To fulfill the increasing need for large power generation by wind turbines, the concept of multirotor wind turbines has recently received attention as a promising alternative to conventional massive single-rotor wind turbines. To shed light on the viability of this concept, large-eddy simulation is employed in this study to compare wake flow properties of a multirotor wind turbine with those of a single-rotor turbine. The wake of a multirotor turbine is found to recover faster at short downwind distances, where the whole wake is characterized as an array of localized high velocity-deficit regions associated with each rotor. However, as the wake moves downstream, rotor wakes start interacting with each other until they eventually form a single wake. This transition from a wake array to a single wake adversely affects the initial fast recovery of multirotor turbine wakes. A budget analysis of mean kinetic energy is performed to analyze the energy transport into the wake before and after this transition. In addition, the effect of different geometrical configurations on wake characteristics of a multirotor turbine was examined. We found that the recovery rate of multirotor turbine wakes is enhanced by the increase in rotor spacing, whereas the number and rotation direction of rotors do not play a significant role in the wake recovery. A simple analytical relationship is also developed to predict the streamwise distance at which the transition from a wake array to a single wake occurs for multirotor wind turbines.
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August 2019
Research Article|
August 06 2019
Multirotor wind turbine wakes
Majid Bastankhah
;
Majid Bastankhah
a)
1
Department of Engineering, Durham University
, Durham DH1 3LE, United Kingdom
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Mahdi Abkar
Mahdi Abkar
b)
2
Department of Engineering, Aarhus University
, 8000 Aarhus C, Denmark
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Majid Bastankhah
1,a)
Mahdi Abkar
2,b)
1
Department of Engineering, Durham University
, Durham DH1 3LE, United Kingdom
2
Department of Engineering, Aarhus University
, 8000 Aarhus C, Denmark
a)
Electronic mail: [email protected]
b)
Electronic mail: [email protected]
Physics of Fluids 31, 085106 (2019)
Article history
Received:
March 24 2019
Accepted:
July 11 2019
Citation
Majid Bastankhah, Mahdi Abkar; Multirotor wind turbine wakes. Physics of Fluids 1 August 2019; 31 (8): 085106. https://doi.org/10.1063/1.5097285
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