混流泵加速流工况瞬态空化形态及其诱导水力振荡特性研究

Transient cavitation in mixed pumps a key problem in national defence facilities, e.g., submarine missile launching system. The investigation of transient flow field, cavitation pattern and the evolution mechanism at accelerated conditions is the basic study to find the solutions. In this project, a mixed-flow pump model will be studied, employing PANS turbulence model, time-resolved PIV and high speed photography. The main contents of the study are as follows: 1) The transient characteristics of pressure and flow rate at the inlet and outlet of the mixed pump at the accelerated conditions will be analyzed. The complex flow structures inside the mixed pump, such as tip leakage vortex, blade channel vortex and seperation flow will be revealed. The pressure field, vorticity field, shear stress, vortex dissipation and turbulent kinetic energy will be discussed. 2) The cavitation patterns in impeller and diffuser at the startup of the pump based on high speed photography and transient numerical simulation of cavitation will be observed to investigate the evolution of tip leakage vortex, tip shear stress layer as well as the circumferential cavity and the height of axial cavity, and then the internal associations between vortex structures and cavitation development will be explained. 3)In order to acquire the oscillation characteristics of the transient pressure and flow rate at different cavitation conditions and different accelerated conditions, the relations of flow rate and pressure curves with cavitation patterns at different time steps will be illustrated. The mechanism of the system oscillation cavitation induced by the transient cavitation will be revealed and the control methods will be proposed to suppress the unstable cavitation based on the law of blade loading and cavity volume distribution. The outcomes of this project will provide theoretical fundation for the design and steady operation of the mixed-pump weapon lauching system.

混流泵瞬态空化是潜艇武器发射装置急需解决的难题之一，研究加速流工况瞬态流场特性和空化形态是解决该问题的基础研究。本项目以混流泵模型为研究对象，采用PANS数值模拟、时间分辨PIV、高速摄影等实验手段开展研究，主要研究内容有：1）分析加速流工况混流泵进出口压力、流量等参数的瞬态特性，探明混流泵内部叶顶泄漏涡、叶道涡、脱流等复杂流动结构，揭示混流泵加速过程压力场、涡量场、剪切应力、涡耗散、湍动能及其生成速率等湍流特性。2）观察泵启动过程叶轮和导叶内各种类型的空化形态及其时空演变过程，阐明各种涡结构与空化形态演化的内在联系；3）掌握不同条件下泵进、出口瞬态压力和流量的振荡特性，阐明混流泵水力振荡曲线在不同时刻点对应的空化形态，基于叶片载荷和空泡体积分布规律揭示瞬态空化诱导系统振荡的机理，并提出控制水力不稳定的方法。本项目预期成果，将为混流泵武器发射装置的设计和稳定运行提供理论基础。

混流泵瞬态空化是潜艇武器发射装置急需解决的难题之一，研究加速流工况瞬态流场特性和空化形态是解决该问题的基础。在密闭的液压系统中，混流泵快速启动产生高强度水压，推动鱼雷加速出仓，发射武器，而启动过程涉及到很多参数，这些参数是随着时间发生变化，具有很强的不确定性。当液压舱中压力不足时，启动过程中就可能会出现空化，影响发射过程，同时水泵内部由于空化产生的振动与噪声更容易被雷达测探出，安全性降低。本项目研究混流泵启动过程中的瞬态空化特性及抑制方法，为我国国防装备领域混流泵“高速化、大型化”发展提供理论基础和技术保障，主要包括以下研究内容及创新成果：.（1）通过数值模拟与实验对比，验证了分离涡湍流模型（DES）和基于Rayleigh-Plesset方程的Zwart空化模型可以较好地预测绕水翼加速流下空化情况，并且能够为后续水力机械启动加速过程的空化特性研究提供参考依据。.（2）对混流泵进行了不同流量工况下的稳态数值模拟，获得了混流泵的扬程和效率曲线；对混流泵进行了额定工况下的稳态空化特性的数值模拟，获得了混流泵额定工况下的空化特性曲线；通过外特性实验对模拟结果进行了验证。.（3）针对混流泵的无空化启动过程，进行了不同启动时间、不同流量工况下的无空化启动过程的数值模拟，发现湍动能较大的区域集中在叶轮的叶顶区域，尤其在混流泵叶顶区容易产生不稳定流动。.（4）针对混流泵启动过程中的瞬态空化特性，分别进行了不同启动时间、不同进口压力和不同流量工况下启动过程瞬态空化特性的数值模拟。发现在启动过程中，叶片背面中部靠近轮缘处最容易发生空化，且在启动时间较长、进口压力较低和大流量工况时，空化的发展程度更为严重。.（5）针对混流泵模型进行了稳态外特性试验、额定工况下的空化试验、启动外特性试验以及采用高速摄影拍摄混流泵启动过程中内部空化流场等四种试验研究，实验结果与数值计算结论一致。