Timescales of dynamic stall development on a vertical-axis wind turbine blade

TL;DR

This study characterizes the sequence and timing of flow events leading to dynamic stall on vertical-axis wind turbine blades, using time-resolved measurements and flow analysis to inform better control strategies.

Contribution

It identifies six key stages of dynamic stall and quantifies their timing and duration across different operating conditions, advancing understanding of unsteady aerodynamics in vertical-axis turbines.

Findings

Six characteristic stall stages identified

Most aerodynamic work occurs during shear-layer growth and vortex formation

Timing of stages best characterized by non-dimensional convective time

Abstract

Vertical-axis wind turbines are great candidates to diversify wind energy technology, but their aerodynamic complexity limits industrial deployment. To improve the efficiency and lifespan of vertical axis wind turbines, we desire data-driven models and control strategies that take into account the timing and duration of subsequent events in the unsteady flow development. Here, we aim to characterise the chain of events that leads to dynamic stall on a vertical-axis wind turbine blade and to quantify the influence of the turbine operation conditions on the duration of the individual flow development stages. We present time-resolved flow and unsteady load measurements of a wind turbine model undergoing dynamic stall for a wide range of tip-speed ratios. Proper orthogonal decomposition is used to identify dominant flow structures and to distinguish six characteristic stall stages: the attached flow, shear-layer growth, vortex formation, upwind stall, downwind stall, and flow reattachment stage. The timing and duration of the individual stages are best characterised by the non-dimensional convective time. Dynamic stall stages are also identified based on aerodynamic force measurements. Most of the aerodynamic work is done during the shear-layer growth and the vortex formation stage which underlines the importance of managing dynamic stall on vertical-axis wind turbines.