F-18 suppresses engine noise

Listening up in the Navy means not just paying attention but being cognizant of the deafening sound emanating from F-18 fighter jets that sometimes fly over residential areas. Starting in December of 2002, noise generated from F-18 engines at full throttle will approach half of what it was at the start of the year thanks to a patent-pending technology developed by Anjaneyulu Krothapalli, the chair of Florida State University's Department of Mechanical Engineering. He reduces noise by siphoning off some of the air travelling through the jet engine and forcing it at high pressure through multiple microjets that fan around the engine's large exhaust. Noise is reduced when the small jets of high-pressure air hit the large stream of lower pressure engine exhaust. "Right now we are trying to figure out the optimum number of microjets that will best suppress noise," says Krothapalli. So far he has achieved a 5-decibel (dB) reduction, but he hopes to achieve a 10-dB noise reduction soon. Krothapalli also reduces noise by forcing water and other liquids through the microjets in place of air. His noise suppression lab uses compressed air at 2,000 psi for simulating running jet engines. In a separate chamber, he measures noise. For more information, call Krothapalli at (850) 644-5885 or (850) 410-6338.