3.2.2. Design of Negative-Pressure Blowers

By measuring the material characteristics of dandelion seeds, the average values of the long and short axes of dandelion seeds were found to be 3.096 and 0.588 mm, respectively, and the suspension speed of dandelion seeds with pappi was found to be about 0.82 m·s<sup>−</sup>1. Due to their characteristically small volume, light weight, and slow suspension speed, it is appropriate to collect dandelion seeds using negative-pressure blowers.

In this paper, based on the planting agronomic requirements of dandelion plants, the row spacing used was 15 cm, the harvester was designed to harvest the seeds of eight rows of dandelion plants at one time, and the fan was used for negative pressure harvesting. Three schemes of collecting devices were designed. The first scheme consists of a small fan used to harvest two rows of dandelion seeds and four small fans used to harvest eight rows. The second scheme uses a larger fan to harvest four rows at a time and uses two larger fans to harvest eight rows; the third scheme involves installing a small fan in the middle and

back of the adjacent two fans of the first scheme and harvesting the dandelion seeds missing from the front fan. Three blower layouts shown in Figure 6 were preliminarily designed, and the optimal one needed to be selected from these layouts. The harvesting breadth was 120 cm, and the maximum diameters of blowers at the small and large feed ports were 30 and 60 cm, respectively. The layout and reliability of the blowers and the specifications of common blowers on the market were considered. Figure 6a shows the single-row layout of four blowers with diameters of 24 cm; Figure 6b illustrates the single-row layout of two blowers with diameters of 50 cm; Figure 6c presents the double-row staggered layout of seven blowers with diameters of 24 cm.

**Figure 6.** Negative pressure fan layout diagram. (**a**) Single row arrangement of small fans. (**b**) Single row arrangement of large fans. (**c**) Small fan double row layout.

### *3.3. Flow-Field Simulation of the Collection Devices*

The collection devices are key devices used to harvest dandelion seeds using the dandelion seed harvester. The objective of improving the collection rate of dandelion seeds can be achieved through the reasonable design and improvement of the collection devices. The size and layout of air inlets greatly influence the collection quality. Through flow-field simulation in the collection covers with the three designed blower layouts using Fluent software, flow fields in the three structures at different wind velocities were compared and analyzed. In this way, the optimal structure of the collection devices was determined [21,22], providing a basis for field harvesting tests.

### 3.3.1. Mesh Generation

The 3D modelling and mesh generation were performed for collection covers with the three different blower layouts, as illustrated in Figure 7.

As displayed in Figure 7d, when simulating flow fields in the collection covers, a cross-section I passing the axis of air outlet was selected to observe and analyze the velocity nephograms in flow-field simulation. The velocity vector diagrams of the entire collection covers were observed and investigated to better understand the motion of airflows in the collection covers.
