Wake steering of multirotor wind turbines

Abstract

In this paper, wake steering is applied to multirotor turbines to determine whether it has the potential to reduce wind plant wake losses. Through application of rotor yaw to multirotor turbines, a new degree of freedom is introduced to wind farm control such that wakes can be expanded, channelled or redirected to improve inflow conditions for downstream turbines. Five different yaw configurations are investigated (including a baseline case) by employing large‐eddy simulations (LES) to generate a detailed representation of the velocity field downwind of a multirotor wind turbine. Two lower‐fidelity models from single‐rotor yaw studies (curled‐wake model and analytical Gaussian wake model) are extended to the multirotor case, and their results are compared with the LES data. For each model, the wake is analysed primarily by examining wake cross‐sections at different downwind distances. Further quantitative analysis is carried out through characterisations of wake centroids and widths over a range of streamwise locations and through a brief analysis of power production. Most significantly, it is shown that rotor yaw can have a considerable impact on both the distribution and magnitude of the wake velocity deficit, leading to power gains for downstream turbines. The lower‐fidelity models show small deviation from the LES results for specific configurations; however, both are able to reasonably capture the wake trends over a large streamwise range.

Modelling the induction, thrust and power of a yaw-misaligned actuator disk

“…The power of the yawed actuator disk in this limiting case is The power and thrust ratios in this limiting case are The power ratio model given by (2.22 a ) was also reported by Speakman et al. (2021), who leveraged the streamwise induction model developed by Shapiro et al. (2018) (same as (2.19)).…”

“…The power ratio model given by (2.22a) was also reported by Speakman et al (2021) ). Fourier collocation is used in the horizontal directions and a sixth-order staggered compact finite difference scheme is used in the vertical direction (Nagarajan, Lele & Ferziger 2003).…”

“…Speakman et al. (2021) used the axial induction equation proposed by Shapiro et al. (2018) to model for a simulation with thrust coefficient , which yielded improved power predictions compared to the model, but higher predictive error than a tuned with set to .…”

“…Using the Bernoulli equation, Shapiro, Gayme & Meneveau (2018) proposed an equation for the dependence of the axial induction factor on the yaw misalignment of an actuator disk. Speakman et al (2021) used the axial induction equation proposed by Shapiro et al (2018) to model P r (γ ) for a simulation with thrust coefficient 0.75, which yielded improved power predictions compared to the cos 3 (γ ) model, but higher predictive error than a tuned cos P p (γ ) with P p set to 1.88.…”

A vortex sheet based analytical model of the curled wake behind yawed wind turbines

“…Analytical wake models can be particularly useful in implementation of wake mitigation strategies such as wake steering, which has been receiving growing attention as an important control approach for increasing wind farm power output (Fleming et al 2014;Gebraad et al 2014;Bastankhah & Porté-Agel 2015;Campagnolo et al 2016;Howland et al 2016;Schottler et al 2017;Bartl et al 2018;Lin & Porté-Agel 2019;Kleusberg, Schlatter & Henningson 2020;Speakman et al 2021). Achieving increased power output through wake steering involves turbines, often in the front rows of wind farms, being intentionally operated in yawed conditions to redirect their wakes away from downwind turbines.…”