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Laminar flow is the smooth flow of fluids or gases. This contrasts with turbulent flow, where whorls, eddies, cross-currents, and other disruptions appear in the stream. The distinction between these two types of movement can be important, as they result in radically different behaviors of fluids and gases. Various tactics can be used to promote the development of a laminar flow pattern, or to create turbulence if this is desired.
An excellent example of laminar flow can be seen with jumbo jets. Air should ultimately flow smoothly around the airfoils, keeping the plane in flight. If the air over and under the wing was visible, passengers on the aircraft would be able to see layers of air sliding past each other at different speeds. When the air is turbulent, the plane rocks in the air, because it is no longer flying smoothly inside a laminar flow of air.
This phenomenon can also be seen with ventilation systems like laminar flow hoods in lab environments. Researchers need to be able to work around hazardous materials and use ventilation systems to pull them up into a hood for processing in an exhaust system. A smooth flow of air creates a steady, even current to pull materials up, off the bench, and into the hood. Turbulence can swirl particles around, which is not desirable, because they might be pushed out into the room.
Fluids can exhibit laminar flow just like air. In tubing and piping, a series of effectively concentric rings can be created. The ring in the middle moves very quickly, leading the flow of fluid in the pipe, while the fluid at the sides barely moves at all. This example of laminar flow can play a key role in pumping and control systems that use fluid in tubes for various functions. Protrusions inside the tube, such as a buildup of material, can create turbulence and disturb the smooth flow of fluid.
In systems design, engineers may need to think about whether they want laminar or turbulent flow, so they can design effectively and appropriately. This can have important implications for everything from creating skyscrapers to designing an efficient cooling fan for a house. Smooth, curved edges can facilitate the creation of layers, while jagged, rough edges can create a rough turbulent flow that swirls and may behave unpredictably. Researchers can use smoke in a wind tunnel to demonstrate how air flows over or through an object of interest and to model the movement of fluids.