Aeroelastic response of an airfoil with structural freeplay in transonic buffeting flow

Transonic shock buffet is a nonlinear, unsteady aerodynamic phenomenon characterized by self-sustained, periodic shock oscillations that can critically affect aircraft structural integrity. While the aerodynamic aspects of shock buffet have been widely studied, its interaction with nonlinear structural dynamics remains largely unexplored. This paper presents, for the first time, a numerical investigation of aeroelastic interactions arising from the coupling of shock buffet with a nonlinear structural model featuring pitch freeplay. Using Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations coupled with a two-degree-of-freedom heave–pitch airfoil model, the study reveals that structural nonlinearity can induce aerodynamic lock-in to superharmonics of the heave natural frequency, resulting in 2:1 and 3:1 lock-in mechanisms and large-amplitude heave limit cycles. These newly identified lock-in behaviors expand the current understanding of transonic aeroelastic instabilities. The influence of key parameters such as structural-to-fluid mass ratio and structural damping on these phenomena is also systematically examined. This work introduces a novel class of aeroelastic lock-in mechanism with significant implications for transonic flight dynamics and aircraft design.