new scientist: feather-like structures help reduce drag

[dave kumar]

Found this is in new scientist:

Coating the rigid wings of airplanes with artificial bristles that mimic feathers could make them more efficient, according to engineers. An Italian team has demonstrated how feather-like structures help reduce drag on a cylinder and says they could have the same effect on underwater and aerial vehicles.

http://www.newscientist.com/article/dn1 ... ights.html

...although they may not look like they can have much of an effect, during gliding some covert feathers stick up at right angles to the wing's surface and vibrate in the airflow. The researchers say that's because the fibres help to cushion the effects of the air flow on the cylinder itself. Normally the air flows rapidly across the cylinder and creates an area of low pressure behind it. This encourages the formation of strong vortices, creating turbulence and increasing the drag on the cylinder.

With the feathers, the low-pressure slipstream does not form, and the vortices affecting the cylinder are weaker. A similar process explains why fresh, fuzzy tennis balls can speed through the air faster than worn ones...

This sounds to me like a win-win situation if it were applied to F1. If the above effect could be applied to a racing car, would we see an improvement in aerodynamic efficiency and at the same time (or as a consequence?) a reduction in wake turbulence.

Could this help cars follow each other more closely through the corners by smoothing the airflow they encounter? Also in the article the object being tested was a cylinder. What effect would these rigid fibres have if placed on the trailing edge of a downforce producing wing? Can you reduce drag without reducing the downforce it generates?

[Callum]

I saw something about this on the "one show" they were talking about how barn owls can fly silently because of the feathers on the trailing edge of their wing.

[jddh1]

I saw something about this on the "one show" they were talking about how barn owls can fly silently because of the feathers on the trailing edge of their wing.

Yeah, I've also seen that show on Discovery or Nat Geo. I remember they were also talking about a team here in the States doing some testing in a wind tunnel using "fake" feathers on a wing that would also fold, kinda like eagle's wings do.
Interesting read though. At the bottom there, it says that the full article is in the Journal of Fluid Dynamics so I'll try to get the entire PDF so we can see some calculations, unless Senna-Toleman already has it.

[DaveKillens]

This appears to be an application of a form of vortex generator.
http://en.wikipedia.org/wiki/Vortex_generator

[noname]

http://www.zipp.com/technologies/aerodynamics/ablc.php#

however bikes travel at a lower speed but I think idea behind is still the same - increase the energy of the boundary layer.

[PNSD]

Energizing the boundary layer perhaps?

[roost89]

This sounds to me like a win-win situation if it were applied to F1. If the above effect could be applied to a racing car, would we see an improvement in aerodynamic efficiency and at the same time (or as a consequence?) a reduction in wake turbulence.

Could this help cars follow each other more closely through the corners by smoothing the airflow they encounter? Also in the article the object being tested was a cylinder. What effect would these rigid fibres have if placed on the trailing edge of a downforce producing wing? Can you reduce drag without reducing the downforce it generates?

It may be easier to follow in the corners but definetly not at speed, as it states here:

Normally the air flows rapidly across the cylinder and creates an area of low pressure behind it. This encourages the formation of strong vortices, creating turbulence and increasing the drag on the cylinder. Racing car drivers exploit that area of low pressure – the slipstream – to stay close to their rivals without having to combat the drag experienced by the car in front.
With the feathers, the low-pressure slipstream does not form, and the vortices affecting the cylinder are weaker

With no slip-stream it'd be alot harder for cars to follow each other, the gaps would become too large down the straight to effect an overtake.

Wouldn't this be classed as moveable aero? As they're vibrating? Also the size of the fibres would need to be changed across the bodywork because at different speeds the frequency of the vortices will change.

[dave kumar]

Sorry jddh1 I haven't seen the original paper that this article was based on and anyway fluid dynamics is way beyond me. It would be strange to see cars covered in these figid fibres but I would think you could classify them as flexing in response to aerodynamic forces as oppossed to moveable areo. This is a passive system and could be allowed without opening the door to active aero devices (which we have anyway!).

The energizing of the boundary layer explanation sounds plausible but is there a cost to increasing aerodynamic efficiency in this way? Does it reduce the amount of lift a wing generates for a given angle of attack?

[mikhak]

senna-toleman wrote:

Sorry jddh1 I haven't seen the original paper that this article was based on and anyway fluid dynamics is way beyond me. It would be strange to see cars covered in these figid fibres but I would think you could classify them as flexing in response to aerodynamic forces as oppossed to moveable areo. This is a passive system and could be allowed without opening the door to active aero devices (which we have anyway!).

This is exactly what flexi-wings were doing and why the teams had to put in support structures to ensure that they do not flex in response to aerodynamic forces and why toyota i think were penalised in qualifying in australia. as we have it now, active devices on the front wing are allowed, passive systems which react to aero forces are banned. theres alot of work for aircraft wings though in morphing wings and all fancy new ideas alot which are taken from research done on birds in flight. i think making it work on an f1 car if it were legal would be a daunting task....its alright on a simple shape such as a sphere travelling through the air, make the flow turbulent, the flow stays attached for longer and less drag. but for such a complex flow system that exists over an f1 car to get it right would be very hard.
Might be more work than its worth for an F1 car because there is constant change to the oncoming flow conditions, braking accelerating etc. and not much time spent just going flat out in a straight line. Aircraft however spend a majority of their time in cruise conditions (long distance anyway) so this technology can be optimised for aircraft with greater benefits.

[dave kumar]

Might be more work than its worth for an F1 car because there is constant change to the oncoming flow conditions, braking accelerating etc. and not much time spent just going flat out in a straight line. Aircraft however spend a majority of their time in cruise conditions (long distance anyway) so this technology can be optimised for aircraft with greater benefits.

Yes, fair point. In the article it is mentioned that during gliding some of these "covert" feathers stick up at right angles to the wing's surface. This implies that the bird doesn't use this in other modes of flight, so may be it is only effective during steady state conditions.

Slightly off topic, why are the FIA so concerned by flexi-wings. Was it banned on safety or performance grounds?

(oh and mikhak, what do you think Mika Hakkinen learnt not to do by watching Mansell?)

[mikhak]

I think it was a safety issue with the flexi wings, i remember kimi raikkonen at hockenheim having a rear wing failure at the first corner and into the tyre barrier and also montoya at the spanish gp also had rear wing failure. People believe this was the effect of flexible wings getting a little bit too flexible!! and so they were banned.

(oh and mikhak, what do you think Mika Hakkinen learnt not to do by watching Mansell?)

i have no idea honestly, i put that quote in when i set up this account nearly 3yrs ago and then didnt post anything for years and was quite perplexed myself as to why i would include that quote. i didnt even watch F1 back in 1995!