Küssner effect
Unsteady aerodynamic forces from a transverse gust on an airfoil.
The Küssner effect is a concept in fluid dynamics concerning the unsteady aerodynamic forces that act on an airfoil or hydrofoil when it hits a transverse gust. This phenomenon is closely tied to the Küssner function, a mathematical tool used to quantify the effect. Both are named for the German aerodynamics engineer Hans Georg Küssner (1900–1984).
Küssner developed an approximate model for an airfoil that experiences a sudden, step-like change in the velocity of a transverse gust. From the perspective of a reference frame moving with the airfoil, this is equivalent to an abrupt shift in the angle of attack. In his model, the airfoil is treated as a flat plate moving at a constant horizontal speed within a potential flow. For this scenario, he derived the impulse response function—the Küssner function—which is necessary for calculating the unsteady lift and moment that the air exerts on the airfoil.
- Named after
- Hans Georg Küssner (1900–1984)
- Field
- fluid dynamics
- Subject
- unsteady aerodynamic forces on an airfoil or hydrofoil
- Cause
- encountering a transverse gust
- Model
- flat plate in a potential flow, moving with constant horizontal velocity
- Derived quantity
- impulse response function (Küssner function)
Lore & Background
The Küssner effect was derived by Hans Georg Küssner, 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.
Reader's Guide
The Küssner effect is significant because it provides a theoretical framework for understanding unsteady aerodynamic forces on airfoils and hydrofoils due to transverse gusts. The Küssner function, derived by Küssner, is the impulse response function needed to compute the unsteady lift and moment exerted by the air on the airfoil. This work is foundational in aeroelasticity and gust response analysis, as referenced in later publications such as those by Bisplinghoff, Ashley, and Halfman, and by Cebeci. The effect is directly related to the Küssner function, which remains a key tool in unsteady aerodynamics.
Did You Know?
- The Küssner effect describes unsteady aerodynamic forces on an airfoil or hydrofoil caused by encountering a transverse gust.
- Both the effect and the Küssner function are named after Hans Georg Küssner (1900–1984), a German aerodynamics engineer.
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