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The Near Noise Field of Static Jets and Some Model Studies of Devices for Noise Reduction

出版	National Advisory Committee for Aeronautics, 1954
URL	http://books.google.com.hk/books?id=6b8b6BCaZCoC&hl=&source=gbs_api
EBook	FULL_PUBLIC_DOMAIN

註釋Experimental studies of the pressure fluctuations near jet exhaust streams were made during unchoked operation of a turbojet engine and a 1-inch-diameter high-termperature model jet and during choked operation of various sizes of model jets with unheated air. The tests for unchoked operation indicate a random spectrum of rather narrow band width which varies in frequency content with axial postion along the jet. Pressure surveys from the model tests along lines parallel to the 15 degree jet boundary indicate that the station of greatest pressure fluctuations is determined by the jet velocity and the radial distance, with a tendency tof the maximum shift downstream as either parameter is increased. From model tests the magnitude of the fluctuations appears to increase as about the second power of jet velocity at points just outside the jet boundary and as increasingly higher powers of jet velocity as distance from the boundary is increased. A laboratory method of noise reduction with model jets was found to produce large decreases in the magnitude of the lower-frequency components of the spectra and thereby also to reduce the total radiated energy.