水下自激吸气式喷嘴脉冲射流的机理研究

Aiming at the problem of sediment perturbation during water and silt regulation of Yellow River, the applicant puts forward a new jet nozzle with low pressure and mass flow,namely underwater self-excited suction nozzle. The nozzle realizes the automatic suction through the arrangement of the suction hole around the cavity,and reaches the purpose of improving the impact properties.The project regards nozzle as research object,the method of combining test research, numerical simulation and time-frequency analysis will be adopted to study the generation mechanism. The two-fluid mathematical model of gas-liquid two-phase flow will be adopted to study the unsteady flow characteristics for water-air two-phase in the nozzle, including the evolution of the large-scale vortex structures in jet shear layer, the spatial-temporal distribution of velocity,pressure,energy and air rate for the water-air two-phase flow,and the pressure numerical signal of internal monitoring points. The underwater jet impact test will be carried out, suction capacity and impact signal is got. The mixing process of water and air, air phase motion process and air rate are analyzed according to the flow images.The time-frequency analysis method will be adopted to extract time-frequency feature of the impact signal and pressure numerical signal of nozzle. The time-frequency distribution,the energy distribution and the influence on jet shear layer instability process of air phase are analyzed. The nozzle system mode is established and the relationship between unsteady flow characteristics and impact signal time-frequency distribution law is analyzed. The nozzle generation mechanism is revealed and provides a theoretical basis for further study of the nozzle.

针对黄河调水调沙过程中的水库泥沙扰动问题，申请者提出了一种新型低压大流量射流喷嘴-水下自激吸气式喷嘴，通过在腔体周围布置吸气孔，实现喷嘴自吸气，达到提高冲击性能的目的。本项目以水下自激吸气式喷嘴为研究对象，采用数值模拟、试验和时频分析相结合的手段对其脉冲射流机理进行研究。建立气液两相流双流体数学模型，研究喷嘴内水气两相的三维非定常流动特性，包括射流剪切层内大尺涡结构的演化过程，水气两相流速、压力、能量和气相含气率的时空分布，监测点压力数值信号；开展水下射流冲击试验，测取吸气量和冲击信号，根据流动图像分析喷嘴内水气混合过程、气相运动过程和含气率；运用时频分析技术提取喷嘴冲击信号与压力数值信号的时频特征，分析信号时频分布与能量分布以及气相对射流剪切层不稳定过程的影响；建立喷嘴系统模型并分析喷嘴内部流动规律与冲击信号时频分布规律之间的关系，揭示喷嘴脉冲射流的机理，为喷嘴的进一步研究提供理论基础。

在黄河调水调沙过程中，水下射流技术对泥沙扰动是塑造协调水沙关系的重要手段，如果将水射流技术用于水库深水段，使库底泥沙扰动、悬浮，不仅有利于形成异重流，而且可以有效地控制减小水库泥沙淤积。项目以水下自激吸气式喷嘴脉冲射流为研究对象，陆续开展了水下自激吸气式喷嘴脉冲射流冲击性能研究、喷嘴内部流动特性的数值模拟研究、冲击力时频分析研究和喷嘴内部水气流动过程的研究，在此基础上，揭示了喷嘴脉冲射流的产生机理。项目取得的研究成果如下：（1）通过试验手段获取了喷嘴在不同工作压力、围压、不吸气和吸气条件下碰撞体测点和冲击力的脉冲效果、冲击力吸气聚能效应和冲蚀效果(冲蚀深度、冲蚀表面积和冲蚀体积)，验证了喷嘴吸气后的优越性，确定了喷嘴的最佳结构参数和冲击射程；（2）通过建立欧拉－欧拉气水双流体数学模型对喷嘴内部压力分布和气水混合过程进行了研究，分析了射流核两侧的气水涡团，比较了吸气和不吸气条件下射流核长度以及下喷嘴出口的中心速度，从理论上解释了喷嘴产生聚能效应的原因；（3）建立了喷嘴内部可视化试验平台，通过高速摄像技术进一步验证了腔内气水旋转涡团的存在，对水气旋转涡团与碰撞体测点压力和冲击力脉冲效果的对应关系进行了分析，解释了喷嘴产生脉冲射流的原因；（4）采用第二代小波变换和Wigner-Ville分布相结合的方法提取了喷嘴冲击力时频特性，分析了喷嘴冲击力能量频带分布范围以及围压、靶距和吸气对频带能量比、冲击力频率成分以及能量密度分布影响规律。水下自激吸气式脉冲射流机理的研究，不仅丰富了水射流理论，而且为水射流泥沙扰动机理的研究奠定了坚实的基础。