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

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 09-18-2012, 01:17 AM   #11 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 12,751
Thanks: 3,084
Thanked 4,149 Times in 3,294 Posts
Quote:
Edit: I may be misunderstanding your question. All three of the shapes you are proposing are "flat bottomed", right?
Yes. I put 'half body of revolution' in the title and showed full bodies in the illustration. In my defense I posted at 4 am. I realized at 2 am I wasn't going to sleep, so I got up and prepared the models. By 4 am, I was sleepy and didn't truncate them properly. I thought I scaled the square sectioned one in all three dimensions, but the length looks the same, so ??????

What I was getting at was if the frontal area is the same, and there is no air movement except out and then back into the center (i.e., no lateral movement that would lead to vortexes), would compound curves be necessary? Or would the simplified construction of the (half) square section carry an aerodynamic penalty?

What strikes me is that even though the superellipse is half way between the square and circle, it looks closer to the circle. That may be because I didn't subdivide the square section equivalently. There are a whole class of superelliptic curves, some would be very close to a square with radiused edges.

I understand that the underbody is a whole separate can of worms, until they re-merge at the rear.

Quote:
dang you! I came on here to post my pics of my latest CFD testing.
ERTW -- Thanks for sharing. That is precisely on-topic. Consider it a preview and do your own separate post if you like.

Is the line at the bottom a ground plane or are they in free air? And if so, why do you think the stream-lines from the top cross the stream-lines from the bottom in the side view? Wasn't that a no-no in Ghostbusters?

Does anyone have a reference for the study done on a body shape with a pronounced arch to the underbody? I know I've seen it referenced here but I didn't save and can't find it now. My recollection is an Italian-sounding name in the 1960s. I wanted that for MTrenk's underbody thread, and the 'Aero concept car -- Bugatti Stratos' thread the mods spun out of that one. TIA

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 09-18-2012, 03:01 AM   #12 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 12,751
Thanks: 3,084
Thanked 4,149 Times in 3,294 Posts
Did someone say car shaped like a fish?
  Reply With Quote
Old 09-18-2012, 04:08 AM   #13 (permalink)
(:
 
Frank Lee's Avatar
 
Join Date: Jan 2008
Location: up north
Posts: 12,470

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: 1,478
Thanked 3,252 Times in 2,056 Posts
http://ecomodder.com/forum/showthrea...-pdf-1028.html

pininfarina banana car
__________________


  Reply With Quote
The Following User Says Thank You to Frank Lee For This Useful Post:
freebeard (09-18-2012)
Old 09-18-2012, 11:20 AM   #14 (permalink)
Master EcoModder
 
NeilBlanchard's Avatar
 
Join Date: May 2008
Location: Maynard, MA Eaarth
Posts: 7,429

Mica Blue - '05 Scion xA RS 2.0
Team Toyota
90 day: 42.48 mpg (US)

Forest - '15 Nissan Leaf S
Team Nissan
90 day: 156.46 mpg (US)

Number 7 - '15 VW e-Golf SEL
TEAM VW AUDI Group
90 day: 155.81 mpg (US)
Thanks: 2,749
Thanked 2,465 Times in 1,519 Posts
My memory is that the computer model of the boxfish was a Cd of 0.06:



The blue quarter scale model has a Cd of 0.095 and the diesel powered concept car has a Cd of 0.19:




Edit: here's a series of screen captures I got from a video about the Boxfish, that show many more angles of the early model:

CarBEN EV Concept :: Mercedes Bionic/Boxfish clay model picture by NeilBlanchard - Photobucket
__________________
Sincerely, Neil

http://neilblanchard.blogspot.com/

Last edited by NeilBlanchard; 09-18-2012 at 11:43 AM..
  Reply With Quote
Old 09-22-2012, 04:30 PM   #15 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 9,823
Thanks: 14,546
Thanked 5,214 Times in 3,046 Posts
half body

Quote:
Originally Posted by freebeard View Post
My understanding is that The Template is a half body of revolution to insure that air doesn't want to move laterally because of pressure differentials between the top and sides, which leads to vortex generation.

If that's the case, wouldn't a half-square cross section serve as well, given equal cross-sectional area? If air is not wrapping across the edge, would no vortexes be created?

Here are three aeroforms, a cylinder, a superellipse and a square. Would their Cd be equivalent?


(These are not dimensionally highly accurate; I just eyeballed the proportions against The Template)

The next question: If the height/width proportion changes, what happens to the respective tapers? If the half revolution form is 7' wide, then it is 3 1/2' high. If the height is proportionally greater, does the side taper increase or relax?

