Power conversion performance of airborne wind turbine under unsteady loads

Abstract The study presents the systematic analysis of power conversion performance of the airborne wind turbine (AWT) using time-resolved air loads. The power harvesting behavior of the rotating blades in shell configuration is numerically investigated to analyze the influence of wind shear, yawed and tilted inflows at design operating conditions. An inherently unsteady scheme of the sliding mesh is incorporated to capture the complex flow field across the 3-bladed rotor. The fully-resolved computations closely match the expected results derived from the empirical calculations. The conversion performance supplements the turbine's power curve as a means of determining the distribution of aerodynamic forces, performance coefficients, vortex structure and shell thrust loadings. The time-marching response of the AWT gradually attains steady flow characteristics after two rotation periods when the wind shear profile is fully aligned with the rotor's axis of rotation. This yields a beneficial gain of 64% more power output with the rotor in shell configuration than those of the bare configuration. Meanwhile, cyclic fluctuations (±21%) significantly undermine the continuous production of power in the case of skewed flow conditions. Moreover, the flow misalignment causes a localized shifting of effective forces on the rotor plane due to the intricate impact of the shell structure. • 3D URANS-CFD simulations are performed using a full-scale model of AWT. • The yaw/tilt misalignments are adopted to predict the power conversion performance. • The time-averaged behavior of the shell rotor is analyzed for unsteady airloads. • A beneficial gain of 64% in power output is yielded for shell rotor configuration. • The output sensitivity is elaborated by in-depth comparison of performance curves.