Structural Optimization of Jet Tee for Non-Rotating Refractive Nozzles

Literature Overview

This 2025 paper by Yuan Weiwei, Wang Xinkun, Yan Hailan, Zhao Qing, Chen Yaqi, and Jia Zongjin from Jiangsu University's National Engineering Research Center for Water Pumps and Systems presents a systematic structural optimization study of a jet tee (injector tee) designed for use with non-rotating refractive nozzles in irrigation systems. The study employs orthogonal experimental design to investigate the influence of four structural parameters—nozzle width, height difference, split distance, and side wall inclination angle—on the hydraulic performance and irrigation uniformity of the jet tee. The optimization is validated through both CFD simulation (using CFX) and hydraulic performance testing.

Research Background and Problem Statement

In irrigation systems, particularly those using refractive (refraction-type) nozzles, the uniformity of water distribution is a critical performance metric. Conventional tees used to split flow from a main line to individual nozzle branches can introduce flow pulsation and non-uniform distribution, particularly when used with non-rotating nozzles that rely on steady flow for consistent spray patterns.

The jet tee (also referred to as an injector tee or pulse tee) is a specialized fitting designed to introduce controlled flow pulsation into the irrigation system. This pulsation can improve the spray pattern of refractive nozzles by promoting better droplet formation and distribution. However, the hydraulic performance of the jet tee is sensitive to its internal geometry, and optimizing these geometric parameters is essential for achieving the desired pulse characteristics and irrigation uniformity.

Experimental Design and Methodology

The authors employed a $L_{25}(5^4)$ orthogonal experimental design to investigate the influence of four factors, each at five levels:

A total of 25 experimental configurations were designed and evaluated. Each configuration was subjected to CFD simulation using CFX to determine the following performance metrics:

• Water head amplitude ($\Delta H$) — The peak-to-peak variation in water head, which characterizes the pulse intensity.
• Water head loss ($\Delta P$) — The pressure drop across the tee, which affects the overall system efficiency.

The optimization objective was to maximize the water head amplitude (to enhance pulse characteristics) while minimizing the water head loss (to maintain system efficiency).

Results and Optimization

The orthogonal design analysis revealed the following order of influence on the performance metrics:

• Water head amplitude — The factors ranked by influence were: nozzle width > height difference > split distance > side wall inclination angle. The nozzle width was the most significant factor, indicating that the cross-sectional area of the nozzle throat has the greatest impact on pulse generation.
• Water head loss — The factors ranked by influence were: split distance > nozzle width > height difference > side wall inclination angle. The split distance was the most significant factor for pressure loss, indicating that the distance between the flow-splitting elements strongly affects hydraulic resistance.

The optimized model was selected based on the combined objective of maximizing amplitude and minimizing loss. The key results are:

The hydraulic performance testing confirmed the CFD predictions, with measured values closely matching simulated results across the tested pressure range of 0.10 to 0.20 MPa. The irrigation uniformity coefficient was calculated using Surfer software by superimposing individual nozzle spray patterns and evaluating the distribution uniformity across the irrigated area.

Engineering Significance and Application Context

The optimized jet tee has significant implications for irrigation engineering:

• Improved water use efficiency — By enhancing the pulse characteristics of the flow, the jet tee promotes better droplet formation and distribution, reducing water waste due to runoff or overspray.
• Enhanced crop yield — More uniform irrigation distribution leads to more consistent crop growth, reducing the risk of water stress in under-irrigated areas and waterlogging in over-irrigated areas.
• Compatibility with non-rotating nozzles — The jet tee provides a cost-effective solution for improving the performance of non-rotating refractive nozzles, which are widely used in agricultural irrigation due to their simplicity and low maintenance requirements.
• Scalability — The orthogonal design methodology and CFD-based optimization approach can be applied to other tee configurations and nozzle types, making the methodology broadly applicable.

Study Insights and Reflections

This paper exemplifies a rigorous engineering optimization approach that combines experimental design, computational simulation, and physical validation. The methodology is sound and the results are practically significant.

Several observations merit attention:

• CFD model validation — The close agreement between CFD predictions and experimental results validates the computational model and gives confidence in the optimization results. However, CFD models for internal flow in complex geometries can be sensitive to mesh quality, turbulence modeling, and boundary condition assumptions. The authors should have provided more detail on the mesh independence study and turbulence model selection.
• Long-term performance — The paper focuses on hydraulic performance under steady-state conditions. In practice, jet tees are subjected to cyclic flow conditions, potential fouling from water quality issues, and mechanical wear. The long-term performance and durability of the optimized tee should be evaluated through accelerated life testing or field trials.
• Manufacturing considerations — The optimized tee geometry, with its specific nozzle width, height difference, split distance, and side wall inclination angle, may require specialized manufacturing techniques. The paper does not discuss the manufacturability of the optimized geometry or the associated production costs. For widespread adoption, the tee must be manufactured at a competitive cost, which may require simplification of the geometry or use of injection molding or 3D printing techniques.
• Standardization — The paper does not address the standardization of the optimized tee geometry. For the technology to be widely adopted, industry standards for jet tee design, testing, and performance rating would need to be developed. This could follow the model of existing standards for irrigation components (such as ISO 9027 for irrigation emitters or ASABE standards for irrigation systems).

The funding from the Shandong Provincial Key R&D Program (2020CXGC10807) indicates that this research is part of a broader effort to develop advanced irrigation technologies in China. The results contribute to the national goal of improving water use efficiency in agriculture, which is a critical issue given China's water scarcity and the growing demand for food production.

For engineers in the irrigation and water management field, this paper provides a valuable example of how systematic experimental design and computational optimization can be used to improve the performance of hydraulic components. The methodology is transferable to other components and systems, and the results offer a practical path toward more efficient irrigation practices.