The volume of the selected object(s) is filled with separate clouds which are animated to gradually move. The preset works by imprinting smoke in the simulator from a noise texture using a Volume Brush mode Source. The Brush Effect is pretty low, so the smoke would gradually appear over time. The noise texture is animated and it also offsets with time, so the cloud shapes would evolve over time and move. There is an additional Turbulence force added to the scene to break the smoke up, and also a Plain Force blowing against the direction of movement of the clouds. In order for the smoke not to fill up the entire simulator over time, Smoke Dissipation is enabled under the Dynamics rollout and it's a tug of war between this option and the Brush Effect of the Source during the simulation.
