In fluid mechanics, external flow is a flow that boundary layers develop freely, without constraints imposed by adjacent surfaces.[1][2] 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, or turbine blade, water flowing around submarines, and air flowing around a truck;[3] a 2000 paper analyzing the latter used computational fluid dynamics to model the three-dimensional flow structure and pressure distribution on the external surface of the truck.[3] In a 2008 paper, external flow was said to be "arguably is the most common and best studied case in soft matter systems.[4]
The term can also be used simply to describe flow in any body of fluid external to the system under consideration.[5][6]
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.[1]
References
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Jendoubi, S.; Strykowski, P. J. (September 1, 1994). "Absolute and convective instability of axisymmetric jets with external flow". Physics of Fluids. 6 (9): 3000–3009. Bibcode:1994PhFl....6.3000J. doi:10.1063/1.868126.
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Chiu, Y-H.; Etheridge, D. W. (April 1, 2007). "External flow effects on the discharge coefficients of two types of ventilation opening". Journal of Wind Engineering and Industrial Aerodynamics. 95 (4): 225–252. Bibcode:2007JWEIA..95..225C. doi:10.1016/j.jweia.2006.06.013.
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Chew, J. W.; Green, T.; Turner, A. B. (February 18, 2015). "Rim Sealing of Rotor-Stator Wheelspaces in the Presence of External Flow". Turbo Expo: Power for Land, Sea, and Air. American Society of Mechanical Engineers. doi:10.1115/94-GT-126. ISBN978-0-7918-7883-5. S2CID110218328.
