Simulation of agricultural air seeding systems using the discrete element method and computational fluid dynamics

The Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) were applied to simulate seed dynamic attributes as affected by air seeding equipment features. The air seeding equipment features in this work included a fluted roller seed meter, a horizontal distributor tube, a horizontal-vertical tube transition, and a vertical seed manifold. Each simulation was validated through a combination of theoretical calculations and experimental measurements. Fluted roller seed meter simulations using DEM demonstrated that varying inputs for mechanical energy dissipation (i.e. damping) did not affect mass flow rate at roller speeds between 10 and 50 rpm. The predicted mass flow rate values of the seed metering simulations were within 10 g/s of the experimental results with the largest relative error as 16.5 %. Coupled CFD-DEM simulations for the horizontal distributor tube showed that solids loading ratios between 0.5 and 3.0 did not have a significant effect on average seed velocity. The horizontal and horizontal-vertical tubing simulations generated average seed velocity data and flow patterns that corresponded well with values calculated from pneumatic conveying theory. Furthermore, simulated seed trajectory and contact force data identified the seed feeding point (horizontal distributor tube) and bend area (horizontal-vertical transition) as the locations with the highest contact forces inside the air seeder distribution system. Comparison of one-way and two-way coupled CFD-DEM simulation for the horizontal-vertical tube indicated that one-way coupling was a suitable option to represent seed dynamic attributes at low solids loading ratios. Seed manifold simulations using one-way CFD-DEM coupling were complementary to experimental observations (R2=0.90) but the accuracy in determining the actual number of seeds per manifold outlet needs improvement. Generally, increasing inlet air velocity promoted more uniform seed distributions but increased seed contact force