Featured Research

from universities, journals, and other organizations

Fighting Sound With Sound, New Modeling Technique Could Quiet Aircraft

Date:
February 24, 2006
Source:
Princeton University
Summary:
Newly published research by a Princeton engineer suggests that understanding how air travels across the sunroof of a car may one day make jet engines less noisy. This research may ultimately lead to modifications of jet engines to make them quieter as they fly over neighborhoods. It also has important military applications.

A screenshot of Rowley's cavity-flow simulations.
Credit: Image courtesy of Princeton University

Newly published research by a Princeton engineer suggests that understanding how air travels across the sunroof of a car may one day make jet engines less noisy.

Clarence Rowley, an assistant professor of mechanical and aerospace engineering, did not actually conduct his experiments on a sunroof. Rather, he and collaborators used computer simulations and subsonic wind tunnels at Princeton and at the U.S. Air Force Academy in Colorado Springs, to experiment with models that resembled the open sunroof of a speeding car.

Rowley showed that his simulations could predict how sunroof air flow would behave under various conditions. Just as important, he figured out how to negate the noise that it produced. Rowley's findings are published in the January issues of the Annual Reviews of Fluid Mechanics and the Journal of Fluid Mechanics.

This research may ultimately lead to modifications of jet engines to make them quieter as they fly over neighborhoods. The research also has important military applications. For example, it would enable stealth aircraft to fly faster because it would reduce buffeting when doors of a weapons bay are open. And Rowley is currently using insights garnered from this work to help develop ultrasmall, unmanned aircraft that would be useful for surveillance or search-and-rescue missions.

Rowley's task was not an easy one. To precisely model the air current would have required solving more than 2 million equations. Solving these equations by themselves is not too great a challenge for today's computers, but manipulating them to figure out how to make the air flow quieter would require far more calculation.

"Basically, it would have been computationally impossible," Rowley said.

So he took an unusual approach. He selectively picked mathematical tools from three different disciplines -- dynamical systems, control theory and fluid mechanics -- and yoked them together to come up with a computer simulation that, by solving only four equations, could approximate almost identically the answer to the problem that normally would have taken 2 million equations to figure out.

Once he figured out the model, Rowley fought sound with sound.

Rowley focused on the layer of air just above his simulated sunroof, where faster moving air "shears" away from slower moving air. "This shear layer flaps and up and down like a flag in the wind," Rowley said.

Each time this layer of air flaps down and hits the leading edge of the sunroof, it makes what scientists call an acoustic wave (most people just call this noise).

In his computer model and in wind-tunnel experiments with collaborator David Williams of the Illinois Institute of Technology, Rowley placed a speaker at the front end of his sunroof and a microphone at the rear of the roof. The microphone monitored the flapping and fed this information to a controller. The controller, relying on predictions from Rowley's model, then sent an opposing signal to the speaker, which is not much different than one found on a typical stereo.

"The physical mechanism is actually very simple," Rowley said. "When the flag wants to push up we pull it down; when it wants to pull up we push it down. This is what makes it quiet."

The same principles can be applied to quiet down a jet engine or silence the open bays of a military craft. Rowley does not have immediate plans to promote the technique to the automotive industry to make quieter sunroofs, but he is is applying the knowledge to a new project involving tiny unmanned airplanes.

As part of a joint research project led by Caltech, Rowley is doing computational modeling, as well as building a controller, for aircraft that are the size of a typical model airplane. One day, the researchers hope, these aircraft will be able to fly with the speed of a bird and maneuver themselves with the three-dimensional agility of an insect.

###

This work was funded by the U.S. Air Force Office of Scientific Research.

Full citations for the Rowley papers:

Rowley, C.W. and D.R. Williams [2006] Dynamics and control of high-Reynolds number flow over cavities. Annual Reviews of Fluid Mechanics, 38:251-276, Jan 2006

Rowley, C.W., D.R. Williams, T. Colonius, R.M. Murray, and D.G. MacMartin [2006] Linear models for control of cavity flow oscillations. J. Fluid Mech., 547:317-330, Jan 2006.


Story Source:

The above story is based on materials provided by Princeton University. Note: Materials may be edited for content and length.


Cite This Page:

Princeton University. "Fighting Sound With Sound, New Modeling Technique Could Quiet Aircraft." ScienceDaily. ScienceDaily, 24 February 2006. <www.sciencedaily.com/releases/2006/02/060224102913.htm>.
Princeton University. (2006, February 24). Fighting Sound With Sound, New Modeling Technique Could Quiet Aircraft. ScienceDaily. Retrieved August 1, 2014 from www.sciencedaily.com/releases/2006/02/060224102913.htm
Princeton University. "Fighting Sound With Sound, New Modeling Technique Could Quiet Aircraft." ScienceDaily. www.sciencedaily.com/releases/2006/02/060224102913.htm (accessed August 1, 2014).

Share This




More Matter & Energy News

Friday, August 1, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Britain Testing Driverless Cars on Roadways

Britain Testing Driverless Cars on Roadways

AP (July 30, 2014) — British officials said on Wednesday that driverless cars will be tested on roads in as many as three cities in a trial program set to begin in January. Officials said the tests will last up to three years. (July 30) Video provided by AP
Powered by NewsLook.com
7 Ways to Use Toothpaste: Howdini Hacks

7 Ways to Use Toothpaste: Howdini Hacks

Howdini (July 30, 2014) — Fresh breath and clean teeth are great, but have you ever thought, "my toothpaste could be doing more". Well, it can! Lots of things! Howdini has 7 new uses for this household staple. Video provided by Howdini
Powered by NewsLook.com
Amid Drought, UCLA Sees Only Water

Amid Drought, UCLA Sees Only Water

AP (July 30, 2014) — A ruptured 93-year-old water main left the UCLA campus awash in 8 million gallons of water in the middle of California's worst drought in decades. (July 30) Video provided by AP
Powered by NewsLook.com
Smartphone Powered Paper Plane Debuts at Airshow

Smartphone Powered Paper Plane Debuts at Airshow

AP (July 30, 2014) — Smartphone powered paper airplane that was popular on crowdfunding website KickStarter makes its debut at Wisconsin airshow (July 30) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins