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

本课题在1997 ~ 1998学年期间，采用涡方法沿着面元法（边界元法），为水平轴风力机转子叶片周围的不可压缩粘性流场的数值计算工具奠定了基础。涡方法是分析高雷诺数非定常外流的有力工具之一。本项目的最终目标是估算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。（梅洛12 ; MITI机械工程实验室设计）进行了分析。在该模型中，来自物体表面的涡被处理为涡面和离表面一定距离处的涡滴。与采用涡方法的第二层模型计算相比，第三层模型由于引入了大量的涡，计算时间长，流场不稳定性大，详细考察了叶片面元离散方法以及面元数对计算结果的影响，特别是在尾缘附近，适用于MELO 12翼型和对称Joukowski翼型。因此，在后缘人为地给定一个较小的厚度可以改善计算的收敛性，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.