PWM间歇喷雾变量喷施系统中压力波动的形成、衰减及耦合机理研究

Variable rate application is an important development direction for agricultural chemicals application technology. Blended-pulse intermittently spraying flow control method is the primary method for variable rate application control. But improvement of spray pattern and flow control precision was impeded by its pressure fluctuations. This project will address the pressure fluctuation problem in the blended-pulse variable rate application system. Numerical computation method, modelling and simulation method and experimental testing method will be combined in the study of this project. Mathematical models of fast acting solenoid valve, diaphragm pump and its damper, proportional overflow valve, pipelines and the blended-pulse variable rate application system will be established by dynamic characteristics analysis of their internal flow field. Emerging mechanism of pressure fluctuation will be revealed by simulation analysis of opening and closing process of the fast acting solenoid valve. Frequency response characteristic of the damper to the pressure fluctuation will be deduced by simulation analysis of the diaphragm pump and its damper. Response characteristics of the proportional overflow valve to the pressure fluctuation will be deduced by simulation analysis. Mechanisn of spreading and coupling of the pressure fluctuations in the pipeline will also be revealed by the simulation of the pipeline. And influence of structural parameters and operational parameters of the hydraulic components to the pressure fluctuation will also be deduced by the simulation. Influence of matching parameters between the hydraulic components to the pressure fluctuation will also be deduced by the simulation of the blended-pulse variable rate application system. Research finding of this project will lay a theoretical foundation for the stable control of the pressure fluctuation and for the simulation and optimal design of agricultural chemicals application equipments.

变量喷施是施药技术的重要发展方向，PWM电磁阀控制间歇喷雾是变量喷施控制的主要方式，但压力波动影响了其雾化特性和喷雾流量控制精度的提高。本项目以PWM间歇喷雾变量喷施系统中的压力波动为研究对象，采用数值模拟、建模仿真和试验测试相结合的方法，通过对高速开关电磁阀、隔膜泵稳压气室、比例溢流阀和药液管路的内部流场的动态特性分析，建立各液压元件及整个PWM变量喷施系统的数学模型；对其压力波动特性进行仿真，揭示高速开关电磁阀启闭过程中压力冲击的形成过程，给出比例溢流阀对压力波动的响应特性，探明稳压气室对隔膜泵周期性压力脉动和管路压力波动的衰减机理和频率响应特性，揭示压力波动在药液管路中的传播和叠加耦合机理，并探明各液压元件主要结构和工作参数以及液压元件之间的参数匹配对压力波动的影响规律。从而为PWM间歇喷雾变量喷施系统中的压力波动稳定控制奠定理论基础，为施药机械的数字化仿真和优化设计提供理论支撑。

变量喷施是施药技术的重要发展方向，PWM电磁阀控制间歇喷雾是变量喷施控制的主要方式，但电磁阀高速启/闭过程会产生较大的液压冲击，再加上隔膜泵的周期性压力脉动，喷头的雾化特性和喷雾流量控制精度会受到显著影响。本项目即以PWM电磁阀控制间歇喷雾变量喷施系统中的压力波动为研究对象，通过对主要液压元件和管路内部流场的CFD模拟仿真和试验测试分析，研究管路压力波动的形成、衰减及耦合机理。.对电磁阀连续启闭过程中内部流场的动态特性进行了CFD数值仿真和试验测试分析，结果表明：液压冲击强度随电磁阀开启/关闭响应时间的增加而减小，随电磁阀公称通径的增加而减小，随阀芯行程的增加而增大。.采用workbench软件的FSI模块完成了“隔膜泵+稳压气室”的流固双向耦合仿真，结果表明：隔膜泵出口管路平均压力与稳压气室的容积和初始气压都基本无关；当初始气压与隔膜泵出口管路平均压力近似相等时，压力波动衰减效果最好，偏离越大，压力波动衰减效果越差；在额定转速和0.5MPa出口压力下，ZMB240型隔膜泵稳压气室的最佳容积为112754mm3，偏离越大，压力波动衰减效果越差。.对比例溢流阀启闭过程中内部流场的动态特性进行了CFD数值仿真和试验测试分析，结果表明：采用比例溢流阀难以实现PWM变量喷施系统管路压力的微调，且会带来新的液压冲击。.完成了管路多源压力波动耦合过程的CFD仿真和试验测试分析，结果表明：多源压力波动耦合对PWM变量喷施系统无显著影响，仅仅是压力波动的频率有所增加；在进行PWM变量喷施系统管路优化设计时，可以不考虑多源压力波动耦合的问题，而仅需对各个管路元件进行单独的优化选配。.以上研究成果为PWM间歇喷雾变量喷施系统的优化设计和压力稳定控制奠定了理论基础。尤其是在隔膜泵流固双向耦合仿真和隔膜泵参数优化方面取得的创新性成果，不仅为隔膜泵的优化设计奠定了理论基础，还可扩展到相关的流固双向耦合仿真领域，具有重要的科学意义和应用前景。