The induction zone/factor and sheared inflow: A linear connection?

AR Meyer Forsting*, MP van der Laan, Niels Troldborg

*Corresponding author for this work

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Abstract

Sheared inflow causes significant periodic load variations in wind turbine blades, but has only limited impact on the mean wake deficit. Following these findings the wind speed reduction upstream of the turbine - referred to as the induction zone - might also show little difference to uniform inflow. Using the local free-stream velocity to normalise the upstream flow-field should then render uniform and sheared inflow induced velocity profiles indiscernible, hinting towards wind shear acting solely as a linear addition. This has great implications in BEM methods for determining the velocity at the blades and also for near-rotor lidar measurements. The latter being applied in for power/loads assessment and turbine control. LES simulations with an actuator line representation of the rotor confirm the linearity assumption for moderate wind shear. To estimate the normal velocities at the disc the annularly averaged thrust coefficient is best suited, when the induction is imposed on the inflow profile. A strictly local relationship breaks down in strongly sheared flow. A simple induction zone model devised for uniform inflow estimates the velocity upstream within ±0.5% even at extreme shear in the upper half of the rotor and at least three rotor radii away from the turbine.
Original languageEnglish
Article number072031
Book seriesJournal of Physics: Conference Series
Volume1037
Issue number7
Number of pages9
ISSN1742-6596
DOIs
Publication statusPublished - 2018
EventThe Science of Making Torque from Wind 2018 - Politecnico di Milano (POLIMI), Milan, Italy
Duration: 20 Jun 201822 Jun 2018
Conference number: 7
http://www.torque2018.org/

Conference

ConferenceThe Science of Making Torque from Wind 2018
Number7
LocationPolitecnico di Milano (POLIMI)
CountryItaly
CityMilan
Period20/06/201822/06/2018
Internet address

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