Go Back   EcoModder Forum > EcoModding > Aerodynamics
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 05-29-2011, 05:10 PM   #11 (permalink)
(:
 
Frank Lee's Avatar
 
Join Date: Jan 2008
Location: up north
Posts: 12,761

Blue - '93 Ford Tempo
Last 3: 27.29 mpg (US)

F150 - '94 Ford F150 XLT 4x4
90 day: 18.5 mpg (US)

Sport Coupe - '92 Ford Tempo GL
Last 3: 69.62 mpg (US)

ShWing! - '82 honda gold wing Interstate
90 day: 33.65 mpg (US)

Moon Unit - '98 Mercury Sable LX Wagon
90 day: 21.24 mpg (US)
Thanks: 1,585
Thanked 3,548 Times in 2,215 Posts
The Chrysler PNGV car had a step for the backlight and it still had very low Cd.

__________________


  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 05-29-2011, 10:53 PM   #12 (permalink)
Master EcoModder
 
Big Dave's Avatar
 
Join Date: Jan 2008
Location: Steppes of Central Indiana
Posts: 1,319

The Red Baron - '00 Ford F-350 XLT
90 day: 27.99 mpg (US)

Impala Phase Zero - '96 Chevrolet Impala SS
90 day: 21.03 mpg (US)
Thanks: 0
Thanked 186 Times in 127 Posts
I've been thinking about this to smooth out the air flow over my pickup tonneau yet retaining visibility out the rear window.
__________________
2000 Ford F-350 SC 4x2 6 Speed Manual
4" Slam
3.08:1 gears and Gear Vendor Overdrive
Rubber Conveyor Belt Air Dam
  Reply With Quote
Old 05-29-2011, 11:21 PM   #13 (permalink)
Master EcoModder
 
JasonG's Avatar
 
Join Date: May 2009
Location: Charlotte NC / York SC
Posts: 727

05 DMax - '05 Chevrolet 2500HD
90 day: 18.48 mpg (US)
Thanks: 108
Thanked 55 Times in 51 Posts
I seem to recall the navy was experimenting with stepped hull design for high speed craft.
They got the idea from some shark or snake, memory not working.......scales/sawtooth shape.
It worked but was impractical to build and keep clean.
Seems it had a side effect of pulling air in from the sides due to the low pressure in the channels. That reduced drag which was the design intent.
__________________



I can't understand why my MPG's are so low..........
21,000lb, 41' Toy Haulers are rough on FE!
  Reply With Quote
Old 05-30-2011, 01:30 AM   #14 (permalink)
(:
 
Frank Lee's Avatar
 
Join Date: Jan 2008
Location: up north
Posts: 12,761

Blue - '93 Ford Tempo
Last 3: 27.29 mpg (US)

F150 - '94 Ford F150 XLT 4x4
90 day: 18.5 mpg (US)

Sport Coupe - '92 Ford Tempo GL
Last 3: 69.62 mpg (US)

ShWing! - '82 honda gold wing Interstate
90 day: 33.65 mpg (US)

Moon Unit - '98 Mercury Sable LX Wagon
90 day: 21.24 mpg (US)
Thanks: 1,585
Thanked 3,548 Times in 2,215 Posts
Quote:
Originally Posted by Big Dave View Post
I've been thinking about this to smooth out the air flow over my pickup tonneau yet retaining visibility out the rear window.
Exactly! If/when I ever dig out the aerocap I started building years ago to finish, I planned on doing the rear window like the Chrysler.
__________________


  Reply With Quote
Old 05-30-2011, 06:49 AM   #15 (permalink)
Master EcoModder
 
euromodder's Avatar
 
Join Date: Jul 2010
Location: Belgium
Posts: 4,683

The SCUD - '15 Fiat Scudo L2
Thanks: 178
Thanked 649 Times in 514 Posts
Quote:
Originally Posted by JasonG View Post
I seem to recall the navy was experimenting with stepped hull design for high speed craft.
Stepped hull designs are nothing new.
It's been used on seaplanes and speedboats for about 100 years.

Quote:
They got the idea from some shark or snake, memory not working.......scales/sawtooth shape.
Probably reinventing the theory and scaling the steps down while adding many more of them ?
It's been done with overlapping plates, on boats and aircraft alike.


