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A vortex generator (VG) is an
aerodynamic Aerodynamics, from grc, ἀήρ ''aero'' (air) + grc, δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dyn ...
device, consisting of a small
vane Vane may refer to: People * Vane (surname) * Vane Featherston (1864–1948), English stage actress * Ivan Vane Ivanović (1913–1999), Yugoslav-British athlete, shipowner, political activist, and philanthropist * Vane Pennell (1876–1938), ...
usually attached to a lifting surface (or
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 turbin ...
, such as an
aircraft wing A wing is a type of fin that produces Lift (force), lift while moving through air or some other fluid. Accordingly, wings have Streamlines, streaklines, and pathlines, streamlined Cross section (geometry), cross-sections that are subject to aer ...
) or a rotor blade of a
wind turbine A wind turbine is a device that converts the kinetic energy of wind into electrical energy. Hundreds of thousands of large turbines, in installations known as wind farms, now generate over 650 gigawatts of power, with 60 GW added each year. ...
.Wind Turbine Vortex Generators
UpWind Solutions.
VGs may also be attached to some part of an aerodynamic vehicle such as an aircraft fuselage or a car. When the airfoil or the body is in motion relative to the air, the VG creates a
vortex In fluid dynamics, a vortex ( : vortices or vortexes) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings, whirlpools in ...
,Peppler, I.L.: ''From The Ground Up'', page 23. Aviation Publishers Co. Limited, Ottawa Ontario, Twenty Seventh Revised Edition, 1996. which, by removing some part of the slow-moving boundary layer in contact with the airfoil surface, delays local flow separation and aerodynamic stalling, thereby improving the effectiveness of wings and control surfaces, such as flaps, elevators,
aileron An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement around ...
s, and
rudder A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other vehicle that moves through a fluid medium (generally air or water). On an aircraft the rudder is used primarily to counter adve ...
s.


Method of operation

Vortex generators are most often used to delay flow separation. To accomplish this they are often placed on the external surfaces of vehiclesClancy, L.J. ''Aerodynamics'', Section 5.31 and wind turbine blades. On both aircraft and wind turbine blades they are usually installed quite close to the leading edge of the
aerofoil 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 turbine. ...
in order to maintain steady airflow over the control surfaces at the trailing edge. VGs are typically rectangular or triangular, about as tall as the local
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 ...
, and run in spanwise lines usually near the thickest part of the wing. They can be seen on the wings and vertical tails of many
airliner An airliner is a type of aircraft for transporting passengers and air cargo. Such aircraft are most often operated by airlines. Although the definition of an airliner can vary from country to country, an airliner is typically defined as an ai ...
s. Vortex generators are positioned obliquely so that they have an
angle of attack In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...
with respect to the local airflow in order to create a tip vortex which draws energetic, rapidly moving outside air into the slow-moving boundary layer in contact with the surface. A turbulent boundary layer is less likely to separate than a laminar one, and is therefore desirable to ensure effectiveness of trailing-edge control surfaces. Vortex generators are used to trigger this transition. Other devices such as
vortilon Vortilons are fixed aerodynamic devices on aircraft wings used to improve handling at low speeds. The vortilon was invented by aerodynamicists working at Douglas Aircraft who had previously developed the engine pylons for the Douglas DC-8. The o ...
s,
leading-edge extension A leading-edge extension (LEX) is a small extension to an aircraft wing surface, forward of the leading edge. The primary reason for adding an extension is to improve the airflow at high angles of attack and low airspeeds, to improve handling a ...
s, and leading-edge cuffs, also delay flow separation at high angles of attack by re-energizing the boundary layer. Examples of aircraft which use VGs include the ST Aerospace A-4SU Super Skyhawk and Symphony SA-160. For swept-wing transonic designs, VGs alleviate potential shock-stall problems (e.g., Harrier,
Blackburn Buccaneer The Blackburn Buccaneer is a British carrier-capable attack aircraft designed in the 1950s for the Royal Navy (RN). Designed and initially produced by Blackburn Aircraft at Brough, it was later officially known as the Hawker Siddeley Buccane ...
,
Gloster Javelin The Gloster Javelin is a twin-engined T-tailed delta-wing subsonic night and all-weather interceptor aircraft that served with Britain's Royal Air Force from the mid-1950s until the late 1960s. The last aircraft design to bear the Gloster na ...
).


Aftermarket installation

Many aircraft carry vane vortex generators from time of manufacture, but there are also aftermarket suppliers who sell VG kits to improve the
STOL A short takeoff and landing (STOL) aircraft is a conventional fixed-wing aircraft that has short runway requirements for takeoff and landing. Many STOL-designed aircraft also feature various arrangements for use on airstrips with harsh condi ...
performance of some light aircraft. Aftermarket suppliers claim (i) that VGs lower stall speed and reduce take-off and landing speeds, and (ii) that VGs increase the effectiveness of ailerons, elevators and rudders, thereby improving controllability and safety at low speeds. For home-built and experimental kitplanes, VGs are cheap, cost-effective and can be installed quickly; but for certified aircraft installations,
certification Certification is the provision by an independent body of written assurance (a certificate) that the product, service or system in question meets specific requirements. It is the formal attestation or confirmation of certain characteristics of a ...
costs can be high, making the modification a relatively expensive process. Owners fit aftermarket VGs primarily to gain benefits at low speeds, but a downside is that such VGs may reduce cruise speed slightly. In tests performed on a
Cessna 182 The Cessna 182 Skylane is an American four-seat, single-engined light airplane built by Cessna of Wichita, Kansas. It has the option of adding two child seats in the baggage area. Introduced in 1956, the 182 has been produced in a ...
and a Piper PA-28-235 Cherokee, independent reviewers have documented a loss of cruise speed of . However, these losses are relatively minor, since an aircraft wing at high speed has a small angle of attack, thereby reducing VG drag to a minimum.Psutka, Kevin, ''Micro-vortex generators'', COPA Flight, August 2003Kirkby, Bob, ''Vortex Generators for the Cherokee 235'', COPA Flight, July 2004 Owners have reported that on the ground, it can be harder to clear snow and ice from wing surfaces with VGs than from a smooth wing, but VGs are not generally prone to inflight icing as they reside within the boundary layer of airflow. VGs may also have sharp edges which can tear the fabric of airframe covers and may thus require special covers to be made. For twin-engined aircraft, manufacturers claim that VGs reduce single-engine control speed ( Vmca), increase zero fuel and gross weight, improve the effectiveness of ailerons and rudder, provide a smoother ride in turbulence and make the aircraft a more stable instrument platform.


