摘要:

An experimental program to demonstrate the effect of unsteady combustion processes in a combustion‐augmented jet flow is described. Characteristics of noise for several combustors, having different flame holders and several lengths, operating in a jet temperature range from 1100°C to 1500° and a jet Mach number range from 0.2 to 0.35 (jet exit velocity ranging between 400 and 800 ft/sec) are presented. Data were collected from six B&K14‐in.microphones positioned at an angular separation of 15°in a quadrant of 50‐ft radius from the 2‐in. diam nozzle exit. Kistler type 601 pressure transducers are mounted in the duct wall of the combustor which is held on a pylon 12 ft above the ground. The experimental data collected and analyzed to date shows a directivity pattern with a nearly circular pattern, which has a peak in the vicinity of 45° to 60° from the jet axis. Comparison of internal pressure fluctuations with the farfield noise shows many simularities in the spectrum, an observation which is verified by the strong cross correlation between the two signals. Combustor and flame holder geometry are found to affect the level and frequency content of the noise. [Supported by NASA grant.]

ISSN:0001-4966    

DOI:10.1121/1.1982735

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The present ASTM procedure for field measurement of the noise reduction between spaces is time consuming and costly because it requires numerous measurements in order to compute the noise isolation class (NIC), particularly when separate measurements must be made at multiple microphone positions to obtain adequate spatial averaging. The purpose of the present investigation is to explore the relationships between NIC values based on13‐octband data and more easily obtained ratings of isolation based on either octave band data or onA‐weighted orC‐weighted sound level data. A large number of curves of13‐octband noise reduction versns frequency were calculated from data on transmission loss of partitions, assumed room geometry, assumed values for the source sound power spectrum, and assumed values for the sound absorption in the source and receive rooms. For each of these13‐octband noise reduction curves, the following quantities were calculated and compared: NIC rating,Iarating (13‐octband data),Iarating (octave band data), theA‐weighted sound level difference, and the difference between theC‐weighted level in the source room and theA‐weighted level in the receive room.

ISSN:0001-4966    

DOI:10.1121/1.1982744

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The exact description of sound transmission through an enclosure depends, in general, on the details of the source radiation characteristics, coupling of the source to the enclosure acoustic space, and coupling of the acoustic space to the resonant and nonresonant motion of the enclosure walls. Moreover, for an extended source, and a relatively small and absorptive enclosed space, an exact description is beyond the present state of the art. In this paper, a simple design procedure based on an energy flow analysis is described, which provides good lower bound estimates of enclosure performance. The performance parameter that is calculated is the lower bound of a space average, or radiated power insertion loss. When formulated in this way, the performance is reciprocal in the sense that it is independent of whether transmission is from outside to inside or inside to outside. Above the first enclosure volume resonance, the result is PIL ⩾ TL + 10 log A/S where PIL is the power insertion loss, TL is the field incidence transmission loss of the enclosure walls, A is the sabine absorption of the enclosure interior, andSis the radiating area of the walls. A result that is applicable below the first enclosure resonance is also presented. A number of experimental results are presented which confirm the analysis procedures. [Work supported in part by General Electric Co., Aircraft Engine Group, Cincinnati, Ohio, and NASA‐Langley Research Center.]

ISSN:0001-4966    

DOI:10.1121/1.1982745

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP