Hierarchical Surface Patterns via Global Wrinkling on Curved Substrate for Fluid Drag Control

Abstract

In this paper, the results of an investigation on the global wrinkling of stiff coatings resting on curved compliant substrates are presented. It is found that the overall stiffness of the corrugated coatings can dominate the deformation mode and induce the global wrinkling when the coating thickness exceeds certain critical value. It is demonstrated that hierarchical wrinkling patterns with small wrinkles superposing on large wrinkles, either parallel or perpendicularly, can be generated via the global wrinkling processes. Through a combination of theoretical model, experimental studies, and numerical simulations, the formation mechanism and controlling parameters of the hierarchical wrinkling patterns are systematically investigated. The quantitative expression of the critical loading strain, critical wavelength, and critical coating thickness of the global wrinkling as a function of the initial substrate curvatures and loading conditions are revealed. Inspired by the resemblance between the hierarchical surface patterns and the surface riblets on sharks and dolphins, the potential application of utilizing the hierarchical wrinkling patterns to reduce fluid drag through computational fluid dynamics (CFD) studies is further investigated. Reduced drag resistance is observed on the hierarchical wrinkled surface with small wrinkles and large wrinkles perpendicular to each other.

Focus on Bioinspired Textured Surfaces toward Fluid Drag Reduction: Recent Progresses and Challenges

“…Reproduced with permission. [111] Copyright 2021, John Wiley and Sons Ltd. diverse denticle sizes on hydrodynamic characteristics. [28] Simplified microstructures mimicking shark skin were fabricated using a Flash Forge Dreamer dual-extrusion 3D printer and acrylonitrile butadiene styrene (ABS).…”

“…Lin et al researched the effect of integral wrinkling of a rigid coating on a bending flexible substrate on reducing flow drag. [ 111 ] Li et al devised and fabricated five kinds of bionic flexible coatings inspired by dolphins with drag reduction performance. [ 154 ] A biomimetic flexible coating was prepared by spraying a mixture of polydimethylsiloxane and ethyl acetate on an aluminum plate with a spray gun and heating.…”

“…Lin et al explored the drag reduction effects of hierarchical fold structures with small and large wrinkles perpendicular to each other inspired by shark and dolphin grooves. [ 111 ] The hierarchical fold structure is shown in Figure 8D. In the case that only a single layer of large wrinkles exists on the surface, the eddy current, which plays the role of “rolling bearing” caused by the roughness, not only greatly reduces the friction drag but also increases the pressure drag due to its shape, so the net drag reduction rate is not high.…”

“…The synergy of the two results in a net drag reduction of up to 8.6% at high Reynolds number laminar flow. [ 111 ] The CFD results of Yang et al show that the drag coefficient of the wrinkled shapes is lower than that of the flat surface. Two factors are considered to be the reasons for the decrease of the drag coefficient: one is that the pressure drag before and after the object is reduced by the low‐pressure region of the wake and the other is that a local slip of the fluid is caused by the vortex between the wrinkles.…”

“…D) Layered fold structure of small and large wrinkles perpendicular to each other. Reproduced with permission [111]. Copyright 2021, John Wiley and Sons Ltd.…”