Unsteady Aerodynamic Modeling Applied to Wing–Vortex Gust Encounters

This study evaluates two low-order models for predicting lift forces during encounters between wings and spanwise vortex gusts. The first is a quasi-steady model that relates lift to the instantaneous effective angle of attack. The second model utilizes the Wagner and Küssner functions to incorporate unsteady wake downwash and non-circulatory vortex forces. Experiments are carried out with a flat-plate wing in a water towing tank facility, with force balance and particle image velocimetry measurements. An isolated vortex gust is produced by linearly pitching an upstream NACA0021 wing. Positive and negative vortex gusts are tested at two wing–vortex chord-normal separations, with gust disturbance velocities of up to 60% of the freestream. The wing incidence is varied between [Formula: see text] and 20°. The gust-induced change in lift coefficient is found to be largely self-similar with respect to angle of attack. The unsteady model significantly outperforms the quasi-steady model, with mean errors of 11% and 33%, respectively. Non-linear effects, such as leading-edge vortex development, reduce model accuracy. Results suggest that a point measurement of the chord-normal gust velocity component is sufficient to predict the lift disturbance. The optimal measurement location is in the mid-chord plane, 0.4–0.8 chord lengths upstream of the leading edge.