Increase in maximum takeoff weight

Some VG kits available for light twin-engine airplanes may allow an increase in
maximum takeoff weight The maximum takeoff weight (MTOW) or maximum gross takeoff weight (MGTOW) or maximum takeoff mass (MTOM) of an aircraft is the maximum weight at which the pilot is allowed to attempt to take off, due to structural or other limits. The analogous ...
. The maximum takeoff weight of a twin-engine airplane is determined by structural requirements and single-engine climb performance requirements (which are lower for a lower stall speed). For many light twin-engine airplanes, the single-engine climb performance requirements determine a lower maximum weight rather than the structural requirements. Consequently, anything that can be done to improve the single-engine-inoperative climb performance will bring about an increase in maximum takeoff weight. In the US from 1945 until 1991,USA Federal Aviation Regulations, Part 23, §23.67, amendment 23-42, February 4, 1991 the one-engine-inoperative climb requirement for multi-engine airplanes with a maximum takeoff weight of or less was as follows: where V_ is the stalling speed in the landing configuration in miles per hour. Installation of vortex generators can usually bring about a slight reduction in stalling speed of an airplane and therefore reduce the required one-engine-inoperative climb performance. The reduced requirement for climb performance allows an increase in maximum takeoff weight, at least up to the maximum weight allowed by structural requirements. An increase in maximum weight allowed by structural requirements can usually be achieved by specifying a maximum zero fuel weight or, if a maximum zero fuel weight is already specified as one of the airplane's limitations, by specifying a new higher maximum zero fuel weight. For these reasons, vortex generator kits for many light twin-engine airplanes are accompanied by a reduction in maximum zero fuel weight and an increase in maximum takeoff weight. The one-engine-inoperative rate-of-climb requirement does not apply to single-engine airplanes, so gains in the maximum takeoff weight (based on stall speed or structural considerations) are less significant compared to those for 1945–1991 twins. After 1991, the airworthiness certification requirements in the USA specify the one-engine-inoperative climb requirement as a gradient independent of stalling speed, so there is less opportunity for vortex generators to increase the maximum takeoff weight of multi-engine airplanes whose certification basis is FAR 23 at amendment 23-42 or later.


Maximum landing weight

Because the landing weights of most light aircraft are determined by structural considerations and not by stall speed, most VG kits increase only the takeoff weight and not the landing weight. Any increase in landing weight would require either structural modifications or re-testing the aircraft at the higher landing weight to demonstrate that the certification requirements are still met. However, after a lengthy flight, sufficient fuel may have been used, thereby bringing the aircraft back below the permitted maximum landing weight.


Aircraft noise reduction

Vortex generators have been used on the wing underside of
Airbus A320 family The Airbus A320 family is a series of narrow-body airliners developed and produced by Airbus. The A320 was launched in March 1984, first flew on 22 February 1987, and was introduced in April 1988 by Air France. The first member of the fam ...
aircraft to reduce noise generated by airflow over circular pressure equalisation vents for the fuel tanks. Lufthansa claims a noise reduction of up to 2 dB can thus be achieved.More than 200 Lufthansa A320 aircraft to become quieter.
Retrieved 2014-05-04


See also

*
Turbulator A turbulator is a device that turns a laminar boundary layer into a turbulent boundary layer. Device Turbulent flow can be desired on parts of the surface of an aircraft wing (airfoil) or in industrial applications such as heat exchangers and t ...
*
Boundary layer suction Boundary layer suction is a boundary layer control technique in which an air pump is used to extract the boundary layer at the wing or the inlet of an aircraft. Improving the air flow can reduce drag. Improvements in fuel efficiency have been est ...
*
Boundary layer control Boundary layer control refers to methods of controlling the behaviour of fluid flow boundary layers. It may be desirable to reduce flow separation on fast vehicles to reduce the size of the wake (streamlining), which may reduce drag. Boundary l ...
*
Circulation control wing A circulation control wing (CCW) is a form of high-lift device for use on the main wing of an aircraft to increase the maximum lift coefficient. CCW technology has been in the research and development phase for over sixty years. Blown flaps were a ...


References

* Kermode, A.C. (1972), ''Mechanics of Flight'', Chapter 11, page 350 - 8th edition, Pitman Publishing, London * Clancy, L.J. (1975), ''Aerodynamics'', Pitman Publishing, London


External links


Vortex Generators: 50 Years of Performance Benefits
a history of VGs {{Aircraft components Aircraft components Aerospace engineering Aerodynamics Aircraft wing design Wind turbines