The structure and shape of the conveyor tube have a significant influence on the performance of the sweet potato seedling recovery machine. In order to reduce the power consumption of the sweet potato seedling recovery machine and increase the recovery rate of the sweet potato seedlings, the CFX software was used to calculate the gassolid twophase flow in the throwing device and analyze the twophase flow distribution law in the throwing device. The simulation results show that the threestage radian combination scheme of the upper wall of the conveying elbow, the contraction transition of a single radius of curvature, and the appropriate opening of the fan inlet are helpful to improve the performance of the throwing device. Taking the arc of the elbow, the radius of curvature of the shrinkage curve, and the entrance opening as the test factors, the specific power consumption of the throwing device of the recovery machine and the recovery rate of the sweet potato seedlings were used to conduct a threefactor threelevel central combination test and test verification. The optimized test results show that the arc of the upper wall of the conveying elbow adopts the threesegment arc are R1 026+R513+R256 mm, the radius of curvature of the shrinkage curve is 850 mm, the fan inlet opening is 216 mm, and the specific power consumption of the throwing device and the recovery rate of sweet potato seedlings are 660 m2/s2  and 93.23%, respectively. The experiment shows that the specific power consumption is reduced by 9.71% after the optimization and improvement of the throwing device, and the recovery rate of sweet potato seedlings is increased by 1.04%, which proves the effectiveness of the simulation optimization of the conveyor elbow of the potato seedling recovery machine.

Given the lack of accurate parameter values in discrete element simulation of sweet potato seedling mechanized recovery, a direct measurement and virtual calibration method was used to study the Discrete Element Method (DEM) simulation parameters of broken sweet potato stems and leaves. The intrinsic parameters, collision recovery coefficient and static friction coefficient of broken seedlings were acquired by physical experiments. Different parameter combinations were designed for DEM simulation. The intrinsic parameters of sweet potato leaves and other unmeasurable DEM simulation parameters were determined by stacking angle optimization simulation. Plackett-Burman test shows that the static friction coefficients of stem-stem and stem-steel and the rolling friction coefficients of stem-stem and stem-leaf all significantly influence the accumulation angle. The parameters that significantly influence the stacking angle of broken seedlings were sent to steepest ascent test and Box-Behnken test. The average stacking angle of 40.51° and the relative error of 0.972% indicate it feasible to calibrate DEM parameters by physical test and optimization simulation and the calibrated parameters can be used in DEM simulation of broken sweet potato stems and leaves.