PLUMES IN SPACE
article compile Henryk Szubinski
Wikipedia: data on plumes
In hydrodynamics, a plume is a column of one fluid or gas moving through another. Several effects control the motion of the fluid, including momentum, diffusion, and buoyancy (for density-driven flows). When momentum effects are more important than density differences and buoyancy effects, the plume is usually described as a jet. Plume is a term in the hydrodynamic movement of pollutants in water or air.
Usually, as a plume moves away from its source, it widens because of entrainment of the surrounding fluid at its edges. Plume shapes can be influenced by flow in the ambient fluid (for example, if local wind blowing in the same direction as the plume results in a co-flowing jet). This usually causes a plume which has initially been ‘buoyancy-dominated’ to become ‘momentum-dominated’ (this transition is usually predicted by a dimensionless number called the Richardson number).
A further phenomenon of importance is whether a plume has laminar flow or turbulent flow. Usually there is a transition from laminar to turbulent as the plume moves away from its source. This phenomenon can be clearly seen in the rising column of smoke from a cigarette. When high accuracy is required, computational fluid dynamics (CFD) can be employed to simulate plumes, but the results can be sensitve to the turbulence model chosen. CFD is often undertaken for rocket plumes, where condensed phase constituents can be present in addition to gaseous constituents. These types of simulations can become quite complex, including afterburning and thermal radiation, and (for example) ballistic missile launches are often detected by sensing hot rocket plumes. Similarly, spacecraft managers are sometimes concerned with impingement of attitude control system thruster plumes onto sensitive subsystems like solar arrays and star trackers.
Another phenomenon which can also be seen clearly in the flow of smoke from a cigarette is that the leading-edge of the flow, or the starting-plume, is quite often approximately in the shape of a ring-vortex
ABOUT THIS IMAGE:
This is a series of close-up views of the complex gas structures in a small portion of the Carina Nebula. The nebula is a cold cloud of predominantly hydrogen gas. It is laced with dust, which makes the cloud opaque. The cloud is being eroded by a gusher of ultraviolet light from young stars in the region. They sculpt a variety of fantasy shapes, many forming tadpole-like structures. In some frames, smaller pieces of nebulosity can be seen freely drifting, such as the 2.3-trillion-mile-long structure at upper right. The most striking feature is a 3.5-trillion-mile-long horizontal jet in the upper left frame. It is being blasted into space by a young star hidden in the tip of the pillar-like structure. A bowshock has formed near the tip of the jet.