Abstract
This study investigates the hydrodynamic benefits of the swimming hairs on the hind legs of diving beetles, characterized by diameters of 10-21 μm and gaps of 6-23 μm. Using the quasi-DNS method provided by OpenFoam platform, we simulated the process of water flowing through these microgaps. Results showed that seam plates can achieve a maximum drag increase of 20-30% compared with seamless plates, primarily due to viscous drag. As the gap to diameter ratio increased, fluid passage and viscous drag rose, enhancing overall drag. Beyond a certain ratio, both viscous and pressure drags decreased rapidly, shifting the seam plate to a drag-reducing state. For individual microcylinders, drag increased with gap enlargement, reflecting the intensified fluid impact and friction. The transition to drag reduction was due to fewer microcylinders. These findings suggest that the unique structure of swimming hairs offers drag advantages, providing valuable insights for designing efficient propulsion systems in small underwater vehicles.