The role of sawtooth-shaped nano riblets on nanobubble dynamics and collapse-induced erosion near solid boundary

In this research, surfaces inspired by shark skin were engineered for aluminum (Al) slabs to investigate the influences of riblets on the collapse dynamics of nanobubbles and the resultant erosion on the slab surfaces. These effects were probed through molecular dynamics simulations. Specifically, surfaces with flat profiles as well as those with small and high sawtooth-shaped nano riblets were modelled for analysis. Near the flat surface, due to the absence of riblets, the water nanohammer, with its semi-spherical shape containing water beads under approximately 30 GPa pressure and 5000 K temperature, impulse the Al slab, transferring both temperature and pressure, thereby inducing maximum erosion. Conversely, surfaces containing riblets separate some parts of water vortices, leading to a shorter collapse time of the nanobubble and the creation of a water nanohammer with a smaller volume compared to their values near a flat surface. Moreover, due to the initial impulse of the water nanohammer to the peak of the riblet, the nanohammer splits into two or three inclined shapes. Then, they diagonally impact the main part of the Al slab, resulting in erosion. The decentralization and diagonal impulse of the water nanohammer in the presence of riblets create a lower erosion volume and depth compared to these values on a flat surface. In summary, it can be inferred that riblets can serve as a passive control method for managing erosion, thereby increasing the lifetime of hulls for ships or submarines.