超高压淹没水射流剪切层空化机制与激励特性研究

Turbulence mechanism, cavitation, excitation characteristics and impingement behavior in the submerged water jet under the jet pressure of 350 MPa are investigated through comprehensive application of experiment, flow simulation and stress field simulation. Planar laser-induced fluorescence(PLIF) and particle image velocimetry (PIV) techniques are utilized to measure quantitatively the velocity distributions of each phase, primary turbulence parameters' distributions and the profile of shear layer cavitation. Dynamic pressure sensors are used to measure the pressure fluctuation in the environment fluid induced by the jet fluid. With the combination of scanning electron microscopy (SEM) and three-dimensional profiling system, the micro-structures and topography features on the surface of the alloy impinged by the water jet are checked and analyzed. By using large eddy simulation (LES), unsteady characteristics in the flow field is simulated. Energy distribution characteristics of the ultra-high pressure submerged water jet, shear layer cavitation and multi-scale flow structures, excitation exerted on the environment fluid by the jet fluid, transient erosion on the solid surface due to high-speed water jet and cavitation are expected to be described. The correlation between flow scale and surface profile scale is consequently established. The study will provide reasonable explanations for the control of ultra-high pressure water jet and the stability mechanism of high Reynolds number water jet, and further improve the understanding of the complex turbulent phenomena of small temporal and spatial scales.

综合运用实验研究、流动模拟和应力场模拟的方法，对350MPa超高压淹没水射流流场中的湍流机制、空化现象、激励特性和冲击性能进行探究。采用面激光诱导荧光法与粒子图像测速法对多相流动速度、湍流参数分布、剪切层空化形态进行定量测量；采用动态压力传感器对射流主体激励的环境水体中的压力脉动进行测量；结合扫描电镜和光学轮廓扫描技术，对水射流冲击的合金试样表面进行显微组织与形貌特征观测；运用大涡模拟方法，对流场的非稳态特性进行数值模拟。拟获得超高压淹没水射流流束的能量特性；描述剪切层空化发生机制及多尺度流动结构、刻画淹没水射流对环境水体的激励特性；量化水射流流束与射流空化对固体表面的破坏机制；进而建立流动尺度与形貌尺度间的关联。为超高压水射流流动控制和高雷诺数水射流的失稳机制提供有力的解释，进一步提升对复杂湍流流动中小时空尺度现象的理解。

综合运用流动测试技术、流动显示方法、压力脉动测量手段和流动模拟方法，对高压和超高压淹没水射流流场中的湍流机制、空化现象、激励特性进行探究。采用面激光诱导荧光法与粒子图像测速法对射流场中的速度分布和涡量分布进行定量测量；对间歇性空化形态进行瞬态显示；采用动态压力传感器对射流激励的环境水体中的压力脉动进行测量；结合扫描电镜和光学轮廓扫描技术，对淹没水射流冲击的试样表面进行显微组织与形貌特征观测；运用离散涡模拟方法，对流场的非稳态特性进行数值模拟。通过研究获得了超高压淹没水射流流束的能量特性；描述了剪切层空化发生的机制及多尺度流动结构、解释了淹没水射流对环境水体的激励特性；量化了水射流流束与射流空化对固体表面的破坏机制。本研究对极端压力条件下的淹没水射流进行了探索，获得的以下三个结论可作为更深入的学术探索的基础，也为相关的工程应用提供了支撑：(1) 在高于100MPa射流压力后，淹没水射流流束的发展初期具有一个加长的核心区，这与低压射流不同，传统的射流束线性扩展理论不适用；(2) 尽管淹没水射流流场中的空化产生机制已明确为速度梯度和剪切效应，但高压力和小喷嘴孔径带来的结果是射流束的速度大，射流初期的空化不会出现在流束中心，但随着射流向下游发展，射流束中心也出现空化泡，这与低压淹没水射流中的环形区域有区别；(3) 高压和超高压条件下，淹没水射流对周围流体的扰动明显，其中出现的低频与高频信号与流动结构和空化存在确定关系，这是信号检测技术的重要增长点，也可以作为激励特征研究的有力支撑。