These forced the droplets outwards by centrifugal force, so that they congregate at the edge. For rain to be precipitated, approximately one in every million droplets needs to acquire a diameter greater than 20 micrometers. It does so by colliding and joining with other droplets. However, there may be other factors that play a role in the precipitation of rain. In the scientists' simulation, it took three hours before the computer's rain was triggered.
Natural clouds work faster - they take only half an hour to start raining under similar conditions.