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

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 04-21-2021, 06:56 PM   #1 (permalink)
EcoModding Apprentice
 
Join Date: Dec 2016
Location: Florida
Posts: 108
Thanks: 16
Thanked 72 Times in 57 Posts
"flutter" is bad, and why exactly?

My question centers here on the "why".
This topic was touched on in the recent Bonneville thread, and I felt best not to clutter that thread up, and sorry if this has been addressed elsewhere, unknown to me.

It seems bad, it looks bad, and "common sense" seems to indicate its absorbing energy, bending the panel that is fluttering, converting some portion of the energy to heat, I suspect.

But the question here is, is there ANY aero benefit (less overall drag?)by allowing the air to seek a path of lower resistance as the fluttering panel reacts to the varying(/) pressure waves, or is just increasing drag, turbulence, etc?

On a slightly related topic, it has always been the goal in high powered speaker cabinet design, to build cabinets as vibration free as practically possible for the situation, because any cabinet vibration has tonal artifacts, and more pertinent to this thread, wastes acoustic energy converting into mechanical energy and the resultant heating.

So is it a fair conclusion that when ever one sees random panel fluctuations in vehicles due to aero loads, the design is lacking in some degree?

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 04-21-2021, 08:53 PM   #2 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 18,936
Thanks: 5,271
Thanked 6,259 Times in 5,015 Posts
How is the heat being generated? Pressure fluctuations. The heat produced is likely minimal compared to the clutching fingers of turbulent air.
__________________
.

Cold hearted orb that rules the night, Removes the colours from our sight, Red is grey and yellow white, But we decide which is right, And which is an illusion.
The Day Begins -- Moody Blues
_________________
  Reply With Quote
Old 04-21-2021, 09:00 PM   #3 (permalink)
Master EcoModder
 
Join Date: May 2012
Location: Tampa, FL
Posts: 1,589

Volt, gas only - '12 Chevrolet Volt Premium
90 day: 38.02 mpg (US)

Volt, electric only - '12 Chevrolet Volt Premium
90 day: 132.26 mpg (US)

Yukon Denali Hybrid - '12 GMC Yukon Denali Hybrid
90 day: 21.48 mpg (US)
Thanks: 177
Thanked 359 Times in 252 Posts
First thing that comes to mind is a flag. How much drag is created by those ripples in a flag. Maybe not apples to apples, but it seems a flag being towed by a car at 30mph is similar to a weak body panel at 300mph, no?
__________________




  Reply With Quote
Old 04-21-2021, 09:37 PM   #4 (permalink)
Master Ecomadman
 
arcosine's Avatar
 
Join Date: Nov 2010
Location: Chicago area
Posts: 1,146

sc1 - '98 saturn sc1
Team Saturn
90 day: 43.17 mpg (US)

Airplane Bike - '11 home built Carp line Tour

rans - '97 rans tailwind

tractor - '66 International Cub cadet 129

2002 Space Odyssey - '02 Honda Odyssey EX-L
90 day: 28.25 mpg (US)

red bug - '00 VW beetle TDI

big tractor - '66 ford 3400

red vw - '00 VW new beetle TDI
90 day: 58.42 mpg (US)

RV - '88 Winnebago LeSharo
90 day: 16.67 mpg (US)
Thanks: 20
Thanked 328 Times in 223 Posts
Flutter will cause a plane to crash out of control. It is an oscillation resonance excited by the energy in the air flow, If the cop ( center of pressure) and CG center of gravity do not coincide, if you look closely at the planes control surfaces, you will see weights ahead of the hinge. A flag waving id the wind is flutter.

https://en.wikipedia.org/wiki/Aeroelasticity
__________________
- Tony

  Reply With Quote
The Following User Says Thank You to arcosine For This Useful Post:
Cd (04-22-2021)
Old 04-22-2021, 10:03 AM   #5 (permalink)
Somewhat crazed
 
Piotrsko's Avatar
 
Join Date: Sep 2013
Location: 1826 miles WSW of Normal
Posts: 1,772
Thanks: 176
Thanked 492 Times in 420 Posts
It is my understanding that you generally want CG in front of COP for a stabilizing effect. If the converse were true, the surface mass weights would be attached to the rear not the front.
  Reply With Quote
Old 04-22-2021, 05:17 PM   #6 (permalink)
EcoModding Apprentice
 
Join Date: Dec 2016
Location: Florida
Posts: 108
Thanks: 16
Thanked 72 Times in 57 Posts
Quote:
Originally Posted by freebeard View Post
How is the heat being generated? Pressure fluctuations. The heat produced is likely minimal compared to the clutching fingers of turbulent air.
My thinking is bending any material, requires energy, and that generates internal heating of the material. Is it likely minor, yes, and I thought obvious, which is why my original question has more of an aero leaning, so does the "flutter" induce additional drag/turbulence/flow separation/etc or is the observed panel flutter simply the result of the above?