If you do the same with a stepped rear deck, you end up approaching the aerodynamic template
__________________
Strayed to the Dark Diesel Side

  Reply With Quote
Old 06-03-2011, 04:39 PM   #16 (permalink)
EcoModding Lurker
 
Join Date: Aug 2010
Location: Netherlands
Posts: 43
Thanks: 0
Thanked 9 Times in 7 Posts
As promised I tested the theory today, mainly becouse I had hopes that the vortexes would reattach the flow even at a greater angle.

I have acces to a flowbank, mainly used for engine tuning (flowing channels).
So today I made a setup through which I could visiualize the flow attachmend with different angles and with smooth and stepped surfaces.

I made a basic druplet shape buth with squared top and sides.
For the modelling of the exact shape I used a kind of clay.

@cfg83 CFD simulations were pretty acurate, but his models were shown at a relative low angel of attack. (which I could make out from the vids)


Brief Summary:
Test with a smooth "druplet kind of shape" shows deattached flow at angles above +/-17degrees.

Test with relative big steps.
Showed attachemend also till 17 degrees, you could clearly see that the flow was turbulant right after the step and reattached half way a step.
See the picture below to give you an idea how the flow unfolded. Red=turbulant
Yellow=laminair


Test with smaller steps.
The flow was often turbulant but reattached with the shallow angle of about 11 degrees.
See picture


Conclusion
Stepped shapes have the same flow-attachment angle as a smooth surface, but the flow must have a chance to reattach to a surface.
  Reply With Quote
Old 06-03-2011, 04:49 PM   #17 (permalink)
EcoModding Lurker
 
Join Date: Aug 2010
Location: Netherlands
Posts: 43
Thanks: 0
Thanked 9 Times in 7 Posts
Quote:
Originally Posted by California98Civic View Post
That flow indicator is kinda cool. BTW, the last set of steps seem the best.
My (real world) test showed that the 2 second vid shown by @cfg83
is the best for flow attachemend with stepped slopes
  Reply With Quote
Old 06-03-2011, 05:23 PM   #18 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 13,041
Thanks: 20,895
Thanked 6,373 Times in 3,958 Posts
flutter

Quote:
Originally Posted by beer View Post
My (real world) test showed that the 2 second vid shown by @cfg83
is the best for flow attachemend with stepped slopes
beer,you'll want to keep an eye out for flutter.The steps will have a natural frequency and harmonics of that frequency in which they'll vibrate like a tuning fork.If not sufficiently stiff enough for dampening they can shake themselves apart in the vortex.
  Reply With Quote
Old 06-03-2011, 06:01 PM   #19 (permalink)
Pokémoderator
 
cfg83's Avatar
 
Join Date: Dec 2007
Location: Southern California
Posts: 5,864

1999 Saturn SW2 - '99 Saturn SW2 Wagon
Team Saturn
90 day: 40.49 mpg (US)
Thanks: 439
Thanked 529 Times in 356 Posts
aerohead -

Quote:
Originally Posted by aerohead View Post
beer,you'll want to keep an eye out for flutter.The steps will have a natural frequency and harmonics of that frequency in which they'll vibrate like a tuning fork.If not sufficiently stiff enough for dampening they can shake themselves apart in the vortex.
So at air speed X it could shake apart. Does that also mean that at air speed Y it could perform at it's best? Is there an optimum step shape for every MPH?

CarloSW2
__________________

What's your EPA MPG? Go Here and find out!
American Solar Energy Society
  Reply With Quote
Old 06-03-2011, 06:02 PM   #20 (permalink)
Aero Deshi
 
ChazInMT's Avatar
 
Join Date: Jan 2010
Location: Vero Beach, FL
Posts: 1,065

MagMetalCivic - '04 Honda Civic Sedan EX
Last 3: 34.25 mpg (US)
Thanks: 430
Thanked 668 Times in 357 Posts
I still think this is one of the coolest pictures ever taken. I marvel at the complexity of the design. It is a sharks skin close up using a scanning electron microscope. I think these look like little alien spacecraft all lined up.


  Reply With Quote
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com