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

Abstract

Growth in wind power production has motivated investigation of wind‐farm impacts on in situ flow fields and downstream interactions with agriculture and other wind farms. These impacts can be simulated with both large‐eddy simulations (LES) and mesoscale wind‐farm parameterizations (WFP). The Weather Research and Forecasting (WRF) model offers both approaches. We used the validated generalized actuator disk (GAD) parameterization in WRF‐LES to assess WFP performance. A 12‐turbine array was simulated using the GAD model and the WFP in WRF. We examined the performance of each scheme in both convective and stable conditions. The GAD model and WFP produced qualitatively similar wind speed deficits and turbulent kinetic energy (TKE) production across the array in both stability regimes, though the magnitudes of velocity deficits and TKE production levels were underestimated and overestimated, respectively. While wake growth slowed in the latter half of the WFP array as expected, wakes did not approach steady state by the end of the array as simulated by the GAD model. A sensitivity test involving the deactivation of explicit TKE production by the WFP resulted in turbulence levels within the array well that were below those produced by the GAD in both stable and unstable conditions. Finally, the WFP overestimated downwind power production deficits in stable conditions because of the lack of wake stabilization in the latter half of the array.

Do wind turbines pose roll hazards to light aircraft?

“…While we have shown that individual wakes in neutrally stratified and stably stratified conditions are unlikely to pose hazards to general aviation aircraft, interactions between wakes could also be explored. Future simulations of wind plants that allow for wake interaction (as in Vanderwende et al, 2016) and larger turbine types could be useful. Our conclusions are drawn from rolling moment calculations, though additional calculations of yawing and pitching moments could also be beneficial.…”

“…Representing turbines in LES can be done via actuator disks, where the turbine rotor is represented by a permeable circular disk with uniformly distributed thrust forces (Vermeer et al, 2003;Calaf et al, 2010;Mirocha et al, 2014;Aitken et al, 2014b;Vanderwende et al, 2016) or by actuator lines, which represent the turbine blades as separate rotating lines (Sørensen and Shen, 2002;Porté-Agel et al, 2011;Nilsson et al, 2015). Martínez-Tossas et al (2015) compare actuator-line and actuator-disk models and conclude that they produce similar wake profiles; however, the actuatorline model can generate fine flow structures near the blades such as root and tip vortices that the actuator-disk model cannot.…”

“…Computational fluid dynamics (CFD) simulations of wind turbine wakes provide insights into turbine wakes (Sanderse et al, 2011). Both actuator-disk (Vermeer et al, 2003;Calaf et al, 2010;Mirocha et al, 2014;Vanderwende et al, 2016) and actuator-line (Sørensen and Shen, 2002;Troldborg et al, 2010;Churchfield et al, 2012;Marjanovic et al, 2017) methods have been used to simulate the rotor and downstream flow to study wake structure.…”

Do Wind Turbines Pose Roll Hazards to Light Aircraft?

“…While we have shown that individual wakes in neutrally stratified and stably stratified conditions are unlikely to pose hazards to general aviation 25 aircraft, interactions between wakes could also be explored. Future simulations of wind plants that allow for wake interaction (as in Vanderwende et al (2016)) could be useful. Our conclusions are drawn from rolling moment calculations, though additional calculations of yawing and pitching moments could also be beneficial.…”

“…Representing turbines in LES can be done via actuator disks, where the turbine rotor is represented by a permeable circular disk with uniformly distributed thrust forces (Vermeer et al, 2003;Calaf et al, 2010;Mirocha et al, 2014;Aitken et al, 2014b;Vanderwende et al, 2016), or by actuator lines, which represent the turbine blades as separate rotating lines (Sørensen and Shen, 2002;Porté-Agel et al, 2011;Nilsson et al, 2015). Martínez-Tossas et al (2015) compare actuator-line and actuatordisk models and conclude that they produce similar wake profiles; however, the actuator-line model can generate fine flow structures near the blades such as root and tip vortices that the actuator-disk model cannot.…”