Study on coupled mode flutter parameters of large wind turbine blades

Area of Science:

• Aerodynamics
• Structural Dynamics
• Wind Energy Engineering

Background:

• Larger wind turbine blades exhibit increased flexibility, making them susceptible to aerodynamic elastic instability during operation.
• Coupled mode flutter, driven by bending-torsion effects, poses a significant risk of blade failure in long blades.

Purpose of the Study:

• To establish a blade flutter characteristic equation using Euler Bernoulli beam theory and Theodorsen aerodynamic loads.
• To analyze the influence of regional parameter variations on the flutter characteristics of NREL 5 MW wind turbine blades.

Main Methods:

• Application of Euler Bernoulli beam theory and Theodorsen non-directional aerodynamic loads.
• Finite element method (FEM) for establishing the blade flutter characteristic equation.
• Parametric analysis of NREL 5 MW wind turbine blades, focusing on different regions and properties.

Main Results:

• Parameter changes in the blade tip region have the most substantial impact on flutter characteristics.
• Increased bending and torsional stiffness generally lead to higher vibration frequencies and flutter speeds.
• Decreasing bending stiffness causes flutter velocity to stabilize, while increased torsional stiffness enhances flutter speed.

Conclusions:

• The radius of gyration is inversely proportional to flutter frequency and velocity.
• Centroid offset has minimal effect on flutter frequency, but significant impact on flutter velocity in the tip region.
• Increasing torsional stiffness is crucial for preventing coupled mode flutter, providing a basis for blade design.