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Benefits Of Serrated Engine Cowlings?  
User currently offlineBrenintw From Taiwan, joined Jul 2006, 1720 posts, RR: 1
Posted (8 years 1 week 2 days 20 hours ago) and read 6745 times:

Looking at the pictures of the 787 and the A350, I've noticed that they're all shown with serrated engine exhausts/cowlings/things at the back (I'm not actually sure what they are).

What are the benefits of this?

Thanks


I'm tired of the A vs. B sniping. Neither make planes that shed wings randomly!
4 replies: All unread, jump to last
 
User currently offlineRichardPrice From , joined Dec 1969, posts, RR:
Reply 1, posted (8 years 1 week 2 days 18 hours ago) and read 6729 times:

Properly designed, they can aid in the mixing of the air from the engine as it exits into the outside airflow. This can reduce drag.

User currently offlineBrendows From Norway, joined Apr 2006, 1020 posts, RR: 4
Reply 2, posted (8 years 1 week 2 days 18 hours ago) and read 6721 times:

Quoting RichardPrice (Reply 1):
Properly designed, they can aid in the mixing of the air from the engine as it exits into the outside airflow. This can reduce drag.

I believe that these chevrons actually increase drag a little bit. And they reduce the available thrust, that was at least what Airbus said in a news article when they were asked why they didn't have chevrons on one of the former versions of the A350. The main purpose with these chevrons is to reduce engine noise, by mixing the bypass/core airflow and bypass air with the air passing around the engine.
The engines on the 787 and 748 will be equipped with chevrons, but I haven't seen any pictures from Airbus where the A350 has chevrons.


User currently offlineTepidHalibut From Iceland, joined Dec 2004, 210 posts, RR: 6
Reply 3, posted (8 years 1 week 2 days 17 hours ago) and read 6708 times:

Quoting Brenintw (Thread starter):
What are the benefits of this?

Quite simply, noise reduction.

In 2001, Boeing and RR went flight testing on the B777, and tried a number of novel noise technologies. One of the most promising was the serrated hot / cold nozzles. I guess AI have done similat testing / analysis and arrived at the same conclusion.


..or have a Google for QTD / Boeing / RR etc


User currently offlineJetlife2 From United States of America, joined Jul 2006, 221 posts, RR: 25
Reply 4, posted (8 years 1 week 2 days 16 hours ago) and read 6687 times:

There was a follow-on program called QTD2 which used a 777-300ER in 2005. Both fan and core chevrons were evaluated as well as splice-less inlet and landing gear fairings. It's described here:

http://www.boeing.com/news/frontiers...archive/2005/december/ts_sf07.html

Chevrons are a design balance between benefits of mixing (noise reduction) and cost in terms of drag and fuel burn. In QTD2 actuating chevrons were studied with good success. In this version the chevrons are in the stream at takeoff (for noise reduction at high power) then out of the stream at cruise (for best fuel burn at low power). Very good idea that will probably make their way on to some airplane in the future.


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