# The Noise-Reduction Characteristics of Microstructure of Dragonfly Wing Leading Vein
## 2 Bionic Modeling of Dragonfly Wing Microstructure
### Modeling and Design of Bionic Wing and Leading-Edge Microstructure  
In order to analyze the aerodynamic characteristics of the leading-edge microstructure conveniently, a bionic wing was designed as the carrier of the bionic microstructure based on the dragonfly's front wing. The bionic wing was designed according to the principle of scale law [8; 9; 10; 11; 12]. The wingspan \(L\), wing area \(S\) and aspect ratio \(AR\) of the bionic wings correspond to the mass of flying objects \(m\). In this paper, the homemade flapping-wing \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & \(E\) & \(T\) & \(H\) & \(W_{1}\) & \(W_{2}\) \\ \hline
**Length (\(\mu\)m)** & 120–137.5 & 26.7–33.3 & 38.9–46.5 & 84.4–166.7 & 120–255.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters of leading-edge wing vein microstructure (\(\mu\)m). Figure 1: SEM images and sample of dragonfly’s front wing leading edge. (**a**) Serration structure of A area leading edge. (**b**) Serration structure of B area leading edge. (**c**) Serration structure of C area leading edge. (**d**) Cross-section of the leading edge. (**e**) Dragonfly’s front wing. micro air vehicle was chosen as the carrier in the design, and its mass \(m\) was about 25 g. The calculation equation is as follows:  
\[L=1.17m^{0.39} \tag{1}\]  
\[S=0.16m^{0.72} \tag{2}\]  
\[AR=L^{2}/S=8.56m^{0.06} \tag{3}\]  
According to the above equations, it can be calculated that: \(L\) = 0.278 m, \(S\) = 0.0112 m, \(AR\) = 6.86. Generally speaking, a wing with a larger area means a larger lift force. A small aspect ratio can improve agility and maneuverability, while a large aspect ratio can improve gliding ability [13]. Small changes to the wing plane design would have a great influence on the aerodynamic force. There was some modification to the wing shape design that the wingtip area was enlarged for better aerodynamic forces [14]. The detailed size of the modified wing in this paper was modified as follows: the half-wing span \(L/2\) = 14 cm, the wing area \(S\) = 126 cm\({}^{2}\), aspect ratio \(AR\) = 6.22. The dragonfly's forewing specimen and its bionic wing model are shown in Figure 2.  
The microstructure near the leading edge fin was modeled as shown in Figure 3, and the parameters of the microstructure are shown in Table 2. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(E\) & \(T\) & \(H\) & \(W_{1}\) & \(W_{2}\) & \(\beta\) \\ \hline
128.75 & 30.0 & 42.7 & 125.55 & 187.8 & 60\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Bionic serration microstructure parameters (\(\mu\)m). Figure 3: Biomimetic leading-edge microstructure model of a dragonfly wing. Figure 2: The morphology of dragonfly’s forewing and its bionic model. (**a**) Dragonfly front wing; (**b**) bionic front wing model and size. Aerodynamic Noise Analysis and Optimization of a Bionic Model of Dragonfly Wings' Leading-Edge Microstructure  
The characteristic dimension parameters of the bionic serrated shape are mainly width \(W_{1}\) (\(W_{2}\)) and height \(H\). In this part, XFlow is used to analyze the aeroacoustic characteristics of the bionic serrated microstructure. The effects of sawtooth structure amplification factor, length \(W_{1}\), length \(W_{2}\) and height \(H\) on wing noise level were investigated. In the simulation analysis, the ambient temperature was set to 20 \({}^{\circ}\)C, and the wind speed was set to 4.7 m/s. Under this condition, the Reynolds number was more than 4000, so the motion of the fluid was turbulent, but the turbulence intensity was not high. Therefore, the aerodynamic noise generated by the bionic wings was determined by the leading edge noise and the self-noise of eliminating the trailing edge noise. However, under this simulation condition, the leading-edge noise generated by the interaction between the incident flow and the leading edge of the wing was the main noise source.