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

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 12-11-2020, 12:21 PM   #21 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 27,562
Thanks: 7,738
Thanked 8,554 Times in 7,041 Posts
Quote:
6) a 'notchback' GOODYEAR blimp would be challenging.
7) a 'squareback' GOODYEAR blimp would be challenging.
8) a 'raked-back' GOODYEAR blimp would be a challenge.
9) GOODYEAR blimps are not a challenge, as their engineering quanta have been known and cataloged since the 1920s.
Today we have a new example, the Celera 500


http://www.aero-news.net/images/cont...500L-0820d.jpg

Why do you think the body has max cross section at 50% instead of 30%? Maybe the pusher prop?

__________________
.
.
Without freedom of speech we wouldn't know who all the idiots are. -- anonymous poster

____________________
  Reply With Quote
The Following User Says Thank You to freebeard For This Useful Post:
aerohead (12-11-2020)
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 12-11-2020, 12:46 PM   #22 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 15,861
Thanks: 23,922
Thanked 7,207 Times in 4,640 Posts
Celera 500 cross section

Its a 'laminar' form.
At altitude, under 'flight' conditions, high above Earth's boundary layer, an aircraft can operate under 'calm', sub-critical Reynolds number conditions.
If an aircraft is very smooth, in very rarified, low-density, low-viscosity air, it's possible to experience a laminar boundary layer and low surface friction drag, up to the location of 'first minimum pressure', which is code for maximum cross-section, as beyond that point, the LBL is now in an adverse pressure gradient of diverging streamlines, flow velocity reduction, and rising pressure, impossible for a LBL to survive. And the LBL immediately transitions to turbulent boundary layer ( TBL ) and concomitant high surface friction drag.
So the term ' laminar' only regards the forebody of the structure. Wings included.
So the trick is to 'delay' the location of minimum pressure by moving the thickness rearwards as much as is practical on these vehicles with tremendous surface area, compared to automobiles.
Shell Mileage Marathon, SAE Economy, World Solar Challenge, and IHPVA bicycle speed record vehicles can take advantage of this effect, as they essentially have sub-critical Reynolds number frontal areas at the speeds they compete at.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Old 12-11-2020, 02:00 PM   #23 (permalink)
Long time lurker
 
AeroMcAeroFace's Avatar
 
Join Date: May 2019
Location: Uk
Posts: 218
Thanks: 110
Thanked 153 Times in 119 Posts
So despite following the template, the car still had separation? And it was caused by a very thin light bar. Click image for larger version

Name:	Audi A7.jpg
Views:	43
Size:	25.5 KB
ID:	29748 So, doesn't that mean that applying a centreline template could be useless unless very small protuberances, such as lights, boot lid gaps or window gaps are taken into account?
  Reply With Quote
The Following User Says Thank You to AeroMcAeroFace For This Useful Post:
aerohead (12-11-2020)
Old 12-11-2020, 02:40 PM   #24 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 15,861
Thanks: 23,922
Thanked 7,207 Times in 4,640 Posts
lightbar

Quote:
Originally Posted by AeroMcAeroFace View Post
So despite following the template, the car still had separation? And it was caused by a very thin light bar. Attachment 29748 So, doesn't that mean that applying a centreline template could be useless unless very small protuberances, such as lights, boot lid gaps or window gaps are taken into account?
Yes, the drop-off created the sudden alteration in cross-sectional area, and positive adverse pressure spike trigger which Hucho tells us always to avoid in an aft-body, and the elevation of the glass, below the streamlined pathway, precluded any reacceleration of the flow to cross back over the spike threshold. Without a constriction to the flow downstream, there's no opportunity for reattachment.
The flip-up spoiler is introduced to provide the flow constriction.
If the roofline had simply continued on, without deformation, like the Honda, Gen-II Insight, there never would have been any separation.
Protuberances would be okay, as they wouldn't constitute a constriction of the body cross-section.
Gaps are okay, as they're not a 'ventilation', as a reverse-step would constitute.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
The Following User Says Thank You to aerohead For This Useful Post:
AeroMcAeroFace (12-12-2020)
Old 12-11-2020, 04:46 PM   #25 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 27,562
Thanks: 7,738
Thanked 8,554 Times in 7,041 Posts


This states that the prolated spheroid has a 15% advantage over a 'bi-hemispherical cylinder' which I assume is a hot dog shape. This is by volume, not frontal area.

