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 ۰۰۱۲ at low to intermediate Reynolds number is investigated numerically through the unsteady ‎two-dimensional 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 fluid-structure 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, ۱۸% and ۳۶% of the airfoil chord length. The ‎airfoil chord measures ۰.۱۵۶ m. The simulations were executed at the free stream velocity ranging from ‎‎۵.۰ m/s to ۱۳ m/s corresponding to the Reynolds number between ۵۱۶۱۸ and ۱۳۴۲۰۷. Two types of ‎oscillation amplitudes were observed at each elastic axis position. At the leading-edge and ۱۸% case, ‎small amplitude oscillations were observed while at ۳۶%, 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.

Keywords:

Stall flutter , Limit cycle oscillation , Flow separation