Simulation Study On The Influence Of Structure And Materials On The Hydraulic Performance Of Pressure Compensating Emitter On The Pipe

Drip irrigation is one of the best water-saving techniques among many irrigation techniques.As the core component of a drip irrigation system,the drip head affects the irrigation efficiency of the system.Compared with conventional emitters,pressure compensated emitters have the advantages of wide working pressure range,stable discharge,and uniform irrigation,making them widely used in water-saving irrigation projects.The compensation element and labyrinth flow channel form a compensation chamber,which are key parameters that affect the flow rate adjustment of the emitter.However,current research on the relationship between the structural characteristics of the compensation chamber and the compensation performance of the emitter is not in-depth enough,making it difficult to predict and design the flow rate of the pressure compensated emitter.The rise of CFD software has provided a new method for studying the flow characteristics of fluids inside the emitter.However,conventional CFD simulation methods are difficult to reflect the compensation effect of elastic diaphragm deformation on the flow rate of the emitter.Further research is needed on the numerical simulation calculation method of pressure compensated emitters.Therefore,this study adopts a combination of numerical simulation and experimental methods to analyze the influence of pressure compensated emitter channel structure and elastic material characteristics on the hydraulic performance of the emitter.At the same time,this paper also explores the simulation method of bidirectional fluid-structure coupling of pressure compensated emitters,analyzes the reasons for the generation of negative mesh,and proposes solutions.In addition,based on the support vector machine regression prediction method,this article establishes prediction models for different compensation cavity structures and emitter flow rates.This provides a reference basis for the structural design and performance optimization of pressure compensation emitters.The main conclusions of this study are as follows:(1)There are two main types of negative mesh that are prone to occur in simulation calculations: penetrating negative mesh and boundary negative mesh.Adding contact constraints at the interface of fluid solid coupling,changing the update frequency of dynamic grids,and reducing the relaxation factor of fluid on solid data transmission in the coupling solver can reduce the generation of negative mesh.The trend of the simulated pressure flow curve is basically the same as the measured value,and the average error between the simulated and measured values is 10.53%.This simulation method can accurately calculate the flow rate of the pressure compensated emitter.(2)Under different pressure conditions,the internal flow channel structure of the pressure compensation emitter has different energy dissipation effects on the water flow.When the inlet pressure is small,the fluid pressure mainly dissipates energy through the maze flow channel.As the pressure increases,the role of the compensation chamber in energy dissipation increases.When the elastic sheet fully contacts the convex boss,the water flow pressure is mainly consumed by the small groove flow cross-section.As the inlet pressure increases,the deformation of the elastic sheet increases,but the deformation increment gradually decreases.Within the pressure range of 0-200 k Pa,the maximum deformation of the elastic sheet when it reaches the outlet of the basically covered convex boss accounts for 93.81% of the entire deformation process.(3)The hardness and thickness of the elastic sheet have a significant impact on the ability of the compensating emitter to regulate flow rate,and the hardness has a greater impact on flow rate and starting pressure.To ensure good compensation performance of the emitter,it is not advisable to use elastic sheets with a hardness greater than 60 HA and a thickness greater than 1.2mm.Different compensation cavity parameter combinations have significant differences in the compensation performance of the emitter.In the process of coupling the flow channel structure with the elastic sheet to regulate the flow rate of the emitter,the adjustment ability of the elastic sheet takes precedence over the flow channel structure.The optimal compensation chamber parameters for hydraulic performance in the experimental plan are the small groove width of 0.7mm,the outlet diameter of 1.4mm,the convex boss height of 0.2mm,and the hardness of 60 HA.(4)This article uses the SVM method to establish a model for predicting emitter flow rate under different structures and pressure conditions after optimizing the penalty parameter C and kernel function parameter gamma.The maximum error between the predicted value and the measured value is 12.13%,and the average relative error is 4.74%,indicating that the model has good accuracy and can provide some reference for the flow design of pressure compensated emitters.