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Transition to bluff-body dynamics in the wake of vertical-axis wind turbines

Araya, Daniel B. and Colonius, Tim and Dabiri, John O. (2017) Transition to bluff-body dynamics in the wake of vertical-axis wind turbines. Journal of Fluid Mechanics, 813 . pp. 346-381. ISSN 0022-1120. http://resolver.caltech.edu/CaltechAUTHORS:20170407-133420635

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Abstract

We present experimental data to demonstrate that the far wake of a vertical-axis wind turbine (VAWT) exhibits features that are quantitatively similar to that of a circular cylinder with the same aspect ratio. For a fixed Reynolds number (Re ≈ 0.8 × 10^5) and variable tip-speed ratio, two-dimensional particle image velocimetry (PIV) is used to measure the velocity field in the wake of four different laboratory-scale models: a 2-bladed, 3-bladed and 5-bladed VAWT, as well as a circular cylinder. With these measurements, we use spectral analysis and proper orthogonal decomposition (POD) to evaluate statistics of the velocity field and investigate the large-scale coherent motions of the wake. In all cases, we observe three distinct regions in the VAWT wake: (i) the near wake, where periodic blade vortex shedding dominates; (ii) a transition region, where growth of a shear-layer instability occurs; (iii) the far wake, where bluff-body wake oscillations dominate. We define a dynamic solidity parameter, σ_D , that relates the characteristic scales of the flow to the streamwise transition location in the wake. In general, we find that increasing σ_D leads to an earlier transition, a greater initial velocity deficit and a faster rate of recovery in the wake. We propose a coordinate transformation using σ_D in which the minimum velocity recovery profiles of the VAWT wake closely match that of the cylinder wake. The results have implications for manipulating VAWT wake recovery within a wind farm.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1017/jfm.2016.862DOIArticle
ORCID:
AuthorORCID
Colonius, Tim0000-0003-0326-3909
Additional Information:© 2017 Cambridge University Press. (Received 21 October 2015; revised 13 December 2016; accepted 14 December 2016; first published online 19 January 2017)
Subject Keywords:turbulent flows, vortex flows, wakes/jets
Record Number:CaltechAUTHORS:20170407-133420635
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20170407-133420635
Official Citation:Araya, D., Colonius, T., & Dabiri, J. (2017). Transition to bluff-body dynamics in the wake of vertical-axis wind turbines. Journal of Fluid Mechanics, 813, 346-381. doi:10.1017/jfm.2016.862
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75854
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:07 Apr 2017 20:54
Last Modified:07 Oct 2017 04:11

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