Optimized three-dimensional cuboidal shark-inspired riblets for enhanced drag reduction in turbulent flow

The unique sharkskin riblets have attracted considerable attention due to their drag-reduction properties. Previous studies have shown that these riblets can reduce drag by generating vortices in turbulent flow and lowering overall shear forces. Drag reductions of 11% have been found when comparing 90°-oriented three-dimensional staggered ribs to smooth surfaces. These studies have highlighted the role of vortex structures in drag reduction. However, some riblet geometries remain unexplored. This study introduces a parametric analysis for three-dimensional cuboidal riblet geometries. Various staggered designs with different riblet heights, counts, and spacings were modeled to compare their vortex structures and drag characteristics. The results indicated that increasing riblet height caused the riblets to protrude more prominently into regions of higher flow speed, thereby increasing drag. Additionally, fewer riblets created a smaller area for vortex-riblet interaction, leading to reduced drag. However, changes in riblet spacing had minimal impact on the projected drag reduction. This investigation determined the optimal riblet dimensions to be a rib count (n) of 3, dimensionless spacing (s⁺) between 8.5 and 28, and height (h⁺) of 5.4, achieving an optimal drag reduction of 13.5%. This deeper understanding of drag-reducing riblet design offers valuable guidelines for developing drag-reducing surfaces in underwater transportation.