Nonlinear Modeling and Thermal Flutter Analysis of a Folding Fin With Free-Play

This paper presents a comprehensive nonlinear modeling and thermal flutter analysis of a folding fin with free-play. The nonlinear dynamic behavior of the folding fin under thermal environments is investigated through a combination of high-temperature vibration experiments and time-domain simulations. A temperature-dependent nonlinear reduced-order model is developed, incorporating both the degradation of material properties and contact stiffness variations with temperature. The aerodynamic forces are modeled using the modified first-order piston theory and coupled with the structural model through an Infinite Plate Spline (IPS) interpolation method. The experimental results reveal that the first-order resonant frequency of the folding fin increases with temperature due to the reduction of contact gaps, while the second-order frequency decreases as a result of the reduction in contact stiffness. The proposed nonlinear reduced-order model accurately reproduces the experimental amplitude–frequency responses. Aeroelastic simulations demonstrate that both the flutter critical speed and divergence speed decrease with rising temperature, and the range of limit-cycle oscillation (LCO) becomes narrower, indicating that high temperatures significantly weaken the aeroelastic stability of the structure. The results provide valuable insights into the design and stability evaluation of deployable aerodynamic control surfaces operating in high-temperature supersonic environments.