Synergistic optimisation of perforated plate parameters and airflow uniformity regulation in Y-type ducting for rice seedling throwers

The pneumatic rice seedling throwing machine suffers from non-uniform airflow distribution in its air duct, which reduces throwing uniformity. To solve this problem, a new machine was designed with Y-shaped short-distance wide-span tapered air duct with integrated perforated plates. In this paper, the working principle is presented with numerical simulation of the duct flow field to investigate how key perforated plate parameters affect outlet airflow uniformity. It revealed that the open area ratio induces intense jet contraction and recirculation zones, which in turn exacerbated energy dissipation and flow field deterioration. The mechanism by which the number of holes regulated jet interaction and the jet siphon effect, thus determining flow field stability, was clarified. Furthermore, development work, including the trade-off mechanism governed by plate thickness between promoting flow development and controlling turbulent dissipation, and determination of factor levels for the Box-Behnken Design were introduced. Through analysis of variance and regression modelling, the significant influence degree of each factor was obtained. The optimal parameter combination was identified as a 34 mm aperture, 24 holes, and 12 mm thickness. Validation results demonstrated that the improved air duct achieved a significantly reduced outlet velocity non-uniformity coefficient of 1.58%, effectively proving the feasibility and effectiveness of the optimisation method. Field tests showed the improved air duct achieved a throwing unevenness coefficient of 0.17 within the 0.25 m 2 basic counting unit, a 51.4% reduction over the original, with an operational efficiency of 8460 m 2 h −1 . This study provides technical support for uniformity control in pneumatic seedling throwing machines.