超低比转速离心泵准三元粘性水力设计及熵产诊断优化方法研究

The ultra-low specific speed centrifugal pump has wide application prospect. However, all the existing hydraulic design methods expose some disadvantages because of many inherent irregular flows. In this research project, based on the quasi-3D inviscid flow theory of impeller, the boundary layer theory will be added. The quasi-3D viscous hydraulic design theory and corresponding method of impeller will be developed by dynamic adjustment of meridional velocity distribution and velocity moment distribution. Meanwhile, the new hydraulic design methods of inducer and volute matched with the impeller are established by fully considering the nonlinear couple interrelations among them. The local entropy production diagnosis theory is added to analyze the hydraulic dynamic mechanism of energy loss inside the pump. The concise hydraulic performance prediction model of the ultra-low specific centrifugal pump is established by combing numerical simulation, orthogonal experimental design and optimal Latin hypercube method. Setting hydraulic efficiency, entropy production and NPSHr (Required Net Positive Suction Head) as objective functions, the multi-condition and multi-objection genetic optimization design method of the ultra-low specific speed centrifugal pump is developed. The numerical simulation and hydraulic performance experiment of the pump will be implemented to verify the hydraulic design and optimization method. The visualization experiment of flow field will be carried out to explore the evolution of cavitation flow in inducer and its influence mechanism on hydraulic performance of the ultra-low specific speed centrifugal pump.

超低比转速离心泵应用前景广泛，但其存在诸多不良流动，已有的各种水力设计方法均有不足。本项目拟在叶轮准三元无粘流动理论基础上引入边界层理论，充分考虑叶轮内流场结构与叶轮形状及其水力特性间的影响关系，动态调整叶轮轴面速度分布及速度矩的增益函数，发展超低比转速离心叶轮的准三元粘性水力设计理论及方法。考虑各过流部件间的水力性能匹配关系，建立前置诱导轮和后接蜗壳与叶轮的非线性耦合水力设计方法。引入局部熵产诊断理论，探究泵内全流道空化流能耗发生的水动力学机理。结合数值模拟、正交试验设计和最优拉丁方设计方法，建立超低比转速离心泵全流道水力性能快速预测模型。将水力效率、熵产及必需汽蚀余量作为目标函数，发展超低比转速离心泵全流道多工况多目标遗传优化设计方法。对优化后的超低比转速离心泵进行数值模拟和水力性能实验验证，同时开展内流场可视化实验，探讨诱导轮内的空化流演变规律及其对超低比转速离心泵性能的影响机理。

超低比转速离心泵应用前景广泛，但由于其内部流动复杂，已有的各种水力设计方法均有不足。为发展准三元粘性水力设计理论及方法，本项目首先将粘性湍流边界层理论应用于二元水力设计中，验证了有粘设计方案的可行性。通过两类流面S1/S2的反复迭代和叶片表面边界层厚度分布规律的计算，最终完成了低比转速离心泵叶轮的准三元粘性水力设计。采用相同的准三元设计方法完成了低比转速离心泵前置诱导轮的水力设计。根据当前叶轮模型尺寸以及设计要求，使用正交试验的方法，以全流道熵产最小为目标函数，得到最优的蜗壳模型。搭建了超低比转速离心泵综合水力测试平台，验证了准三元粘性水力设计方法的可靠性与有效性。开展了空化及进气的两相流动可视化实验，深入研究了不同空化数与进气工况下叶轮流道内流型演变规律。在单相流动熵产计算的基础上，结合两相动量方程、内能输运方程、吉布斯自由能方程及克劳修斯-杜赫姆不等式等，综合考虑相间滑移作用和相间质量、动量及热量传递中的能量耗散，发展了新的空化流熵产诊断模型，分析了不同工况水力损失变化规律并探明了空化前后高能耗区域出现的水动力学原因。以熵产最小化和临界汽蚀余量最低为优化目标，完成了适用于液化天然气（LNG）的两级低比转速潜液泵的多目标优化设计，同时深入分析了优化前后水力性能变化的微观流场原因。该项目成果能为高性能叶片的设计与优化提供重要的理论方法和分析手段。