TIA
The streamline bodies of revolution are of the lowest drag 3-dimensional bodies known.
And their half-bodies lend themselves okay to a 2-door coupe or sedan and such.
Today's Bochum University', Cd 0.14 solar car would be a recent example.
There has been a tremendous interest in the 1948 NACA mathematical algorithm which became the 1976 Morelli shape as used by Aptera,although,with ground proximity and wheels,the Morelli form has failed to demonstrate lower drag than a half-body 'pumpkin seed.'
If you'll look at the full-boat-tail trailer thread there should be some pictorial drag tables which demonstrate the drag increase when side radii are lost on the streamline half-body.
An example would be the square fuselage of the 'Spirit of St.Louis' with Cd 0.247 and the 'round' fuselage of the Arado 'Smooth' of similar fineness ratio,at Cd 0.06.
You will never see a high performance,low drag fish,bird,airship,fuselage,submarine,torpedo,etc., with square edges.
There are a lot of graphical drag coefficient tables in the public domain from which to compare architectures.
I believe that if you will exhaust all avenues,you will come to the realization that you're not going to beat the 'Template.'I've been actively looking since 1973.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Old 09-22-2012, 04:35 PM   #16 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 9,823
Thanks: 14,546
Thanked 5,214 Times in 3,046 Posts
boxfish

Quote:
Originally Posted by NeilBlanchard View Post
My memory is that the computer model of the boxfish was a Cd of 0.06:



The blue quarter scale model has a Cd of 0.095 and the diesel powered concept car has a Cd of 0.19:




Edit: here's a series of screen captures I got from a video about the Boxfish, that show many more angles of the early model:

CarBEN EV Concept :: Mercedes Bionic/Boxfish clay model picture by NeilBlanchard - Photobucket
It would have been really instructive had Mercedes published a plan-view image of the fish.This decides the flow path and the side view makes it as difficult to understand as if they offered a photo of panties when speaking of brassieres.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Old 09-22-2012, 05:45 PM   #17 (permalink)
EcoModding Apprentice
 
ERTW's Avatar
 
Join Date: Jan 2012
Location: Toronto
Posts: 120

Bu - '08 Chevrolet Malibu LS
90 day: 32.29 mpg (US)
Thanks: 50
Thanked 65 Times in 31 Posts
It's not called a bodyofrevolution fish . Mb was surprised at the low Cd. They also mention that it's very stable and maneuvrable. We can't say for sure what the most streamlined animal is until we test them. In the meantime we just have to drive cigar shaped cars.

I was at the big al's the other day and noticed the shark's head is elliptical. The body is almost triangular.

Imo as long as the air on the top and side is the same, sharp edges won't hurt. It's when there is a pressure differential that sharp edges will accentuate it and create vortices. In that case a round edge will allow a gradient, and not feed vortices

Last edited by ERTW; 09-22-2012 at 05:51 PM..
  Reply With Quote
Old 09-22-2012, 07:34 PM   #18 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 12,751
Thanks: 3,084
Thanked 4,149 Times in 3,294 Posts
Aerohead -- Thanks for you thoughts. Have you posted your Bonneville stories anywhere? I have a post at Project the third that I would appreciate your comments on.

Quote:
...the Morelli form has failed to demonstrate lower drag than a half-body 'pumpkin seed.' ... I believe that if you will exhaust all avenues,you will come to the realization that you're not going to beat the 'Template.'I've been actively looking since 1973.
I'm not looking so much to beat it, as to find some way to accommodate it into my life. Life full of compromise, if you take the half body of revolution and hang a license plate on it, you've already compromised.

Quote:
An example would be the square fuselage of the 'Spirit of St.Louis' with Cd 0.247 and the 'round' fuselage of the Arado 'Smooth' of similar fineness ratio,at Cd 0.06.
Now that right there is what I was looking for. One would expect the superllipse to have Cd ~0.15.


ERTW -- This is how I'm seeing it:
Quote:
Imo as long as the air on the top and side is the same, sharp edges won't hurt. It's when there is a pressure differential that sharp edges will accentuate it and create vortices. In that case a round edge will allow a gradient, and not feed vortices
So we have a preferred shape (or shapes), with the wheels spats and departure angles; we know that surface dirt and duct tape are trivial. That leaves the scale from drip rails and door handles up to rear view mirrors to think about. Maybe air scoops behind the rear view mirror to eat its vortex?
  Reply With Quote
Old 09-24-2012, 04:22 PM   #19 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 12,751
Thanks: 3,084
Thanked 4,149 Times in 3,294 Posts
Aerohead -- I found your Bonneville post. I also rediscovered this picture this morning. Perhaps it is what started my thought process. It out-boxes the boxfish.
  Reply With Quote
Old 09-24-2012, 06:05 PM   #20 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 9,823
Thanks: 14,546
Thanked 5,214 Times in 3,046 Posts
picture

Quote:
Originally Posted by freebeard View Post
Aerohead -- I found your Bonneville post. I also rediscovered this picture this morning. Perhaps it is what started my thought process. It out-boxes the boxfish.
It would be nice if Honda published a Cd for the pictured car,then we'd know what we were 'looking' at.Have you seen the Honda P-NUT?
Some of the current minis are running on the order of Cd 0.3.
If you wanted lower drag you'd have to extend the rear.
--------------------------------------------------------------------------
If you'd like to depart from the 'Template,' you might want to find out all you can about Wolfgang Klemperer's 'minivan' of Cd 0.16 (in naked model form) which he tested in 1921.Klemperer was a doctoral student working under Paul Jaray at the Zeppelin Werke.This 'minivan' is what VW used as the basis for the VW 2000 concept car.
I might be more excited about it if there was more data available on it.After extensive shaping in their new wind tunnel,VW got a 'production-ready' model to about Cd 0.25.
If you weren't interested in going below Cd 0.16 it would be a good way to go.

__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2019, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com