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Transonic drag of several jet-noise suppressors

Description: Investigation of the aerodynamic drag of several jet noise suppressors over a range of Mach numbers and several nozzle pressure ratios. The least drag was caused by lobe-type suppressors. The eight-lobe nozzle with ejector caused the greatest amount of drag.
Date: April 1958
Creator: North, Warren J.
Partner: UNT Libraries Government Documents Department

Ground reflection of jet noise

Description: Report presenting the effect of a reflecting plane on the propagation of jet noise investigated theoretically and experimentally. The primary focus of the study is to determine the free-field spectrum of subsonic-jet noise from measurements made in the presence of a ground plane.
Date: April 1958
Creator: Howes, Walton L.
Partner: UNT Libraries Government Documents Department

Experiments to Determine Neighborhood Reactions to Light Airplanes With and Without External Noise Reduction

Description: "The work reported was part of a program of experimentation with external noise reduction on light airplanes. This particular study was in effect a byproduct survey conceived to utilize already available equipment and personnel to further the findings of the original research and to determine reactions in populated neighborhoods to light aircraft with and without noise-reduction equipment. The findings indicate that at the 10 sites within and about metropolitan Boston the degree of noise reduction previously found to be aerodynamically and structurally feasible did eliminate substantially all neighborhood objections to noise per se" (p. 1155).
Date: May 5, 1950
Creator: Elwell, Fred S.
Partner: UNT Libraries Government Documents Department

Experiments in External Noise Reduction of Light Airplanes

Description: This note is part of a program with the objective of finding practical ways of reducing the external noise level of light airplanes in order to make them less objectionable to people on the ground. The current report covers noise measurements on standard light airplanes and on similar airplanes equipped with engine mufflers, propeller reduction gears, and propellers with various numbers of blades and blade shapes. The results indicate that reductions in noise level were found to result from muffling the engine and from reducing propeller tip speed and blade loading.
Date: May 1950
Creator: Beranek, Leo L.; Elwell, Fred S.; Roberts, John P. & Taylor, C. Fayette
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

Investigation of Jet-Engine Noise Reduction by Screens Located Transversely Across the Jet

Description: Note presenting an investigation of screens placed transversely across the jet as a noise-reduction device on a full-scale turbojet engine to determine the effect on the sound field of screen mesh, wire diameter, and screen location. The investigation showed that the screens, when properly placed, lower the noise level in the area downstream of the jet exit and increase it upstream.
Date: May 1955
Creator: Callaghan, Edmund E. & Coles, Willard D.
Partner: UNT Libraries Government Documents Department

Investigation of far noise field of jets 2: comparison of air jets and jet engines

Description: Report presenting a comparison of the noise generation of air jets and turbojet engines under similar free-flight conditions. Results regarding a comparison of the sound power, afterburner data, spectrum measurements, noise data for engine thrust, and frequency distribution for the two engines are provided.
Date: January 1956
Creator: Coles, Willard D. & Callaghan, Edmund E.
Partner: UNT Libraries Government Documents Department

Noise From Two-Blade Propellers

Description: "The two-blade propeller, one of the most powerful sources of sound known, has been studied with the view of obtaining fundamental information concerning the noise emission. In order to eliminate engine noise, the propeller was mounted on an electric motor. A microphone was used to pick up the sound whose characteristics were studied electrically. The distribution of noise throughout the frequency range, as well as the spatial distribution about the propeller, was studied. The results are given in the form of polar diagrams. An appendix of common acoustical terms is included" (p. 359).
Date: January 17, 1935
Creator: Stowell, E. Z. & Deming, A. F.
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

The Effect of White Noise on a Visual Discrimination Task

Description: Previous studies have demonstrated that in some instances certain types of auditory stimulation have facilitated a subject's ability at a visual task while in other instances, the subject's ability has been inhibited. The primary objective of this experiment was to investigate the effect of auditory stimulation upon a subject's performance on a visual discrimination task.
Date: January 1969
Creator: Smith, James Larry
Partner: UNT Libraries

Spontaneous Brain Activity as a Source of Ideal 1/f Noise

Description: In this article, the authors study the electroencephalogram (EEG) of 30 closed-eye subjects with a technique of analysis recently proposed to detect punctual events signaling rapid transitions between different metastable states.
Date: December 18, 2009
Creator: Allegrini, Paolo; Menicucci, Danilo; Bedini, Remo; Fronzoni, Leone; Gemignani, Angelo; Grigolini, Paolo et al.
Partner: UNT College of Arts and Sciences

Noise survey of a 10-foot four-blade turbine-driven propeller under static conditions

Description: Report presenting an analysis of overall sound-level measurements and frequency analyses of tape recordings of the noise emitted from a 10-foot-diameter, four-blade propeller mounted on a turbine-powered vehicle under static conditions at stations equally spaced on a 75-foot-radius circle. Results regarding the distribution of overall sound-pressure levels and distribution of sound-pressure levels for the first four propeller harmonics are provided.
Date: July 1955
Creator: Kurbjun, Max C.
Partner: UNT Libraries Government Documents Department

Intensity, scale, and spectra of turbulence in mixing region of free subsonic jet

Description: Report presents the results of the measurements of intensity of turbulence, the longitudinal and lateral correlation coefficients, and the spectra of turbulence in a 3.5-inch-diameter free jet measured with hot-wire anemometers at exit Mach numbers from 0.2 to 0.7 and Reynolds numbers from 192,000 to 725,000.
Date: April 24, 1956
Creator: Laurence, James C.
Partner: UNT Libraries Government Documents Department

Investigation of noise field and velocity profiles of an afterburning engine

Description: Report presenting sound pressure levels, frequency spectrum, and jet velocity profiles for an engine-afterburner combination at various values of afterburner fuel-air ratio. Lower sound pressure levels were obtained from a current fighter aircraft with a different afterburner configuration. Results regarding the jet temperature, jet Mach number and velocity, and sound measurements are provided.
Date: September 24, 1954
Creator: North, Warren J.; Callaghan, Edmund E. & Lanzo, Chester D.
Partner: UNT Libraries Government Documents Department

Acoustic, thrust, and drag characteristics of several full-scale noise suppressors for turbojet engines

Description: From Introduction: " Considerable analytical and experimental research has been done to find means of reducing the noise levels of the turbojet transports. Noise levels can be decreased by engine redesign to reduce the jet-exit velocity (ref. 1), proper flight-climb techniques (ref. 2), and the use of noise-suppression exhaust nozzles (refs. 3 to 5). The present report is concerned with the last method."
Date: April 1958
Creator: Ciepluch, Carl C.; North, Warren J.; Coles, Willard D. & Antl, Robert J.
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

Preliminary flight survey of aerodynamic noise on an airplane wing

Description: Report presenting a brief series of airplane-wing aerodynamic-noise and boundary-layer-profile measurements made in flight as part of an extended investigation of boundary-layer noise. Results regarding the boundary layer data and ratio of root-mean-square sound pressure to the dynamic pressure are provided.
Date: March 2, 1956
Creator: Mull, Harold R. & Algranti, Joseph S.
Partner: UNT Libraries Government Documents Department