Aeroelastic Simulation of Stall Flutter Undergoing High and Low Amplitude Limit Cycle Oscillations

The aeroelastic behaviour of an airfoil oscillating in large and small pitch amplitudes due to nonlinearity in aerodynamics is examined. The phenomenon of stall flutter resulted in the limit cycle oscillations of NACA 0012 at low to intermediate Reynolds number is investigated numerically through the unsteady twodimensional aeroelastic simulation. The simulations employed unsteady Reynolds Average Navier Stokes shear stress transport k-ω turbulent model with the low Reynolds number correction. The simulations of the fluidstructure interaction were performed by coupling the structural equation of motion with a fluid solver through the user-defined function utility. Numerical simulations were executed at three different elastic axis positions; the leading-edge, 18% and 36% of the airfoil chord length. The airfoil chord measures 0.156 m. The simulations were executed at the free stream velocity ranging from 5.0 m/s to 13 m/s corresponding to the Reynolds number between 51618 and 134207. Two types of oscillation amplitudes were observed at each elastic axis position. At the leading-edge and 18% case, small amplitude oscillations were observed while at 36%, the system underwent high amplitude oscillations. The analysis revealed the cause for small oscillation amplitude is due to the separation of the laminar boundary layer on the suction side of the airfoil starting at the trailing edge. High amplitude oscillations occurred due to the existence of the dynamic stall phenomenon beginning at the leading-edge. Small amplitude LCOs only occurred within a limited range of airspeed before it disappeared due to increasing airspeed.