Unsteady Viscous Flow Analysis around Horizontal Axist Wind Turbine Rotor using Vortex and Panel Methods

本课题于1997、1998学年度开展，采用旋涡法结合面板法（边界元法），为分析水平轴风力机动叶周围不可压缩粘性流场的数值计算工具奠定基础。涡旋法是分析高雷诺数、非定常和外流的有力工具之一。该项目的最终目标是估计转子叶片附近的三维流动性质，包括叶根附近的流动分离，这是现有预测模型难以描述的。在项目开始时，对二维翼型截面（MELO 12，由MITI机械工程实验室设计）的绕流进行了分析，主要采用涡法的三级模型。在该模型中，将来自物体表面的涡视为涡片，将距离物体表面一定距离的涡团视为涡团。与旋涡法的二级模型计算相比，三级模型由于引入的旋涡数量较多，计算时间更长，流场的不稳定性更大。应用于MELO12翼型截面和对称Joukowski翼型截面，仔细研究了叶片表面离散成面板的方法以及面板数对计算结果的影响，特别是在靠近尾缘的地方。因此，在尾缘处人为设置较小的厚度可以提高计算的收敛性，提供更真实的结果。

This project has been proceeded to establish a basis of numerical calculation tool for analyzing incompressible viscous flow fields around rotor blades of horizontal axis wind turbines, adopting a vortex method along with a panel method (boundary element method) within the period of 1997 and 1998 of academic years. The vortex method is one of the powerful tool for the analysis of high Reynolds number, unsteady and outer flows. The final objective of the project is to estimate three dimensional flow nature in the vicinity of the rotor blade including the flow separation near the blade root, which has been difficult for the existing prediction models to describe.At the beginning of the project, the flow around two dimensional airfoil section (MELO 12 ; designed by Mechanical Engineering Laboratory of MITI) was analyzed applying mainly the third level model of the vortex method. In this model the vortices from the surface of the body are treated as the vortex sheets and the vortex blobs at a certain distance from the surface. Compared with the calculation by the second level model of the vortex method, the third level model consumes longer calculation time and provides larger instability of the flow fields because of larger number of vortices introduced for the calculation.Effects of discretizing method of the blade surface into panels as well as panel number on the calculated results were examined carefully especially near the trailing edge, applying to the airfoil sections of MELO12 and symmetric Joukowski. As a result, a small thickness artificially given at the trailing edge can improve the convergency of the calculation and provide more realistic results.