Field testing to assess and mitigate standstill vibrations (Essential)

WHY

Modern wind turbines can experience significant vibrations in idling and standstill conditions during storms due to unsteady aerodynamic blade loads. These vibrations may cause fatigue damage in blades and associated components, making them a concern for both manufacturers from a design perspective and operators from a maintenance and reliability perspective. The issue is becoming more pronounced as turbines continue to increase in size and blade slenderness, which makes them more susceptible to flow-induced instabilities. In addition, future grid and market conditions are expected to result in more frequent curtailment and standstill periods, further increasing the relevance of this problem for the wind sector.

From a physical standpoint, these vibrations are associated with stalled flow and vortex shedding around the blades. They are typically referred to as stall-induced vibrations, vortex-induced vibrations, or both. Although the general mechanisms are understood, current aeroelastic modelling approaches are not yet able to capture these effects adequately under idling and standstill conditions. This limitation is mainly due to an incomplete understanding of the complex flow behaviour around stationary blades and the difficulty of representing these processes in computationally efficient engineering models. Improving this understanding is therefore essential. It would enable the development of more robust design tools for future turbines and support the creation of digital twin approaches to monitor fatigue accumulation during operation. Such tools must remain computationally efficient, given the large number of time steps and simulations required.

Standstill vibrations have become an important topic within the wind energy research community. Recent collaborative projects have investigated the phenomenon using aeroelastic simulations and targeted experiments. However, most existing studies rely on computational fluid dynamics-based modelling or wind-tunnel experiments at airfoil scale. There remains a lack of full-scale validation data capturing standstill and idling conditions at the turbine level, and obtaining such data is crucial for improving models and enabling tangible progress in both design and operation.

WHAT

The project aims to improve understanding of stall- and vortex-induced vibrations that occur in wind turbines during idling and standstill conditions. We therefore want to obtain high-quality full-scale measurements under controlled standstill storm conditions. By combining targeted field measurements with exploratory simulations, the project seeks to identify the key physical drivers of SViV and evaluate how current modelling tools represent these. The project activities focus on a dedicated field-test campaign of a multi-megawatt research turbine at the Wieringermeer test site.

A detailed test matrix will first be developed in collaboration with industrial and academic partners, defining the relevant combinations of pitch, yaw, rotor position, and wind speed that trigger standstill vibrations. The turbine will then be instrumented with blade-root strain gauges, tower load measurements, accelerometers and ground-based LiDAR to capture both structural response and inflow conditions. Field tests will be conducted during high-wind standstill conditions, with multiple campaigns planned to ensure sufficient coverage of relevant operating conditions.

In parallel, exploratory simulations will be conducted using state-of-the-art aeroelastic models to compare predicted and measured behaviour and to identify modelling shortcomings. The work also includes stakeholder engagement, safety assessments for the test campaign, and knowledge exchange through workshops and collaboration within the wider research programme.

EXPECTED RESULTS

The project delivers a unique dataset of full-scale wind turbine behaviour under standstill storm conditions, obtained from measurements on a fully instrumented multi-megawatt turbine. The dataset contains detailed information on structural loads, vibrations and inflow conditions associated with stall- and vortex-induced vibrations. It provides a consolidated basis for improved understanding of the underlying aeroelastic mechanisms. The analysis of the measurements will identify the operating conditions most prone to standstill vibrations and characterise their spectral content and structural response.

A comparison of measurement data and results from state-of-the-art engineering and aeroelastic models will provide insight into the level of agreement between simulations and reality. The evaluation will highlight the strengths and limitations of current modelling approaches and yield concrete recommendations for model improvements needed to capture stall- and vortex-induced behaviour more accurately. These findings provide a basis for improving efficient engineering models that can be integrated into aeroelastic toolchains and digital-twin frameworks to monitor structural loading and fatigue during standstill conditions.

The outcomes will be documented in scientific publications and shared in dedicated workshops. In addition, the project will define key conditions and modelling aspects that require further investigation, thereby providing a building block for a broader roadmap to reduce modelling uncertainty and advance validated simulation approaches for large, flexible wind turbines under standstill conditions.