Half a croissant, on a plate, with a sign in front of it saying '50c'
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spikey high speed objects creates turbulence reducing drag

perhaps a 'spikey' or deliberately un-smooth object creates turbulance which shields it from direct wind-flow and therefor reduces drag?
  (+4, -1)
(+4, -1)
  [vote for,

As air drags alongside a missile (for example) it directly slows it down. However, if the missle has weird spikey pockets which trap air, or move it out - it may create a 'puffer jacket' of turbulent air around it - reducing its drag. Question mark.

Perhaps other counter-intuative shaping (Such as a concave - ie bowl shape) nose-cone. Might be advantageous.

@maxwell, yay! my first portion of croissant!

@bad-jim, no the other concave. so the bowl on the jet ... would hold milk in it ... if the jet ... were standing upright. like i said, counter intuative...

@david_scothern - thanks for info, no i have no idea what i'm talking about.

@freefall - well, this is the half-bakery...

nicholaswhitworth, Apr 02 2010

Like this? http://en.wikipedia...resistant_aerospike
[ShawnBob, Apr 12 2010]

see page 9 http://facta.junis....02/macar2002-06.pdf
[ShawnBob, Apr 12 2010]


       The air will still need to get out of the way. There "cone" of stable air that you imagine sitting at the front of the airfoil still needs to push the other air out of they way, by so doing pushes on the surface of the airfoil (pressure differential) and thus slows the airfoil. It matters very little if the shape of the airfoil is formed exclusively with conventional solid surfaces or by means of laminar/turbulent effects, neither is inherently more or less efficient.
WcW, Apr 02 2010

       You mean a bit like the spike on the front of supersonic jet fighters?
Bad Jim, Apr 02 2010

       nicholaswhitworth, welcome to the HalfBakery (I speak on behalf of..... and also with a slight slur).   

       As regards the idea, yes. As I understand it, the rough texture of sharkskin, and the dimples on golf-balls, are all related to this idea. So, even though this is sort of baked, you get a [+] from me for an eminently good idea.
MaxwellBuchanan, Apr 02 2010

       On Mythbusters they proved that a car with golf-ball style dimples gets better gas mileage. That works on the same principle.
DIYMatt, Apr 03 2010

       The idea is not to induce turbulence, but to thicken the layer of still air between the surface and the moving air. This allows the latter to slip more readily over the still air, producing a smoother travel.
MechE, Apr 03 2010

       look up "supercavitating". It's concept is mostly referred to with water/submarines but at extreme speed could apply to atmosphere as well.
AutoMcDonough, Apr 05 2010

       It pretty much makes no odds what you do with the nose-cone section, as long as it's convex and smooth. In other words, what [WcW] said. The rear end is much more critical, because you're looking to get the flow you've disturbed back together again without generating monster vortices. Granted, for a rocket, the rear end aerodynamics are utterly dominated by the rocket's gas plume and you don't have such a problem.   

       I'd suggest that aerodynamics are pretty well understood though - do you have any reason, other than intuition, to believe that trying something very unusual like this will bring benefits?
david_scothern, Apr 05 2010

       The effect of the dimples is to increase the energy in the boundary layer. When the boundary layer is energetic, it is less likely to separate from a surface which curves away from the flowstream. In the case of a car, the effect is to allow the air to close back in around the back end of the car, thereby producing a smaller wake.   

       While this does reduce the drag on a car, it also (depending on the car) increases the lift, making the car less stable at speed.   

       If the flow is already smooth, with a gradual pressure gradient (such as around a wing in cruise flight), this is not beneficial. However, in other configurations, such as high angle-of-attack operation during landing, a high-energy boundary layer is very beneficial. The benefit is not in reducing drag, but in keeping the flow attached and delaying stall.   

       This idea is an example of "Concept X does this in situation A, maybe it will work in situation B." That is a great start and an important step, but in this case, this particular field of aerodynamics is fairly well understood, and the concept is already being utilized where it shows a net benefit.
Freefall, Apr 05 2010

       Interesting article I read somewhere not about fluid dynamics but actually civil engineering: some researchers discovered that they could facilitate evacuation from a building by sticking a big pole a few feet in front of the exit. It created "turbulence" in the "flow" of people preventing big mobs from forming and blocking the doorway allowing more people to leave faster. Sadly I can't seem to find it anywhere. Either way, [+] for all the funny missile shapes this inspired in my head.
Postscript, Apr 05 2010

       [Postscript], yes, I recall that too. It might have been reported in the UK in either "The Engineer" or "Eureka", both of which are advert-supported free magazines from the same publisher. Alternatively, it might not. You're not making it up, either way.
david_scothern, Apr 06 2010

       Thirded. I read that too.   

       By the way, welcome aboard [nicholas]. Yes it's true as others have stated that this effect is known and being studied and used; the fact that you arrived at the same point by intuition - //spikey pockets/puffer jacket// earns you a crusty bread treat from me [+]   

       Bye for now, I'm off to load ravers into my trebuchet and seeing how far they fly with and without spikey rubber backpacks and puffer jackets.
BunsenHoneydew, Apr 06 2010

       Nic, you comments would make more sense in the thread of the comments overall.
bungston, Apr 12 2010

       It's called an aerospike [links]
ShawnBob, Apr 12 2010

       blobs on whales supposedly make them more efficient, so there are a variety of fluid dynamic realms where this works
beanangel, Feb 10 2012

       //blobs on whales supposedly make them more efficient// I find that hard to believe. Whales have had several tens of millions of years with nothing much to do apart from eat krill. If blobby skin were such a great thing, they'd have evolved it by now. Instead, they seem to rely on barnacles to create blobs, which seems a less than ideal solution.
MaxwellBuchanan, Feb 11 2012


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