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Three-dimensionality of the wake recovery behind a vertical axis turbine

Ouro, Pablo, Runge, Stefan, Luo, Qianyu and Stoesser, Thorsten 2019. Three-dimensionality of the wake recovery behind a vertical axis turbine. Renewable Energy 133 , pp. 1066-1077. 10.1016/j.renene.2018.10.111
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Abstract

The wake recovery downstream of a vertical axis turbine operating in a turbulent channel flow is investigated via detailed velocity measurements using an Acoustic Doppler Velocimeter. Three distinct wake regions are identified: (i) a near-wake region which extends until two rotor diameters (2D) downstream and characterised by a low-momentum area isolated from the ambient flow and the presence of energetic dynamic stall vortices; (ii) a transition region (2D-5D), characterised by a fast momentum recovery, high levels of turbulence and vertical expansion of the wake; and (iii) a far-wake region beyond 5D where the velocity recovers to approximately 95% of the free-stream velocity. Albeit the wake deficit recovery is mostly accomplished at 5D behind the turbine, rotor-induced effects are still present beyond 10D as indicated by high-order flow statistics, such as high velocity fluctuations and flow skewness. The analysis of the streamwise momentum budget reveals that advection is the main mechanism for momentum replenishment through most of the wake and turbulent transport terms play only a minor role. This study evidences the anisotropic nature of the turbulence and asymmetry of the flow in horizontal, vertical and cross-sectional planes downstream of the vertical axis turbine.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Engineering
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
T Technology > TC Hydraulic engineering. Ocean engineering
Publisher: Elsevier
ISSN: 1442-133X
Date of First Compliant Deposit: 2 November 2018
Date of Acceptance: 30 October 2018
Last Modified: 01 Jul 2019 09:14
URI: http://orca.cf.ac.uk/id/eprint/116392

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