A LARGE HEMIANECHOIC ENCLOSURE FOR COMMUNITY-COMPATIBLE AEROACOUSTIC TESTING OF AIRCRAFT PROPULSION SYSTEMS

A large hemi-anechoic (sound-absorbing walls and acoustically hard flo or) noise control enclosure was erected around a complex of test stand s at the NASA Lewis Research Center in Cleveland, Ohio. This new state -of-the-art Aeroacoustic Propulsion Laboratory provides an all-weather , semisecure test environment while minimizing noise levels in surroun ding residential neighborhoods. The 39.6-m-diam (130-ft-diam) geodesic dome houses the new nozzle aeroacoustic test rig, an ejector-powered Mach 0.3 free-jet facility for acoustical testing of supersonic aircra ft exhaust nozzles and turbomachinery. A multiaxis, force-measuring po wered lift facility stand for testing short-takeoff vertical-landing v ehicles is also located in the dome. The design of the Aeroacoustic Pr opulsion Laboratory efficiently accommodates the research functions of the two separate rigs, while providing a specialized environment for measuring far-field sound-pressure levels from the nozzle aeroacoustic test rig. Sound-absorbing fiberglass wedges on the interior surface o f the dome provide a hemi-anechoic environment. The Aeroacoustic Propu lsion Laboratory is the first known geodesic dome structure to incorpo rate transmission-loss properties as well as interior absorption in a free-standing community-compatible, hemi-anechoic test facility.