Calendar
Coaches
Fitters
Retailers
Triathlon Clubs
Stack & Reach
Custom Geometry Calculator
Training Log
MAIN
INDEX
RULES &
LEGEND
LOG
IN
Search
this forum
this category
all forums
for
All words
Any words
Whole Phrase
(
options
)
Newsletter Signup
Slowtwitch Forums
:
Triathlon Forum
:
Mythbusters to test aerodynamics of dimples
1
2
3
View All
Tri Forum
Classifieds
Lavender Room
Jobs
The Womens
Print Thread
Sully
Oct 21, 09 13:57
Post #1 of 65 (3295 views)
Mythbusters to test aerodynamics of dimples
Can't Post
Tonight on Discovery Channel, Mythbusters looks at aerodynamics.
2, n=1, tests they show in the previews is whether or not a dirty car is more fuel efficient than a clean car and WHAT HAPPENS WHEN YOU DIMPLE A CAR!
TomNYC
Oct 21, 09 14:03
Post #2 of 65 (3263 views)
Re: Mythbusters to test aerodynamics of dimples [Sully]
[
In reply to
]
Can't Post
that's ridiculous ... my personal experience has taught me that my car accelerates faster, corners more crisply and is more fuel efficient when washed/waxed/detailed. I'm also pretty sure that a layer of Turtle Wax Ice interior polish makes me better looking and raises my V02 Max by 17%.
and red IS the fastest color.
formerly TomAnnapolis
oktriguy
Oct 21, 09 14:12
Post #3 of 65 (3220 views)
Re: Mythbusters to test aerodynamics of dimples [Sully]
[
In reply to
]
Can't Post
http://www.racecar-engineering.com/...ynamic-surfaces.html
Torps
Oct 21, 09 19:16
Post #4 of 65 (2973 views)
Re: Mythbusters to test aerodynamics of dimples [Sully]
[
In reply to
]
Can't Post
11% increase. pretty significant advantage with the dimpled car.
Raptor
Oct 21, 09 20:49
Post #5 of 65 (2810 views)
Re: Mythbusters to test aerodynamics of dimples [Sully]
[
In reply to
]
Can't Post
Who needs dimples? I went to the unveiling of the new Porsche Panamera over the weekend at the Universal Studios Backlot. The car has a spoiler that changes shape at three different speeds, 50 mph it comes out, 80 it gets bigger, and at 127mph, it changes its angle. Dimples cannot do that.
ndenezzo
Oct 21, 09 21:42
Post #6 of 65 (2745 views)
Re: Mythbusters to test aerodynamics of dimples [Sully]
[
In reply to
]
Can't Post
Interesting to note that the 850 lbs of clay did not affect fuel efficiency when the car was already up to speed. I guess weight really doesn't matter.
P2SLowry
Oct 22, 09 1:59
Post #7 of 65 (2614 views)
Re: Mythbusters to test aerodynamics of dimples [ndenezzo]
[
In reply to
]
Can't Post
Quote:
Interesting to note that the 850 lbs of clay did not affect fuel efficiency when the car was already up to speed. I guess weight really doesn't matter.
As noted on the show, the extra weight would affect fuel economy during acceleration so I imagine that overall mpg is either unchanged or worse. It would depend on the ratio of city and highway driving.
One thing they didn't mention/consider is the ground effects the 800+ lbs. of clay may have produced. If the car was lowered by the weight then there would could possibly be less air traveling beneath the car to create drag, resulting in better fuel economy. Just a hunch of mine that their results are a little skewed.
-------------------------------------------------------------------------------
"Go that way, really fast. If something gets in your way, turn." - Charles De Mar
(This post was
edited
by P2SLowry on Oct 22, 09 2:05)
jart0806
Oct 22, 09 2:15
Post #8 of 65 (2602 views)
Re: Mythbusters to test aerodynamics of dimples [P2SLowry]
[
In reply to
]
Can't Post
Both tests had the same amount of clay on (or in) the car. So even if the clay lowered it enough to better the aerodynamics, it was the same across the two tests and doesn't matter.
