Skimmer bird beak (Rynchops) surface for fluid drag reduction in turbulent flow

Abstract

Nature has evolved many aquatic species with low drag surfaces, which include fish, dolphins, and sharks. Low drag surfaces are of interest in both internal and external fluid flow applications. The skin of fast-swimming sharks is a design inspiration for low-drag surfaces (Bhushan 2009; Dean and Bhushan 2010; Bixler and Bhushan 2013a, b). Sharks are able to move quickly through turbulent water flow due to the surface features on their scales. These scales called dermal denticles have riblets, which are microscopic grooves aligned parallel to fluid flow. Adequately-sized riblets lift streamwise vortices that are responsible for large shear stresses and drag. Streamwise vortices are approximately cylindrical vortices rotating along an axis in the streamwise direction. By lifting these vortices from a surface, shear stresses are decreased, resulting in low drag (Martin and Bhushan 2014, 2016a, b).