Laminar

Laminar describes a flow regime or structure characterized by smooth, orderly motion with layers that slide past one another and little mixing between them. In fluid dynamics, laminar flow is the opposite of turbulent flow, which features chaotic fluctuations and eddies.

Laminar flow typically occurs at low Reynolds numbers, a dimensionless quantity that compares inertial and viscous forces. In pipes, the laminar regime is often observed when Reynolds number is below about 2,000, though the exact threshold depends on geometry and surface roughness. In microfluidic devices and very small channels, flows are almost always laminar. In biological contexts, blood flow is usually laminar in healthy vessels, while turbulence can arise near high flow rates, stenoses, or pathological conditions.

In fully developed laminar pipe flow, the velocity profile is parabolic: maximum speed at the center and zero at the wall due to the no-slip condition. Laminar flow yields predictable, low-mixing transport and relatively uniform heat and mass transfer across layers. It is generally easier to model than turbulent flow, though the associated friction losses can be higher per unit area at given throughput.

Applications include piping systems, chemical reactors, and microfluidic devices that require predictable transport. Cleanroom laminar flow hoods use filtered air to produce unidirectional flow and minimize contamination. In materials science, laminar also describes layered structures, such as laminar composites, where distinct layers contribute specific mechanical or thermal properties.