Küssner effect

File:Kussner effect.svg

An airfoil flying into a gust region. The airfoil speed is denoted with V and is constant, the lift force on the airfoil is given by L, and its moment of force by M. The gust has a transverse (vertical) velocity w, which is assumed to be a constant in the gust region, left of the dashed line.

In fluid dynamics, the Küssner effect describes the unsteady aerodynamic forces on an airfoil or hydrofoil 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 (1900–1984), a German aerodynamics engineer.

Küssner derived an approximate model for an airfoil encountering a sudden step-like change in the transverse gust velocity — or, equivalently, as seen from a frame of reference moving with the airfoil: a sudden change in the angle of attack. The airfoil is modelled as a flat plate in a potential flow, moving with constant horizontal velocity. For this case he derived the impulse response function — known as Küssner function — needed to compute the unsteady lift and moment exerted by the air on the airfoil.

References

• Page 3

External links

• Page 13.