Transition Delay Using Biomimetic Fish Scale Arrays

TL;DR

This study demonstrates that biomimetic fish scale arrays can delay laminar-to-turbulent transition in boundary layers, potentially reducing drag by stabilizing laminar flow, inspired by aquatic animals' natural strategies.

Contribution

The paper introduces a novel bio-inspired surface design using fish scale arrays that significantly delays flow transition and reduces drag in a controlled experimental setting.

Findings

Transition delayed by 55% with fish scale arrays.

Approximate 27% reduction in theoretical drag.

Fish scales generate streamwise streaks that stabilize the boundary layer.

Abstract

Aquatic animals have developed effective strategies to reduce their body drag over a long period of time. In this work, the influence of the scales of fish on the laminar-to-turbulent transition in the boundary layer is investigated. Arrays of biomimetic fish scales in typical overlapping arrangements are placed on a flat plate in a low-turbulence laminar water channel. Transition to turbulence is triggered by controlled excitation of a Tollmien-Schlichting (TS) wave. It was found that the TS wave can be attenuated with scales on the plate which generate streamwise streaks. As a consequence, the transition location was substantially delayed in the downstream direction by 55% with respect to the uncontrolled reference case. This corresponds to a theoretical drag reduction of about 27%. We thus hypothesize that fish scales can stabilize the laminar boundary layer and prevent it from early transition, reducing friction drag. This technique can possibly be used for bio-inspired surfaces as a laminar flow control means.