来流扰动诱导涡与离心叶轮内部既有涡相互干涉机理

With the further development of centrifugal pump to the high speed, high pressure and high power density, the effect of upstream perturbation to the vortex structure in centrifugal pump, the stability, efficiency and anti-cavitation performance of pump is more obvious. Thus it's necessary to systematically study the evolution mechanism of the upstream perturbation and internal complex vortex in centrifugal impeller and to reveal the influence of upstream perturbation to the performance of centrifugal pump. The key issues are looking for the representation of the complex vortex structure and the accurate simulation method of the perturbation..This project is aiming at the most common structural and regulating upstream perturbation, with obvious shear effects, in the centrifugal pump delivery system, and a systematic study is carried out by theoretical analysis, numerical simulation and visualization experiment. The subgrid stress model based on the Lagrangian trajectory average and combined constraints is established, the evolution of the perturbation in the inlet pipe and impeller under different flow and structure parameters is simulated employed the high-accuracy numerical discretization method. The interaction mechanism between the vortex induced by upstream perturbation and the internal vortex in centrifugal impeller is revealed. The relationship between the upstream perturbation parameter, the vortex flow in the impeller and centrifugal impeller performance, such as head-flow rate and pressure fluctuation is established. At last, the theoretical support for the elimination of the influence of the upstream perturbation on the inner and outer performance of the centrifugal pump and the design and development of the high performance centrifugal pump is provided.

随着离心泵向高转速、高压、高功率密度的进一步发展，来流扰动对离心泵内流涡系结构作用越加明显，对泵稳定性、效率和抗汽蚀性能的影响也越大，因而亟需系统地研究来流扰动与离心叶轮内部复杂涡流的演化机理，揭示来流扰动对离心泵外特性的影响规律，这其中的关键问题是寻找复杂旋涡结构的合理表征和扰动的精确模拟方法。.本项目拟针对离心泵输送系统中常见且剪切较强的结构式和调节式来流扰动，从理论分析、数值模拟、实验研究等三方面开展深入研究。构建基于拉格朗日轨迹平均的联合约束动态亚格子应力模式，用高精度数值方法进行离散，模拟离心泵进口管、叶轮内不同来流参数、结构特征参数的扰动场发展演化过程，揭示来流扰动诱导涡与离心叶轮内部既有涡相互干涉机理，并建立来流扰动参数、内部旋涡流动与离心叶轮扬程－流量特性线和出口压力脉动等外特性表征参数之间的关联，为消除来流扰动对离心泵内外特性的影响和高性能离心泵的设计开发等提供理论支撑。

随着离心泵向高转速、高压、高功率密度的进一步发展，亟需系统地研究来流扰动与离心叶轮内部复杂涡流的演化机理，揭示来流扰动对离心泵外特性的影响规律，这其中的关键问题是寻找复杂旋涡结构的合理表征和扰动的精确模拟方法。.本项目针对不同形式、结构的来流扰动对离心泵内流及外特性的影响，分别从复杂湍流数值方法、离心泵内部弱可压流动特性、基于螺旋度修正LES的离心泵内部旋涡演化特征、进口导叶对泵内外特性影响和引射离心泵内流及空化特性等五个方面来开展研究，揭示了进口导叶、引射回流等不同形式来流扰动与离心泵内部旋涡间的相互作用规律，明确了不同形式来流扰动对离心泵扬程、效率和空化性能等外特性的影响。.1）在模型方法方面，项目组将螺旋度影响以UDF形式写入亚格子模型，通过与旋转管道内速度剖面的实验值对比，显示在流道压力面，修正模型预测的流向速度剖面峰值更靠近压力面、峰值也更高，这都与实验分布、大小更吻合，可见发展的新模型能更加精确的预测旋转湍流的内部流场。2）在结构式扰动影响方面，对离心泵入口段不同结构参数的导叶扰动的研究显示，在中等流量时，偏移角25°的导叶对离心泵内部流场改善效果最佳，泵出口的压力脉动最小，且能提升离心泵外特性扬程及效率。3）在调节式扰动方面，项目组使用引射装置从泵出口引回部分高压流体到泵进口，通过实验获得了引回流量对泵外特性和空化性能的影响规律：随着引回流量的增大，泵扬程和效率略微减小，临界汽蚀余量先减小再增大，设计工况引回6%流量时模型泵空化性能最佳；通过数值模拟分析了引回流量对泵内部流动的影响，发现随着引回流量增大，叶轮进口压力增加，叶轮进出口湍动能减少；在设计工况最佳引回流量下，对泵内部空化流动进行了分析，发现在低装置汽蚀余量时，空化破坏了叶轮径向力的规律性，使叶轮出口压力脉动频率低于10 Hz，导致泵内流动不稳定。