page_title: Laminar flow
section_title: Examples
hierarchical_section_title: Laminar flow / Examples
caption_attribution_description: English: Victoria Falls waterfall.Nederlands: Victoria Falls waterval.
context_page_description: In fluid dynamics, laminar flow is characterized by fluid particles following smooth paths in layers, with each layer moving smoothly past the adjacent layers with little or no mixing. At low velocities, the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards. There are no cross-currents perpendicular to the direction of flow, nor eddies or swirls of fluids. In laminar flow, the motion of the particles of the fluid is very orderly with particles close to a solid surface moving in straight lines parallel to that surface.
  Laminar flow is a flow regime characterized by high momentum diffusion and low momentum convection.
  When a fluid is flowing through a closed channel such as a pipe or between two flat plates, either of two types of flow may occur depending on the velocity and viscosity of the fluid: laminar flow or turbulent flow. Laminar flow occurs at lower velocities, below a threshold at which the flow becomes turbulent. The velocity is determined by a dimensionless parameter characterizing the flow called the Reynolds number, which also depends on the viscosity and density of the fluid and dimensions of the channel.
context_section_description: A common application of laminar flow is in the smooth flow of a viscous liquid through a tube or pipe. In that case, the velocity of flow varies from zero at the walls to a maximum along the cross-sectional centre of the vessel. The flow profile of laminar flow in a tube can be calculated by dividing the flow into thin cylindrical elements and applying the viscous force to them.
  Another example is the flow of air over an aircraft wing. The boundary layer is a very thin sheet of air lying over the surface of the wing (and all other surfaces of the aircraft). Because air has viscosity, this layer of air tends to adhere to the wing. As the wing moves forward through the air, the boundary layer at first flows smoothly over the streamlined shape of the airfoil. Here, the flow is laminar and the boundary layer is a laminar layer. Prandtl applied the concept of the laminar boundary layer to airfoils in 1904.
  An everyday example is the slow, smooth and optically transparent flow of shallow water over a smooth barrier.
  When water leaves a tap with little force, it first exhibits laminar flow, but as acceleration by the force of gravity immediately sets in, the Reynolds number of the flow increases with speed, and the laminar flow can transition to turbulent flow. Optical transparency is then reduced or lost entirely.
  In waterfalls a large scale version of examples 3 and 4 occurs, as now broad sheets of smoothly flowing water fall over a ridge or edge of the waterfall. Immediately the transition to turbulence sets in with speed due to acceleration (the Reynolds number crosses the threshold for turbulence) and foamy aerated water obscures the falling flow.
caption: Combination of laminar and turbulent flow at a waterfall. Laminar (exactly over the ridge) and turbulent flow (immediately downstream with white foam) of the Victoria Falls
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