Broad‐Band Noise Generation in Turbofan Engines

1969 ◽  
Vol 46 (1A) ◽  
pp. 78-78
Author(s):  
Colin G. Gordon
Keyword(s):  
Broad Band ◽  
Noise Generation ◽  
Turbofan Engines ◽  
Band Noise

Basic Flow Analyses Used in the Study of Broad-Band Noise in Compressors

1976 ◽  
Vol 98 (1) ◽  
pp. 23-28
Author(s):  
F. Buckens
Keyword(s):  
Broad Band ◽  
Wave Number ◽  
Frequency Noise ◽  
Noise Generation ◽  
Noise Sources ◽  
Left Hand ◽  
Dispersive Effect ◽  
Band Noise ◽  
Axisymmetrical Flow ◽  
The Right

The propagation of sound in a moving compressible fluid displays interesting features which are important in the problem of noise generation in compressors. Without considering the discrete frequency noise generated by interacting rotating blades and stationary parts, a perturbation method applied to the equations of flow motion in an idealized continuous medium leads to an equation of density waves propagation in a nonhomogeneous moving fluid. The right-hand side is considered as describing distributed noise sources which involve velocity fluctuations. On the left-hand side there appears a negative diffusive effect due to a negative divergence of the velocity field, which downstream entails a streamwise amplification of the intensity of the sound generated upstream. Further, there is a dispersive effect entailing, for a given wave number, a group velocity which in a simple example is shown to be larger than the phase velocity and to become imaginary for a velocity divergence sufficiently high in absolute value. This, together with the amplification effect, may explain the relative importance of the high frequency band in the actual noise spectra of compressors. An attempt at determining the coefficients of the acoustical equation for compressors is made in the schematic Beltrami-Gromeka case of a helicoidal axisymmetrical flow. With simplified assumptions on the behavior of density, depending either solely on the axial coordinate or only on the radial one, both types of axial and radial compressors are considered simultaneously and the method of analytical solution applied. It is emphasized that this treatment is restricted to the mechanical aspect of the broad-band noise generation.

scholarly journals Searching for energy-resolved quasi-periodic oscillations in AGN

2021 ◽  
Author(s):  
Dominic I Ashton ◽  
Matthew J Middleton
Keyword(s):  
Power Law ◽  
Spectral Component ◽  
Broad Band ◽  
Initial Study ◽  
Periodic Oscillations ◽  
Single Observation ◽  
Curved Space ◽  
Multiple Observations ◽  
Band Noise ◽  
The Impact

Abstract X-ray quasi-periodic oscillations (QPOs) in AGN allow us to probe and understand the nature of accretion in highly curved space-time, yet the most robust form of detection (i.e. repeat detections over multiple observations) has been limited to a single source to-date, with only tentative claims of single observation detections in several others. The association of those established AGN QPOs with a specific spectral component has motivated us to search the XMM-Newton archive and analyse the energy-resolved lightcurves of 38 bright AGN. We apply a conservative false alarm testing routine folding in the uncertainty and covariance of the underlying broad-band noise. We also explore the impact of red-noise leak and the assumption of various different forms (power-law, broken power-law and lorentzians) for the underlying broad-band noise. In this initial study, we report QPO candidates in 6 AGN (7 including one tentative detection in MRK 766) from our sample of 38, which tend to be found at characteristic energies and, in four cases, at the same frequency across at least two observations, indicating they are highly unlikely to be spurious in nature.

Acceptable Levels of Tonal and Broad-Band Repetitive and Continuous Sounds during the Performance of Nonauditory Tasks

1995 ◽  
Vol 81 (3) ◽  
pp. 803-816 ◽  
Author(s):  
Ulf Landström ◽  
Anders Kjellberg ◽  
Marianne Byström
Keyword(s):  
Reaction Time ◽  
Sound Pressure ◽  
Broad Band ◽  
Reaction Time Task ◽  
Simple Reaction Time Task ◽  
Reasoning Test ◽  
Band Noise ◽  
Time Test ◽  
The Difference ◽  
Reaction Time Test

Three groups of 24 subjects were exposed to a 1000–Hz tone or broad band noise in a sound chamber. During the exposures subjects were engaged in an easy reaction time test or a difficult grammatical reasoning test. For each exposure and work subjects adjusted the noise to a tolerance level defined by its interference with task performance. During the simple reaction-time task significantly higher sound-pressure levels were accepted than during the reasoning test. At the tonal exposure, much lower levels were accepted than during the exposure to broad-band noise. For continuous sound exposures much higher levels were accepted than for noncontinuous exposures. For tonal exposures the difference was approximately 5 dB, for the broad-band exposures approximately 9 dB. In a separate study the effects of the noncontinuity of the noise and pauses were analysed. The raised annoying effect of the noncontinuous noise was not more affected by the noncontinuity of the noise periods than by the noncontinuity of the pauses. The results imply that the annoying reactions to the sound will be increased for repetitive noise and that the reaction is highly influenced by the over-all noncontinuity of the exposure.

The Prediction of Hearing Loss in Persons With Cerebral Palsy Using Contralateral Acoustic Reflex Threshold for Broad-Band Noise

2003 ◽  
Vol 12 (2) ◽  
pp. 91-95
Author(s):  
Michele B. Emmer ◽  
Shlomo Silman
Keyword(s):  
Hearing Loss ◽  
Cerebral Palsy ◽  
Broad Band ◽  
Screening Method ◽  
Accurate Method ◽  
Normal Hearing ◽  
Acoustic Reflex ◽  
Band Noise ◽  
Reflex Threshold ◽  
Acoustic Reflex Threshold

The utility of R. Keith’s (1977) method of screening for hearing sensitivity using the contralateral acoustic-reflex threshold (ART) for broad-band noise (BBN) was tested in persons with cerebral palsy (CP). Three groups of participants were included in this prospective study. The first group comprised 20 normal-hearing individuals without CP whose results were used as normative data. The second group comprised 16 participants with normal hearing and CP. The third group comprised 22 participants with sensorineural hearing loss and CP. The results of this study indicate that Keith’s screening method employing ART for BBN can be used successfully in a population with multiple handicaps where a quick, inexpensive, readily available, and accurate method is needed.

scholarly journals Coupling between QPOs and broad-band noise components in GRS 1915+105

2011 ◽  
Vol 413 (3) ◽  
pp. 1819-1827 ◽  
Author(s):  
Thomas J. Maccarone ◽  
Philip Uttley ◽  
Michiel van der Klis ◽  
Rudy A. D. Wijnands ◽  
Paolo S. Coppi
Keyword(s):  
Broad Band ◽  
Band Noise
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