Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Foo Off-Topic chit chat with no general subject.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 10-02-07, 03:23 PM   #1
Psydotek
Body By Nintendo
Thread Starter
 
Psydotek's Avatar
 
Join Date: Sep 2006
Location: Videogames ruined my life. Good thing i have 2 extra lives.
Bikes: Giant TCR2, Giant TCX, IRO BFSSFG SE, Salsa Casseroll, IRO Rob Roy.
Posts: 3,187
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
If dimpled bike wheels are more aero (i.e. Zipps), why not...

Why not the body panels on cars?

Because it would look "ugly"?
__________________

Quote:
Originally Posted by jsharr View Post
A girl once asked me to give her twelve inches and make it hurt. I had to make love to her 3 times and then punch her in the nose.
Psydotek is offline   Reply With Quote
Old 10-02-07, 03:27 PM   #2
Serendipper 
(((Fully Awake)))
 
Serendipper's Avatar
 
Join Date: Oct 2005
Location: ~Serenading with sensous soliloquies whilst singing supple sentences that are simultaneously suppling my sonnets with serenity serendipitously.~ -Serendipper
Bikes: Guerciotti Pista-Giant Carbon-Bridgestone300- Batavus Type Champion Road Bike, Specialized Hardrock Commuter, On-One The Gimp (SS Rigid MTB/hit by a truck)- Raleigh Sports 3-speed,Gatsby Scorcher, comming soon...The Penny Farthing Highwheel!
Posts: 5,597
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Yes.



It would look like it just came out of a hailstorm. Besides, car aerodynamics are way different than a rotating mass. Different means to lower the cd I bet.
Serendipper is offline   Reply With Quote
Old 10-02-07, 03:33 PM   #3
lyeinyoureye
Senior Citizen
 
lyeinyoureye's Avatar
 
Join Date: Feb 2005
Location: no
Bikes: yes
Posts: 1,347
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Iono if the Zipps advantage is more about the dimples, or just having a faired wheel. Wheel fairings work the same for cars mas o menos.
lyeinyoureye is offline   Reply With Quote
Old 10-02-07, 03:33 PM   #4
x136 
phony collective progress
 
x136's Avatar
 
Join Date: Sep 2006
Location: San Hoosey
Bikes: http://velospace.org/user/36663
Posts: 2,981
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I think some race cars (or maybe luxury cars) have dimpled underbodies.

And yeah, it would look fugly as hell on the body of a car.

Can you imagine the "Is your car ribbed for her pleasure?" jokes?
__________________
x136 is offline   Reply With Quote
Old 10-02-07, 04:45 PM   #5
Luwin1026
.
 
Luwin1026's Avatar
 
Join Date: Aug 2006
Location: Los Angeles
Bikes:
Posts: 1,220
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
The reason we do not see dimples on other shapes, like wings, is that these particular forms of boundary layer trips only work well on a blunt body like a sphere or a cylinder. The most dominant form of drag on these kinds of shapes is caused by pressure, as we have seen throughout this discussion. More streamlined shapes like the airfoils used on wings are dominated by a different kind of drag called skin friction drag. These streamlined bodies, like that pictured above, have a teardrop shape that creates a much more gradual adverse pressure gradient. This less severe gradient promotes attached flow much further along the body that eliminates flow separation, or at least delays it until very near the trailing edge. The resulting wake is therefore very small and generates very little pressure drag.


Taken from the following website: http://www.aerospaceweb.org/question...cs/q0215.shtml
Luwin1026 is offline   Reply With Quote
Old 10-02-07, 04:55 PM   #6
DannoXYZ 
Senior Member
 
DannoXYZ's Avatar
 
Join Date: Jul 2005
Location: Saratoga, CA
Bikes:
Posts: 11,606
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Also, on a bicycle, the wheels are much more exposed than on a car. And they represent a much larger portion of total drag than on a car. And that more exposed and larger percentage of area flows at 2x your speed at the top of the wheel. Aero-drag reductions here would pay big dividends at TT speeds. The extra 0.1hp savings on a car won't make that big of a deal.
DannoXYZ is offline   Reply With Quote
Old 10-02-07, 05:02 PM   #7
p4nh4ndle
coffeeeeee
 
p4nh4ndle's Avatar
 
Join Date: Aug 2007
Location: somewhere in Pennsyl-tucky
Bikes: all that I ride
Posts: 238
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
um, what about open wheel cars. I don't remember seeing many F1 cars w/ dimpled surfaces.
p4nh4ndle is offline   Reply With Quote
Old 10-02-07, 06:03 PM   #8
DannoXYZ 
Senior Member
 
DannoXYZ's Avatar
 
Join Date: Jul 2005
Location: Saratoga, CA
Bikes:
Posts: 11,606
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
yeah, I suspect the savings aren't worth it. I suppose the turbulence from the open tyres is so high, any aero smoothing/dimpling of the wheels gives no benefits. Having the wheel-surfaces open for ducting hot air away from the brakes yields more benefits than any savings from aerodynamics. F1 cars aren't about aerodynamics anyway, they're set up for +4g of downforce @200mph for maximum cornering and braking. Indy/IRL cars tend to be more aero with wheel-covers and 2-2.5g of downforce.

