基于致动及浸入边界理论的风力机准三维覆冰计算模型研究

The wind energy in cold climate is the most important potential resource. However the three dimensional (3D) effect, wind shear and high turbulence features of the flow field result in significant non-linear effects during the process of wind turbine ice accretion. A lot of new research aspects appeared in this phenomenon and these issues become the most important and difficult points in the study of wind turbine ice accretion. In the numerical analysis of wind turbine 3D ice accretion, a lot of problems exist, such as the difficulties in the large scale 3D flow field calculation and the problems in body-fitted grid generation. In order to solve these problems, a new wind turbine ice accretion model is proposed in this application which is based on the Actuator Model and Immersed Boundary Method (IBM). The theoretical, numerical and experimental methods are used during the study and the following content will be discussed, including: (1) based on the geometric representation of the 3D Improved Actuator Surface Model, the characters of the water droplets’ trajectory will be analyzed and the mechanism of the water droplets’ distribution in 3D flow field under wind shear and vortex influence will be summarized. After that the flow field transfer mode from the 3D Improved Actuator Surface Model to the 2D IBM model will be created. (2) According to the character of Ghost Cell IBM in the high Re flow calculation, a grid optimization method based on curvature analysis of the ice boundary will be established to strengthen the ability of the Ghost Cell IBM in 2D ice accretion analysis. This model will not only provide a solid foundation for the wind turbine ice accretion theory but also promote the industrial technology.

寒冷气候条件下的风资源开发是最具潜力的风能发展方向。三维、风剪切、高湍流等流场特征给风力机覆冰过程带来高度非线性效应，衍生出科学研究的新内涵，是风力机覆冰研究亟待解决的重点和难点。本申请针对风力机三维覆冰数值计算模型中大尺度三维流场计算困难、固壁贴体网格重构障碍等问题，提出基于致动和浸入边界理论，构建新型风力机覆冰求解模型。拟采用理论分析、数值计算、风洞试验相结合的手段，开展以下研究内容：1、依托三维改进致动面模型对固壁体积力的几何表征优势，详细对比分析三维风剪切条件下液滴运动轨迹的规律与特征，摸清风剪切及近尾流涡系对液滴分布作用机理，构建三维致动模型向二维浸入边界模型的高效流场信息传递模式；2、利用虚拟单元浸入边界模型对高雷诺数流动的计算特征，建立基于冰形曲率分析的浸入边界局部网格优化策略，完善浸入边界模型的二维覆冰计算能力。该模型将为风力机三维覆冰分析提供坚实理论基础与重要技术指导。

寒冷气候条件下的风力机结冰问题是限制寒冷气候地区风能大规模开发的核心瓶颈。目前，复杂结冰环境下风力机结冰数值计算手段缺乏是影响风力机覆冰分析及风力机结冰防护系统开发的重要条件。本项目围绕风力机结冰数值计算问题，提出基于三维改进致动面模型（IASM）及直接作用力浸入边界方法（DFIBM）构建风力机准三维结冰计算模型，同时利用有限面积方法（FAM）发展描述液膜复杂动力学特征的结冰相变模型。在此基础上，依托中国空气动力研究与发展中心3米×2米大型结冰风洞开展风力机翼型结冰风洞试验，利用试验结果以及NASA-IRT结冰风洞试验结果，验证数值计算模型的准确性。. 研究结果表明：IASM 通过表面体积力的形式表征风力机固壁，能够较准确地捕捉风力机风轮平面内的流场特征信息，为风力机结冰计算提供了高效可靠的三维流场信息条件；DFIBM 模型通过在固壁边界与流场的交界区域修正流场解，直接模拟固壁边界的无滑移条件，能够较好地把握当地二维流场结构特征，为当地翼型结冰计算奠定基础；基于FAM方法的结冰相变模型，实现了三维液膜的二维简化，能够描述风剪切作用力、环境压力、表面张力、重力、离心力等复杂力系作用下的液膜结冰相变过程；HQ63-17翼型3米×2米结冰风洞试验首次获得了大型兆瓦级风力机的结冰冰形特征。通过该翼型及NASA-IRT NACA0012翼型结冰风洞试验数据验证了数值计算模型的可靠性和准确性；利用发展的结冰数值计算模型，分析了NREL Phase VI 风力机的三维结冰现象，结果显示风力机旋转叶片导致的相对入流速度及液态水收集差异对结冰冰形特征影响显著。通常条件下叶根区域更易形成形状规则的楔形冰、叶尖区域更易形成形状复杂的角状冰。本项目构建的风力机结冰数值计算模型，为大型风力机覆冰计算分析及结冰防护系统设计开发提供了重要的计算手段。