Galura: Béda antarrépisi

Dina [[dinamika cairan]], '''galura''' (''turbulence'', ''turbulénsi'') téh hartina cara aliran nu cirina mangrupa parubahanparobahan sipat nu kacow sarta [[stokastik]], ngawengku difusi [[moméntum]] handap, [[konvéksi]] moméntum luhur, jeung variasi [[tekenan]] jeung [[kacepetan]] anu gancang dina rohangan jeung waktu. Aliran nu teu ngagalura disebutna [[aliran laminér]]. <!--The ([[dimensional analysis|dimensionless]]) [[Reynolds number]] characterizes whether flow conditions lead to laminar or turbulent flow; e.g. for pipe flow, a Reynolds number above about 2300 will be turbulent. The statistical description of turbulent flow was suggested by the [[Russia]]n mathematician [[Andrey Kolmogorov]]; this description is known to be approximate at best.

Consider the flow of water over a simple smooth object, such as a sphere. At very low speeds the flow is laminar, i.e., the flow is smooth (though it may involve vortices on a large scale). As the speed increases, at some point the transition is made to turbulent ("[[Chaos theory|chaotic]]") flow. In turbulent flow, unsteady vortices appear on many scales and interact with each other. [[Drag (physics)|Drag]] due to [[boundary layer]] skin friction increases. The structure and location of boundary layer separation often changes, sometimes resulting in a reduction of overall drag. Because laminar-turbulent transition is governed by Reynolds number, the same transition occurs if the size of the object is gradually increased, or the [[viscosity]] of the fluid is decreased, or if the [[density]] of the fluid is increased.

Turbulence causes the formation of eddies which are defined by the [[Kolmogorov]] length scale and a turbulent [[diffusion coefficient]]. In large bodies of water like oceans this coefficient can be found using [[Lewis Fry Richardson|Richardson]]'s four-third power law and is governed by the [[random walk]] principle. In rivers and large ocean currents, the diffusion coefficient is given by variations of Elder's formula.