Airflow distribution law of multi-branch pipe of pneumatic rice direct seeder based on dimensional analysis

In order to investigate the flow characteristics and distribution law of airflow in multi-branch pipe of pneumatic rice precision direct seeder and obtain the mathematical model between airflow parameters and pipe geometry structure. In this study, the airflow flow law of the multi-branch pipeline of the pneumatic system was studied, the mechanism of airflow flow in the multi-branch pipe was analyzed, and it was clarified that the main factors affecting the airflow flow in the pipe, namely, air density, air dynamic viscosity, the total flow rate of the inlet branch pipe, the length of the closed end of the header, the inner diameter of the outlet branch pipe, and the outlet branch pipe spacing. Numerical simulations were carried out using Fluent simulation software to elucidate the cause of multi-branch pipes of uneven distribution of airflow in multi-branch pipes, the empirical equation among these factors and the flow velocity of the outlet branch pipe are established by dimensional analysis method. The bench test results show that the established empirical equations are applicable in the following ranges: 0.018 m3/s≤Q≤0.054 m3/s, 0.045 m≤d≤0.05 m, 0.075 m≤L≤0.125 m, 0.7 m≤Y1≤0.875 m (0.5 m≤Y2≤0.75 m, 0.36 m≤Y3≤0.45 m), the prediction accuracy can be controlled within 10% of the empirical formula, which can provide a reference for the prediction and optimization design of outlet velocity of the multi-branch pipe.