CONTACT: Anjaneyulu Krothapalli(850) 644-5885, or (850) 410-6338
By Jeffery SeayMarch 2002
LISTEN UP: AN FSU PROFESSOR HAS DEVELOPED A QUIETER FIGHTER JET ENGINE
TALLAHASSEE, Fla.-Beginning this December, noise suppression technology developed at Florida State University will become standard equipment on U.S. Navy F-18 fighter jets. The technology, which is patent-pending, was developed at the FSU Fluid Mechanics Research Laboratory under the direction of Anjaneyulu Krothapalli.
Krothapalli, the Don Fuqua Eminent Scholar in Engineering and Science at FSU and the chairman of the university's department of mechanical engineering, is developing technologies that achieve a quieter jet engine in a lab that is unlike any other in the nation.
"Nobody wants to live near military bases that fly jet fighters, but residential communities do spring up near them," Krothapalli said. "There is a need to provide jet noise mitigation to minimize the environmental noise exposure of military aircraft, which are louder than commercial jets. The public may not accept the operation of these military jets so close to commercial and residential complexes unless their noise can be effectively controlled."
As air is forced through a jet engine, it accelerates so that its pressure is considerably lower than the high pressure within the engine by the time the air is exhausted. Krothapalli has found that noise can be reduced by cyphoning off some of the air traveling through the engine and forcing it, at high pressure, through multiple microjets that fan around a jet engine's large exhaust. When the small jets of high pressure air hit the large stream of relatively low pressure jet exhaust, a reduction in noise is achieved. Even more noise is suppressed by forcing liquid, such as water or an aqueous polymer, through the microjets.
So far, Krothapalli has achieved a 5 decibel (dB) noise reduction, with 6 dB representing a 50 percent reduction. He hopes to achieve a 10 dB noise reduction by year's end.
"Right now, we're trying to figure out the optimum number of microjets and the optimum level of water or air pressure that will best suppress this noise," Krothapalli said.
Another method, active noise cancellation, uses opposite sound waves to cancel the sound waves of a particular noise. However, this method works best on low amplitude, low frequency sounds.
"We're trying to adapt this method to high frequency, broadband sounds," Krothapalli said. "Our research into this area isn't as far along, but shows promise."
The research is being funded by a $2.6 million, three-year Office of Naval Research grant. The work is further funded by NASA Ames Research Center and Boeing to apply the technologies to civilian aircraft.
Krothapalli conducts his investigations in a $1.2 million noise suppression lab that is a bunker-like building with a mechanism that uses air compressed at 2,000 pounds per square inch to simulate a rocket or jet engine being fired, and a separate chamber that measures the noise levels of the firing. The building is equipped with heat and gas sensors that trigger pressure-release valves and other safety measures if trouble is detected. The noise measuring chamber is outfitted with multiple microphones placed among sound-dampening foam that can withstand temperatures of 400 degrees Fahrenheit.
FSU mechanical engineering Professor Luiz Lourenco, Assistant Professor David Cartes and Visiting Professor Vijay Arakeri, and graduate students Brent Greska and Tom Joseph participate in the research program.
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