http://www.indolink.com/SciTech/fr071904-060858.php
Prof. Anjaneyulu Krothapalli Improves Stealth Fighters
by: Francis C. Assisi
Science & Technology - Thursday, July 29, 2004
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Boston, 19 July -- Beginning next year, noise suppression technology developed at Florida State University by Prof Anjaneyulu Krothapalli at the Fluid Mechanics Research Laboratory will become standard equipment on U.S. Navy F-18 fighter jets.
Krothapalli, the Don Fuqua Eminent Scholar in Engineering and Science at FSU and the chairman of the university´s department of mechanical engineering, has been developing technologies for achieving quieter jet engines. With a $2.6 million grant from the Office of Naval Research Krothapalli has found a method to dampen the noise created by warplanes´ screaming jets.
Fighter planes with high-performance jet engines roar during takeoff and landing, and people living near military bases often complain about the noise. Residents living near a Virginia Navy base complained about new F-18s making a lot of noise during practice landings and takeoffs, and Krothapalli says he hopes to reduce the noise pollution.
"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."
Also a recent study conducted in Germany has found further evidence that exposure to chronic noise can have serious health, learning and motivational effects in children and adults.
DAMPENING JET NOISE
Krothapalli has found that siphoning 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 can reduce the jet noise. 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.
"Injecting the high-pressure air through very small micro jets into the tailpipe of an engine will reduce the noise," Krothapalli said. "It doesn´t reduce all the noise generated by the jets, just the one that is most annoying to people. It kills it."
Krothapalli works in a $1.2 million noise-suppression lab. It´s a bunker-like building that uses air compressed at 2,000 pounds per square inch to simulate a rocket or jet engine being fired from an engine. The noise-measuring chamber is outfitted with multiple microphones placed among sound-dampening foam, withstanding temperatures of up to 400 degrees Fahrenheit.
So far Krothapalli, with the help of his students, has achieved a 5-decibel noise cut -- a reduction of 50 percent. He said he hopes to achieve a 10-decibel noise reduction by the end of the year.
The US military believes the technology may have other uses. NASA, and industrial R&D giants such as McDonnell Douglas and General Electric have begun field tests using the technology.
"Boeing has asked us to look into applying the same technology into what they call unmanned combat air vehicles. So we´re applying that technology towards that. And another [at] NASA Ames is funding us to look at the rocket noise," Krothapalli said
"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.
STEALTH TECHNOLOGY
Without knowing it at the time, Krothapalli says he developed some of the data that eventually produced the F-117´s Stealth bomber’s rectangular exhaust system. It was during his doctoral student days at Stanford, where he worked a research project funded by NASA and the Air Force. Only years later did he learn of his contribution to the F-117 project, he said.
The plane´s sharply angled features included a jet exhaust nozzle that exhibited a striking departure from conventional designs--instead of being round, it was rectangular.
For aircraft where stealth is important--obviously fighters and bombers--the role of round-nozzled jet engines is so much military history, says Krothapalli.
As much as the stealth considerations involved, it´s the aerodynamic aspects of jet nozzle design that makes some of Krothapalli´s latest work a fascinating engineering challenge. It´s a new twist to what aerospace engineers call thrust vectoring. The idea is to be able to fly and maneuver an aircraft simply by changing the direction (the vector) of the jet thrust, or exhaust.
Since coming to Tallahassee, Krothapalli has won increasing support from both industry and the government to develop and test new configurations of jet nozzles. Most of the research has been through contracts with General Electric. The company recently underwrote the lab´s work in designing and testing a diamond-shaped nozzle.
ENGINEERS VS SCIENTISTS
Krothapalli believes that Florida State is clearly a leader in one fundamental aspect of aerospace engineering--fluid mechanics. "We´re certainly in the top five nationally in fluid mechanics research. The only other places that come close to us are Stanford, Cal Tech, Michigan and Georgia Tech."
Krothapalli spelled out his views on scientists versus engineers this way: "One of the big problems we´ve had in the last 20 or 30 years is that all engineers wanted to be scientists--mostly physicists--instead of engineers. At Stanford, fundamental research was all I did, and what all my professors did, too, with never a thought of putting any of it to use.
"When I graduated, I looked around and realized that this was not what the country needed. In fact, I felt quite strongly that by not applying what we were learning in basic research we were ruining the nation.
"So I came to Florida State with my mind made up--I wanted to do something different, something unconventional. I wanted to build a lab expressly designed to develop technologies that could be transferred to industry right away. That´s essentially what we´ve done, and it´s paying off."
Proud of his lab´s record in meeting the research needs of industry, Krothapalli is equally proud of the caliber of graduate students attracted to his program in fluid mechanics. At this writing, the lab´s team includes 10 students working toward Ph.D.s, and another four working toward masters.
"We´ve got some very sharp people around here. We do our best to expose them to what they´ll encounter when they leave…when they leave here, our graduates will be applied- oriented. If they aren´t, then we´ve failed to educate them properly."
Krothapalli explains: "These people are engineers, not scientists; they are highly skilled at taking basic scientific knowledge and translating it into things that will directly benefit society.
"That´s what real engineers do, and it´s exactly what this program is all about."
Dr. Krothapalli received his Ph.D. degree from Stanford University in 1979 under the guidance of Professors Krishnamurti Karamcheti in the department of aeronautics and astronautics. Among his Indian collaborators are Profs. Vijay Arakeri and G.S. Bhat of the Indian Institute of Science
With recent resurgence of interest in alternative energy technologies, Krothapalli has started a new university wide center (Sustainable Energy Science & Engineering Center) to focus on sustainable energy systems using solar radiation. Initially, the focus of the research activity is on solar electricity generation, including electrolytic hydrogen production and storage and fuel cells.
