A field measurement on the aerodynamic load evolution in the start-up procedure of a wind turbine

Abstract

The start-up procedure of wind turbines is one of the most complex operating conditions, which includes the dynamic changes of pitch angle decreasing, rotor speed increasing and generator grid-connected, and implies the complex evolution of attack of angle and aerodynamic load. Besides, the velocity and direction of the inflow have strong unsteadiness in the field, which makes the variation of the angle of attack more complex. To reveal the aerodynamic behaviors of the full-scale wind turbine in the start-up procedure, a field measurement campaign was conduct on a 100 kW wind turbine with blade angle of attack, aerodynamic pressure distribution and operating parameters measured in this paper. Aerodynamic power, lift and drag, angle of attack, lift coefficient and pressure distribution were analyzed. As results, the start-up procedure can be divided into free acceleration stage, fast acceleration stage, tip-speed ratio adjustment stage and normal operation stage. The normal forces of airfoils produce the main power to drive the turbine to accelerate in the acceleration stages. The standard deviation of angle of attack decreases continuously with the increase of rotor speed. The flow around the thick airfoil at the blade inner section presents a three-dimensional stall delay effect, and the effect is weakening with the increase of rotor speed. The results reveal the variation of angle of attack and aerodynamic load during the start-up process of a full-scale wind turbine in the field, and provide valuable field measured data for the validation of aerodynamic model.