Modelling transverse gusts using pitching, plunging and surging airfoil motions

Three model-motions were developed to replicate the aerodynamic response of a transverse gust. These motions included a pure-plunging and two three degree-of-freedom motions that approximated the angle-of-attack distribution produced by the gust. Using inviscid models and viscous flow simulations, the response of the gust and model-motions were compared as a function of the non-dimensional reduced frequency. The inviscid model was found to overestimate the influence of the rotational added-mass in the three degree-of-freedom motions. In contrast, the viscous flow simulations showed that the two primary sources of discrepancy between the gust and model-motions lie in the non-linear angle-of-attack distribution caused by the gust, and the wake development during the model-motions. Flow simulations showed that all three motions experienced greater than 90% agreement in lift for gusts with reduced frequencies less than 0.5, indicating that under this reduced frequency: 1) the effect of the gust convection is minimal; and 2) a pure-plunging motion may suffice for modelling gusts. However, at higher reduced frequencies the pure-plunging motion experiences greater than 10% worse agreement than the three degree-of-freedom motions. Overall, the motions provide a good approximation with greater than 90% accuracy in lift for gusts of reduced frequencies less than k = 0.75