Measurement of Natural Frequency and Damping of a Slender Model in Mach 5 Flow

ifasd2024 Tracking Number 172

Hypersonic vehicles that have a high slenderness ratio are prone to aerothermoelastic deformations that can affect maneuverability. The goal of this study is to assess the effectiveness of different types of structural excitation as well as damping extraction algorithms to identify the natural frequency and damping of a representative cone-cylinder model in Mach 5 flow. The conical and cylindrical sections were rigid, but were connected by a flexure element that restricted the cone’s dynamics to a pitching motion only. This single degree of freedom system was excited in Mach 5 flow using two different structural excitation methods: exposing the model to free-stream turbulence, and harmonically forcing the structure with an embedded vibrating motor. These excitation techniques were used to infer the aerodynamic stiffness and aerodynamic damping using several analysis techniques. Algorithms such as the Random Decrement technique and the Natural Excitation technique were used to generate a free-decay response from the free-stream turbulence forcing cases. The Moving-Block technique and the Continuous Wavelet Transform were used to calculate the wind-on damping ratio from all wind-on signals. Wind-off and wind-on comparisons of the structure’s natural frequency and damping ratio were made. Wind-on natural frequencies were measured to be lower than wind-off cases, while wind-on damping ratios were measured to be higher than the wind-off cases. These results indicate that aerodynamic forces contribute negative stiffness and positive damping to the system for this particular structural setup. In summary, both structural excitation methods prove useful for aeroelastic studies in long-duration hypersonic wind tunnels.