轮毂高度差或上游风力机偏航角对风力机总功率输出的影响

Influence of hub height difference or upstream wind turbine yaw angle on wind turbines total power output

为了研究风力机间轮毂高度差或上游风力机偏航角对风力机总功率输出的影响,该文以NREL5MW风力机作为研究对象,基于OpenFOAM开源软件,使用致动线模型和大涡模拟相结合的数值方法。首先对致动线模型中的重要参数高斯分布因子(ε)做了研究,并对数值方法做了可靠性验证;其次对风力机不同叶尖速比下的尾流速度特性进行了分析;最后研究了2种能减小上游风力机尾流效应而使下游风力机输出功率增大的方法。结果表明:在致动线模型中,风轮直径上有50个网格节点,ε取值为1.6倍的网格尺度时,风力机功率的相对误差最小,为1.1%;风力机尾流速度分布与叶尖速比有关,叶尖速比较大时,近尾流区的速度亏损大,尾流场的速度恢复比较快,叶尖速比比较小时,近尾流区的速度亏损小,尾流场的速度恢复比较慢;串列风力机轮毂高度不同或上游风力机存在偏航角时,可以增大下游风力机功率输出从而增大2台风力机的总功率输出。在入流速度为7 m/s,两台风力机间距离为6倍风轮直径的条件下,当上游风力机轮毂高度减去下游风力机轮毂高度的差值为0.25、0.5和0.75倍的风轮直径时,相比于上、下游风力机不存在轮毂高度差,下游风力机功率输出依次增大了1.36、2.50、4.50倍,2台风力机总功率依次增大了20%、56%和66%。当上游风力机偏航角为15°、30°和45°时,相比于上游风力机偏航角为0°,下游风力机功率输出依次增大了1.58、3.36和4.26倍,两台风力机总功率依次增加了18%、30%和22%。此研究结果可为探究提高风场总功率输出的方法提供参考。

In this paper,in order to obtain a method of increasing the power output of the downstream wind turbine by reducing the wake effect of the upstream wind turbine,NREL 5 MW wind turbines were used as research objects,and we coupled large-eddy simulation with an actuator line technique based on OpenFOAM open-source software as our numerical method.Firstly,the Gaussian width(ε)in the actuator line model was studied at the rated wind speed,we found that the error of the calculation result was the smallest when there were 50 mesh nodes along the direction of rotor diameter andεwas 1.6 times grid scale;Secondly,numerical simulations were carried out for a single wind turbine with tip-speed ratios(λ)of 15,10,8 and 7,respectively(corresponding to inflow wind speeds was 3,5,7,11.4 m/s).It was found that the wake velocity distribution was“W”type in the near-wake of the wind turbine,and with the development of the wake,the wake velocity distribution was“inverted bell”type in the far-wake of the wind turbine.The wake velocity distribution of wind turbine was related toλ.Whenλwas larger,the velocity loss in the near-wake field was larger,and the velocity of the wake field recovers faster.λwas smaller,the velocity loss in the near wake region was small,and the velocity recovery in the wake field was relatively slow.Whenλwas 15,10,8,and 7,respectively,the average speed loss at a position of 1 times rotor diameter(D)after the wind turbine was 45.7%,42.4%,38.8%,and 33.8%,respectively.When the wake developed to 18D,compared to the 1D position,the velocity recovered by 35.4%,32.4%,29.6%and 18.6%in order.Finally,through the numerical simulation of two wind turbines in tandem,two strategies by reducing the wake effect of upstream wind turbine to increase the output power of downstream wind turbine were studied.During the simulation,the distance between the two wind turbines was six times of the rotor diameter,and the inflow speeds was 5 m/s,7 m/s and 11.4 m/s,respectively.It was found that when the hub heights of the two wind turbines were different or the upstream wind turbine had a yaw angle,the power output of the downstream wind turbine can be increased.Under the condition that the inflow velocity was 7 m/s,when the difference between the hub heights of the upstream and downstream wind turbines was 0.25D,0.5D and 0.75D,respectively,compared with the situation of 0D,the power output of the downstream wind turbine increased by 1.36,2.50,4.50 times and the total power of the two wind turbines increased by 20%,56%and 66%,respectively.When the yaw angles of the upstream wind turbines were 15°,30°and 45°,respectively,compared with the situation of 0°,the power outputs of the downstream wind turbines increased by 1.58,3.36,4.26 times and the total rate of the two wind turbines increased by 18%,30%and 22%,respectively.The above research results can provide reference for wind turbine selection in wind farms and increase wind farm power output by controlling operating conditions of upstream wind turbine.