Coupled Bionic Drag-Reducing Surface Covered by Conical Protrusions and Elastic Layer Inspired from Pufferfish Skin

Abstract

Inspired by the drag-reducing properties of the cone-like spines and elastic layer covering the pufferfish skin, important efforts are underway to establish rational multiple drag-reducing strategies for the development of new marine engineering materials. In the present work, a new drag-reducing surface (CPES) covered by conical protrusions (sparse “k-type” with rough height k + = 13–15) and an elastic layer are constructed on copper substrate via a hybrid method, combining the sintering and coating processes. The drag-reducing feature of the prepared CPES biomimetic surface is achieved by rheometer and particle image velocimetry (PIV) experiments. To comprehensively investigate its drag reduction mechanism, the porous copper substrate (PCS), copper substrate (CS), conical protrusion resin substrate (CPRS), and conical protrusion porous copper substrate (CPPCS) were used for a comparative analysis. In laminar flow, we discovered that the conical protrusion structure and wettability of the elastic surface coupling affect the CPES sample’s drag-reducing performance (7–8%) and that the interface produced slip to reduce the viscous drag. In turbulent flow, the CPES biomimetic surface exhibits an 11.5–17.5% drag-reducing performance. Such behavior was enabled by two concurrent mechanisms: (i) The conical protrusions as vortex generators enhance the number of vortices and the wake effect, enabling faster movement of downstream strips, reducing viscous drag; (ii) The conical protrusion elements break and lift large-scale vortices to produce numerous small-scale vortices with low energy, effectively weakening perturbations and momentum exchange. Additionally, the elastic layer shows high adhesion and stability on copper substrate after sandpaper abrasion and water-flow erosion tests. The copper substrate surface formed by the sintering method is also covered with dense porous structures, which gives the elastic layer and conical protrusions excellent combined robustness. Our findings not only shed new light on the design of robust drag-reducing surfaces but also provide new avenues for underwater drag reduction in the field of marine applications.

Superhydrophobic Surfaces with Excellent Ice Prevention and Drag Reduction Properties Inspired by Iridaceae Leaf

“…The sliding theory was first proposed by Navier; the fluid between the rotor and the sample is in a laminar state. According to the slip length formula M f l a t M s l i p = 1 + b s l i p h where M flat and M slip are the friction of the flat substrate and the sample surface, individually, b slip is the slip length, and h is the fluid height between the sample and the rotor . The sliding velocity is positively correlated to the velocity gradient.…”

“…According to the slip length formula 30 where M flat and M slip are the friction of the flat substrate and the sample surface, individually, b slip is the slip length, and h is the fluid height between the sample and the rotor. 31 The sliding velocity is positively correlated to the velocity gradient. When the solid−liquid contact turns into the gas−liquid contact, the velocity gradient increases significantly, and the slip velocity increases.…”

Numerical investigation into turbulent drag reduction via the application of pufferfish spine-inspired cone microstructures in Suboff models

“…The unique arrangement of sharp spines covering the dorsal and ventral surfaces of pufferfish serves as a defensive mechanism against threats and minimizes hydrodynamic drag when swimming. Cone microstructures (figure 1(b)) taken from the pufferfish skin show notable resistance-lowering properties [38,39]. Figures 1(c) and (d) show how cone microstructures are integrated into the head or tail sections of the suboff bare hull submarine model [40], which consists of the main body, bow, and stern.…”

Drag reduction capacity of multi‐scale and multi‐level riblet in turbulent flow

“…The scale of the fish Ctenopharyngodon idellus has many micro crescent units distributed on its surface, which can generate a "water-trapping" effect and form fluid lubrication to abate skin friction [5]. The conical protrusions on the skin of the pufferfish can break large-scale vortices into numerous small-scale ones with low energy, effectively weakening perturbations and momentum exchange [6][7][8]. Many unique scale structures of other fishes also show outstanding drag reduction capacity [9][10][11].…”