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Energies 2015, 8(1), 370-386; doi:10.3390/en8010370

Altering Kinetic Energy Entrainment in Large Eddy Simulations of Large Wind Farms Using Unconventional Wind Turbine Actuator Forcing

Department of Mechanical Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
This paper is an extended version of our paper published in VerHulst, C., Meneveau, C. LES Study of the Impact of Various Wind Turbine Actuator Forcings on Kinetic Energy Entrainment in Large Wind Farms. In Proceedings of the International Conference on Aerodynamics of Offshore Wind Energy Systems and Wakes, Copenhagen, Denmark, 17–19 June 2013; pp. 657–668.
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Author to whom correspondence should be addressed.
Academic Editor: Frede Blaabjerg
Received: 30 October 2014 / Accepted: 30 December 2014 / Published: 6 January 2015
(This article belongs to the Collection Wind Turbines)
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Abstract

In this study, horizontally periodic large eddy simulations (LES) are utilized to study turbulent atmospheric boundary-layer flow over wind turbines in the far-downstream portion of a large wind farm where the wakes have merged and the flow is fully developed. In an attempt to increase power generation by enhancing the mean kinetic energy (MKE) entrainment to the wind turbines, hypothetical synthetic forcing is applied to the flow at the turbine rotor locations. The synthetic forcing is not meant to represent any existing devices or control schemes, but rather acts as a proof of concept to inform future designs. The turbines are modeled using traditional actuator disks, and the unconventional synthetic forcing is applied in the vertical direction with the magnitude and direction dependent on the instantaneous velocity fluctuation at the rotor disk; in one set of LES meant to enhance the vertical entrainment of MKE, a downward force is prescribed in conjunction with a positive axial velocity fluctuation, whereas a negative axial velocity fluctuation results in an upward force. The magnitude of the forcing is proportional to the instantaneous thrust force with prefactors ranging from 0.1 to 1. The synthetic vertical forcing is found to have a significant effect on the power generated by the wind farm. Consistent with previous findings, the MKE flux to the level of the turbines is found to vary along with the total power produced by the wind turbine array. The reverse strategy of downward forcing of slow axial velocity flow is found to have almost no effect on the power output or entrainment. Several of the scenarios tested, e.g., where the vertical force is of similar magnitude to the horizontal thrust, would be very difficult to implement in practice, but the simulations serve the purpose of identifying trends and bounds on possible power increases from flow modifications through action at the turbine rotor. View Full-Text
Keywords: wind turbines; large eddy simulation (LES); kinetic energy entrainment; actuator disk model wind turbines; large eddy simulation (LES); kinetic energy entrainment; actuator disk model
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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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VerHulst, C.; Meneveau, C. Altering Kinetic Energy Entrainment in Large Eddy Simulations of Large Wind Farms Using Unconventional Wind Turbine Actuator Forcing. Energies 2015, 8, 370-386.

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