Dynamic model and numerical simulation of direct-acting pressure regulator for irrigation system

A direct-acting pressure regulator is a key device for agriculture irrigation system used to ensure the equal operating pressure of the emitter or sprinkler nozzle required for high uniformity. This study develops a dynamic model for the pressure regulator by applying computational fluid dynamics (CFD) method. For this purpose, after analyzing the structure and basic working principle of the direct-operated pressure regulator, the fluid-rigid body interaction model of the regulating plunger was built by force balance approach. The mathematical model consists of the fluid governing equations, the equation of dynamic mesh for regulator and an equation of motion for the regulating plunger. The Navier-Stokes equation along with standard k-ε turbulent closure was solved numerically in the incompressible flow regime by commercial ANSYS Fluent code. The dynamic mesh technique using a layering algorithm was performed for the displacement of domain boundaries and mesh deformation due to the movement of the regulating plunger. A user defined function (UDF) was compiled in the ANSYS Fluent code for solving the equation of motion for the regulating plunger in every time step during the unsteady calculation. With a geometrically accurate CFD model of the pressure regulator, the complete transient process of the regulating plunger from the initial position to the final position device from force balance was simulated under inlet pressure ranging from 0.025 to 0.4 MPa and flow rate ranging from 350 L/h to the maximum within regulation range conditions. The regulating performance curves and the pressure distributions through the regulator at each time step were obtained with the response parameters, including the force acting on the regulating plunger, the displacement of the plunger, and the outlet pressure of the regulator. A series of experimental tests matching to the conditions of the calculation were performed on pressure regulator with preset pressure of 0.05, 0.075 and 0.1 MPa. The experimental determination of the outlet pressure was carried out and compared to the computational values. The results showed that the regulating performance curves obtained by simulation were close to that obtained by experimental tests, and the numerical and experimental preset pressure agreed within -13.4%, which was considered to be quite acceptable. The effects of the flow rate and spring parameter son regulating performance were investigated, which showed that the preset pressure was affected by the flow rate. For the same type pressure regulator, a lower flow rate corresponded to a slightly higher outlet pressure. Thus the spring preload hade linear relationship with the preset pressure. By increasing the spring per-stressed force, the preset pressure increased proportionally. On the basis of the experimentally valid model, the dynamic simulative results, which consisted of the force acting on the regulating plunger verse time, the motion characteristics of the plunger, and the outlet pressure of the regulator verse time, were analyzed and accounted for the pressure regulating mechanism of the direct-acting pressure regulator. The detail pictures of the pressure distributions through the regulator provided an improved understanding on operating characteristic of the pressure regulator. The numerical model is reliable to predict the preset pressure and regulating performance of the regulator, which has great potential of assisting the designers to optimize the direct-operated pressure regulator. ©, 2015, Chinese Society of Agricultural Engineering. All right reserved.