Experimental validation of parked loads for a floating vertical axis wind turbine: wind–wave basin tests

Abstract

Parked loads are a major design load case for vertical axis wind turbines (VAWTs) because of persistent high loads on the rotor when in standstill conditions. This paper examines the aerodynamic parked loads of model-scale floating troposkein VAWTs tested in a wind–wave basin to support development and validation of a parked load model for floating VAWTs. We analyze the effects of wind speed, turbine solidity (varying number of blades), and rotor azimuth on parked loads and investigate the impact of different wind–wave platform conditions (comparing locked (fixed tower base) versus floating cases with and without waves). The experimental results indicate that parked loads (for both locked and floating platform conditions) and the amplitude of turbine tilting increase with the wind speed, which is expected. The parked loads also increase with the increase in solidity; however, the variation in loads in a revolution decreases for three blades versus two blades. If only aerodynamic parked loads are considered, the turbine with a floating platform exhibits lower parked loads compared to turbine with a locked platform (fixed base) due to the effect of the tilted condition of the floating platform. Moreover, comparison between floating with wind–wave and floating with wind only cases shows that although both exhibit parked loads of similar magnitude, the former exhibits more high-frequency variation due to coupled effects of wind, wave, and floating platform dynamics. Additionally, we present a semi-numerical tool for estimating parked loads of VAWTs that we improved and validated to predict the floating parked loads. The semi-numerical model accurately predicts the parked load behavior of VAWTs for the range of effects noted above. The datasets from this experimental work can serve as benchmarks for validating other computational parked load estimating tools, while the semi-numerical tool provides a way to gain insight into the unmeasurable quantities.