We evaluate the accuracy of the actuator line model (ALM) approach by performing simulations for the NREL~5~MW wind turbine in uniform inflow using three large eddy simulation codes. The power and thrust coefficients obtained using the three codes agrees within $1\%$ when the grid spacing $Δ_{\rm grid} \le 5.25$~m, and are cross-validated against blade element momentum (BEM) theory. We find that the results of ALM converge towards BEM theory without the need for tip correction when the numerical resolution is increased. For $Δ_{\rm grid}=0.98$~m the difference between the power and thrust coefficient obtained using ALM and BEM is $4.5\%$ and $2.1\%$, respectively, although we note that no absolute convergence between ALM and BEM can be obtained as both models use different assumptions, such as the use of a force projection method in the ALM. The difference in the local axial and tangential forces along the blades obtained from ALM simulations using $Δ_{\rm grid} = 1.97$~m and $Δ_{\rm grid} = 0.98$~m can be as large as $10\%$. The effect of the number of actuator points on the obtained turbine power and thrust coefficients is limited as the results converge when the spacing between the actuator points is about three times the grid spacing. This insight on the required number of blade points can be used to improve the efficiency of actuator line simulations.
The present investigation provides the first field characterization of the influence of turbulent inflow on the blade structural response of a utility-scale wind turbine (2.5MW), using the unique facility available at the Eolos Wind Energy Research Station of the University of Minnesota. A representative one-hour dataset under a stable atmosphere is selected for the characterization, including the inflow turbulent data measured from the meteorological tower, high-resolution blade strain measurement at different circumferential and radiation positions along the blade, and the wind turbine opera…
Here we have investigated the usage of a Dielectric Barrier Discharge (DBD) plasma actuator to improve the aerodynamic performance of an offshore 6MW wind turbine. By controlling the aerodynamic load at different blade sections, the overall generated power and the blade loading is improved. The blade is divided to seven segments and the analysis is applied to each segment. To study effects of configuration and location, actuators were installed in a single or tandem configuration, spread between 46% and 56% of the span length, at different chord wise locations. The improved phenomenological mo…
Yaw control has proven to be promising in alleviating the wake effects that plague the efficiency of wind farms. In this work, the actuator line modeling (ALM) method is adopted to simulate the flows over two tandem turbines distanced by $3 - 7$ rotor diameters, with the yaw angle of the upstream rotor varying from $γ_1=0^{\circ}$ to $50^{\circ}$. The aim is to provide a comprehensive aerodynamic characterization of a simple wind farm under yaw misalignment. With increasing yaw angle, the power generated by the downstream rotor increases, compensating the power loss in the upstream rotor, and …
We present first results of an implicit large eddy simulation of the MTU T161 low pressure turbine at a Reynolds number of 90,000 and Mach number of 0.6, both based on isentropic exit conditions, using a high order discontinuous Galerkin method. The aim is to validate the numerical setup with respect to available experimental data. We discuss the steps taken to create realistic inflow boundary conditions in terms of end wall boundary layer thickness and free stream turbulence intensity. This is achieved by tailoring the input distribution of Reynolds stresses and turbulent length scale to a Fo…
Wind turbines operate under constantly changing turbulent inflow conditions. In the rotating system, wind gusts lead to variations in the angle of attack at local blade segments resulting in dynamic effects such as dynamic stall. Such highly non-linear effects are known to produce a significant overshoot in the lift and thus an increase in loads acting on the wind turbine, leading to long-term fatigue. To better understand these effects, it is essential to perform experiments under defined conditions on 2D airfoil segments in the wind tunnel. In this study, a so-called 2D active grid is presen…
Rotor blades of wind turbines in the atmospheric boundary layer regularly experience the aerodynamic phenomenon of dynamic stall consisting of a temporary overshoot of lift and detrimental fatigue loads. Particularly the formation of dynamic stall under three-dimensional inflow conditions raises open questions. Aerodynamic behavior of a DU 91-W2-250 wind profile undergoing light dynamic stall is thus analyzed in a wind tunnel. Effects of a gust with streamwise and spanwise periodic variation are investigated by comparing total and local lift generation with flow formation above the airfoil. Th…
Atmospheric turbulent velocity fluctuations are known to increase wind turbine structural loading and accelerate wake recovery, but the impact of vortical coherent structures in the atmosphere on wind turbines has not yet been evaluated. The current study uses flow imaging with natural snowfall with a field of view spanning the inflow and near wake. Vortical coherent structures with diameters on the order of 1 m are identified and characterized in the flow approaching a 2.5 MW wind turbine in the region spanning the bottom blade tip elevation to hub height. Their impact on turbine structural l…
Two configurations typical of fixed-wing aircraft are simulated with the actuator line method (ALM): a wing with winglets and a T-tail. The ALM is extensively used in rotor simulations to model the blades by body forces, which are calculated from airfoil data and the relative flow velocity. This method has not been used to simulate airplane aerodynamics, despite its advantage of allowing coarser grids. This may be credited to the failure of the uncorrected ALM to accurately predict forces near the tip of wings, even for simple configurations. The recently-proposed vortex-based smearing correct…
High-order gas-kinetic scheme for numerical simulations of wind turbine with nacelle and tower using ALM and IBM
Beijing Normal University（北京师范大学）；University of Oxford（牛津大学）；Suzhou Stream Energy Technology Co., Ltd.（苏州流能源科技有限公司）；Institute of Mechanics, Chinese Academic of Sciences（中国科学院力学研究所）；University of Chinese Academy of Sciences（中国科学院大学）；Beihang University（北京航空航天大学）；University of Bristol（布里斯托大学）
Generalisation of the two-scale momentum theory for coupled wind turbine/farm optimisation
提出了一种扩展的理论方法来预测大型有限规模风电场中风力机的平均功率。该方法基于最近提出的用于模拟理想超大型风力发电场的双尺度动量理论，但该理论现在通过引入由发电场上游和下游侧之间的发电场引起的附加压差的影响而得到推广，使该方法适用于大但不像驱动气流的相关大气系统的大小那样大的实际风电场农场为了验证广义理论模型，在八种不同的条件下，对大阵列（25 x 25）的致动器（阻力）盘上的边界层流进行了三维雷诺平均Navier-Stokes模拟。结果表明，广义模型可以嵌入到一个区域尺度的大气模型，以预测一个给定的风电场的平均功率有效。该方法还可以与叶片单元动量（BEM）理论相结合，用于耦合的风力机/农场优化。
