An intuitive representation and analysis of multi-rotor wind turbine whirling modes

TY - JOUR

T1 - An intuitive representation and analysis of multi-rotor wind turbine whirling modes

AU - Filsoof, Oliver Tierdad

AU - Zhang, Xuping

N1 - Publisher Copyright: © 2021 The Authors. Wind Energy published by John Wiley & Sons Ltd.

PY - 2022/3

Y1 - 2022/3

N2 - A multi-rotor wind turbine (MRWT) is a concept that can reduce the size of the rotor blades compared to a single-rotor wind turbine (SRWT). Making a cost-optimized MRWT requires a detailed understanding of its stability properties. This paper aims to establish a physical and intuitive representation of whirling modes for three-bladed isotropic SRWT and MRWT. An aeroelastic simulation of a nonlinear SRWT model is presented to empathize the importance of whirling. The whirling concept is introduced by simplifying the complexity of the wind turbine rotor into two models. From the models, edgewise and flapwise whirling modes are analyzed. An analytical model of a two-rotor wind turbine is examined to present the edgewise whirling modes of MRWT. The flapwise whirling modes for MRWT are introduced by using results from edgewise whirling and findings from previous research. The MRWT whirling analysis shows whirling from multiple rotors creates reaction forces to the supporting structure when the rotors have the same speed. This results in whirling coupling modes at the same natural frequency. One is a rotor symmetric whirling mode where the rotors whirling are in phase and a rotor asymmetric mode where whirling of the rotors are out of phase. The whirling coupling effects are minimized in the case that the rotors have different speeds.

AB - A multi-rotor wind turbine (MRWT) is a concept that can reduce the size of the rotor blades compared to a single-rotor wind turbine (SRWT). Making a cost-optimized MRWT requires a detailed understanding of its stability properties. This paper aims to establish a physical and intuitive representation of whirling modes for three-bladed isotropic SRWT and MRWT. An aeroelastic simulation of a nonlinear SRWT model is presented to empathize the importance of whirling. The whirling concept is introduced by simplifying the complexity of the wind turbine rotor into two models. From the models, edgewise and flapwise whirling modes are analyzed. An analytical model of a two-rotor wind turbine is examined to present the edgewise whirling modes of MRWT. The flapwise whirling modes for MRWT are introduced by using results from edgewise whirling and findings from previous research. The MRWT whirling analysis shows whirling from multiple rotors creates reaction forces to the supporting structure when the rotors have the same speed. This results in whirling coupling modes at the same natural frequency. One is a rotor symmetric whirling mode where the rotors whirling are in phase and a rotor asymmetric mode where whirling of the rotors are out of phase. The whirling coupling effects are minimized in the case that the rotors have different speeds.

KW - modal analysis

KW - multi-rotor wind turbine

KW - whirling

UR - http://www.scopus.com/inward/record.url?scp=85117609866&partnerID=8YFLogxK

U2 - 10.1002/we.2686

DO - 10.1002/we.2686

M3 - Journal article

AN - SCOPUS:85117609866

SN - 1095-4244

VL - 25

SP - 553

EP - 572

JO - Wind Energy

JF - Wind Energy

IS - 3

ER -