An approximate method for natural frequency analysis of variable-pitch vertical axis wind turbine blades

Abstract

This study aims to enhance the operational stability and efficiency of flexible blades in variable-pitch vertical-axis wind turbines, providing significant engineering applications. Currently, research on blade dynamic behavior often simplifies blades to slender beam models, yet this approach has limitations in analyzing blades of small and medium-sized vertical-axis wind turbines, particularly for variable-pitch vertical-axis wind turbines, where the blades do not always meet the slender beam assumption. To address this, the study constructs a variable-pitch dynamic model based on the Euler-Bernoulli and Timoshenko beam theories. Using an assumed mode method combined with a multi-scale approach, the dynamic characteristics of the blades under different models are systematically analyzed, and the impact of variable pitch on frequency is further explored. Results indicate that the Timoshenko beam model demonstrates higher accuracy in predicting high-order modal frequencies, especially under larger pitch amplitudes, allowing for a more precise description of blade flap responses. Additionally, pitch amplitude significantly affects the natural frequency, whereas the effects of pitch frequency and phase are relatively minor. This research provides a theoretical foundation for optimizing variable-pitch vertical-axis wind turbines blade structural design and offers crucial technical guidance for enhancing stability and efficiency in long-term operation.