Wagner function: Wagner function expresses the lift due to a unit change of the angle of attack. This function is used for sudden changes in angle of attack.
Küssner function: Küssner function which corresponds to indicial admittance which is the lift induced by a sharp gust of unit amplitude.
Indicial admittance: The response of the linear system to a unit step function. It describes the time dependency of the aerodynamic lift.
Reduced frequency: Number of oscillations in radians per half chord travel of the airfoil. k=wb/U
Reduced time: It can be regarded as the distance of the travelling airfoil in semi-chord. sb/u
Theodorsen function: It is a ratio which shows the phase difference between quasi unsteady lift coefficient and quasi steady lift coefficient as the effect of the circulatory wake term.
Kutta condition: zero velocity at trailing edge or no vortex sheet at near wake or no pressure difference at the wake region.
References: Unsteady Aerodynamics Lecture Notes, 2013, İTÜ.
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