scholarly journals Reduction of fan noise in an anechoic chamber by reducing chamber wall induced inlet flow disturbances

1978 ◽  
Vol 63 (S1) ◽  
pp. S22-S22
Author(s):  
J. H. Dittmar
Keyword(s):  
Anechoic Chamber ◽  
Chamber Wall ◽  
Fan Noise ◽  
Inlet Flow ◽  
Flow Disturbances

scholarly journals Characteristics of an Anechoic Chamber for Fan Noise Testing

1977 ◽  
Author(s):  
J. A. Wazyniak ◽  
L. M. Shaw ◽  
J. D. Essary
Keyword(s):  
Mechanical Design ◽  
Full Scale ◽  
Anechoic Chamber ◽  
Nasa Lewis Research ◽  
Design Features ◽  
Fan Noise ◽  
Inlet Flow ◽  
Noise Characteristics ◽  
Scale Levels ◽  
Acoustic Evaluation

Acoustical and mechanical design features of NASA Lewis Research Center’s engine fan noise facility are described. Acoustic evaluation of the 1420-m (50,000-ft) chamber, which is lined with an array of stepped wedges, is described. Results from the evaluation in terms of cut-off frequency and non-anechoic areas near the walls are detailed. Fan models with 0.51-m (20-in.) diameters are electrically driven to 20,600 rpm in either the inlet mode (drawing air from the chamber) or exhaust mode (discharging air into the chamber) to facilitate study of both fore and aft fan noise. Inlet noise characteristics of the first fan tested, the JT8D Refan, are discussed and compared to full-scale levels. Turbulence properties of the inlet flow and acoustic results are compared with and without a turbulence reducing screen over the fan inlet.

The influence of inlet flow disturbances on transition of Poiseuille pipe flow

AIChE Journal ◽  
1979 ◽  
Vol 25 (1) ◽  
pp. 181-183 ◽  
Author(s):  
Richard W. Hanks ◽  
James M. Peterson ◽  
Carlos Narvaez
Keyword(s):  
Pipe Flow ◽  
Inlet Flow ◽  
Flow Disturbances

scholarly journals Estimation of the lower cut-off frequency of an anechoic chamber: An empirical approach

2020 ◽  
Vol 19 (1-2) ◽  
pp. 57-72
Author(s):  
Singh K Sushil ◽  
Mohit Garg ◽  
S Narayanan
Keyword(s):  
Sound Source ◽  
Calibration Procedure ◽  
Broadband Noise ◽  
Anechoic Chamber ◽  
Chamber Wall ◽  
Empirical Expression ◽  
Inverse Square Law ◽  
Total Distance ◽  
Chamber Volume ◽  
Noise Measurements

This paper deals with the development of an empirical expression to determine the lower cut-off frequency of an anechoic chamber when the source volume, chamber volume, wedge height as well as the major dimensions (i.e., total distance between the source and the chamber wall) are known. The frequency obtained from the empirical expression compares well within ±3% of the lower cut-off frequency obtained from the experiments. The paper also addresses the construction details and calibration procedure of the anechoic chamber. The chamber is calibrated by verifying the inverse square law for different directions from the sound source, and the lower cut-off frequency of the chamber is found to be 315 Hz within ±0.5 dB. Further, the fan broadband noise measurements are made, inside and outside, of the anechoic chamber in order to demonstrate the echo-free nature of the chamber and the spectra clearly shows that the chamber is anechoic for a broad range of frequencies.

Inlet Flow Distortion Effects on Rotating Stall

1990 ◽  
Author(s):  
J. Fortin ◽  
W. C. Moffatt
Keyword(s):  
Low Frequency ◽  
Rotating Stall ◽  
Full Scale ◽  
Experimental Investigations ◽  
Jet Engines ◽  
Flow Distortion ◽  
Inlet Flow ◽  
Rotation Direction ◽  
Flow Disturbances ◽  
Hot Film

For many years there has been a significant effort to better understand rotating stall/surge phenomena in axial compressors, as well as the effects of inlet flow distortions. Most experimental investigations to date, whether on laboratory compressors or on full scale jet engines, have tended to focus separately on the effects of these two flow disturbances on compressor performance. The purpose of the present study was to experimentally assess the influence of inlet flow distortions on the inception and nature of rotating stall in a full scale engine compressor. This paper reports results obtained for the first stage rotor of a 10-stage compressor subjected to screen-induced inlet pressure distortions. Previous investigations had shown that during part-speed operation, the front stages operated in rotating stall, and hot-film probe measurements made during the present study showed that the presence of the distortion screens did not affect the speed of the rotating stall pattern, but in some instances changed the number of cells present. However, low frequency flow fluctuations characteristic of surge were much more prevalent when the screens were in place. Also, the further the sensing probe was displaced tangentially in the rotor rotation direction from the screens, the more intense the fluctuations, leading one to conclude that the screens had a localized damping effect on the surge cycle.

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