Harvesting energy from vehicle air flow using piezoelectrics
Using the new technology automobiles and aircraft, like this Airbus A380, could harness currently wasted kinetic energy to power some systems (Photo: Axwel via Flickr)
Previously, we’ve looked at technology to generate electricity from roads embedded with piezoelectric crystals that produce electricity when squeezed. Now a group of researchers is looking to shift the technology from the road to the vehicles themselves and use piezoelectrics placed on the vehicles to convert their kinetic energy into electricity.
About a half-inch by one inch, these piezoelectric devices might be mounted on the roof or tail of a car or on an airplane fuselage where they would vibrate inside a flow, producing an output voltage. Although the power generated would not be enough to replace that supplied by the combustion engines, it could be enough to run some systems, such as batteries that would be used to charge control panels and other small electronic devices such as mobile phones.
The group of researchers from the City College of New York (CCNY) led by Prof Yiannis Andreopoulos, is currently attempting to optimize these devices by modeling the physical forces to which they are subjected in different air flows - on the roof of a car, for instance, or on the back of a truck.
When the device is placed in the wake of a cylinder - such as on the back of a truck - the flow of air will cause the devices to vibrate in resonance, says Andreopoulos. On the roof of a car, they will shake in a much more unsteady flow known as a turbulent boundary layer. Andreopoulos and his colleagues have conducted wind tunnel tests showing how the devices work in both situations.
"These devices open the possibility to continuously scavenge otherwise wasted energy from the environment," says Andreopoulos.
About the Author
Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.
All articles by Darren Quick
Actually that is a good idea and it exists:
Would it not be simpler to use a magnet inside a shock absorber with a coil on the outside to produce dampening and electricty at the same time?Potholes could charge your battery!!
Wouldn\'t an attached device caused to vibrate in the airstream (turbulent as it is), cause more drag than than any energy it would create? I think I saw a Youtube video with an idiot that put a dozen fans on his car thinking it would create more electricity in the windstream than the energy to move the car forward... this is similar.
Now, where you can extract energy is where one would normally be trying to slow a vehicle down anyway (deceleration ramps, drive up windows, speed bumps, toll booths, etc.). The idea to generate electricity with the shock absorbers is also a case where you want to dampen (or slow) the car\'s vertical motion... same principle and would work, but don\'t know to what amount of absolute power it would generate on regular roads...
Doc, in answer to your question, there are 2 things to consider:
1) the device they\'re talking about is streamlined, so it doesn\'t add much, if any, drag. It just uses the turbulent airflow to induce vibrations which generate the voltage.
2) In the turbulent flow range, which is Reynolds number flow over a certain amount (I forgot the actual Reynolds number for turbulent vs. laminar flow), the shape and size of an object in the airflow doesn\'t induce drag, like it would in a laminar flow. The concept of laminar and turbulent flow near the boundary layer is how designs are optimized for streamlining airflow over wings and flight surfaces of planes and over a car\'s surfaces.
Therefore, the small devices described here, or an array of such devices could generate power without significantly adding to drag.
I have had someone ask me if he could install a ducted fan on his car or a series of them installed on a trailer towed by his car, could be used to generate electricity which would provide some of the power required to move the car. The problem is that these fans generate drag when the air flows over their blades, which is what causes the blades to rotate, but it also causes the engine to have to work harder to move the vehicle. They\'re trying to create a sort of perpetual motion machine, but that won\'t work, because the drag added is more than the power produced, and this doesn\'t take into account the mechanical losses at each change of state of mechanisms; mostly from friction and transmission losses.
Transition occurs at Reynolds numbers between 2000 and 4000. Turbulence does not make an object\'s drag independent of its shape and usually results in increased drag. The exception to the rule is when some turbulent mixing helps delay flow detachment. The only way I can see this idea working is if these devices can actually harvest more of the turbulent energy that is being generated by the airflow around the vehicle than they generate in drag. In a perfect vehicle with completely laminar flow and no separations (NACA0012 at zero angle of attack, but there goes the lift...) these devices should be nothing but an added source of drag. Count me skeptical, but at least they admit that it can never achieve break even energy production.
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