Effects of upstream rotor tilt on a downstream floating wind turbine

P Doubrawa,M Godvik,S Sirnivas

doi:10.1088/1742-6596/1934/1/012016

Abstract

This work quantifies the relationship between the design tilt of an upstream rotor and the structural response of a spar floating offshore wind turbine located in its wake. Three wind speed scenarios are considered: below, at, and above rated operation. The inflow is generated with the Mann model and the wake and loads are simulated with FAST.Farm. As the upstream rotor tilt goes from 0° to 6°, we find that the mean wake is displaced upward by more than 0.2 rotor diameters (D) by a downstream distance of 7 D. The vertical velocities increase by up to 35 cm/s in the center of the wake. As a result, the downstream rotor is partially waked and experiences a rotated velocity vector. With a higher upstream rotor tilt, the velocities and moments on the downstream turbine increase their mean axial value and their lateral and vertical standard deviation. These changes affect the blade and tower loading and the floater motion primarily in the out-of-plane direction: the damage-equivalent loads for the tower pitch moment and blade-root moment increase by up to 10% because of higher variability at the first mode for the tower and at one blade passing frequency for the blade root. Lesser effects are observed for the roll moments and for floater sway and heave. When the joint effect of rotor tilt and platform motion is considered, the load response on the downstream system is amplified primarily for tower pitch and blade out-of-plane moment.

Highlights

The tilt angle of a wind turbine rotor directly affects its wake and, the power and loads on downstream turbines
This is the exact distance between the two turbines, so we performed a separate simulation for each case to include only the upstream turbine and sample the wake flow field at the exact location where the downstream turbine sits
This study revealed that rotor tilt, as a design parameter, has a direct effect on the structural loading of a floating offshore wind turbine

Summary

Introduction

The tilt angle of a wind turbine rotor directly affects its wake and, the power and loads on downstream turbines. While the effect of rotor tilt on wakes has been extensively analyzed, no studies have considered how these changes in the wake affect the structural response of a downstream, floating wind turbine. To support the design of floating systems, we need to understand how rotor tilt, as a design parameter, affects the wake and downstream turbines even before the effects of platform pitch are considered.

Results

Conclusion