实度对垂直轴风轮功率系数影响的数值模拟分析

垂直轴风轮是风能转换的主要设备之一，CFD方法是对其复杂绕流场进行数值模拟的有效手段。实度是影响垂直轴风轮性能的主要参数之一，由叶片数、翼型弦长及转子半径三个参数共同决定。为研究不同参数组合工况下垂直轴风轮的气动力学行为，采用SST-DDES方法对垂直轴风轮二维模型进行了数值模拟，并与已有研究结果对比分析，评估了SST-DDES预测垂直轴风轮气动性能的准确性。其次，对模拟结果有关键影响的计算域、网格精度以及时间步长进行了无关性研究，减少计算资源消耗并增进数值模拟的可靠性。最后，对多组不同实度的工况进行数值模拟，得到每种工况下功率系数与尖速比的关系曲线。结果表明，风轮实度在0.2 ~ 0.5之间时其功率系数峰值最大；两叶片风轮比多叶片风轮具有更高的功率系数峰值和更宽的有效尖速比范围；增大风轮的半径可显著提高风轮的功率峰值系数；风轮实度及半径一定时，不同叶片数和弦长组合具有相似的功率系数曲线 Vertical axis wind turbine (VAWT) is one of the main equipment for wind energy conversion, and computational fluid dynamics (CFD) is the most effective method to study its aerodynamic behavior. Rotor solidity, which is defined by three physical parameters, blade number, chord length and rotor radius, has been identified as a key parameter on the performance of a VAWT. However, there is a lack of systematic studies on these three parameters in the literature. To examine the effect of the solidity, two-dimensional numerical simulations were performed based on the shear stress transport-delayed detached eddy simulation (SST-DDES) method. The SST-DDES model was validated against published experiment data by comparing the power coefficient (CP) and drag coefficient (CD). Besides, domain size, mesh density and time step were analyzed and optimized in order to reduce the computational time cost and to improve the reliability of the simulations. Cases of different solidities were computed and curves of CP were obtained. There exists a maximum CP when the solidity value varies between 0.2 and 0.5. VAWTs with two blades achieve a higher peak of CP and a wider range of effective tip speed ratio. Increasing the radius of the rotor can significantly increase the peak CP of VAWTs. By keeping the solidity and rotor radius constant, VAWTs with different blade numbers have similar CP curves.