Fish scales could hold the key to cutting aircraft emissions

Fish scales could be the unlikely key to reducing aircraft drag, a team of researchers has said.

The team, led by aerodynamicist Professor Christoph Bruecker at City, University of London, have transferred the idea of fish scales to ‘bio-inspired’ arrays that could reduce skin friction drag by more than 25% – therefore boosting aircraft speed and reducing fuel consumption.

Through biomimetic study, Professor Bruecker's team discovered that fish scale surfaces produce a zig-zag motion of fluid in overlapping regions of the surface of the fish, which in turn causes periodic velocity modulation and a ‘streaky flow’ that can eliminate Tollmien-Schlichting wave induced transition. The result reduces skin friction drag by more than 25%.

The team used computational fluid dynamics (CFD) to examine oil flow visualisation. Studying the flow pattern over the surface revealed an unknown effect of the scales, described as ‘a mechanism to generate a regular pattern of parallel streamwise velocity streaks in the boundary layer’.

Oil flow visualisation was done on sea bass and common carp to prove the mechanism’s existence on real fish. The authors then hypothesised a possible mechanism for transition (or drag) delay, inspired by previous studies, where streaky structures generated by cylindrical roughness elements or vortex generator arrays have shown a delay of transition.

The team tested the hypothesis of drag delay with a smooth, flat plate and a flat plate covered with biomimetic fish scale arrays in a specially equipped laminar water tunnel at the University of Stuttgart.

According to a research announcement, the findings “run counter to the common belief that roughness promotes by-pass transition. Instead, the scales largely increase the stability of the base flow, similar to an array of vortex generators.”

Recreating such patterns on aerodynamic surfaces could pave the way towards a drastic reduction in fuel consumption and future zero-emission flight, the announcement said.

The findings were published in Nature: Scientific Reports, and the Journal of Experimental Biology.

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