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Tea [Camellia sinensis (L.) O. Ktze] is loved by people all over the world. For accurate simulation of the falling motion characteristics of fresh tea leaves, this study took one bud and two leaves of fresh tea leaves as the research object, and established a 1:1 three-dimensional (3D) model of fresh tea leaves by using 3D scanning and reverse modeling technologies. The 3D fresh tea leaves model was filled with discrete element particles, and the motion pattern of fresh tea leaves within a certain distance from the ground was simulated. The falling shape of fresh tea leaves was captured by the high-speed camera to verify the established model. By adjusting parameters to optimize the model, it was concluded that the simulation was in good agreement with the test, indicating that the established model is correct. According to the simulation, the fall analysis of four kinds of fresh tea leaves, A, B, C, and D, placed on the transmission belt was carried out. The distance between the transmission belt and the ground was 80 cm. Among them, A leaves were 45 cm, B leaves were 55 cm, C leaves were 55 cm, and D leaves were 65 cm away from the ground. The movement characteristic of fresh tea leaves is vertical on the ground. In different positions from the ground during the falling process, it was found that all kinds of fresh tea leaves were rotated around the stalk axis and the middle part of the fresh tea leaves. In conclusion, the establishment of a discrete element model of fresh tea leaves’ movement morphology and the analysis of movement morphology during the falling process laid a theoretical foundation for the study of air suction sorting of fresh tea leaves in the later period.

To explore the falling morphology of multiscale fresh tea leaves at different speeds, this study evaluated the multiscale fresh tea leaves (one bud with two leaves, one bud with one leaf, single leaf, and damaged leaf) at different heights (0.7 m, 0.5 m, 0.3 m, and 0.1 m from the ground) during the process of dropping on the conveyor belt at different speeds (0.6 m/s and 1.2 m/s). The motion morphology of fresh tea leaves on multiple scales was analyzed by discrete element simulation, the results showed that the movement patterns of multiscale fresh tea leaves at different positions from the ground were different when the conveyor was dropping at different speeds, and that the multiscale fresh tea leaves all rotated around the long axis, short axis, and root of the fresh tea leaves. When the conveying speed of the conveyor belt was 0.6 m/s, the movement patterns of one bud with two leaves and of one bud with one leaf of fresh tea were near the ground, and the movement patterns of the fresh tea leaves were mostly oriented toward the ground. The leaf tips of the fresh tea leaves were mostly on the side near the ground, the damaged leaves were near the ground, and the movement patterns of the fresh tea leaves were mostly parallel to the ground. When the conveyor belt throwing speed was 1.2 m/s, the roots of one bud with two leaves moved toward the ground when they were close to the ground. When one bud with one leaf was close to the ground, the leaf tip moved toward the ground, and the single leaf and damaged leaf rotated around the root because of the inertia of the conveyor belt throwing.

To provide reference for the design of the air-suction tea sorting device, the coupled numerical simulation model was established by the coupling method of computational fluid dynamics (CFD) and discrete element method (DEM) with tea of different quality as test objects, and the model was verified experimentally. Regarding tea particles of different quality, when the test tea particle mass was 0.215, the test value was located in the simulation value with a minimum error of 9 mm, which an error rate of 3.33%, and maximum error of 19 mm, with an error rate of 7.03%. When the test tea particle mass was 0.145, the minimum error of the test value was 5 mm and the error rate was 1.54%, and the maximum error was 9 mm and the error rate was 3.33%. The verification results established the accuracy of the model. During the suspension test and simulation, tea particles were affected by the air flow field of the observation tube, and tea particles fluctuated. During suspension, tea particles were attached to the inner wall of the observation tube under the action of the air flow field. An in-depth study showed that the relationship between the different distances from the initial position of the particles during suspension and the simulation time was a peak function. The extreme function is used to fit the actual trajectory, and the fitting degree is good. The fitting degree of the particle closest to the initial position was 0.9455, and the fitting degree of the particle farthest from the initial position was 0.9981.