Dolphin-inspired drag reduction coatings clarify the effects of elasticity and viscosity
Dolphin-inspired drag reduction coatings clarify the effects of elasticity and viscosity lead image
Thanks in part to their smooth and elastic skin, dolphins are among the fastest swimming animals on the planet. In an effort to emulate this low drag for marine applications, Li et al. compared different types of surface coatings to determine the roles of elasticity and viscosity in drag reduction.
“At present, reducing the navigation resistance of vehicles is a research hotspot. Many drag reduction technologies have been proposed,” said author Longyang Li. “However, their own shortcomings limit their large-scale application in the complex environment of the ocean.”
The authors were surprised to find the elasticity of the surface coating has a larger impact on drag than its viscosity. In particular, the surface’s ability to deform under stress is the primary influence on improvements in drag reduction. Even though the viscosity plays a secondary role, its effects are not negligible.
In order to characterize the contributions of these properties, the group made five different bionic flexible coatings inspired by dolphin skin. By varying the ratios of the polymer polydimethylsiloxane (PDMS) and curing agent in the coatings, they tuned the relative effects of elasticity and viscosity, with an increase in PDMS resulting in decreased elasticity, and vice versa. They sprayed each coating mixture over aluminum disks and monitored the effects on its motion to characterize their surface properties.
By adjusting the PDMS and curing agent ratios, the drag reduction performance can be optimized for applications at specific velocities.
To verify the large-scale applicability of the coating, the group next plans to carry out a series of sea tests to study its corrosion and anti-biological adhesion.
Source: “Investigation of the drag reduction performance of bionic flexible coating,” by Luncao Li, Bing Liu, Hanlin Hao, Longyang Li, and Zhixiang Zeng, Physics of Fluids (2020). The article can be accessed at https://doi.org/10.1063/5.0016074 .
