The transonic safe mode as an enabler of next-generation wind turbines

The wind energy industry is moving towards larger and more powerful turbines, with next-generation designs expected to operate at blade tip speeds exceeding 100 ms^-1. These developments introduce new aerodynamic challenges that have not yet been explored. Here we show, using the IEA 22 MW reference turbine as a case study, that large-scale wind turbines may become susceptible to localised transonic flow effects even under normal operating conditions. By analysing the local inflow conditions along the blade and their operational settings, we identify a significant likelihood of transonic flow onset at high wind speeds above 20 ms^-1 in the outer 10% of the blade span. This is particularly driven by the inherently unsteady nature of wind turbine operation. To address this, we propose and demonstrate a Transonic Safe Mode, a framework designed to limit exposure to transonic conditions. Beyond the specific case study, the paper presents a targeted analysis methodology that highlights the additional investigations proposed to assess and ensure a safe design and operation of large-scale wind turbines. In this context, the Transonic Safe Mode offers a pragmatic and forward-looking pathway for next-generation turbines, enabling proactive risk management while focused research efforts continue to close existing knowledge gaps regarding the impact of transonic flow on wind turbine aerodynamics and structural response.