Go Back   EcoModder Forum > Off-Topic > The Lounge
Register Now
 Register Now
 


Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 10-20-2010, 07:34 PM   #1 (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
Sawtooth edges on 747 engines

I saw this on another forum and thought it might make an interesting discussion.
I have no idea what the sawtooth edges are for on these engines, but my guess would be to manage the airflow better by creating small vortices.

Since the airstream then meets the turbulent jet-wash, I'm puzzled as to how that this could be useful.

So what is the real purpose ?

Photos: Boeing 747-8R7F/SCD Aircraft Pictures | Airliners.net

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 10-20-2010, 07:57 PM   #2 (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 532 Times in 358 Posts
Cd -

Some say it's primarily for reducing noise :

Quote:
Originally Posted by Sayyad View Post
The image I've attached is that of the engine of a 787 Dreamliner. The guy who worked on the sawtooth design wrote that it reduces noise. This means less energy wasted energizing air to produce that noise. I'd guess that there would be small vortices forming at each point on the trailing edge, but that all the vortices combined would take less energy to maintain than a possible single large one trailing from a smooth trailing edge.
Others say it's just a Batman thing, :



What *is* interesting is that the design has evolved. In the pictures above, it's on the external cowling only. In this picture it is also part of a second cowling closer to the exhaust :



CarloSW2
__________________

What's your EPA MPG? Go Here and find out!
American Solar Energy Society
  Reply With Quote
The Following 2 Users Say Thank You to cfg83 For This Useful Post:
Cd (10-20-2010), Piwoslaw (10-21-2010)
Old 10-20-2010, 08:10 PM   #3 (permalink)
...beats walking...
 
Join Date: Jul 2009
Location: .
Posts: 6,190
Thanks: 179
Thanked 1,525 Times in 1,126 Posts
...look up "scalloped fins" on whales.
  Reply With Quote
Old 10-21-2010, 11:37 AM   #4 (permalink)
Master EcoModder
 
euromodder's Avatar
 
Join Date: Jul 2010
Location: Belgium
Posts: 4,683

The SCUD - '15 Fiat Scudo L2
Thanks: 178
Thanked 652 Times in 516 Posts
Quote:
Originally Posted by Cd View Post
So what is the real purpose ?
Noise reduction.

Boeing: Boeing, Rolls-Royce Verify Jet Noise Reductions

The technology behind serrated trailing edge design is described in US patent 6612106 filed by Boeing in 2001.

Segmented mixing device having chevrons for exhaust noise reduction in jet engines - Patent 6612106


I wouldn't be surprised if they also reduced wake drag.
__________________
Strayed to the Dark Diesel Side

  Reply With Quote
Old 10-21-2010, 11:48 AM   #5 (permalink)
EcoModding Lurker
 
Join Date: Mar 2010
Location: Leicester UK
Posts: 16
Thanks: 0
Thanked 2 Times in 1 Post
The idea is that the cold, slow surrounding air mixes smoothly with the hot, high speed jet exhaust.

In fact the jet exhaust is also the bypass air surrounding the core air, and if all these can mix with minimum turbulence that's as quiet as you can get.

Anyone old enough to remenber the lobed jetpipes of 707s - same solution to a much worse problem
illustrations and explanation here:
Noise Control/Supression
andrew
  Reply With Quote
The Following 2 Users Say Thank You to lightflite For This Useful Post:
cfg83 (10-21-2010), Piwoslaw (10-21-2010)
Old 10-21-2010, 12:28 PM   #6 (permalink)
EcoModding Lurker
 
Join Date: Aug 2010
Location: New Mexico
Posts: 41
Thanks: 3
Thanked 3 Times in 3 Posts
Their usage is a balance between performance (thrust) and noise (i.e. a trade off). Mixers have been around since the 60's (the sooner you get the flow mixed the quieter the engine is). What's new is the use of them on the fan cowl. The chevrons increase drag but decrease noise. Noise is a major issue these days. Ecomodders have no use for "sawtooth edges".
  Reply With Quote
Old 10-21-2010, 01:07 PM   #7 (permalink)
EcoModding Lurker
 
Join Date: Mar 2010
Location: Leicester UK
Posts: 16
Thanks: 0
Thanked 2 Times in 1 Post
stealth radar dissipators?
andrew
  Reply With Quote
Old 10-21-2010, 03:36 PM   #8 (permalink)
aero guerrilla
 
Piwoslaw's Avatar
 
Join Date: Oct 2008
Location: Warsaw, Poland
Posts: 3,745

Svietlana II - '13 Peugeot 308SW e-HDI 6sp
90 day: 58.1 mpg (US)
Thanks: 1,324
Thanked 749 Times in 476 Posts

Attached Thumbnails
Click image for larger version

Name:	b2a.jpg
Views:	560
Size:	61.2 KB
ID:	7178  
__________________
e·co·mod·ding: the art of turning vehicles into what they should be

What matters is where you're going, not how fast.

"... we humans tend to screw up everything that's good enough as it is...or everything that we're attracted to, we love to go and defile it." - Chris Cornell


[Old] Piwoslaw's Peugeot 307sw modding thread
  Reply With Quote
Reply  Post New Thread




Similar Threads
Thread Thread Starter Forum Replies Last Post
sawtooth trailing edge lunarhighway Aerodynamics 61 10-22-2020 03:03 PM
dual two cylinder engines dcb EcoModding Central 25 04-16-2010 01:56 AM
Getting 45 MPG at 207 MPH .... can you pulse and glide an airplane? MetroMPG Hypermiling / EcoDriver's Ed 43 03-03-2010 03:20 AM
Poll for Americans: What about Diesel engines? hal9999 General Efficiency Discussion 117 01-07-2009 08:23 AM
The Cars GM Needs To Make Big Dave General Efficiency Discussion 66 01-05-2009 04:18 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