New PDF release: Aeroacoustic Measurements

Measurements

By Thomas J. Mueller, Christopher S. Allen, William K. Blake, Robert P. Dougherty, Denis Lynch, Paul T. Soderman, James R. Underbrink

ISBN-10: 3642075142

ISBN-13: 9783642075148

ISBN-10: 3662050587

ISBN-13: 9783662050583

The aim of aeroacoustic measurements is to supply a foundation for assessing mechanisms of noise new release, and to improve tools of decreasing noise to extra applicable degrees. although, the measurements themselves are advanced, and require a deep figuring out of the experimental facility applied (such as a wind tunnel), dimension instrumentation, and knowledge research ideas.
In this quantity contemporary advances within the dimension and realizing of aerodynamically generated sound are provided by way of leaders within the improvement of latest innovations during this box. either simple and utilized difficulties are coated in detail.

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Example text

22 illustrates the effect of refraction on sound propagation within the context of the assumptions just mentioned. The solid line labeled 'acoustic ray actual path' represents the refracted acoustic ray, the dashed line labeled 'path in large stream' represents the propagation path of the same ray propagating in a uniform velocity field without a shear layer. The dashed line labeled 'path in still air' is the path the acoustic ray would take with the jet at zero velocity, assuming that the noise source generation was not modified by the flow.

J 1 5 10 20 microphone distance from SOlU"Ce, m Fig. 20. Sound decay interference levels computed for a random noise source at 2500 Hz in a 12 by 24-m test section. 0. 0115 dB/m. 8 m above the floor and aligned toward a sidewall. An example of measured wind tunnel sound decay in a 2500 Hz third-octave band is also plotted (Soderman et al. 2000) vious data or computational acoustic models. The analysis is best done with narrow band data. For comparison with older data, or for calculation of A-weighted levels, third-octave spectra are also popular.

2 m from the jet centerline was approximately 25 dB quieter than in-airstream noise. When extrapolated back to 6 m, the DNW data agree with Allen and Reed's finding. The reduction of noise outside the jet is attributed to removal of flow-induced noise at the microphone and walls, partial shielding of drive-fan noise by the nozzle and collector, and sound absorption at the anechoic chamber walls. In-airstream microphones are usually much closer to a test model than outof-airstream microphones. 2 m from the model (at the expense of near-field effects - see below).

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Aeroacoustic Measurements by Thomas J. Mueller, Christopher S. Allen, William K. Blake, Robert P. Dougherty, Denis Lynch, Paul T. Soderman, James R. Underbrink


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