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

本项目在1997-1998学年采用涡旋法和面元法(边界单元法)，为分析水平轴风力机叶片周围不可压缩粘性流场的数值计算工具奠定了基础。涡旋法是分析高雷诺数、非定常和外流的有力工具之一。本项目的最终目标是估计旋翼叶片附近的三维流动特性，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，主要应用涡流方法的第三级模型对二维翼型截面(由工信部机械工程实验室设计)的流动进行了分析。在该模型中，来自物体表面的涡流被视为离物体表面一定距离处的涡片和涡团。与旋涡方法中的二级模型相比，由于引入了较多的涡量，第三级模型的计算时间较长，流场的不稳定性也较大。以MELO12翼型和对称Joukowski翼型为例，详细研究了叶片面片离散化方法和面元数目对计算结果的影响。因此，在后缘人为地给出较小的厚度可以改善计算的收敛并提供更真实的结果。

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.