On limit cycle oscillations of typical aeroelastic section with different preset angles of incidence at low airspeeds

Helicopter blades and wind turbines are examples of aeroelastic systems that can reach high angles of attack and can vibrate due to the effects of the dynamic stall, thereby leading to fatigue problems or performance loss. Structural and aerodynamic nonlinearities influence the aforementioned behavior and their modeling is crucial for phenomena characterization. Such system modeling requires proper knowledge of the physical events during the stall, which can be better achieved by validating the model with experimental data. This work investigates the nonlinear dynamics of a NACA 0012 airfoil under the influence of structural and aerodynamic nonlinearities due to dynamic stall effects at high angles of attack. Experimental and numerical analyses are carried out. Moreover, different preset incidence angles for the typical aeroelastic section are also considered. The aeroelastic signals are used for estimating the Hopf bifurcation onset and to build the bifurcation diagrams. By using a typical section model with two degrees of freedom coupled to the Beddoes-Leishman aerodynamic model, numerical results have been able to capture with good precision experimental features. The onset of the Hopf bifurcations allows the determination of the flutter critical airspeed. Results for zero preset angle show that limit cycle oscillations from small to moderate displacements are mostly driven by the hardening nonlinearity. After reaching larger angles of incidence the dynamic stall nonlinearities supplant those from structural sources. For higher preset angles, the dynamic stall effects tend to increase the energy associated with pitching motion and to reduce amplitudes in plunge motion. Another effect related to the aerodynamic nonlinearities relies on the increase of the flutter velocity by around 10% for preset angles ranging from zero up to ten degrees. For higher preset angles an abrupt reduction in the flutter onset velocity is observed.