*3.2. Analysis of Simulation Results*

3.2.1. Terminal Speed Analysis of the Pick-Up Device

In Fluent, the SIMPLE algorithm is used, the mesh model is a hexahedral mesh, and the simulation model is a standard k-epsilon model. The inlet is set as the velocity inlet, the velocity is consistent with the initial velocity of the Rocky particle inlet, the velocity is 20 m·s−1, and the fan port is set as the pressure outlet condition. In Rocky, the particle inlet initial velocity is set to be the same as the inlet wind velocity in Fluent, in the direction normal to the inlet plane. Air flow velocity clouds were obtained for the hazelnut harvester

at three air flow speeds, as shown in Figure 8. In the simulation experiment, there was no adhesion between the hazelnut and the leaf, and a contact model without sliding was used between the particles and the wall, with the gravitational acceleration direction along the negative direction of the Z-axis. The feeding time was 2.5 s, total feeding 1.7 kg, total simulation time 3 s, and interval time 0.05 s.

**Figure 8.** Velocity contour map of the pick-up device: (**a**) air velocity 15; (**b**) air velocity 18; (**c**) air velocity 21.

#### 3.2.2. Analysis of the Working Process of the Sorting Device

The particle flow trajectory inside the hazelnut harvester corresponding to 0~3 s time was obtained by coupling simulation with Fluent fluid dynamics software and Rocky discrete element software. The working process is shown in Figure 9. At t = 0.55 s, the particles began to fall by the discharge device, and the particle mixture was blown to the sieve plate by the positive-pressure wind. After the leaves and hazelnuts hit the sieve plate, the lighter leaves were blown to the miscellaneous collection box in front, the gravity of the hazelnuts themselves was greater than the blowing force of the air flow, and the hazelnuts fell by gravity to the hazelnut collection box. At t = 1.65 s, the particle mixture was further separated through the sieve plate. The lighter leaves were partly blown to the debris collection box in front and partly blown out through the air outlet, and more hazelnuts fell by gravity to the vibrating screen waiting for further sorting. At t = 2.55 s, the number of falling particles reached 1.7 kg. The hazelnut collection box had a small number of leaves, and the vibrating sieve further separated the hazelnuts by size. The device in line with the expected design effect.

**Figure 9.** The working process of wind sorting device: (**a**) start sorting at t = 0.55 s; (**b**) during sorting at t = 1.65 s; (**c**) end sorting at t = 2.55 s.

Simulation of the whole process was completed for a total of 3 s with a sieve leaf plate angle of 50~60 ◦, air flow velocity of 10~20 m·s−1, and distance of the sieve plate of 15~50 mm for seventeen groups of simulation. The results show that the particles with different densities can be sorted by the screening of the baffles. The comparison curves of the total mass of material with time between the simulation experiment of the sorting device and the field experiment are shown in Figure 10. The trend of the total mass of the particle mixture in the pick-up device with time is shown in Figure 11. The results show that the sorting effect is most obvious, and the net fruit rate is high at the sieve plate angle of 55◦, air flow velocity of 15 m·s<sup>−</sup>1, and distance of the sieve plate of 30 mm.

**Figure 10.** Variation in the mass profile of each material in the sorting device.

**Figure 11.** Variation in the total material mass profile in the pick-up device.

The coupled CFD-DEM simulation analysis shows that after the granular mixture material goes down from the discharge device, the mixture material collides with the screen plate, the leaves are blown to the impurity collection box with the air flow, and the hazelnuts flow to the hazelnut collection box under the action of gravity. The air flow in the designed sorting device model follows the expected trajectory and the particle mixture is effectively separated. The CFD-DEM simulation experiment obtained the distribution and movement of particles in the separation device, and the overall process of simulation is reasonable and more consistent with the actual working conditions, which can be used to simulate the harvesting and sorting process of hazelnuts.
