An investigation of the impact of turbulence intermittency on the rotor loads of a small wind turbine

Abstract Small wind turbines (SWT) are designed according to the IEC 61400-2, which assumes the SWT experiences a set of standard wind conditions, developed through assumptions of flat terrain and normal turbulence models. In practice, other wind conditions can exist at SWT sites including winds, influenced by terrain, that feature speed and turbulence behaviour outside the set of standard conditions. In this study, wind conditions at two contrasting locations; one from built environment (Port Kennedy) and another from open terrain (Ostergarnsholm), are analysed using two-point statistical approach for small-scale fluctuations. The probability density function (PDF) of the wind speed increments obtained from the two-point statistics reveals that the PK wind cases show the highest intermittency of turbulence at small timescales and this appears to manifest as higher intermittency of the rotor dynamic loads. The PDFs of rotor torque, thrust, and blade flapwise bending moment all show an increased likelihood of larger load fluctuations and occurrence of more extreme events for the turbine operating in the built environment site. The heavier tails of their PDF suggest that the turbine needs to be structurally robust and have better control system to handle these extreme events when operated in sites with complex terrain.