laminær

Laminær, or laminar, describe a regime of fluid flow in which the motion is smooth and orderly, with adjacent layers of fluid sliding past one another without significant mixing. The flow lines are generally parallel and stable, in contrast to turbulent flow, where eddies and fluctuations dominate. Laminar flow is common at low Reynolds numbers or in very smooth channels and can be sustained by maintaining moderate speeds, smooth surfaces, and minimal obstructions.

A central concept in laminar flow is the Reynolds number, Re = ρvL/μ, a dimensionless quantity that compares inertial to viscous forces. At low Re, viscous forces dominate and the flow tends to be laminar. In pipes, flow is typically laminar for Re below about 2000, though the exact transition varies with geometry and surface roughness. At very low Re (creeping flow, Re much less than 1), the motion is entirely viscous and predictable.

In a circular pipe under laminar conditions, the velocity profile is parabolic (Poiseuille flow), with the maximum velocity at the center and zero at the walls. In other geometries, the velocity distribution still changes smoothly across the cross-section, without the chaotic swirls characteristic of turbulence.

Applications and implications include microfluidics and precision coating, where smooth, predictable flow enables controlled operations; lubrication films that rely on stable, layered flow to reduce wear; and clean-air practices such as laminar-flow cabinets in clinical and laboratory settings, which aim to protect sterile environments by delivering a uniform, directed air stream.

Etymology derives from Latin lamina, meaning layer, reflecting the layered nature of the flow. See also laminar flow, turbulent flow, Reynolds number, Poiseuille’s law.