My question is why it looks faster backwards. I surmise the area ahead of the propellor acts as an invert Coanda nozzle. Laminar flow all the way to the tail. Maybe a little Meredith Effect?
__________________
.
.
Without freedom of speech we wouldn't know who all the idiots are. -- anonymous poster

____________________
  Reply With Quote
The Following 2 Users Say Thank You to freebeard For This Useful Post:
aerohead (12-11-2020), Cd (12-11-2020)
Old 12-11-2020, 05:20 PM   #26 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 15,861
Thanks: 23,922
Thanked 7,207 Times in 4,640 Posts
advantage

Quote:
Originally Posted by freebeard View Post


This states that the prolated spheroid has a 15% advantage over a 'bi-hemispherical cylinder' which I assume is a hot dog shape. This is by volume, not frontal area.

My question is why it looks faster backwards. I surmise the area ahead of the propellor acts as an invert Coanda nozzle. Laminar flow all the way to the tail. Maybe a little Meredith Effect?
I'd call it a prolate ellipsoid.
Hot dog is exactly correct. Hoerner has a Cd for that.
Volumetric drag coefficients were also very common for airships and submarine outer hulls.
Just beyond the hatch on the side with the porthole would be about the limit for LBL on the fuselage. It would pop over to TBL beyond there.
All the wings and stabilizers would behave in kind. LBL up to max thickness, then, pow!
Some of the reflexive tail region will be filled in with the sloughing boundary layer.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Old 12-11-2020, 06:02 PM   #27 (permalink)
Cd
Ultimate Fail
 
Cd's Avatar
 
Join Date: Feb 2008
Location: Austin,Texas
Posts: 3,585
Thanks: 2,872
Thanked 1,121 Times in 679 Posts
Fascinating video.
My first thoughts are of the "backwards" shapes of H.P.V.s.
At 6:31, it is stated that the ventral fin reduces drag from the fuselage upsweep.
Interesting !
Attached Thumbnails
Click image for larger version

Name:	20201211_164949.jpg
Views:	11
Size:	86.1 KB
ID:	29749  
  Reply With Quote
Old 12-14-2020, 06:59 AM   #28 (permalink)
-----------------
 
IRONICK's Avatar
 
Join Date: Jun 2009
Location: Romania
Posts: 128
Thanks: 22
Thanked 57 Times in 44 Posts












LaFerrari's Rear Diffuser In Motion

https://drivetribe.com/a4ec1f0a-542d...7-ca019268d0c1

Last edited by IRONICK; 12-14-2020 at 07:09 AM..
  Reply With Quote
Old 12-14-2020, 03:42 PM   #29 (permalink)
Banned
 
Join Date: Nov 2017
Location: Australia
Posts: 2,060
Thanks: 107
Thanked 1,605 Times in 1,136 Posts
Interesting. But keep in mind a few things:

1) In the videos I watched, the airflow was all faked / simulated - no smoke testing in a tunnel for example. Also, some of the descriptions of how things are meant to work seemed a bit strange.

2) The Cl and drag figures seemed a bit odd - are the Cl figures meant to be negative?

3) Rumour only - someone who should know told me that Ferraris never meet their advertised aero specs when tested in other company wind tunnels.

4) Ferrari, as far as I know, never publish any peer-reviewed tech papers on their cars (and if I have that wrong, I'd love to see some).

Worth watching - but I'd suggest with a skeptical and analytical eye, perhaps.
  Reply With Quote
Old 12-14-2020, 04:05 PM   #30 (permalink)
Moderator
 
Vman455's Avatar
 
Join Date: Feb 2012
Location: Urbana, IL
Posts: 1,935

Pope Pious the Prius - '13 Toyota Prius Two
Team Toyota
SUV
90 day: 51.62 mpg (US)

Tycho the Truck - '91 Toyota Pickup DLX 4WD
90 day: 22.22 mpg (US)
Thanks: 198
Thanked 1,797 Times in 937 Posts
Quote:
Originally Posted by JulianEdgar View Post
3) Rumour only - someone who should know told me that Ferraris never meet their advertised aero specs when tested in other company wind tunnels.
I laughed out loud at this. Reminds me of the time I was laying on the floor at an auto show, taking pictures of the underside of an SUV, when one of the booth attendants asked who I was working for.

__________________
UIUC Aerospace Engineering
www.amateuraerodynamics.com
  Reply With Quote
The Following User Says Thank You to Vman455 For This Useful Post:
JulianEdgar (12-14-2020)
Reply  Post New Thread


Thread Tools




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