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.