Dissipation of Turbulence in the Wake of a Wind Turbine

Abstract

The wake of a wind turbine is characterized by increased turbulence and decreased wind speed. Turbines are generally deployed in large groups in wind farms, and so the behaviour of an individual wake as it merges with other wakes and propagates downwind is critical in assessing wind-farm power production. This evolution depends on the rate of turbulence dissipation in the wind-turbine wake, which has not been previously quantified in field-scale measurements. In situ measurements of winds and turbulence dissipation from the wake region of a multi-MW turbine were collected using a tethered lifting system (TLS) carrying a payload of high-rate turbulence probes. Ambient flow measurements were provided from sonic anemometers on a meteorological tower located near the turbine. Good agreement between the tower measurements and the TLS measurements was established for a case without a wind-turbine wake. When an operating wind turbine is located between the tower and the TLS so that the wake propagates to the TLS, the TLS measures dissipation rates one to two orders of magnitude higher in the wake than outside of the wake. These data, collected between two and three rotor diameters D downwind of the turbine, document the significant enhancement of turbulent kinetic energy dissipation rate within the wind-turbine wake. These wake measurements suggest that it may be useful to pursue modelling approaches that account for enhanced dissipation. Comparisons of wake and non-wake dissipation rates to mean wind speed, wind-speed variance, and turbulence intensity are presented to facilitate the inclusion of these measurements in wake modelling schemes.

Do Wind Turbines Pose Roll Hazards to Light Aircraft?

“…Our conclusions are drawn from rolling moment calculations, though additional calculations of yawing and pitching moments could also be beneficial. Our results may also be supported by field tests, in which tethersondes (Lundquist and Bariteau, 2015) or unmanned aircraft vehicles (Kocer et al, 2012;Lawrence and Balsley, 2013;Bȧserud et al, 2014) would fly through the wake of a real utility-scale turbine during variable conditions to Roll hazard calculations were conducted using the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI1053575. JKL's effort was supported by an agreement with NREL under APUP UGA-0-41026-65.…”

Simulating effects of a wind‐turbine array using LES and RANS

“…The significant overestimation of TKE generation at 300 m resolution suggests possible scaling issues with either the explicit turbulence source in the WFP, or the rate of turbulent mixing and dissipation in the WRF model physics. Future investigations could compare observed turbulence dissipation rates [Lundquist and Bariteau, 2015] with those simulated by LES and RANS wake models. The use of an explicit TKE source in the WFP appears justified, as downwind TKE production is nearly nonexistent otherwise, resulting in unphysical wake turbulence levels.…”

U.S. East Coast Lidar Measurements Show Offshore Wind Turbines Will Encounter Very Low Atmospheric Turbulence

“…Various techniques to retrieve turbulence dissipation rates from sonic anemometers (Champagne et al, 1977;Oncley et al, 1996), high-frequency hot-wire anemometers suspended on tethered lifting systems (Frehlich et al, 2006;Lundquist & Bariteau, 2015), or flown on aircrafts (Fairall et al, 1980) or unmanned aerial vehicles (Lawrence & Balsley, 2013) have been developed. Despite the potential drawback of their inherent volume averaging (Frehlich & Cornman, 2002;Wang et al, 2016), the ease of deployment and extended measurement range of remote sensing instruments have fueled research to derive methods to Geophysical Research Letters 10.1029/2019GL082636 retrieve from lidars (Banakh et al, 1996;Frehlich, 1994;O'Connor et al, 2010;Wulfmeyer et al, 2016) and radars (McCaffrey et al, 2017;Shaw & LeMone, 2003).…”