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2 Aerodynamic Model
气动模型
The basic principle of the DMST model is explained in following. A more detaileddescription may be found e.g. in [2]. The rotor swept area is pided into a series ofadjacent stream-tubes. The loading on a blade element passing the stream-tube depends on the local relative velocity, which is the resultant of the local wind speed Uu,d and the rotational motion ωR. But Uu,d depends on how much the turbine has retarded the ambient wind, which in turn is a function of the blade load. To break this circular cycle of dependence, the DMST model uses a combination of actuator disc and blade element theories. As depicted in Figure 2, each stream tube intersects the airfoil path twice; once on the upwind pass, and again on the downwind pass. At these intersections we imagine the turbine replaced by a tandem pair of actuator discs, upon which the flow may exert force. The DMST model simultaneously solves two equations for the stream-wise force at the actuator disk; one obtained by conservation of momentum and other based on the aerodynamic coefficients of the airfoil (lift and drag) and the local wind velocity. These equations are solved twice; for the upwind and for the downwind part of the rotor. The uncertainties of the model are due to the aerodynamic coefficients which are typically available only for a small range of static change of angle of attack. The empirical model of Gormont [1], implemented in the DMST model found to be successful in the analysis of Darrieuswind turbines. In the present model, static aerodynamic coefficients for the NACA-4418 available in [4] are used. These coefficients are experimentally obtained for the Reynolds number Re = 850000 and the range of the angle of attack
α = ±90◦.
DMST模型的基本原理解释如下。转子扫过的区域被划分成一系列的相邻的流管通过流管上的通过流管上叶片的负载取决于局部相对速度，这是局部速度U和旋转速度Wr
的结果。但是U 取决于发电机阻碍环境风的多少，而这又是一个叶片载荷的函数结合使用的执行器盘和叶片元件理论能打破这个循环周期DMST模型的依赖性。正如图2中所示，每个流管翼型件的路径相交两次，一次上面的风穿过，另一次下面的风穿过。
我们可以想象在这些交叉点通过串联的双致动器光盘更换涡轮机，该流可发挥强制。DMST模型同时解决了流向力在驱动盘上的两个方程，一个得到势头的保护另一个基于翼型（升力和阻力）和当地风速的空气动力系数。这些方程求解两次，分别是转子的上风和下风。由于典型的空气动力系数的模型的不确定性，这些仅可用于一个小范围的攻角的静态变化。Gormont模型的实证DMST模型的应用在分析Darrieuswind发电机上成功的。在本模型中，静态空气动力系数的NACA-4418可在[4]使用。这些系数是实验获得的的雷诺数Re=850000和攻角的范围内的α=±90◦
3 Computational Model
计算模型
In the CFD analysis of unsteady rotor dynamics two different software packages areused: the commercial package ANSYS-CFX and the TAU code developed at the German Aerospace Center - DLR [5]. Both codes numerically solve Reynolds Averaged Navier-Stokes (RANS) equations.Various turbulence models are available in both packages. In this work, the k−ω SST turbulencemodel in association with the ANSYS-CFX simulation cases and the Spalart-Almaras turbulencemodel in association with the TAU simulation cases are used.
在不稳定转子动力学CFD分析中使用两个不同的程序软件包，在德国航空航天中心使用的商业包装ANSYS-CFX和TAU代码。这两个代码数值求解雷诺平均纳文 - 斯托克斯方程（RANS）。在这项工作中各种发电机模型都可以在这两个软件包中使用，K-ωSST发电机模型与ANSYS-CFX ANSYS-CFX模拟个案联系在一起，关的TAU的选用Spalart-Almaras turbulencemodel的模拟案件被使用。