基于OPEE-OR算法的水泵自适应网格生成研究

According to the errors in flow field, the adaptive mesh technique can automatically adjust local grid scale, so it can reflect local flow characteristics precisely and efficiently. It is an effective way to improve the accuracy and efficiency of pump CFD calculation. The critical scientific issues which exist in posteriori error estimation, adaptive refinement and mesh optimization of pump adaptive mesh generation algorithm will be studied based on OPEE-OR algorithm in this project. The model of posteriori error estimation based on multi-adjoint variables will be built through researching the effect of each adjoint variable which characterizes the pump internal flow on the result of error estimation. The ill-posed problem occurring in marking element will be studied by using bidirectional change threshold method. The method to avoid generating hanging nodes in the process of adaptive refinement will be studied. The homogeneous transition algorithm of mesh among complex geometrical regions will be established. The objective function which considers the element shape and the errors in flow field will be built, and the solving algorithm to get dynamic global optimum solution will be developed. Numerical calculation, PIV measurement and energy characteristic experiment will be done to discuss the computational performance of the proposed algorithms in the pump unsteady flow numerical caculation. The objective of this project is to build adaptive mesh generation algorithm for pump based on OPEE-OR with high quality. This project will extend the applicability of adaptive mesh, and promote the development and application of pump CFD technology.

自适应网格技术根据流场误差自动调整网格局部尺度，能够准确高效地反映局部流场特性，是提高水泵CFD计算精度和效率的有效途径。本项目拟基于OPEE-OR算法，针对水泵自适应网格生成算法中后验误差评估、自适应加密和网格优化等方面存在的关键科学问题展开研究。 通过研究表征水泵内部流动特征的各伴随变量对于误差评估效果的影响，建立多伴随变量后验误差评估模型，采用双向变化阈值方式解决单元标记时出现的病态问题；研究自适应加密过程中避免生成悬点的方法，构建复杂几何特征间网格均匀过渡的算法；建立考虑单元形状和流场误差的目标函数，发展动态全局最优的求解算法；综合采用数值计算、PIV测量和外特性实验等方式，探讨所提算法在离心泵不稳定流动数值计算中的应用。 本项目旨在建立基于OPEE-OR的水泵高质量自适应网格生成算法，拓展自适应网格的适用性，促进泵CFD技术的发展和应用。

CFD广泛应用于泵内流计算和性能预测，以优化泵的设计、提高泵的效率和可靠性。由于泵内部流动是涉及边界层、流动分离和分层效应等具有不同特征尺度的局部流场及其相互干扰的复杂流动，对其进行数值计算时，所用网格必须计及这些尺度所体现的物理特性。自适应网格技术的特点正在于，依据迭代计算过程中流场参数的变化自动调整网格局部尺度，以求更加细致、准确地反映局部流场特性，并能够在计算机资源的合理消耗和求解精度之间达到平衡。本项目在理论分析、数值计算以及试验的基础上，对泵自适应网格现有的衡量准则、动态误差评估方法、自适应加密算法等方面进行了研究。.建立一种的网格质量评估准则。选取9种常用衡量准则进行比较，结果表明新准则在对劣质单元、单元形状变化的评判以及判别网格质量所耗费时间方面都显示出了较好的优势。在此基础上，结合弯管数值计算和PIV试验，探讨了构建网格质量与误差之间关系的方法。提出了一种离心泵的自适应网格动态加权误差评估方法，在归一化处理后每次递减误差阈值，从而加快了自适应网格的加密过程，可以实现对各种类型网格的进行误差评估，且评估效率高。提出并实现了一种复合的自适应网格尺寸控制策略，采用特征扫描算法，将曲线和曲面的曲率信息以度量矩阵的形式存储到八叉树背景网格中，并将此矩阵与曲面自身的黎曼度量相接合，使得复杂几何特征间网格能够均匀过渡，并能够满足几何自适应和消除映射畸变的要求，进而实现网格了自适应加密。通过PIV和外特性试验对比可知，自适应网格计算外特性和内流场更加接近实验值，且时间最短。