P2SLowry
Oct 22, 09 2:19
Post #9 of 65 (2599 views)
Re: Mythbusters to test aerodynamics of dimples [jart0806]
[
In reply to
]
Can't Post
Quote:
Both tests had the same amount of clay on (or in) the car. So even if the clay lowered it enough to better the aerodynamics, it was the same across the two tests and doesn't matter.
Ah! I missed that part as I was half watching, half on the PC.
Thanks for the clarification.
-------------------------------------------------------------------------------
"Go that way, really fast. If something gets in your way, turn." - Charles De Mar
gibson00
Oct 22, 09 5:00
Post #10 of 65 (2456 views)
Re: Mythbusters to test aerodynamics of dimples [Torps]
[
In reply to
]
Can't Post
Didn't see the show...
What speed were they testing at? And I wonder what the advantage would be if they slowed to 40km/h.
ttocsmi
Oct 22, 09 5:04
Post #11 of 65 (2449 views)
Re: Mythbusters to test aerodynamics of dimples [Sully]
[
In reply to
]
Can't Post
by far, the coolest part of the test was when they put the plastic model in the water channel with the fluorescent dye.
i'm not allowed to nitpick the show any more, so that's all i have to say. :)
-
Yeah, I saw your grunge band, staring at your shoes on stage, wearing that dirty flannel shirt, when you gonna learn dirtball, you just can't f**k with Twisted Sister.
jackmott
Oct 22, 09 5:26
Post #12 of 65 (2403 views)
Re: Mythbusters to test aerodynamics of dimples [ttocsmi]
[
In reply to
]
Can't Post
In Reply To:
by far, the coolest part of the test was when they put the plastic model in the water channel with the fluorescent dye.
i'm not allowed to nitpick the show any more, so that's all i have to say. :)
lol
----
Sunglasses:
http://www.framesdirect.com/sunglasses
Tri Gear:
http://www.atctrishop.com
rear wheel
disc ALWAYS
http://www.wheelbuilder.com
if poor
front wheel
whatever torodial rim wheel you want, or H3. deeper if yer faster shallower if yer slower
tires
-
http://www.biketechreview.com
has crr data, use it
frames
- position trumps aero trumps weight trumps paintjob trumps stiffness
water bottle
between your arms or not at all if its a sprint
swim
get some swim lessons, its cheaper than buying bike speed
train more and HTFU
Abu
Oct 22, 09 6:12
Post #13 of 65 (2332 views)
Re: Mythbusters to test aerodynamics of dimples [ttocsmi]
[
In reply to
]
Can't Post
In Reply To:
by far, the coolest part of the test was when they put the plastic model in the water channel with the fluorescent dye.
That was cool. I must say, I was a bit surprised at the outcome. I thought that there might be a tiny increase, but not 11%. But you just have to wonder what the "catch" is. I mean, car manufactures take these things to wind tunnels don't they? Surely this has been thought of before? Maybe it's an aesthetic thing. But, since that eye-sore called a Prius has been so successful perhaps they will add dimples, knowing that greenies will buy ugly.
Sully
Oct 22, 09 6:20
Post #14 of 65 (2303 views)
Re: Mythbusters to test aerodynamics of dimples [Abu]
[
In reply to
]
Can't Post
I also wonder what material they would need to use?
First, you need to make dimples that are structurally sounds. Second, you need a material that can tolerate rain, gunk, and crap sitting in the bowl for extended period of time without corroding.
bryan913
Oct 22, 09 6:21
Post #15 of 65 (2300 views)
Re: Mythbusters to test aerodynamics of dimples [Torps]
[
In reply to
]
Can't Post
Wow, when are they going to dimple actual bikes?
I should patent that before Cervelo does. Damn
In Reply To:
11% increase. pretty significant advantage with the dimpled car.
------
Bryan
Eagleman 70.3 - Ironman Canada
angryirish
Oct 22, 09 7:36
Post #16 of 65 (2155 views)
Re: Mythbusters to test aerodynamics of dimples [Sully]
[
In reply to
]
Can't Post
Actually, dimpling sheetmetal would be pretty simple in the stamping process, and is often stronger structurally than flat sheet metal.
