Limit Cycle Wing Flutter in the Transonic Regime: Insights from Immersed Boundary FSI Simulations

At transonic speeds, wing flutter typically presents as a limit cycle oscillation (LCO): a sustained oscillatory motion at constant amplitude. Such behavior can cause increased fatigue loading, pilot discomfort, and targeting issues for military aircraft. The root cause and behavior of LCOs in transonic flow is still an open research question but it likely depends on several non-linear mechanisms such as shock-induced separation, shock type and oscillations and vortex-shock interactions. In this work, we present direct numerical simulation data for a NACA0012 airfoil at a Reynolds number of 10,000 undergoing flow-induced vibrations. The results are produced using a recently developed high-order sharp interface immersed boundary solver (ViCAS3D) for compressible flows. Both single-degree-of-freedom and two-degree-of-freedom motions are simulated to ascertain the relationship between pitching and heaving that promotes instability growth. A range of transonic Mach numbers from 0.6 to 0.9 are considered, and these show drastically different behaviors including both stall-flutter and buzz-type flutter. Additionally, insights into the non-linear damping mechanism which leads to limit cycle behavior are explored.