Impact of Neutral Boundary-Layer Turbulence on Wind-Turbine Wakes: A Numerical Modelling Study

Abstract

The wake characteristics of a wind turbine in a turbulent boundary layer under neutral stratification are investigated systematically by means of large-eddy simulations. A methodology to maintain the turbulence of the background flow for simulations with open horizontal boundaries, without the necessity of the permanent import of turbulence data from a precursor simulation, was implemented in the geophysical flow solver EULAG. These requirements are fulfilled by applying the spectral energy distribution of a neutral boundary layer in the wind-turbine simulations. A detailed analysis of the wake response towards different turbulence levels of the background flow results in a more rapid recovery of the wake for a higher level of turbulence. A modified version of the Rankine-Froude actuator disc model and the blade element momentum method are tested as wind-turbine parametrizations resulting in a strong dependence of the near-wake wind field on the parametrization, whereas the far-wake flow is fairly insensitive to it. The wake characteristics are influenced by the two considered airfoils in the blade element momentum method up to a streamwise distance of 14D (D = rotor diameter). In addition, the swirl induced by the rotation has an impact on the velocity field of the wind turbine even in the far wake. Further, a wake response study reveals a considerable effect of different subgrid-scale closure models on the streamwise turbulent intensity.

Wind-Turbine and Wind-Farm Flows: A Review

“…As a result, understanding turbine far-wakes is essential for improving the prediction and optimization of wind-turbine power output in wind farms. In recent years, a great deal of attention has been paid to studying mean flow distribution in turbine far-wakes by means of field measurements (e.g., Barthelmie et al 2004Barthelmie et al , 2006Käsler et al 2010;Trujillo et al 2011;Hirth et al 2012;Iungo et al 2013b;McKay et al 2013;Smalikho et al 2013;Aitken et al 2014b;Banta et al 2015;Marathe et al 2016;Fuertes et al 2018), laboratory experiments (e.g., Medici and Alfredsson 2006;Chamorro and Porté-Agel 2009;Maeda et al 2011;Chamorro et al 2012;Aubrun et al 2013;Singh et al 2014;Chu and Chiang 2014;Muller et al 2015;Li et al 2016;Bastankhah and Porté-Agel 2017a, b, c), and numerical simulations (e.g., Jiménez et al 2010;Porté-Agel 2011, 2012;Churchfield et al 2012b;Lee et al 2013;Mo et al 2013;Castellani and Vignaroli 2013;Chatelain et al 2013;Bastine et al 2015;Abkar and Porté-Agel 2015a;Foti et al 2016;Englberger and Dörnbrack 2017). Due to the entrainment of the outer flow, the wake is found to grow in both lateral and vertical directions as it moves downstream, and the value of the streamwise velocity component increases until the wake completely recovers far downstream (Barthelmie et al 2003;Iungo et al 2013b;Aitken and Lundquist 2014).…”

Sound propagation through the wake flow of a hilltop wind turbine—A numerical study

“…The turbine‐induced forces F in Equation are parametrized with the blade element momentum method as rotating actuator disc with a rather large nacelle, covering 20% of the blades, to avoid any kind of instabilities in the numerical model (Englberger and Dörnbrack; ED17). The tower is not considered, as it is not the major source of turbulence.…”

Erosion of the nocturnal boundary layer in the central Amazon during the dry season

“…It consists of a convective phase during the day, the convective boundary layer (CBL) and a stable phase during the night, the nocturnal boundary layer (NBL). Because of this variation throughout the day, the determination of the daily cycle of the height of the PBL has been the focus of much research Englberger and Dörnbrack 2017;Ramos et al 2018). The PBL is also a link between the surface and the free atmosphere (Neves and Fisch 2015).…”