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Noise survey of a full-scale supersonic turbine-driven propeller under static conditions

Description: Report presenting an analysis of the overall sound-pressure levels and frequency spectra of the noise emitted from a full-scale, 7.2-foot-diameter, 3500-rpm, three-blade, supersonic propeller mounted on a turbine-powered airplane under static conditions at stations about the propeller at a 100-foot radius. Variations in power produced the variations in overall sound-pressure levels predicted by theory.
Date: July 1957
Creator: Kurbjun, Max C.
Partner: UNT Libraries Government Documents Department

Screen-type noise reduction devices for ground running of turbojet engines

Description: Report presenting testing of the use of screens placed across the jet as a means of suppressing jet noise during ground running, which was somewhat offset by increased noise levels ahead of the engine. Air-jet tests showed negligible reduction in sound generation with additional screens. The large reductions obtained by using screens show that noise generated inside the engine by the turbine or combustion contribute only a minor part of the total noise.
Date: July 1957
Creator: Coles, Willard D. & North, Warren J.
Partner: UNT Libraries Government Documents Department

Near Noise Field of a Jet-Engine Exhaust

Description: From Summary: "Aircraft structures located in the near noise field of a jet engine are subjected to extremely high fluctuating pressures that may cause structural fatigue. Studies of such structures have been limited by lack of knowledge of the loadings involved. The acoustic near field produced by the exhaust of a stationary turbojet engine having a high pressure ratio was measured for a single operating condition without burning. The maximum overall sound pressure without afterburning was found to be about 42 pounds per square foot along the jet boundary in the region immediately downstream of the jet-nozzle exit."
Date: 1957
Creator: Howes, Walton L.; Callaghan, Edmund E.; Coles, Willard D. & Mull, Harold R.
Partner: UNT Libraries Government Documents Department

Survey of the acoustic near field of three nozzles at a pressure ratio of 30

Description: The sound pressures radiating from the exhaust streams of two convergent-divergent and one convergent nozzle were measured. Exit diameters were 1.206 in. for the expanded nozzle and 0.625 in. for the convergent nozzle. The results are presented in a series of contour maps of overall and fine 1/3-octave-band sound pressures. The location of the source of the noise in each 1/3-octave band in the frequency range of 30 to 16,000 cps and the total power radiated were determined and compared with those of subsonic jets.
Date: April 1957
Creator: Mull, Harold R. & Erickson, John C., Jr.
Partner: UNT Libraries Government Documents Department

Full-Scale Investigation of Several Jet-Engine Noise-Reduction Nozzles

Description: A number of nozzles which use the mixing interference of adjacent jets for noise suppression were investigated. Reductions in sound power of nearly 70 percent (5 db) with thrust losses of 1 percent were achieved. A method of calculating the limiting frequency affected by this type of suppression nozzle, that is , multiple-slot nozzles, is presented. Data are shown which indicate that further large reductions in sound power are not likely with mixing-interference nozzles.
Date: April 1957
Creator: Coles, Willard D. & Callaghan, Edmund E.
Partner: UNT Libraries Government Documents Department

Far Noise Field of Air Jets and Jet Engines

Description: "An experimental investigation was conducted to study and compare the acoustic radiation of air jets and jet engines. A number of different nozzle-exit shapes were studied with air jets to determine the effect of exit shape on noise generation. Circular, square, rectangular, and elliptical convergent nozzles and convergent-divergent and plug nozzles were investigated" (p. 1).
Date: 1957
Creator: Callaghan, Edmund E. & Coles, Willard D.
Partner: UNT Libraries Government Documents Department

Full-Scale Investigation of Several Jet-Engine Noise-Reduction Nozzles

Description: "A number of noise-suppression nozzles were tested on full-scale engines. In general, these nozzles achieved noise reduction by the mixing interference of adjacent jets, that is, by using multiple-slot-nozzles. Several of the nozzles achieved reductions in sound power of approximately 5 decibels (nearly 70 percent) with small thrust losses (approx. 1 percent). The maximum sound-pressure level was reduced by as much as 18 decibels in particular frequency bands" (p. 1249).
Date: January 22, 1957
Creator: Coles, Willard D. & Callaghan, Edmund E.
Partner: UNT Libraries Government Documents Department