Measurements and modelling of the wind speed profile in the induction zone of an offshore wind turbine

Abstract

Large wind turbine rotors require the measurement of the wind speed profile across the whole rotor for accurate performance and load assessments. Acquiring these measurements close to the rotor - in the induction zone - has the advantage of high correlation between the wind at the measurement location and the wind that acts on the rotor. In this paper measurements of the wind speed field upstream of a multi-megawatt wind turbine are presented and compared with a simple model of the deceleration of wind speeds in the induction zone. The measurements are taken at several distances in front of the rotor and include the full shear profile across the rotor, which is incorporated into the model by scaling the radial induction field with a free stream shear profile. The model captures the observations very accurately if a mirror turbine is included to model the effect of the ground plane. This model validation provides further evidence of the feasibility to conduct power curve verifications with measurements in the induction zone.