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

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 08-31-2017, 05:16 AM   #671 (permalink)
s_t
EcoModding Lurker
 
Join Date: Aug 2017
Location: Brisbane, Australia
Posts: 26
Thanks: 1
Thanked 7 Times in 7 Posts
Quote:
Originally Posted by freebeard View Post
I wouldn't worry about it too much. The Template presumes taper in plan to equal the taper in elevation, and a half-circular cross section. The racer's aphorism is "It isn't how you punch the hole in the air, it's how you close the hole in the air." IOW the rear is more important than the front.

That said the bluff forebody of the Template insures the flow is uniform enough that it can support the taper without shedding vortexes. Any disruption such as the windshield header you mention can spoil airflow 'downstream'.
Thanks. Been looking at more modelling and theory to try and understand it, and seems I was wrong about the 'high pressure' just above the windscreen. It's high velocity; which is low pressure I understand. But the transition between roof and windscreen would have to be rounded enough to prevent turbulence? Which i gather is what shedding vortexes are? Any guidelines on acceptable radii in this area?


Quote:
Originally Posted by freebeard View Post
Why not go with the curved header and then a Tropfenwagen style rear with a flat top and tapered sides? It would have more interior space.
To avoid taking this thread off-topic I'll reply to this on my other thread (35515).

  Reply With Quote
The Following User Says Thank You to s_t For This Useful Post:
aerohead (09-02-2017)
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 08-31-2017, 01:39 PM   #672 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 28,652
Thanks: 8,127
Thanked 8,916 Times in 7,359 Posts
The guideline for rectangular bodies is 4% of the gross width. Think of U-Haul trailers.

My basis for comparison is always the VW Beetle. The original Beetle had a windshield header that rolled 90° to meet the glass. Over the years the windshield was increased in height, later models had the header meet the glass at more like 45°. But the overall contour didn't change.
  Reply With Quote
The Following User Says Thank You to freebeard For This Useful Post:
aerohead (09-02-2017)
Old 09-02-2017, 03:18 PM   #673 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 16,294
Thanks: 24,425
Thanked 7,378 Times in 4,776 Posts
rounded enough

Quote:
Originally Posted by s_t View Post
Thanks. Been looking at more modelling and theory to try and understand it, and seems I was wrong about the 'high pressure' just above the windscreen. It's high velocity; which is low pressure I understand. But the transition between roof and windscreen would have to be rounded enough to prevent turbulence? Which i gather is what shedding vortexes are? Any guidelines on acceptable radii in this area?




To avoid taking this thread off-topic I'll reply to this on my other thread (35515).
The big dogs will tell you that there is no 'magic' radius for forebody edges.
4% of the square-root of the frontal area of the body itself is still a good guide.
In the forebody,up to the location of maximum body cross-section,there is a positive pressure gradient as the vehicle attacks the air in front of it.The air is essentially held against the body by this impingement.
A look at a 1975 VW Rabbit/Golf will show you a working minimum for radii.There is fully-attached flow everywhere on the VW's forebody.
It's the aft-body where the challenge comes,as all this area is in a unfavorable pressure regime,with no reason for the flow to remain attached,unless the body cross-section varies as it would in a streamline body.Hence the Template.
Any vehicle manufactured after 1982 would have respected Hucho's shape optimization techniques published in 1978.
Since forebody drag constitutes less than 6% of the overall drag,it's better to spend your energy and money on the aft-body.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
The Following User Says Thank You to aerohead For This Useful Post:
COcyclist (10-05-2017)
Old 09-02-2017, 08:03 PM   #674 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 28,652
Thanks: 8,127
Thanked 8,916 Times in 7,359 Posts

https://en.wikipedia.org/wiki/Audi_80

Maybe aerohead knows the improvement between the Audi 80 and the B1 Passat. DuckDuckGo gets confused by the Audi CD turbodiesel.
  Reply With Quote
The Following User Says Thank You to freebeard For This Useful Post:
aerohead (04-07-2018)
Old 09-30-2017, 05:54 PM   #675 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 16,294
Thanks: 24,425
Thanked 7,378 Times in 4,776 Posts
Finally,confirmation on the shape

'finally got to test the 'Template' at DARKO,September 15,2017, 9-years after the latest 'Template'-C thread was published.
As a full-tail she came in at Cd 0.1209.
At Kamm's recommended 50% frontal area truncation,she measured Cd 0.1487.
With a 2% race-inspired cooling system she'd grow to Cd 0.1233.
As a mirror-less 'camera' car she'd remain at Cd 0.1233
A single,legal,SCCA-type race mirror would bump it to Cd 0.1283.
The 1/3-scale model has arbitrarily-wide fairings,to accommodate strap fastening to a ground-board.I suspect that the drag could be trimmed when at 1:1 scale.
IVECO has an 18-wheel, tractor, 'Glider', with a zero-porosity cooling system,
Such technology would allow for a zero-drag cooling system.
Also,with such little horsepower required to propel the 'Template' at highway velocity,there'd be little heat flux to deal with in the first place.
The model required 26-horsepower to overcome air resistance at an indicated 200-mph according to measurements.
NOTE:
During smoke flow imaging we could not exceed 30-mph air velocity in the test section,placing the body in a sub-critical Reynolds number flow regime.Streamline filaments diverged as expected,with smoke traces widening.A wake survey conducted with smoke revealed strong surface shear all around the transom,indicating fully-attached aft-body flow even at low Reynolds number.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
The Following 8 Users Say Thank You to aerohead For This Useful Post:
BamZipPow (10-08-2017), California98Civic (04-07-2018), COcyclist (04-09-2018), Frank Lee (09-30-2017), freebeard (10-01-2017), sendler (09-30-2017), slowmover (10-07-2017), Vekke (12-01-2020)
Old 09-30-2017, 06:23 PM   #676 (permalink)
Master EcoModder
 
