Plume (fluid dynamics)

Several effects control the motion of the fluid, including momentum (inertia), diffusion and buoyancy (density differences).

"Buoyancy is defined as being positive" when, in the absence of other forces or initial motion, the entering fluid would tend to rise.

Situations where the density of the plume fluid is greater than its surroundings (i.e. in still conditions, its natural tendency would be to sink), but the flow has sufficient initial momentum to carry it some distance vertically, are described as being negatively buoyant.

[1] Usually, as a plume moves away from its source, it widens because of entrainment of the surrounding fluid at its edges.

When high accuracy is required, computational fluid dynamics (CFD) can be employed to simulate plumes, but the results can be sensitive to the turbulence model chosen.

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.

Spacecraft designers are sometimes concerned with impingement of attitude control system thruster plumes onto sensitive subsystems like solar arrays and star trackers, or with the impingement of rocket engine plumes onto moon or planetary surfaces where they can cause local damage or even mid-term disturbances to planetary atmospheres.

[3] Plumes are of considerable importance in the atmospheric dispersion modelling of air pollution.

A classic work on the subject of air pollution plumes is that by Gary Briggs.

Simple modelling will enable many properties of fully developed, turbulent plumes to be investigated.

[6] Many of the classic scaling arguments were developed in a combined analytic and laboratory study described in an influential paper by Bruce Morton, G.I.

[14] For calculating the expected concentration of a one dimensional instantaneous point source we consider a mass