Precision optimization of pipeline-type micro-hydraulic turbine performance under multi-operating-condition application scenarios

Pipeline hydropower generation is one of the most important means for green energy and wireless operation in smart irrigation. Micro-hydraulic turbines can be expected for energy recovery from irrigation pipelines. However, it is often required for systematic screening to balance power generation efficiency and hydraulic stability, due mainly to the complex relationship between impeller parameters and hydraulic performance. Moreover, blade angle can be expected to adjust with pipe diameters under various parameters, such as water-fertilizer solution density and terrain head. In this study, a precise optimization was proposed to integrate transient–steady simulations and flow field visualization. (1) 30 transient simulations were conducted to determine the rated speed range using dynamic mesh technology, followed by 66 steady-state simulations to evaluate power, head loss, and hydraulic efficiency. The optimal configuration was identified after flow field contour analysis. Power comparison tests were also conducted on a simulated irrigation pipeline platform under inlet pressures of 0.06–0.26 MPa. Blade angle adaptability of the optimal impeller was assessed under 32, 90, and 110 mm pipe diameters, according to geometric similarity criteria. A systematic simulation was also conducted to determine power output and flow field stability under fertigation solution densities (1 000–1 200 kg/m³) and terrain height differences (4 and 8 m). The results showed that the impeller with 20 blades and a blade angle of 76° achieved the best overall performance under baseline conditions, thus delivering the maximum output power and hydraulic efficiency with the lowest head loss. Internal flow fields showed that the blade angle preserved a uniform velocity gradient to suppress flow separation for stable flow paths. The uniform pressure distribution moderately intensified the high-pressure zone without severe impact losses. Streamline diagrams further confirmed that the flow closely followed the blade surfaces with negligible backflow. Physical experiments verified that the optimal design outperformed a commonly used 24-blade commercial turbine over a wide range of inlet pressures. The optimal blade angle varied with pipe diameter, due to the different internal velocity distribution and fluid inertia. Specifically, the optimal blade angle of 76° was recommended for 32 and 90 mm pipes to enhance flow guidance, whereas 75° was recommended for 110 mm pipes to avoid flow separation for streamline smoothness. Power output increased markedly with higher fertigation solution density; Main pipes with larger flow areas were more sensitive to density, but excessive density induced flow disturbances, vortex intensification, and backflow in smaller pipes. Power output also rose substantially with greater terrain heights. In the 90 mm main pipe, the output reached 2 700 W under an 8 m head difference, indicating considerable power supply potential with a stable and orderly flow field. In the 32 mm branch pipe, the output was about 245 W, sufficient to power low-power sensor nodes, although local turbulence was observed at larger drops. The optimal impeller parameters were identified using transient–steady simulation rather than single-indicator evaluation. Blade parameters can be adjusted for actual performance in practice. These findings can provide practical guidance to optimize micro-hydro turbines in modern agriculture, particularly in hilly orchard irrigation.