Numerical simulation of hydraulic performance on bidirectional flow channel of drip irrigation emitter using Fluent

Abstract: The hydraulic performance of bidirectional flow channel is better than the hydraulic performance of labyrinth-channel, especially in 0.05-0.10 MPa. So bidirectional flow emitter can save more energy and the drip irrigation tube can be thinner, it can reduce investment cost and has good application in irrigation. In this study, numerical simulation method was used to accurately and efficiently design various kinds of channels of drip irrigation emitters. In order to improve the efficiency of research and reduce the cost of development, Fluent was used to simulate the bidirectional flow channel and analyze the mechanism of energy dissipation. A channel was designed within a reasonable range of structural parameters to study the grid partition and model selection. The results showed that unstructured grid was suitable for numerical simulation of bidirectional flow channel. Mesh cell sizes of 0.1 mm, 0.2 mm and 0.5 mm were chosen to calculate the flux of the channel under different pressures. Mesh cell size 0.2 mm under the numerical simulation was more accurate and efficient than the ones of 0.1 mm and 0.5 mm. In this paper, five turbulence models including standard k-ε, RNG k-ε, realizable k-ε, standard k-ω and SST k-ω were compared. The simulating results of realizable k-ε and standard k-ω were better than that from other models. The correlation coefficients between the test results and the simulation values of these two models were 0.998 and 0.998, respectively, in 0.05-0.30 MPa. In 0.10-0.25 MPa, the simulation values were much closer to the test results. So Fluent can be used to simulate the water flow of the bidirectional flow channel and the simulation results had high precision. In addition, by orthogonal design method, we chose three key factors from the structural parameters and arranged nine experimental schemes to study the hydraulic performance and mechanism of energy dissipation. According to the main principle of the bidirectional flow channel, the flux of the backward flow to the flux of the forward flow ratio has important influence on hydraulic performance. For the different kind of channels, when the field angles of V-shape walls were the same, the higher the ratio, the better the hydraulic performance. For the same kind of channel, the higher the pressure was, the higher the ratio and the better the hydraulic performance. The flow index of the third experimental scheme was the smallest among the nine experimental schemes. The velocity vector distribution of the third experimental scheme showed flow conditions in bidirectional flow channel including high velocity area, low velocity area and mixing area of the forward flow and the backward flow. The pressure profile of the third experimental scheme showed the change of pressure in bidirectional flow channel, which further validated the mechanism of energy dissipation and the effect of energy dissipation. When the inlet pressure was 0.05 MPa, the pressure changed from about 0.042 MPa to 0.026 MPa at the mixing area of the forward flow and the backward flow, pressure drop was quite obvious. These conclusions can be directly used to improve the structure of bidirectional flow channel and promote the effect of energy dissipation.