169:
Air in contact with a body will stick to the body's surface and that layer will tend to stick to the next layer of air and that in turn to further layers, hence the body is dragging some amount of air with it. The force required to drag an "attached" layer of air with the body is called skin friction drag. Skin friction drag imparts some momentum to a mass of air as it passes through it and that air applies a retarding force on the body. As with other components of parasitic drag, skin friction follows the
31:
168:
arises from the friction of the fluid against the "skin" of the object that is moving through it. Skin friction arises from the interaction between the fluid and the skin of the body, and is directly related to the wetted surface, the area of the surface of the body that is in contact with the fluid.
192:
from laminar to turbulent flow depends on the shape of the object. There are two ways to decrease friction drag: the first is to shape the moving body so that laminar flow is possible. The second method is to increase the length and decrease the cross-section of the moving object as much as
94:
of the object. The general size and shape of the body are the most important factors in form drag; bodies with a larger presented cross-section will have a higher drag than thinner bodies; sleek ("streamlined") objects have lower form drag. Form drag follows the
125:
and fuselage meet at the wing root, two airstreams merge into one. This mixing can cause eddy currents, turbulence, or restrict smooth airflow. Interference drag is greater when two surfaces meet at perpendicular angles, and can be minimised by the use of
247:
in the denominator for skin friction coefficient's relation, as its value is increased (in laminar range), total friction drag is reduced. While decrease in cross-sectional area decreases drag force on the body as the disturbance in air flow is less.
603:
514:
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around the object. The boundary layer at the front of the object is usually laminar and relatively thin, but becomes turbulent and thicker towards the rear. The position of the
797:
359:
276:
540:
245:
222:
197:, which is the length of the aircraft divided by its diameter at the widest point (L/D). It is mostly kept 6:1 for subsonic flows. Increase in length increases
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The first is called parasite because it in no way functions to aid flight, while the second, induced drag, is a result of an airfoil developing lift.
107:
697:
721:
837:
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Form drag is a type of pressure drag, a term which also includes lift-induced drag. Form drag is pressure drag due to separation.
551:
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99:, meaning that it increases with the square of the velocity, and thus becomes more important for high-speed aircraft.
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102:
Form drag depends on the longitudinal section of the body. A prudent choice of body profile is essential for a low
369:. For boundary layers without a pressure gradient in the x direction, it is related to the momentum thickness as
867:
622:
75:. Parasitic drag is named as such because it is not useful, whereas lift-induced drag is the result of an
30:
121:
Form drag includes interference drag, caused by the mixing of airflow streams. For example, where the
52:
that acts on any object when the object is moving through a fluid. Parasitic drag is a combination of
545:
For a laminar flow over a plate, the skin friction coefficient can be determined using the formula:
136:, also known as supersonic wave drag or compressibility drag, is a component of form drag caused by
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generating lift. Parasitic drag comprises all types of drag except lift-induced drag.
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64:. It affects all objects regardless of whether they are capable of generating
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692:(Eighth ed.). New York, NY: McGraw Hill Education. p. 242.
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91:
29:
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812:"Skin friction coefficient -- CFD-Wiki, the free CFD reference"
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Total drag on an aircraft is made up of parasitic drag and
798:"How Interference Drag Affects Your Plane's Performance"
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681:
679:
27:
Aerodynamic resistance against the motion of an object
598:{\displaystyle C_{f,lam}={\frac {1.328}{\sqrt {Re}}}}
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509:{\displaystyle C_{f,tur}={\frac {0.074}{Re^{0.2}}},}
324:{\displaystyle C_{f}\equiv {\frac {\tau _{w}}{q}},}
193:practicable. To do so, a designer can consider the
769:. FAA. p. Chapter 5, Aerodynamics of flight.
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838:"Drag coefficient (friction and pressure drag)"
784:"Interference Drag - SKYbrary Aviation Safety"
736:Influence of Attachment Line Flow on Form Drag
421:{\displaystyle C_{f}=2{\frac {d\theta }{dx}}.}
8:
763:Pilot's Handbook of Aeronautical Knowledge
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140:generated when an aircraft is moving at
662:(2nd ed.). New York: McGraw-Hill.
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716:, Sub-section 5.9. Pitman Publishing.
7:
733:Gowree, Erwin Ricky (20 May 2014).
37:for a lifting body in steady flight
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173:and rises with the square of the
435:empirical relation known as the
112:separation of the boundary layer
251:The skin friction coefficient,
688:Anderson, John D. Jr. (2016).
658:Anderson, John D. Jr. (1991).
54:
1:
660:Fundamentals of aerodynamics
365:, and q is the free-stream
180:Skin friction is caused by
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836:tec-science (2020-05-31).
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110:should be continuous, and
354:{\displaystyle \tau _{w}}
542:is the Reynolds number.
690:Introduction to flight
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90:arises because of the
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712:Clancy, L.J. (1975).
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271:{\displaystyle C_{f}}
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431:For comparison, the
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443:Theodore von Kármán
118:should be avoided.
114:with its attendant
816:www.cfd-online.com
628:Skin friction line
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535:{\displaystyle Re}
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437:One-seventh Power
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351:
321:
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240:{\displaystyle Re}
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217:{\displaystyle Re}
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166:Skin friction drag
161:Skin friction drag
155:Skin friction drag
61:skin friction drag
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699:978-0-07-802767-3
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363:wall shear stress
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73:lift-induced drag
16:(Redirected from
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190:transition point
104:drag coefficient
50:aerodynamic drag
44:, also known as
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868:Drag (physics)
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195:fineness ratio
186:boundary layer
159:Main article:
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42:Parasitic drag
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361:is the local
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171:drag equation
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97:drag equation
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845:. Retrieved
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819:. Retrieved
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741:. Retrieved
735:
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714:Aerodynamics
713:
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689:
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441:(derived by
440:
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333:
250:
182:viscous drag
179:
165:
164:
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132:
120:
101:
87:
86:
70:
59:
53:
46:profile drag
45:
41:
40:
842:tec-science
138:shock waves
108:Streamlines
847:2020-06-25
739:(doctoral)
634:References
620:Jet engine
146:supersonic
35:Drag curve
615:NACA duct
433:turbulent
402:θ
343:τ
305:τ
299:≡
142:transonic
134:Wave drag
88:Form drag
83:Form drag
55:form drag
18:Form drag
862:Category
821:22 April
743:22 March
623:ram drag
609:See also
224:). With
175:velocity
148:speeds.
128:fairings
116:vortices
184:in the
77:airfoil
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519:where
334:where
767:(PDF)
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92:shape
823:2018
745:2022
718:ISBN
694:ISBN
664:ISBN
144:and
123:wing
66:lift
58:and
496:0.2
439:Law
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201:(
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