Aeroelastic Coupling Effects in Globally Unstable Transonic Wing Flow

This work concerns the phenomenon of shock buffet and its mutual interaction with the flexible wing structure. The latter aspect is key to our contribution, since, even though renewed interest in edge-of-the-envelope flow unsteadiness can be observed in recent years, the multidisciplinary aeroelastic interaction is typically overlooked. Previous work by Timme [1] applied stability theory to a large aircraft wing, specifically the NASA Common Research Model, to reveal a global instability linked to shock buffet. Herein, we expand upon that work by adding the dimension of wing vibration to scrutinise its impact on the flow unsteadiness. We consider fluid-structure interaction solving the unsteady Reynolds-averaged Navier–Stokes equations with an industry-grade computational fluid dynamics solver to model the aerodynamics and a modal structural model of the actual wind-tunnel geometry to describe the flexible wing. Our focus experimental flow condition is a reference free-stream Mach number of 0.85 with a chord Reynolds number of 5 × 106 and a supercritical angle of attack of 3.75◦ . Results show that the initial aerodynamic unsteadiness, when started from a well converged static aeroelastic solution (validated with wind-tunnel data), is nearly independent of the presence of the flexible wing structure as long as the amplitudes are small. Indeed wing vibration follows the dominant shock-buffet excitation. Once transitioned into the non-linear aerodynamic regime (while noting that at the time of writing a longer time history is still required), most of the structural degrees-of-freedom are active close to their respective natural frequencies and also within the shock-buffet frequency range. An aeroelastic global stability analysis presented in our companion paper [2] has revealed that several of these modes become unstable due to the fluid-structure coupling. Overall the impact of the flexible wing results in lower amplitudes in integrated aerodynamic coefficients with a broader frequency content peaking around the first bending frequencies and the shock-buffet frequency range, which is in contrast to the rigid (yet statically deformed) wing where the shock-buffet excitation clearly dominates