fluid dynamics In physics, physical chemistry and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids – liquids and gases. It has several subdisciplines, including (the study of air and other gases in motion ...

, the Küssner effect describes the unsteady

aerodynamic Aerodynamics () is the study of the motion of atmosphere of Earth, air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dynamics and its subfield of gas dynamics, and is an ...

force In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...

s on an

airfoil An airfoil (American English) or aerofoil (British English) is a streamlined body that is capable of generating significantly more Lift (force), lift than Drag (physics), drag. Wings, sails and propeller blades are examples of airfoils. Foil (fl ...

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. 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 14 September 1900 in Bartenstein, then part of the ...

(1900–1984), a German

aerodynamics Aerodynamics () is the study of the motion of atmosphere of Earth, air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dynamics and its subfield of gas dynamics, and is an ...

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

velocity Velocity is a measurement of speed in a certain direction of motion. It is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of physical objects. Velocity is a vector (geometry), vector Physical q ...

; 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 (mathematics), origin, orientation (geometry), orientation, and scale (geometry), scale have been specified in physical space. It ...

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 Airfoil#Airfoil terminology, reference line on a body (often the chord (aircraft), chord line of an airfoil) and the vector (geometry), vector representing the relat ...

. The airfoil is modelled as a flat plate in a

potential flow In fluid dynamics, potential flow or irrotational flow refers to a description of a fluid flow with no vorticity in it. Such a description typically arises in the limit of vanishing viscosity, i.e., for an inviscid fluid and with no vorticity pre ...

, moving with constant horizontal velocity. For this case he derived the impulse response function (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 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