By Thomas J. Mueller, Christopher S. Allen, William K. Blake, Robert P. Dougherty, Denis Lynch, Paul T. Soderman, James R. Underbrink
The objective of aeroacoustic measurements is to supply a foundation for assessing mechanisms of noise iteration, and to enhance tools of decreasing noise to extra appropriate degrees. despite the fact that, the measurements themselves are advanced, and require a deep figuring out of the experimental facility applied (such as a wind tunnel), dimension instrumentation, and information research innovations.
In this quantity fresh advances within the dimension and knowing of aerodynamically generated sound are provided via leaders within the improvement of latest concepts during this box. either easy and utilized difficulties are coated in detail.
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Additional resources for Aeroacoustic Measurements
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). Hence, the microphone outside the jet has a signal-to-noise ratio 24 Microphone Measurements In and Out of Airstream advantage of 9 dB over the in-airstream microphone. Any extraneous noise outside the flow because of recirculating flows induced by the jet requires the use of wind screens (e. , foam balls) on the microphones. Microphone Placement To determine where to place microphones in a wind tunnel, several characteristics of the model and facility must be considered - source directivity, nearfield extent, background noise, and possible reverberations.
35 mm diameter condenser microphones) (Allen et al. 1995) Microphone Corrections at High Frequency 45 To substitute microphone diaphragms for those used during the in-situ pressure response calibrations, the following procedure is used. 43) where HPRik is the pressure response curve of the ith microphone channel in-situ calibration using the kth microphone diaphragm, and HPRlabk and HpRlilbj are the pressure response curves obtained in the laboratory with the kth and jth diaphragms, respectively, mounted to common power supply/amplifiers.
1995) Microphone Corrections at High Frequency 47 field response curve (middle). The deviation of the free-field response from 0 dB is on the order of 5 dB at 100 kHz, and could be used to correct data to true sound levels. This is an example of a free-field microphone that has a pressure response designed to almost cancel the free-field effect. 28 change with angle of acoustic incidence. If available, corrections provided by microphone manufacturers can be used to correct for directionality effects.
Aeroacoustic Measurements by Thomas J. Mueller, Christopher S. Allen, William K. Blake, Robert P. Dougherty, Denis Lynch, Paul T. Soderman, James R. Underbrink