Unsteady Aerodynamic Response of a High-Speed, Separated Flow to a Deforming Cantilever Plate

Multi-scale fluid dynamic nonlinearities, such as shock motions, turbulent flow and separation, challenge accurate and efficient treatment of fluid-structural interactions in high-speed flow. Motivated by this, a numerical investigation into the response of a Mach 2.0 separated flow to prescribed motion of a cantilever plate - which exhibits a rich interplay of these effects - is carried out to understand the sensitivity of the fluid dynamics to structural motion. The fluid dynamic response is computed at three levels of fidelity in order to facilitate identification of the dominant energy transfer mechanisms: unsteady Reynolds-averaged Navier-Stokes (URANS), delayed detached eddy simulation (DDES), and implicit large-eddy simulation (ILES). Spectral and modal analyses are conducted to characterize the multi-scale dynamics of the rigid configuration, revealing an inherent low-frequency fluid unsteadiness due to interactions between the separated region, shear layer, and reattachment shock-dominated pressure field reconstruction. For the configuration studied, the unsteadiness is on the order of typical structural dynamic response scales. The impact of fluid-structural interaction on the fluid dynamics is investigated through forced simple harmonic oscillations of the cantilever in the first bending mode. Upward deflection of the cantilever displaces the shear layer reattachment location downstream proportionally with oscillation amplitude. This causes additional momentum flux through the open boundary of the cavity. The importance of this momentum flux on the induced loads is characterized through consideration of a closed cavity, which has a 50% reduction in induced load when the momentum flux through the open boundary is suppressed. The induced loading is consistently predicted by each level of fidelity, suggesting that resolving the medium and high-frequency dynamics of the shear layer may not be necessary for capturing the combined fluid-structural response.