# Simulation and Experimental Research on the Energy Loss of Confluence Pipelines
## 1 Introduction  
Pipeline conveyance systems are indispensable in the process of industrial and agricultural fluid transportation. The accuracy and rationality of pipeline design play an important role in the performance of all equipment and the entire system. The three-way pipe is one of the main connection methods used in water transmission and distribution network systems, with it being widely used in the petroleum, chemical, hydraulic, and other pipeline transportation fields [1]. Common confluence pipeline shapes include T-shaped, Y-shaped, and bifurcated, as shown in Figure 1. Compared with straight pipes and elbow pipes, the velocity distribution of fluid particles in the junction of a confluence pipe is uneven, and there are mutual mixing, jacking, momentum, and energy changes in water flow in this type of pipe [2]. Studying the energy loss mechanism of a confluence pipe is useful in calculating the energy loss within it and providing a reference for the accurate design of such pipes. The energy loss caused by fluid flowing in these types of confluence pipelines is large, especially in the process of confluence, when the energy loss is extremely severe. Figure 1: Confluence pipelines with different structures. (**a**) T shape; (**b**) Y shape; (**c**) bifurcated; and (**d**) arc shape. [PERSON]. [PERSON] [3] conducted a theoretical analysis of the energy loss of a Y-shaped confluence pipe and obtained the empirical formula for calculating the energy loss of such a pipe, which was then modified to make it applicable to the calculation of energy loss of an elbow, sudden expansion pipe, and a sudden contraction pipe. [PERSON] [4] attempted to reduce the local energy loss by adding fillets inside a T-shaped confluence pipe or adding barriers before the confluence. [PERSON] and [PERSON] [5] carried out a numerical simulation of a 90\({}^{\circ}\) T-shaped confluence pipe using Fluent, and the simulation results showed slightly higher values than the experimental and theoretical results. [PERSON] and [PERSON] [6] conducted a numerical simulation study on the steady flow of non-viscous and viscous fluid in a T-shaped confluence pipe. By adjusting Fluent's setting parameters, they obtained models and algorithms that were similar to the theoretical calculation results. [PERSON] and [PERSON] [7] also conducted a numerical simulation of the fluid in a pipe using the RNG model in Fluent 2020 R2 software, analyzed the mechanism of the energy loss by observing the internal pressure distribution cloud, and verified that the energy loss calculated by Fluent could predict the actual flow state of the fluid in the pipe. [PERSON] [8] used Fluent to perform numerical simulations of T-shaped confluence pipes with different cross-sectional areas for main and branch pipes and different angles. The relative error between the numerical calculation results and the experimental results was small. [PERSON] [9] and [PERSON] [10] proposed a theoretical calculation formula for the local energy loss coefficient with consideration of the unique flow characteristics at the confluence of a 90\({}^{\circ}\) T-shaped bus pipe. [PERSON] [11] and [PERSON] [12] used Fluent to conduct numerical simulation research on the energy loss inside bush pipes with different structures, whose results show that, compared with T-shaped and Y-shaped manifold, the circular arc manifold has the smallest head loss. With the increase in inlet velocity, the amplitude of energy loss of circular and Y-shaped busses is more stable than that of T-shaped busses. [PERSON] [13] analyzed and studied the energy loss mechanism inside Y-shaped manifold pipes with different structures and working conditions in the Xilongchi pumped storage power Station. [PERSON] [14] used Fluent to numerically simulate the flow state of fluid particles inside a Y-shaped open channel intersection. [PERSON] [15] used Fluent to simulate the flow characteristics of water inside a three-dimensional manifold.