Laminar
and turbulent flow over an airfoil.
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Laminar
Flow
The term laminar flow describes one of the three types of behavior
that a boundary layer can exhibit. (The other two are transitional
and turbulent.) In laminar flow, fluid particles travel along well-ordered
non-intersecting paths.
When a fluid (such as air) moves (or flows) past a solid surface,
such as an airplane wing, a thin layer develops adjacent to the
surface where frictional forces tend to retard the motion of the
fluid. This layer is defined as the boundary layer. The boundary
layer generally exists in one of three states and behaves in a corresponding
fashion: (1) laminar, where fluid particles travel along well-ordered
non-intersecting paths, or layers; (2) transitional, where disturbances
become amplified causing smooth "layered" flow to become
disrupted with some mixing of particles between layers; and (3)
turbulent, where fluid particles from adjacent layers become totally
mixed.
In general, the most desirable state is one with a high degree
of laminar flow, i.e., exhibits a low degree of friction drag. In
particular, a high degree of laminar flow reduces the amount of
fuel consumed by an aircraft and also increases its flight range.
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