This question was first considered by me decades back when Nascar had roof mounted live action cameras and it was apparent the severely lightened hoods would deflect/flutter grossly at speed or when it the wake of another car, and wasn't sure if it mattered little, or they felt it was of no real consequence. It seemed the Bonneville car thread had similar issues.
  Reply With Quote
Old 04-22-2021, 06:43 PM   #7 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 18,936
Thanks: 5,271
Thanked 6,259 Times in 5,015 Posts
But what is causing the material heating? Viscosity transferring energy from the turbulence in the unseparated flow. The turbulence itself robs energy that flows away in the [slightly] heated air.
Quote:
Parasitic drag is drag that acts on an object when the object is moving through a fluid. In the case of aerodynamic drag, the fluid is the atmosphere. Parasitic drag is a combination of form drag and skin friction drag.[1] Parasitic drag does not result from the generation of lift on the object, and hence it is considered parasitic.
en.wikipedia.org/wiki/Parasitic_drag
__________________
.

Cold hearted orb that rules the night, Removes the colours from our sight, Red is grey and yellow white, But we decide which is right, And which is an illusion.
The Day Begins -- Moody Blues
_________________
  Reply With Quote
Old 04-23-2021, 01:12 PM   #8 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 12,460
Thanks: 20,041
Thanked 6,224 Times in 3,843 Posts
why bad

* flutter is cyclic deformation
* cyclic deformation can lead to 'work-hardening'
* work-hardening can lead to embrittlement of the panel
* embrittlement can lead to fracture
* fracture leads to panel failure
* Panel failure alters pressure distribution in the vicinity of the failed panel
* the altered pressure distribution can affect aerodynamic stability.
* Flutter-induced aerodynamic instability has killed a number of people. Aircraft and record cars.
__________________
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 (04-23-2021)
Old 04-23-2021, 10:49 PM   #9 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 18,936
Thanks: 5,271
Thanked 6,259 Times in 5,015 Posts
What could possibly go wrong?


On the return pass, at 427 mph, the lack of good body mounting, and not enough clearance at speed with air pressure, centrifigal force, and kinematics, caused tire deflection which allowed a panel to rub the tire. Which killed the left rear tire.
__________________
.

Cold hearted orb that rules the night, Removes the colours from our sight, Red is grey and yellow white, But we decide which is right, And which is an illusion.
The Day Begins -- Moody Blues
_________________
  Reply With Quote
Old 04-26-2021, 10:14 AM   #10 (permalink)
Master EcoModder
 
kach22i's Avatar
 
Join Date: Jul 2011
Location: Ann Arbor, Michigan
Posts: 3,809
Thanks: 46
Thanked 2,531 Times in 1,772 Posts
Quote:
Originally Posted by freebeard View Post
How is the heat being generated? Pressure fluctuations. The heat produced is likely minimal compared to the clutching fingers of turbulent air.
In stereo-speak "heat" is the mysterious energy created by vibration and resonance when absorbed into a structure (rack/stand/enclosure).

Interesting incident on the Flashpoint car, thanks for posting.

I think buffeting and flutter is energy at random vectors, and we want all those energies and vectors parallel to the direction our body is moving for maximum efficiency.

Analogy, if I may:

Walking in a crowd with people constantly knocking into you is harder and takes more energy than walking a path unencumbered by rude idiots.

__________________
George
Architect, Artist and Designer of Objects

1977 Porsche 911s Targa
1998 Chevy S-10 Pick-Up truck
1989 Scat II HP Hovercraft

Chin Spoiler:
http://forums.pelicanparts.com/off-t...effective.html

Rear Spoiler Pick Up Truck
http://forums.pelicanparts.com/off-t...xperiment.html

Roof Wing
http://ecomodder.com/forum/showthrea...1-a-19525.html
  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