What speed were we talking again? I always thought that dimples had a better affect on the laminar flow at higher speeds (spinning golf balls). 11% seems a bit high.
I will say that I've personally seen a 4-5 knot increase in top speed (around 200knot range) of aircraft when cleaned and waxed versus a leading edge covered with bugs, and top surfaces covered in soot/dirt/dust.
burnman
Oct 22, 09 8:05
Post #17 of 65 (2055 views)
Re: Mythbusters to test aerodynamics of dimples [angryirish]
[
In reply to
]
Can't Post
Dimpling introduces turbulence, thus delaying the onset and magnitude of flow separation on bluff bodies (e.g. a spherical golf ball). For bodies that are already streamlined, such as an airfoil, the advantages to dimpling become trivial.
-------------------------------------------------------------------------
"He lives on Sesame Street, dumbass."
Sasquatch
Oct 22, 09 8:05
Post #18 of 65 (2055 views)
Re: Mythbusters to test aerodynamics of dimples [angryirish]
[
In reply to
]
Can't Post
As of now my car is no longer hail damaged, it is dimpled for improved aerodynamics.
brikins13
Oct 22, 09 8:06
Post #19 of 65 (2049 views)
Re: Mythbusters to test aerodynamics of dimples [Sully]
[
In reply to
]
Can't Post
I'm thinking I saw a Lexus ad maybe 5 years ago- it had a dimpled plate on the bottom of the car- supposedly to smooth air flow- and make the ride quieter. They took the car, flipped it upside down, and showed how smoothly the air flowed by showing a jet of smoke or something along those lines...
Makes sense- as far as laminar flow goes... Why wouldnt they continue that thought process? it was probably a 400lb plate of sheet metal they screwed into the bottom of the vehicle- probably reduced fuel efficiency greatly in city driving... maybe that idea busted- anyone know?
Just found this
and this
_____________________________________
Six five, two hundred plus...
61 P2C
62 AllezComp
(This post was
edited
by brikins13 on Oct 22, 09 8:09)
clyde_s_dale
Oct 22, 09 8:17
Post #20 of 65 (2011 views)
Re: Mythbusters to test aerodynamics of dimples [Sully]
[
In reply to
]
Can't Post
One thin to keep in mind is that air drag is very scale and speed sensitive. The key variable is the Reynolds num, which is a func of vehicle size and speed- and results from different Reynolds mums can absolutely not be applied to others. This is why scale
models don't work very well in wind tunnels, or have to be rested at odd speeds to create similiar Reynolds mums. So if this is true, it's very hard to extrapolate
let's talk about dimple theory here- q
want to address a few misconceptions:
a) golf bAlls are dimpled Bc they don't know ahead of time which side is the front. Objects that have a distinct front ( cars, bikes, helmets, water bottles) should have sideways ridges not dimples.
B) the point of dimples is to seperate laminar flow from sticking to the back of smooth objects and slowing them down. This happens to be important if two conditions are met: 1) the flow must Already be undisturbed by other bumpy things (this is why dimpled waterbottles are dumb- air already disturbed by time it gets to bottle) 2) the speed/ size rsship must be in a narrow range. It happens that golf balls And baseballs fit both criteria- but very few othe things do- cars are wrong speed and bumpy enough in front ( grille anyone), bike wheels are wrong speed, as are bike helmets.
So in summary: bumps rarely work, they should be ridges not bumps, scale testing doesn't work well, and golfballs are an exception not the rule.
Clyde
~~~~~~~~~~~~~~~
-Cartels: Serotta, Zipp 2001, Guru, eh?
-"It was kinda long and then i got really tired"
burnman
Oct 22, 09 8:23
Post #21 of 65 (1980 views)
Re: Mythbusters to test aerodynamics of dimples [brikins13]
[
In reply to
]
Can't Post
I work in the fuel/energy industry, and I'm continually amazed by the trends of corporate R&D, and appropriated gov't funds. Auto manufacturers spend billions of dollars developing alternative fuel systems and balance of plant equipment, all in an effort to gain some marginal improvement in fuel economy. If they just payed Joe Schmo from Detroit $30 an hour to stand on the assembly line with a hammer and beat the hell out of their sheet metal forms, they could nearly reach their goal. Annual cost to employer would be under $100k.