Anyone see the 2003 GP at Montreal where these cars could finally be compared?
DannoXYZ is offline   Reply With Quote
Old 10-02-07, 06:16 PM   #9
p4nh4ndle
coffeeeeee
 
p4nh4ndle's Avatar
 
Join Date: Aug 2007
Location: somewhere in Pennsyl-tucky
Bikes: all that I ride
Posts: 238
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
hmm, no. Interesting premise. what was the result?
My money would still be on an F1 car&driver. you can always tune the downforce down to get more speed and it is the automotive equivalent of a euro-pro cycling team.
p4nh4ndle is offline   Reply With Quote
Old 10-02-07, 06:18 PM   #10
Psydotek
Body By Nintendo
Thread Starter
 
Psydotek's Avatar
 
Join Date: Sep 2006
Location: Videogames ruined my life. Good thing i have 2 extra lives.
Bikes: Giant TCR2, Giant TCX, IRO BFSSFG SE, Salsa Casseroll, IRO Rob Roy.
Posts: 3,187
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Hmmm, well my thinking would be how it would apply to "normal" cars on the road today in terms of MPG and effeciency. I do know that there's more than just aerodynamics to the overall performance for a car but the situation i'm envisioning is what the majority of a car's driving time is and that's your everyday commute at 50-75mph for 30-60 minutes a day (well, at least that's what my car gets despite being set up to handle alot more than that).

So i'm guessing if dimpling were to be used on cars it would be effective but probably not cost effective then?
__________________

Quote:
Originally Posted by jsharr View Post
A girl once asked me to give her twelve inches and make it hurt. I had to make love to her 3 times and then punch her in the nose.
Psydotek is offline   Reply With Quote
Old 10-02-07, 06:52 PM   #11
iamlucky13
Footballus vita est
 
iamlucky13's Avatar
 
Join Date: Jun 2002
Location: Portland, OR
Bikes: Trek 4500, Kona Dawg
Posts: 2,118
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Luwin1026 View Post
The reason we do not see dimples on other shapes, like wings, is that these particular forms of boundary layer trips only work well on a blunt body like a sphere or a cylinder. The most dominant form of drag on these kinds of shapes is caused by pressure, as we have seen throughout this discussion. More streamlined shapes like the airfoils used on wings are dominated by a different kind of drag called skin friction drag. These streamlined bodies, like that pictured above, have a teardrop shape that creates a much more gradual adverse pressure gradient. This less severe gradient promotes attached flow much further along the body that eliminates flow separation, or at least delays it until very near the trailing edge. The resulting wake is therefore very small and generates very little pressure drag.


Taken from the following website: http://www.aerospaceweb.org/question...cs/q0215.shtml
That's not quite right.

The dimples are intended to cause airflow over the body to become turbulent (tiny little eddies and swirls, as opposed to laminar). Turbulent airflow is actually worse for skin drag than laminar airflow, if I remember right, but as the above explains, much better for what is called form or pressure drag.

However, the dominant type of drag in automobiles is form drag (contrary to the quoted text), so you actually want turbulent airflow.

So why don't car manufacturers do something to get this? Because it actually occurs naturally beyond a certain threshold. The threshold is related to the Reynolds number, a engineering quantity that depends on the speed, the size of an object, and the viscosity of the fluid. Although the threshold is very complex, it typically is expected at a Reynolds number somewhere around 200000 for flat surfaces. On an object the size of a car, this could happen at around 30-40 mph, or even lower depending on the surface finish and various obstructions like windshield wipers and hood ornaments.

In short, the desired effect is is already achieved without dimples on cars.

Lexus was touting a dimpled read underbody (in nice shiny chrome) a couple years back, but I haven't heard anything about it since. I would guess they found no benefit other than marketing. I also read that BMW has started putting dimples around the roots of the side-view mirrors. In that location it might actually have some benefit because of the small size and relatively blunt shape of the mirrors.

Actually, hold on a second...this other thread:
Is aero tubing a gimmick?
includes a claim that Lexus included the dimples to reduce buffeting over isolated portions of the car. That actually sounds quite plausible.
__________________
"The internet is a place where absolutely nothing happens. You need to take advantage of that." ~ Strong Bad
iamlucky13 is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 04:45 AM.