3 | RESULTS

3.1 | Microstructure of cross-section of hindwings

The hindwing is cut along chordal direction in Fig. 3(a). The whole morphological features of cross section are observed as shown in the Fig. 3(P1~P3) by the 3D microscope system. The result indicates that the beetle hindwing is corrugated, not flat. And, the position of the cross section affects the corrugation shape, which is related to the trend of the veins. There are veins exist in the inflection point of up and down (Kim et al., 2009). Some studies shows that the corrugation shape make the whole wings have good concavity which can improve the flight aerodynamic (Chen et al., 2016), and flexural rigidity and prevent fatigue fracture (Kim et al., 2009; Eshghi et al., 2022). Fig. 3(b) - 3(d) showed microstructures of the leading edge first groove on position P1, P2 and P3, respectively. It is obviously that those grooves are irregular.
From Fig.3(b), the first groove(G1) is located at the start of the entire airfoil(P1). Its thickness of DS (dorsal side) and VS (ventral side) is 7.53±0.19 μm and 4.91±0.51 μm, respectively. The thickness of DS is 53.36% larger than The VS. From Fig.3(c), the first groove(G2) is located at the one-fourth of the entire airfoil(P2). Its thickness in DS and VS is 1.55±0.03 μm and 5.38±0.03 μm, respectively. The thickness of DS is 71.19% smaller than The VS. From Fig.3(d), the first groove(G3) appears at the one-third of the entire airfoil(P3). The G3 is flatter and small radian than G1 and G2. Its thickness value of DS is increased 13.52% than VS. So, the groove’s thickness is different in the three positions. In the same groove, the thickness of DS is also different from VS. In addition, the position of the first groove relative to the entire chordal cross-section of the wing gradually moves backwards. This phenomenon may have an impact on hindwing flight aerodynamic performance. Because corrugation is directly related with insect wings’ aerodynamic (Nguyen et al., 2021; Mukherjee et al., 2021; Krishna et al., 2020). Next, we will use simulation method to analyze the aerodynamic of three 2D corrugated airfoil models (CA models) during flapping.