Biomimicry to improve automobile aerodynamics:
the art of reducing friction
The correlation is inevitable: to reduce a vehicle's emissions, you must find a way to reduce its consumption.
The work on shapes and coatings makes it possible to optimise the aerodynamics of the vehicle and the air profile. A 10% reduction in the drag coefficient thus allows a reduction in consumption of around 2% in the new European driving cycle, and up to almost 5% at 130 km/h on the motorway.
Another major issue linked to this theme concerns the handling of the vehicle and the energy efficiency of the tires. The best performing tires have the lowest rolling resistance possible. This depends, among other things, on aerodynamic resistance, mass, structure and shape of the tread, micro-slip and pressure level. By minimising this resistance, the energy required to move the vehicle is minimised.
How can we rethink the design and components of vehicles to improve their air penetration? Nature has unrivaled know-how in this area:
To hunt or defend themselves, to be mobile over short distances or long distances, to be fast or enduring, animals must have extremely optimised movement techniques, whatever their environment.
To guarantee survival, it is also necessary to be able to minimise the effect. Each movement is therefore as simple as possible, intelligently thought out, stable and functional. In a universe where only the fastest or the most enduring can capture their prey, escape from their predators, or survive, the issue of aerodynamics, hydrodynamics and reduction of friction is central.
Nature works on form, on materials, on surfaces. The schemes are as varied as the species. These natural properties, these strategies, form a source of very effective solutions and approaches to reduce the air resistance of a vehicle.
Biomimicry has been carefully studied for several years now by aeronautical manufacturers, for whom each small reduction in friction can bring considerable fuel savings.
Beyond the design of structures and materials for lightweight purposes, biomimicry can also unlock its full potential in the automobile in terms of aerodynamics.
Thanks to a detailed understanding of the functions and techniques present in species, we can extrapolate these biological "best practices" to guide the design of vehicles, their shapes and component surfaces to optimise their aerodynamics and thus reduce consumption.
Here too, Bioxegy offers you an overview of the bio-inspired applications already existing in this area and also discusses a certain number of avenues of interest!
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Shark skin: a morphology optimised for rapid movement
To study the optimisation of movement in nature, it is particularly relevant to focus on animals occupying the top of the food chain. What's better than watching sharks swim?
Sharks are experts in controlling flow and can reach nearly a hundred km/h in water for certain species.
Sharks manage to control the flow thanks to their morphology, more precisely thanks to their rough skin. This is made up of micro-grooves which create turbulence and which attract the water into hollows where the flow is then slowed down. Thanks to this, friction is reduced and drag is reduced. The flow disturbed on a small scale is modified on a large scale to make it favorable for the movement of the shark.
Inspired by this mechanism called the Riblet effect, German researchers (DLR and Fraunhofer Institut) have managed to design a coating reproducing these micro-grooves to reduce aircraft drag. These varnishes are fitted to prototype aircraft of the German company Lufthansa.
Completely transposable to automobiles, this principle was adopted in 2014 by Peugeot. Presented at the Paris Motor Show, the Peugeot Exalt concept car was covered at the rear by the same type of covering inspired by shark skin. This made it possible to reduce the resistance to advancement and considerably improve the drag coefficient.
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Crédits images : ©Fraunhofer Institute ©Ken Fielding
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The wings of large birds of prey: understanding natural behaviour to reduce consumption.
Do you fly often? If so, looking out the porthole, you have surely already noticed these little growths at the tips of the wings? Called winglets, these vertical fins have become widespread throughout the aeronautical sector. They may seem insignificant, yet they play a major role in the aerodynamics of aircraft. We must once again thank a pioneer of biomimicry.
In the early 1970s, NASA engineer Richard Whitcomb became interested in the behaviour of large raptors. They adapt the shape of their wings to form curvatures on their tips. These help reduce turbulence and vortices that form in the wake of the wing.
Following this principle, he tested the first winglets on a US Army Boeing. These fins help reduce the vortices that appear at the end of an airplane wing. This turbulence is responsible for induced drag, one of the major components of the total drag of an aircraft.
The winglets that equip commercial and military aircraft today therefore make it possible to improve the aerodynamics of the device and reduce consumption by around 3 to 4%. A considerable economic and environmental gain given the scales considered.
Biomimicry applied to aerodynamics could bring the same type of improvements to the automotive sector, to better think about the penetration profile of vehicles and understand how to control air flows.
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Crédits images : ©Paul Bonfils
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The kingfisher's beak: reduce air resistance and improve energy efficiency of movement.
In the early 1990s, engineer Eiji Nakatsu was responsible for developping new trains for the Shinkansen, the Japanese TGV. It is faced with a major problem: the density of tunnels on the new lines is high. However, launched at full speed in these tunnels, the trains compress the air that is present, which transforms into a shock wave at the exit. A nuisance for passengers and even some local residents. How do we remove these sound booms?
E.Nakatsu also happens to be an ornithologist. He knows that the kingfisher is a specialist in moving from a sparse environment to a dense environment. This bird dives head first at more than 50 km/h in lakes and ponds to hunt small fish. To avoid concussion and to avoid alerting its prey, entry into the water must be as gentle as possible.
E.Nakatsu therefore asks his teams to reproduce the morphology of the kingfisher's beak and apply it to the head of the Shinkansen 500 locomotive in development. Measuring more than 10m long at the front, this new train will no longer experience shock wave problems.
The bio-inspired design of the locomotive will allow a speed gain of 10 km/h and above all will reduce electricity consumption by around 15%! E.Nakatsu even went so far as to ask his engineers to take inspiration from the serrated feathers of the owl, this very silent predator, to equip the pantographs with sound attenuation systems.
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