If additional control
of the time step in the initial stages of a simulation is needed, then
that should be achieved with a more explicit user control.
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