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Energies 2017, 10(10), 1599; https://doi.org/10.3390/en10101599

Sensitivity Analysis to Control the Far-Wake Unsteadiness Behind Turbines

1
ETSIAE (School of Aeronautics)—Universidad Politécnica de Madrid, Pza Cardenal Cisneros 3, E-28040 Madrid, Spain
2
Center for Computational Simulation—Universidad Politécnica de Madrid, Boadilla del Monte, E-28660 Madrid, Spain
3
Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ 85721, USA
*
Author to whom correspondence should be addressed.
Received: 19 August 2017 / Revised: 9 October 2017 / Accepted: 10 October 2017 / Published: 13 October 2017
(This article belongs to the Collection Wind Turbines)
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Abstract

We explore the stability of wakes arising from 2D flow actuators based on linear momentum actuator disc theory. We use stability and sensitivity analysis (using adjoints) to show that the wake stability is controlled by the Reynolds number and the thrust force (or flow resistance) applied through the turbine. First, we report that decreasing the thrust force has a comparable stabilising effect to a decrease in Reynolds numbers (based on the turbine diameter). Second, a discrete sensitivity analysis identifies two regions for suitable placement of flow control forcing, one close to the turbines and one far downstream. Third, we show that adding a localised control force, in the regions identified by the sensitivity analysis, stabilises the wake. Particularly, locating the control forcing close to the turbines results in an enhanced stabilisation such that the wake remains steady for significantly higher Reynolds numbers or turbine thrusts. The analysis of the controlled flow fields confirms that modifying the velocity gradient close to the turbine is more efficient to stabilise the wake than controlling the wake far downstream. The analysis is performed for the first flow bifurcation (at low Reynolds numbers) which serves as a foundation of the stabilization technique but the control strategy is tested at higher Reynolds numbers in the final section of the paper, showing enhanced stability for a turbulent flow case. View Full-Text
Keywords: stability analysis; sensitivity analysis; wake unsteadiness; wake meandering; passive control; wind turbine; tidal turbine; discontinuous Galerkin stability analysis; sensitivity analysis; wake unsteadiness; wake meandering; passive control; wind turbine; tidal turbine; discontinuous Galerkin
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Ferrer, E.; Browne, O.M.; Valero, E. Sensitivity Analysis to Control the Far-Wake Unsteadiness Behind Turbines. Energies 2017, 10, 1599.

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