Unstable flow
Unstable currents and other unstable processes (from the Latin unstable , without a firm stance) are movements whose course cannot be foreseen, or only with uncertainty. They are decisively influenced by external and internal disturbances - what they have in common with the umbrella term "unstable systems" .
Unstable flows are movements in fluids (liquids and gases) that are not "smooth" or orderly (technical term "laminar" ), but rather unordered. In contrast to laminar flow (such as in oil pipes or on the wings of aircraft), there is no one or two-dimensional movement, but the particles also have “random” and 3D movements.
Their course shows strong spatial or temporal changes and they are associated with mixing processes - especially with turbulence or stationary and unsteady eddies .
A measure of the instability of a flow is the so-called Reynolds number ( Re ), which goes back to Osborne Reynolds . In 1883, during experiments with colored water, he discovered that turbulence only formed in the glass tube at a certain speed. The Reynolds number depends on the flow velocity , the pipe diameter and the viscosity of the liquid. If the speed or the pipe cross-section is too great or the viscosity too small, then the flow becomes unstable with regard to small disturbances such as unevenness or lateral inflows.
In technology , medicine and many natural sciences , the investigation of such instabilities is an important research topic - for example for
- Blood circulation and other circuits ( circulation , also with applications of circular processes )
- Hydrology , water supply and disposal
- Cultural technology , white water and avalanche control
- Mechanical engineering and engine construction
- Meteorology and Oceanography
- Physical processes
- Shipping and removal of its obstacles, especially in docks