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recirculating flow and the flow through the central region of the duct is called the dividing streamline. The point where the dividing streamline attaches to the wall again is called the reattachment point. As the flow goes farther downstream it eventually achieves an equilibrium state and has no reverse flow.
655:
Boundary layer separation can occur for internal flows. It can result from such causes such as a rapidly expanding duct of pipe. Separation occurs due to an adverse pressure gradient encountered as the flow expands, causing an extended region of separated flow. The part of the flow that separates the
116:
differential between the front and rear surfaces of the object. It causes buffeting of aircraft structures and control surfaces. In internal passages separation causes stalling and vibrations in machinery blading and increased losses (lower efficiency) in inlets and compressors. Much effort and
276:
638:
distribution, the separation resistance of a turbulent boundary layer increases slightly with increasing
Reynolds number. In contrast, the separation resistance of a laminar boundary layer is independent of Reynolds number — a somewhat counterintuitive fact.
687:. Vortices shed from the bluff downstream surface of a structure at a frequency depending on the speed of the flow. Vortex shedding produces an alternating force which can lead to vibrations in the structure. If the shedding frequency coincides with a
691:
of the structure, it can cause structural failure. These vibrations could be established and reflected at different frequencies based on their origin in adjacent solid or fluid bodies and could either damp or amplify the resonance.
539:
163:
125:
surface contours and added features which delay flow separation and keep the flow attached for as long as possible. Examples include the fur on a tennis ball, dimples on a golf ball,
85:
Separation occurs in flow that is slowing down, with pressure increasing, after passing the thickest part of a streamline body or passing through a widening passage, for example.
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96:
that the speed of the boundary layer relative to the surface has stopped and reversed direction. The flow becomes detached from the surface, and instead takes the forms of
793:
345:
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When the boundary layer separates, its remnants form a shear layer and the presence of a separated flow region between the shear layer and surface modifies the outside
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70:
present in the layer of fluid close to the surface. The flow can be externally, around a body, or internally, in an enclosed passage. Boundary layers can be either
305:
385:
365:
676:
and loss of lift, all of which are undesirable. For internal flows, flow separation produces an increase in the flow losses, and stall-type phenomena such as
104:. The fluid exerts a constant pressure on the surface once it has separated instead of a continually increasing pressure if still attached. In
145:
Graphical representation of the velocity profile in the boundary layer. The last profile represents reverse flow which shows separated flow.
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395:
The tendency of a boundary layer to separate primarily depends on the distribution of the adverse or negative edge velocity gradient
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461:
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flow, the former being able to tolerate nearly an order of magnitude stronger flow deceleration. A secondary influence is the
833:
Fielding, Suzanne. "Laminar
Boundary Layer Separation." 27 October 2005. The University of Manchester. 12 March 2008 <
271:{\displaystyle u{\partial u \over \partial s}=-{1 \over \rho }{dp \over ds}+{\nu }{\partial ^{2}u \over \partial y^{2}}}
451:
along the surface, which in turn is directly related to the pressure and its gradient by the differential form of the
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858:
78:. A reasonable assessment of whether the boundary layer will be laminar or turbulent can be made by calculating the
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and pressure field. In the case of airfoils, the pressure field modification results in an increase in
398:
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Wilcox, David C. Basic Fluid
Mechanics. 3rd ed. Mill Valley: DCW Industries, Inc., 2007. 664-668.
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Marie Curie
Network on Advances in Numerical and Analytical Tools for Detached Flow Prediction
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157:. The streamwise momentum equation inside the boundary layer is approximately stated as
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Another effect of boundary layer separation is regular shedding vortices, known as a
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Aerodynamics in Sports
Equipment, Recreation and Machines – Golf – Instructor
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are streamwise and normal coordinates. An adverse pressure gradient is when
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and possibly go to zero if the adverse pressure gradient is strong enough.
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https://www.aps.org/units/dfd/resources/upload/prandtl_vol58no12p42_48.pdf
455:, which is the same as the momentum equation for the outer inviscid flow.
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Fundamentals of
Aerodynamics 5th edition, John D. Anderson, Jr. 2011,
92:. The boundary layer separates when it has travelled far enough in an
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https://community.dur.ac.uk/suzanne.fielding/teaching/BLT/sec4c.pdf
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on a glider, which induce an early transition to turbulent flow;
88:
Flowing against an increasing pressure is known as flowing in an
101:
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is the detachment of a boundary layer from a surface into a
902:
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White (2010), "Fluid
Mechanics", Section 7.1 (7th edition)
534:{\displaystyle \rho u_{o}{du_{o} \over ds}=-{dp \over ds}}
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Detachment of a boundary layer from a surface into a wake
108:, flow separation results in reduced lift and increased
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exists whenever there is relative movement between a
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651:A schematic of internal boundary layer separation
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800:, from School of Engineering and Electronics,
347:, which then can be seen to cause the velocity
19:For the repainted ship by Tauba Auerbach, see
585:required for separation are much greater for
672:, and if severe enough will also result in
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153:imposed on the boundary layer by the outer
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149:The flow reversal is primarily caused by
32:Airflow separating from a wing at a high
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117:research has gone into the design of
871:, Pitman Publishing Limited, London
660:Effects of boundary layer separation
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444:{\displaystyle du_{o}/ds(s)<0}
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544:But the general magnitudes of
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82:of the local flow conditions.
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893:-Golf Ball Dimples & Drag
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791:Separation of Boundary Layers
747:, Section 4.20 (5th edition)
722:
7:
695:
10:
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849:Anderson, John D. (2004),
743:Anderson, John D. (2004),
340:{\displaystyle dp/ds>0}
18:
631:{\displaystyle du_{o}/ds}
578:{\displaystyle du_{o}/ds}
151:adverse pressure gradient
137:Adverse pressure gradient
94:adverse pressure gradient
90:adverse pressure gradient
66:and a solid surface with
49:boundary layer separation
908:2 November 2018 at the
802:University of Edinburgh
851:Introduction to Flight
745:Introduction to Flight
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597:. For a given adverse
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391:Influencing parameters
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643:Internal separation
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367:to decrease along
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127:turbulators
119:aerodynamic
919:Categories
844:References
723:Footnotes
589:than for
587:turbulent
509:−
466:ρ
253:∂
239:∂
231:ν
202:ρ
194:−
182:∂
174:∂
76:turbulent
906:Archived
867:(1975),
794:Archived
696:See also
114:pressure
102:vortices
824:, Fig 3
759:(1975)
591:laminar
72:laminar
875:
857:
776:
281:where
98:eddies
837:>.
674:stall
64:fluid
873:ISBN
855:ISBN
774:ISBN
436:<
332:>
121:and
100:and
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