Gust alleviation strategy and mechanism for an airfoil encountering periodical vertical gusts

Unsteady loads induced by gusts are a significant concern affecting flight safety. This study concentrates on gust load alleviation, exploring the strategy and mechanism of dynamic airfoils in alleviating gust-induced load. Based on classical aerodynamic theory, this paper proposes three distinct airfoil motion strategies aimed at alleviating gust-induced loads. Experimental analyses employing a two-dimensional NACA 0012 airfoil subjected to periodic vertical gusts with various prescribed motions are undertaken to assess the efficacy of the proposed load alleviation strategy. It is found that compared to static airfoil configurations, dynamic motions devised according to Theodorsen-Sears theory yield substantial gust load reduction, with lift fluctuations reduced by up to 90%. The dynamic airfoil alleviates gust-induced disturbances around the airfoil, thereby maintaining flow attachment on the airfoil surface or inducing minor-scale flow separation. Quantitative assessments establish a relationship between flow field momentum changes and lift fluctuations, suggesting that even in scenarios where precise aerodynamic force measurements are unavailable, the efficacy of load alleviation can be deduced through an analysis of flow field momentum. Furthermore, dynamic airfoil configurations notably dampen fluctuations at the stagnation point along the airfoil's leading edge. Consequently, in practical flight scenarios, an effective control of stagnation point stability holds promise for effective gust load alleviation.