摘要:

The motion of the gas in and near a tube open at one end and closed at the other by a piston driven in nearly sinusoidal motion is investigated. Experiments disclose that when the frequency of the piston motion is near the fundamental acoustic resonance frequency of the gas column an intermittent air jet associated with a system of vortex rings is expelled from the tube's open end. This results in an appreciable average thrust on the tube which, however, is much less than might be expected from purely acoustic considerations. A theoretical analysis has been made which takes account of the intermittent vortex and jet formation, as well as of the acoustic radiation field. The analysis leads to formulas for the average thrust and power dissipation and to a relation between the driving frequency and the amplitude of the gas motion at the open end. An empirical parameter κ which represents the fraction of energy dissipated in vortex motion appears in these formulas. It is found possible to evaluate this parameter in terms of the observed thrust at resonance. From this datum the curve of thrustversusdriving frequency is calculated and is found to agree well with experiment.

ISSN:0001-4966    

DOI:10.1121/1.1907916

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

Recent experimental studies revealed a close connection between spontaneous excitation of organ‐pipe oscillations by flames propagating in tubes and flame front instability characterized by cellular structure. On the basis of these observations a dominant mechanism of vibratory flame movement is proposed, consisting of the following two steps:1. As a consequence of acceleration instability, the oscillation of the gas column alternatingly distorts and flattens the flame front, thus creating the observed vibration‐induced cell structure.2. The distortions of the flame front cause in turn periodic changes of flame surface area and therefore of burning rate. Spontaneous oscillations are excited if the phase relation between burning rate variation and pressure oscillation is favorable.In this paper only the first step is analyzed. The linearized treatment yields stability limits in terms of dimensionless parameters representing amplitude and frequency of gas column oscillation and wavelength of flame front distortion. The properties of the flame front entering into the analysis are the ratio of densities of unburned and burned gases, the burning velocity of the plane flame front, and a characteristic length that determines its stability in the absence of oscillations. Results in qualitative agreement with experimental observations are derived.

ISSN:0001-4966    

DOI:10.1121/1.1907918

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

The sound fields induced in a real gas by boundary temperature variations are examined to illustrate how the pressure, temperature, and vorticity modes of motion interact. The pressure mode describes the irrotational propagation of longitudinal disturbances, the temperature mode, convective heat diffusion, and the vorticity mode, the diffusion of vorticity introduced at boundaries by the no‐slip condition (boundary layer). The plane sound wave due to an instantaneous wall temperature rise is a sharp pulse, traveling at sonic speed and proportional to the inverse fourth root of the acoustic Reynolds number based on distance traveled; its thickness grows as the square root of elapsed time. Along a wall, it generates a boundary layer whose friction coefficient is proportional to the inverse square root of the acoustic Reynolds number based on distance from the front. The resulting effective wall slope induces a secondary circular pressure pulse generated by the foot of the plane wave; because this source moves at sonic speed, a pressure singularity appears there, due to the contributions piled up since the beginning of the motion.

ISSN:0001-4966    

DOI:10.1121/1.1907920

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

Some sample experimental results relating to the nature and sources of noise in jets are presented. Previous work is extended to include more detailed information about the jet structure. In this regard noise data are compared for jets having somewhat different turbulence profiles. High temperature jets are noted to have different radiation patterns and to be more efficient noise radiators than low temperature jets. Noise data for the high temperature supersonic jet of a rocket engine are included for comparison with those of subsonic jets. Some experiments have shown the noise levels at the low frequencies can be markedly reduced by the use of grids in the jet stream.

ISSN:0001-4966    

DOI:10.1121/1.1907922

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

The extension of classical statistical mechanical methods to non‐Hamiltonian systems is discussed. The statistical equilibrium of a confined adiabatically compressible fluid is examined on the basis of a generalized phase space representation, and it is found that there exists a tendency toward equipartition of energy between compressive and vorticity modes which is modified by the viscous dissipation forces. The application of the method to determining nonequilibrium energy transfers between acoustic modes and vorticity modes is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1907924

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

An approximate method is developed for the estimation of the acoustic power frequency spectrum of the sound generated from isotropic turbulence. The method is based on a hypothetical model for the sound sources, originally produced by Lighthill, consisting of an assembly of quadrupoles extending over the region of turbulence.

ISSN:0001-4966    

DOI:10.1121/1.1907926

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

An analysis of sound production by vortices in air jets is given. Specifically, the flow of air through sharp‐edged orifices is considered, and it is shown how the results of Anderson on the excitation of jet‐tones under these conditions may be explained. The analysis also covers excitation of resonant cavities by the jet, a phenomenon giving rise to pipe‐tones.

ISSN:0001-4966    

DOI:10.1121/1.1907928

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

This paper presents some recent data on the acoustical behavior of certain components of engine test cell structures. These data include information on (a) the directivity patterns of vertical stacks and (b) the noise reduction provided by some water‐spray systems, (c) the Soundstream absorber, and (d) a 90° vertical bend.

ISSN:0001-4966    

DOI:10.1121/1.1907929

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

It is difficult to ascertain the absolute loudness of typing noise by objective measurement. However, it may be practical to use such measurement to determine the loudness level difference in a comparison of the sounds from two typewriters. The requirements that must be met by an accurate measurement technique depend on the degree of accuracy required. Information pertaining to the accuracy necessary has been obtained by employment of two loudness matching procedures over a period of several months. The purpose of the tests was to determine the difference in sound‐pressure level of typing noise necessary to enable a person to identify reliably the louder of two typewriters operated simultaneously in a quiet background. It was found that under the conditions adopted for the investigation, differences in sound‐pressure level had to be nearly one decibel before they could be recognized 50 percent of the time.Characteristics of typing noise other than pressure level are discussed. The opinion is expressed that these will, in many cases, not cause significant measurement error, and that difference in loudness between typing noises can often be measured with practical accuracy by means of a sound‐level meter.

ISSN:0001-4966    

DOI:10.1121/1.1907931

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP

摘要:

Description of the development of an earplug with soft elastic walls and a viscous core malleable at body temperature. The problems of suitable material, shape, and size are considered as well as the shape and size adaptability. People have found these earplugs sufficiently comfortable to sleep with, and they ensure a sound attenuation equal to or better than any known earplug. One size fitted 90 percent of the ears of the 25 people tested sufficiently well.

ISSN:0001-4966    

DOI:10.1121/1.1907933

出版商:Acoustical Society of America    

年代:1955

数据来源: AIP