Reply on RC1

D Todd Griffith

doi:10.5194/wes-2021-60-ac1

Abstract

A good understanding of aerodynamic loading is essential in the design of vertical axis wind turbines (VAWTs) to properly capture design loads and to estimate the power production. This paper presents a comprehensive aerodynamic design study for a 5 MW Darrieus offshore VAWT in the context of multi-megawatt floating VAWTs. This study systematically analyzes the effect of different, important design variables including the number of blades (N), aspect ratio (AR) and blade tapering in a comprehensive loads analysis of both the parked and operating aerodynamic loads including turbine power performance analysis. Number of blades (N) is studied for 2- and 3-bladed turbines, aspect ratio is defined as ratio of rotor height (H) and rotor diameter (D) and studied for values from 0.5 to 1.5, and blade tapering is applied by means of adding solidity to the blades towards blade root ends, which affects aerodynamic and structural performance. Analyses were carried out using a three-dimensional vortex model named CACTUS (Code for Axial and Crossflow TUrbine Simulation) to evaluate both instantaneous azimuthal parameters as well as integral parameters, such as loads (thrust force, lateral force, and torque loading) and power. Parked loading is a major concern for VAWTs, thus this work presents a broad evaluation of parked loads for the design variables noted above. This study also illustrates that during the operation of a turbine, lateral loads are on par with thrust loads, which will significantly affect the structural sizing of rotor and platform & mooring components.

Highlights

A good understanding of aerodynamic loading is essential in the design of vertical axis wind turbines (VAWTs) to properly capture design loads and to estimate the power production
Parked loading is a major concern for VAWTs, this work presents a broad evaluation of parked loads for the design variables noted above
The wind energy community has been mostly focused on Horizontal Axis Wind Turbines (HAWTs), but recently another type of turbine named Vertical Axis Wind Turbines (VAWTs) (Bhutta et al (2012); Sutherland et al (2012)) have garnered interest especially in offshore locations (Griffith et al (2018); Möllerström et al (2016))

Summary

Introduction

In order to improve the current situation of global climate change there is a push for more environmentally sustainable sources of energy in the power grid. As wind energy costs have come down, the opportunity to fill this need by advancing the potential of wind turbine technology is at an all-time high as a part of the initiative to reduce greenhouse gas emissions and provide greater generation by renewable sources. The wind energy community has been mostly focused on Horizontal Axis Wind Turbines (HAWTs), but recently another type of turbine named Vertical Axis Wind Turbines (VAWTs) (Bhutta et al (2012); Sutherland et al (2012)) have garnered interest especially in offshore locations (Griffith et al (2018); Möllerström et al (2016)). VAWTs have some distinct advantages over HAWTs because of their low center of gravity (c.g), absence of pitch and yaw mechanism, directional independence to wind and low sound emission (due to low operational TSR) (Griffith et al (2018); Möllerström et al (2016)).

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