sendler's Avatar
 
Join Date: May 2011
Location: Syracuse, NY USA
Posts: 2,935

Honda CBR250R FI Single - '11 Honda CBR250R
90 day: 105.14 mpg (US)

2001 Honda Insight stick - '01 Honda Insight manual
90 day: 60.68 mpg (US)

2009 Honda Fit auto - '09 Honda Fit Auto
90 day: 38.51 mpg (US)

PCX153 - '13 Honda PCX150
90 day: 104.48 mpg (US)

2015 Yamaha R3 - '15 Yamaha R3
90 day: 80.94 mpg (US)

Ninja650 - '19 Kawasaki Ninja 650
90 day: 72.57 mpg (US)
Thanks: 326
Thanked 1,315 Times in 968 Posts
What is the approximate percentage of length discarded for the Kamm?
  Reply With Quote
The Following User Says Thank You to sendler For This Useful Post:
aerohead (10-07-2017)
Old 10-07-2017, 01:07 PM   #677 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 16,294
Thanks: 24,425
Thanked 7,378 Times in 4,776 Posts
percentage of length

Numbskull Knox never bothered to record it! I'll have to get back to you on that.Apologise for the delay.
Lookin' at the drawing,I'd estimate that the truncation is @ around 45% aft-body,measured from the roof apex,or,zero-point.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/

Last edited by aerohead; 10-07-2017 at 01:10 PM.. Reason: add data
  Reply With Quote
Old 04-07-2018, 05:07 PM   #678 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 16,294
Thanks: 24,425
Thanked 7,378 Times in 4,776 Posts
Audi/Passat

Quote:
Originally Posted by freebeard View Post

https://en.wikipedia.org/wiki/Audi_80

Maybe aerohead knows the improvement between the Audi 80 and the B1 Passat. DuckDuckGo gets confused by the Audi CD turbodiesel.
I've been going back through my mags and even when they mentioned Audi 80 (4000) 'facelifts,' there was never any expansion on details of what was done.
With the Passat (Quantum) I've never seen anything said in detail.Sucks!
Hucho went into detail for changes between the Audi 100-II and III.
*They optimized the boot height.
*They optimized the boot length.
*They optimized the backlight angle.
*And a few other tricks concerning the side elevation profile,however that's at home in Hucho's book.Sorry!
I do recall that the changes were so subtle,that unless you were paying close attention,you'd never discern the difference between the two.
I'll get back to you.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Old 04-07-2018, 07:38 PM   #679 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 28,652
Thanks: 8,127
Thanked 8,916 Times in 7,359 Posts
S'okay.

That was a reply to s_t, who hasn't posted since January. I wasn't looking for what was done so much as the change in Cd value.

[My Dasher is down until the diesel fuel pump is rebuilt and paid off.]
__________________
.
.
Without freedom of speech we wouldn't know who all the idiots are. -- anonymous poster

____________________
.
.
Three conspiracy theorists walk into a bar --You can't say that is a coincidence.
  Reply With Quote
The Following User Says Thank You to freebeard For This Useful Post:
aerohead (04-18-2018)
Old 04-18-2018, 02:20 PM   #680 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 16,294
Thanks: 24,425
Thanked 7,378 Times in 4,776 Posts
Dasher

Quote:
Originally Posted by freebeard View Post
S'okay.

That was a reply to s_t, who hasn't posted since January. I wasn't looking for what was done so much as the change in Cd value.

[My Dasher is down until the diesel fuel pump is rebuilt and paid off.]
I looked at home,and it looks like I've never had anything for the Dasher/Passat.
The Quantum/Passat was reported at Cd 0.39.
Between the Audi 100-II and III,VW changed everything about the body,and dropped the Cd from 0.43,to 0.30 (Euro versions).
Hope the pump turns out perfect and leaves you enough cash to eat on.

__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
The Following User Says Thank You to aerohead For This Useful Post:
freebeard (04-18-2018)
Reply  Post New Thread


Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Maximum angle for boat tail? abcdpeterson Aerodynamics 80 11-03-2021 01:55 PM
Aerodynamic Streamlining Template Part-B aerohead Aerodynamics 8 05-31-2013 01:23 PM
LED Headlight captainslug DIY / How-to 82 11-15-2011 02:32 AM
Aerodynamic Streamlining Template: Part-A aerohead Aerodynamics 0 07-18-2009 03:37 PM
All items I scanned in the new product showcase dremd The Lounge 0 11-08-2008 05:14 PM



Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com