Küssner effect

In fluid dynamics, the Küssner effect describes the unsteady aerodynamic forces on an airfoil or hydrofoil caused by encountering a transverse gust.

Both the effect and function are named after Hans Georg Küssner (1900–1984), a German aerodynamics engineer.

[1] 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.

[2] For this case he derived the impulse response function (known as Küssner function[3]) needed to compute the unsteady lift and moment exerted by the air on the airfoil.

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 pitching moment 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.