Interaction between Instabilities in Vertical-Axis Turbine Blades

Abstract

This work investigates five different instability mechanisms that may occur and interact in straight-bladed H-rotor vertical-axis turbines. Specifically, it considers the static instabilities of divergence and centrifugal buckling as well as the dynamic instabilities of flutter, main resonance, and parametric resonance. This is done by applying Theodorsen’s model for unsteady aerodynamics with traditional finite element methods. The resulting model comprises bend-twist-coupled elements that inherently account for fluid and centrifugal effects. Comparisons with experimental results in the literature are used to assess the accuracy and limitations of the model. Eigenvalue analysis is used on time-averaged equations to predict divergence, flutter, and centrifugal buckling, as well as identify regions where main and parametric resonance may be excited. Time history analysis is used to provide further insight and show main and parametric resonance explicitly. Stability plots are constructed using both methods of analysis and presented in the forcing parameter space. Interaction between the different instability mechanisms is observed, including a region of parametric stabilization that is found to extend beyond the expected boundaries of both divergence and flutter.