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

Abstract

Vertical-axis wind turbines are excellent 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.

Optimal blade pitch control for enhanced vertical-axis wind turbine performance

“…Here, we demonstrate the potential of individual dynamic blade pitching to enhance the efficiency and maintain the structural integrity of vertical-axis wind turbines across tip-speed ratios using our unique set-up that consist of a scaled-down one bladed instrumented turbine model with dynamic blade pitching capabilities (Le Fouest and Mulleners, 2022;Le Fouest et al, 2023). The turbine's efficiency is conventionally expressed by its power coefficient, which is defined as the ratio of the net power generated by the turbine P and the power carried by the flow crossing the blade's swept area A swept :…”