fluid dynamics In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids— liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) an ...

, the Küssner effect describes the unsteady

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 ...

force In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a p ...

s on an

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 turbine. ...

hydrofoil A hydrofoil is a lifting surface, or foil, that operates in water. They are similar in appearance and purpose to aerofoils used by aeroplanes. Boats that use hydrofoil technology are also simply termed hydrofoils. As a hydrofoil craft gains sp ...

caused by encountering a transverse

gust Gust may refer to: People Given name * Gust Avrakotos (1938–2005), CIA case officer known for the arming of Afghanistan's Mujahideen against the Soviet invasion under Operation Cyclone * Gust Hagberg (19th-century–20th-century) * Gust Kunde ...

. This is directly related to the Küssner function, used in describing the effect. Both the effect and function are named after

Hans Georg Küssner Hans Georg Küssner (14 September 190021 March 1984) was a German physicist and aeronautical scientist known for his work in the field of aeroelasticity. Work Hans Georg Küssner was born on September 14, 1900 in Bartenstein, then part of the E ...

(1900–1984), a German

aerodynamics 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 ...

engineer. Küssner derived an approximate model for an airfoil encountering a sudden step-like change in the transverse gust

velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity is a ...

; or, equivalently, as seen from a

frame of reference In physics and astronomy, a frame of reference (or reference frame) is an abstract coordinate system whose origin, orientation, and scale are specified by a set of reference points― geometric points whose position is identified both mathema ...

moving with the airfoil: a sudden change in the

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 ...

. The airfoil is modelled as a flat plate in a

potential flow In fluid dynamics, potential flow (or ideal flow) describes the velocity field as the gradient of a scalar function: the velocity potential. As a result, a potential flow is characterized by an irrotational velocity field, which is a valid appr ...

, moving with constant horizontal velocity. For this case he derived the

impulse response function In signal processing and control theory, the impulse response, or impulse response function (IRF), of a dynamic system is its output when presented with a brief input signal, called an impulse (). More generally, an impulse response is the reacti ...

(known as Küssner functionBisplinghoff, Ashley and Halfman (1996) pp. 287–288.) needed to compute the unsteady

lift Lift or LIFT may refer to: Physical devices * Elevator, or lift, a device used for raising and lowering people or goods ** Paternoster lift, a type of lift using a continuous chain of cars which do not stop ** Patient lift, or Hoyer lift, mobile ...

and

moment Moment or Moments may refer to: * Present time Music * The Moments, American R&B vocal group Albums * ''Moment'' (Dark Tranquillity album), 2020 * ''Moment'' (Speed album), 1998 * ''Moments'' (Darude album) * ''Moments'' (Christine Guldbrand ...

exerted by the air on the airfoil.

Notes

References

* * H.G. Küssner (1937), "Flügel- und Leitwerkflattern" (in German) * H.G. Küssner (1940), "Der schwingende Flügel mit aerodynamisch ausgeglichenem Ruder" (in German) * H.G. Küssner (1940), "Allgemeine Tragflächentheorie" (in German) * * * * Page 3 * *

External links

* Page 13. * Aerodynamics Aerospace engineering Aircraft wing design Fluid dynamics {{fluiddynamics-stub