# Parameter Design and Optimization of Grass Aerial Seeding Tower Based Computational Fluid Dynamics
## 3 Parameter Design and Optimization of Basic Nozzle Unit
### Structural Optimization Design  
To address the issue of non-uniform airflow distribution at the outlet of the original structure, different inclination angles were designed. The velocity contours for the basic nozzle unit with various inclination angles were obtained through simulation, followed by the calculation of outlet velocity non-uniformity, using Equation (1) for different inclination angle conditions.  
In the comparison analysis, inclination angles of 11\({}^{\circ}\), 13\({}^{\circ}\), 15\({}^{\circ}\), 17\({}^{\circ}\), and 19\({}^{\circ}\) were chosen. The inlet velocity was set to v\({}_{0}\) = 0.5 m\(\cdot\)s\({}^{-1}\), and the inlet radius was consistently set to 500 mm. Figure 13 displays velocity contour inside and outside the basic nozzle unit under different inclination angle conditions.  
In these figures, blue regions indicate lower velocities while red regions denote higher velocities. At an inclination angle of 11\({}^{\circ}\), the velocity field of the air entering the nozzle exhibits a relatively uniform distribution, with velocity gradually increasing at the nozzle exit. The low inclination angle prevents significant backflow and turbulence after the air enters the nozzle, resulting in a relatively smooth overall flow. When the inclination angle increases to 13\({}^{\circ}\), the fluid velocity field begins to show more variations. Although the internal velocity distribution within the nozzle remains relatively uniform, the exit area starts to display regions of more pronounced velocity changes. As the inclination angle further increases to 15\({}^{\circ}\), the velocity field undergoes more noticeable changes. The high-velocity regions at the nozzle exit expand significantly, and the larger inclination angle induces more turbulence, particularly at the nozzle exit, where the flow starts to become unstable and the internal velocity distribution becomes less uniform. At an inclination angle of 17\({}^{\circ}\), a more complex velocity distribution appears both inside and outside the nozzle. Notably, at the nozzle exit, there are alternating regions of high and low velocity within the velocity field. The significant inclination angle induces more turbulence and velocity gradient changes, resulting in more complex and less uniform flow, with the possible formation of localized backflow zones. When the inclination angle reaches 19\({}^{\circ}\), the velocity field shows the most dramatic changes. The 19\({}^{\circ}\) inclination angle triggers intense turbulence and backflow, leading to extremely unstable flow, with distinct backflow and vortex regions. The velocity field undergoes significant variations, and the overall flow is considerably disrupted.  
Figure 12: Velocity contour of the fundamental unit of the nozzle.  
10.611 m\(\cdot\)s\({}^{-1}\), marking an increase of 133%. Simultaneously, the relative standard deviation \(CV\) increases, the uniformity index \(\gamma_{v}\) decreases, and the velocity direction index \(S_{x}\) gradually decreases. This indicates that with a larger inclination angle, although the exit velocity becomes greater, the uniformity of exit velocity decreases, and the directionality worsens.  
Although the average exit velocity increases with the increase in inclination angle, as seen in Figure 13, various factors such as structural shape contribute to the lighter color of the velocity contour at an inclination angle of 19\({}^{\circ}\) compared to 17\({}^{\circ}\).  
Taking factors, such as machining cost, processing difficulty, range of grass seed dispersal, uniformity of velocity, and directionality, into account, the inclination angle is determined to be 15\({}^{\circ}\).