Vortex-induced vibration and frequency lock-in of an airfoil at high angles of attack
Vortex-induced vibration is a fluid instability present in many areas, including offshore platforms, wind turbines, and turbomachinery. The vortices due to secondary flows exert an periodic unsteady force on the elastic structure, leading to potentially dangerous vibrations. Under certain circumstances, the shedding frequency can lock into the structure natural frequency and lead to limit cycle oscillations. These high amplitude vibrations can cause material fatigue, and are a common source of structural failure. This work uses a frequency domain, harmonic balance, CFD code to predict the lock-in of an airfoil at very high angles of attack. The natural shedding frequency is found using a delta phase per iteration method, and the lock-in region is identified by enforcing airfoil motion at different oscillation amplitudes and frequencies. The numerical results are successfully compared to experimental data from wind tunnel testing on a NACA0012 airfoil at deep stall conditions.
