In
fluid mechanics
Fluid mechanics is the branch of physics concerned with the mechanics of fluids (liquids, gases, and plasmas) and the forces on them.
It has applications in a wide range of disciplines, including mechanical, aerospace, civil, chemical and ...
, external flow is a flow that
boundary layer
In physics and fluid mechanics, a boundary layer is the thin layer of fluid in the immediate vicinity of a bounding surface formed by the fluid flowing along the surface. The fluid's interaction with the wall induces a no-slip boundary cond ...
s develop freely, without constraints imposed by adjacent surfaces.
It can be defined as the flow of a fluid around a body that is completely submerged in it. Examples include fluid motion over a flat plate (inclined or parallel to the free stream velocity) and flow over curved surfaces such as a sphere, cylinder,
airfoil
An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of an object whose motion through a gas is capable of generating significant lift, such as a wing, a sail, or the blades of propeller, rotor, or tur ...
, or
, water flowing around submarines, and air flowing around a truck;
a 2000 paper analyzing the latter used
computational fluid dynamics
Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid flows. Computers are used to perform the calculations required to simulate t ...
to model the three-dimensional flow structure and pressure distribution on the external surface of the truck.
In a 2008 paper, external flow was said to be "arguably is the most common and best studied case in
soft matter systems.
The term can also be used simply to describe flow in any body of fluid external to the system under consideration.
In external co-flow, fluid in the external region occurs in the same direction as flow within the system of interest; this contrasts with external counterflow.
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Aerodynamics
Flow regimes
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