On the other hand, the Joe Schmos of the world could very well put me out of business ...
-------------------------------------------------------------------------
"He lives on Sesame Street, dumbass."
stephen J
Oct 22, 09 8:29
Post #22 of 65 (1962 views)
Re: Mythbusters to test aerodynamics of dimples [burnman]
[
In reply to
]
Can't Post
In Reply To:
Dimpling introduces turbulence, thus delaying the onset and magnitude of flow separation on bluff bodies (e.g. a spherical golf ball). For bodies that are already streamlined, such as an airfoil, the advantages to dimpling become trivial.
I don’t thing that is entirely accurate. The effect is not trivial; but a dimple is not the best way to arrive at that 'trip' introducing turbulence. Dimples are useful if
you do not know the orientation
of the object as it travels through the air; or if it is a changing orientation of the object. If you have a object that has the same orientation in relation to travel direction, then you are better off with trip lines; which I have most often seen a chevrons. These are available as 'stickers' that you can put on your glider, Cessna, small aircraft, etc. Going from my foggy memory, you put them just before the maximum diameter of your airfoil for maximum effect. There are even YouTube videos online which show how to test the placement of the strips to get the maximum effect using oil (there must be some flyers on this list who know more about this than me). Anyway, with this given, dimples would be good for golf balls, bicycle wheels, but not really frames, helmets, or bodies. Maybe cranks; but that I think gets more into the realm of marketing.
Stephen J
____________________________________________
Genius is recognizing when you are damn lucky
MITaerobike
Oct 22, 09 8:32
Post #23 of 65 (1947 views)
Re: Mythbusters to test aerodynamics of dimples [clyde_s_dale]
[
In reply to
]
Can't Post
Generally agreed -- Reynolds number comparison is key! A 50 ft wide plane going 200 mph, a Prius going 55 mph, and a triathlete on an aero bike going 20 mph see entirely different Reynolds Numbers.
There is a place for ridges and dimples in the bike world but generally not as they've been used in the past 10 years.
Mark
--
Mark Cote
MITAerobike (ST, Twitter)
Specialized Bicycle Components
Road Engineer/Aerodynamicist
zebragonzo
Oct 22, 09 9:15
Post #24 of 65 (1843 views)
Re: Mythbusters to test aerodynamics of dimples [MITaerobike]
[
In reply to
]
Can't Post
Something else that's not been mentioned thus far; because dimples transform flow from laminar to turbulent, a greater amount of airflow is affected by the direction of movement of the surface (a turbulent flow is 'deeper' than laminar).
Let me explain in terms of a wheel. On the front of a wheel, the rim moves downwards relative to the bike. In doing so, it re-directs a small amount of airflow downwards. If you make the rim dimpled, it re-directs more air downwards.
I'm not sure how this is advantageous though!
slimfast
Oct 22, 09 9:34
Post #25 of 65 (1799 views)
Re: Mythbusters to test aerodynamics of dimples [clyde_s_dale]
[
In reply to
]
Can't Post
On a side note, in a previous life I was a competitive whitewater kayaker. As I was getting out of the sport several companies were experimenting with dimpled and ridged hulls on both slalom race boats (ridges/rails became very popular but I don't think this dimples ever gained much traction) as well as freestyle boats. ON freestyle boats you could plane the hull on a green wave very easily and could really feel the dimples disturb the water. I think the principal was that it broke the surface tension (or suck) against the hull and loosened the hull on the wave so that the boat could be spun very easily while surfing. The feeling was really different and you could either carve the boat on edge or spin it flat. On the right wave (green wave, not a hydraulic), you could actually surf a boat sideways down the face of a wave, because there was so little surface drag. Really cool feeling and was quite revolutionary in terms of the freestyle tricks that were opened up based on this technology.
Not sure what it adds here, but just another manner in which this concept has been applied.
1
2
3
View All
Print Thread
Your tri bike position
Your biggest need is more:
Comfort
Power
Aerodynamics
It's perfect
MAIN
RULES &
LOG
