Effect of Vortex-Wing Interaction in Aeroelastic Flutter of Wings in Transonic Flows

Transonic flutter on aircraft wings causes detrimental limit cycle oscillations responsible for structural damage and pilot discomfort. External stores on the wing are known to exacerbate this instability and deeper understanding of the shock and wake-induced effects are needed. We consider a cylinder underneath a NACA0012 airfoil as a model problem to gain fundamental insights into the aerodynamics of this coupled system. We conduct several simulations of flow over a two-dimensional sinusoidally pitching cylinder-airfoil system at transonic Mach numbers using a sharp-interfaced immersed boundary method at Re=10000. We used energy maps to characterize the flutter boundaries and identified that the cylinder-airfoil system is susceptible to flutter at much lower Mach numbers than a pitching airfoil system. To isolate the physical mechanisms responsible for energy transfer, we leverage and extend the framework of force and power partitioning method for compressible flows. We identified that the shock-induced stall on the airfoil is more pronounced due to the presence of the cylinder and contributes to the flutter instability. This study shows the potential of compressible force partitioning methods to gain insights into a wide range of high-speed unsteady flow problems.