Design and Simulation Optimization for Hydrodynamic Fertilizer Injector Based on Axial-Flow Turbine Structure  
[PERSON]  
1 College of Water Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China; zcl183100126.com(C.Z. ); [PERSON]DDRESS](J.X. )1 College of Water Sciences and Engineering, Taiyuan University of Technology, Taiyuan 030024, China; zcl183100126. total irrigated area [2], which is used primarily in sprinkler and drip irrigation systems. Compared with traditional fertilizer broadcasting or burial methods, integrated water and fertilizer technology in drip irrigation systems has increased crop yield by 5% to 12% and fertilizer utilization efficiency by 30% to 50% [3]. The fertilizing devices for integrated water and fertilizer can be divided into the hydraulic type and the electric-driven type. Hydraulic-driven fertilizer injectors include venturi injectors, proportionate fertilizer pumps, and pressure-differential fertilizer tanks [4]. The first two are proportional fertilization systems where the fertilizer concentration does not change significantly over time, but the inlet pressure (\(H\)) required is relatively high, generally above 0.14 MPa (with the outlet pressure (\(H_{\text{out}}\)) calculated at 0.1 MPa) [5]. The pressure-differential fertilizer tank is a fixed-rate fertilization system that requires a lower \(H\) (\(H\geq\) 0.11 MPa, \(H_{\text{out}}\) = 0.1 MPa) [6], but it faces the issue of rapid concentration decay over time, resulting in reduced fertilization uniformity and crop yield [7]. To increase the irrigation area for each wheel irrigation system and prevent damage to driplines from excessive pressure, many farmers operate drip irrigation systems at low pressures (\(H\)< 0.12 MPa). Therefore, most drip irrigation systems in China for food crops use pressure-differential fertilizer tanks [8]. For traditional surface irrigation (furrow irrigation and border irrigation), the use of integrated water and fertilizer technology has been shown to significantly improve nitrogen fertilizer distribution uniformity, the nitrogen storage rate, and crop yield by 4.0% to 14.5%, 2.2% to 14.3%, and 1.7% to 19.9%, respectively [9; 10]. However, owing to the lack of pipeline water supply infrastructure and fertilizer injection equipment [4], integrated water and fertilizer technology for traditional surface irrigation has not been widely applied. To reduce water transport losses and improve transport efficiency, some irrigation areas in China have shifted to low-pressure pipeline systems recently for water delivery to field distribution points (\(H\) = 0.05 to 0.15 MPa) [11]. This shift provides a platform for implementing integrated water and fertilizer technology in surface irrigation systems, which account for 85% of China's total irrigated area [2]. Therefore, for sprinklers, drip irrigation, or surface irrigation systems, the need for low-pressure hydrodynamic fertilizer injectors to inject fertilizer solution proportionally into the pipeline system is urgent. To reduce the minimum inlet pressure (\(H_{\text{min}}\)) required for the operation of venturi injectors and proportional fertilizer pumps, as well as to increase the fertilizer injection flow rate (\(Q_{\text{inj}}\)) under the same pressure conditions, researchers have conducted extensive studies using hydraulic performance testing and CFD simulations. Structural parameters such as the angle of the suction port, the throat diameter and length, and the length-to-diameter ratio are key factors influencing the fertilizer injection performance of venturi injectors. Studies on the response of \(Q_{\text{inj}}\) to these parameters through hydraulic performance testing have shown that optimized venturi injectors achieve 70.8% to 90.2% increases in \(Q_{\text{inj}}\)[12; 13]. Traditional venturi injectors have symmetrical structures in which negative pressure is annularly distributed around the throat.