3.3.2. Simulation Results and Analysis

Figure 8 shows the velocity nephograms and velocity vector diagrams of the collection devices with the single-row layout of small blowers that rotate at 1.0, 1.5, and 2.0 m·s−1. The velocity nephograms demonstrate that the velocity changes slightly in adjacent areas in the collection cover and is uniform while the amount of air at the air outlet is large; thus, the wind velocity is fastest there. As displayed in velocity vector diagrams, the airflow field in the collection cover varies slightly with changes in the wind velocity. Roughly two flow directions are observed at the air inlet: part of the airflow moves towards the outlet while the residue converges with the other part of airflow after being reflected by the wall of the collection cover to flow from the air outlet. This indicates that the intake air is confluent in the collection cover.

**Figure 7.** Grid division of collection device model. (**a**) Grid division of the collection hood for the first type of fan layout, (**b**) Grid division of the collection hood for the second type of fan layout, (**c**) Grid division of the collection hood for the third type of fan layout, (**d**) Cross section schematic diagram of velocity cloud map.

Figure 9 illustrates the velocity nephograms and velocity vector diagrams of the collection devices with the single-row layout of large blowers that rotate at 1.0, 1.5, and 2.0 m·s<sup>−</sup>1. The velocity vector diagrams show that airflow is poorly confluent in the collection devices with the single-row layout of large blowers, and a large blank area of airflow can be seen in the center. The airflow entering the collection cover from the air inlet does not converge well with the airflow in other directions, which flows towards the air outlet after being reflected at the wall. Instead, some air flows obliquely downward after reflection at the wall, which disturbs the flow field in the collection cover and inhibits airflow at the air inlet, slowing its progress into the collection cover. As a result, the collected dandelion seeds are less readily passed out in the collection process.

(**c**) Wind speed V = 2.0 m·sƺ<sup>1</sup>

**Figure 8.** Velocity nephogram and velocity vector diagram under different wind speeds.

Figure 10 shows the velocity nephograms and velocity vector diagrams of the collection devices with the double-row layout of small blowers that rotate at 1.0, 1.5, and 2.0 m·s−1. Analysis of the velocity nephograms reveals that the velocity changes little and is uniform in the collection cover, while there is a significant difference in wind velocities at the inlet and outlet. By observing the velocity vector diagrams, it was found that there is a large blank area of airflow in the collection cover with the double-row layout of small blowers. In addition, the same problem that arose in the collection devices with the single-row layout of large blowers also arises in this layout. That is, some air flows downward after being reflected by the walls, which disturbs the flow field in the collection cover and inhibits the otherwise smoother inflow of air at the air inlet to the collection cover.

(**c**) Wind speed V = 2.0 m·sƺ<sup>1</sup>

**Figure 9.** Velocity nephogram and velocity vector diagram under different wind speeds.

Comprehensive analysis of the flow-field simulation results of collection devices with the three blower layouts indicates that the single-row layout of small blowers shows the best effect compared with the other two layouts. The layout enables smooth motion of airflow, meets requirements for collecting and transporting dandelion seeds, saves materials, and is easily machined. The wind field generated by the fan in Figure 7b is large and not concentrated in the lower part of the collection device. The collection rate in the pre-test is small, and it is easy to inhale other impurities into the machine. In the pre-test, the rear fan of the collection device shown in Figure 7b collects fewer seeds, and the overall collection rate is almost the same as that shown in Figure 7a. During the pre-test verification of the collection rate of the three schemes, it was found that the collection device of the style shown in Figure 7a had a higher collection rate than the other two schemes, and that the airflow in the flow field was stable and the cost was low. In summary, we chose the collection device of the style shown in Figure 7a.

(**c**) Wind speed V = 2.0 m·sƺ<sup>1</sup>

**Figure 10.** Velocity nephogram and velocity vector diagram under different wind speeds.
