Powdered organic fertilizer is crucial for sustainable agriculture, but its poor flowability and hygroscopic compaction and caking nature cause frequent blockages during mechanized strip application. While a single Johnson–Kendall–Roberts (JKR) discrete element method (DEM) model simulates powder flow well, it fails to reflect the mechanical breakage of hard caked lumps. Thus, this study established a comprehensive DEM model simultaneously simulating both powder and caked lumps. Based on coarse-graining theory, 0.147 mm particles were scaled to 2 mm spheres. Contact parameters (e.g., JKR surface energy) were calibrated using response surface methodology, yielding a repose angle simulation error of only 0.18%. The actual three-dimensional (3D) geometry of caked lumps was reconstructed via 3D scanning, and breakage mechanical parameters were accurately calibrated by combining uniaxial compression tests with a Bonding model (errors for ultimate load and displacement < 2%). Applying this model to an anti-blocking fertilizer discharge device, simulations and performance tests demonstrated an acceptable macroscopic representation of both powder flow and lump breakage. The optimized device achieved a strip application uniformity coefficient of variation of 3.87–6.40%. By simulating the complex coexistence of powder flow and lump breakage, this study provides a feasible parameter calibration method and numerical reference for optimizing anti-blocking discharge devices.

Subsoiling can break the plough pan and improve the root growth environment. The effect of the traditional subsoiler is poor, as it relies only on the chisel tine, but pneumatic subsoiling can improve the soil structure more efficiently through the negative pressure generated by the jet hole. This research used computational fluid dynamics and the discrete element method to optimize the biomimetic structure of the jet hole, model the pneumatic subsoiling process at a depth of 330 mm, and observe the movement of soil particles as airflow passes through. The effect of the jet hole at different positions and sizes on the plough pan soil was analyzed, and fluid domains and measurement areas were set up to observe the upward movement, diffusion, stabilization, and settling of soil particles under the action of airflow. The results of the soil bin experiment validated the accuracy of the simulation model through draft force and vertical force, and the average error between the simulation and experimental data was 2.8%. The study revealed that the increase in the rate of soil porosity reached a maximum of 3.65% when the jet hole was positioned above the chisel tine with a radius of 4 mm. The biomimetic jet hole pneumatic subsoiler designed in this study, along with the established CFD-DEM coupled simulation model capable of predicting pneumatic subsoiling performance, can provide references for the design and application of a pneumatic subsoiler. Furthermore, it also provides a theoretical basis for understanding the mechanism of airflow on soil during pneumatic subsoiling operations.

Flow distortion generated by L-shaped elbows in plant-protection spraying equipment disturbs the inlet flow of flat-fan nozzles, causing non-uniform outlet velocity distributions and reduced foliar deposition uniformity. This study developed a flat-fan nozzle with built-in flow-straightening vanes to improve spray stability under complex pipeline conditions. A three-dimensional CFD model integrating an L-shaped elbow, nozzle, and external spray region was established, and the Volume of Fluid (VOF) model was used to examine the effects of flow-dividing channel number, vane geometry, and vane insertion depth on velocity distribution on the spray fan plane. Structural parameters were optimized using a Box–Behnken response surface design. Field experiments on soybean seedlings evaluated droplet deposition using a carmine tracer assay with microplate reader measurement. The built-in vanes reduced elbow-induced flow deflection, swirl, and localized high-velocity zones, thereby improving spray fan velocity uniformity. The influence on the coefficient of variation of normal velocity followed the order: vane geometry > insertion depth > channel number. The optimal configuration comprised four channels, a star-shaped vane, and a 10 mm insertion depth, yielding a normal-velocity coefficient of variation of 16.12% at 400 mm downstream of the nozzle. Field trials showed that the developed nozzle reduced droplet deposition CV from 4.46% to 2.03% compared with the conventional flat-fan nozzle, a 54.5% decrease, with a significant difference between nozzles (p = 0.006). These results indicate that built-in flow-straightening vanes can improve spray stability and foliar deposition uniformity under elbow-induced flow distortion.