A Cancellation Technique for Reducing Background Noise Within Turbulent Flow Environments Characterized by Pipes and Annuli
Interim rept. Jun 1985-Jul 1988
NAVAL RESEARCH LAB WASHINGTON DC
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Experimental studies of turbulent boundary layer wall pressure fluctuations are typically complicated by flow generated acoustic pressure levels which are superimposed on the turbulent fluctuations of interest. This problem can be particularly acute when the test fluid is water or similar liquid with a high bulk wave propagation velocity. The present paper describes a method for addressing this problem which permits wall pressure fluctuation experiments of high quality to be conducted within internal flow geometries over a bandwidth of 1 kHz. The method improves on a technique of using 3 flush mounted transducers located within a coaxial plane, thereby providing up to 20 dB reduction over previous measurements for the bandwidth investigated. Experimental results show that using the improved technique allows measurements of both the nearfield and farfield pressure components. Excellent agreement with previously reported wall pressure fluctuation measurements is demonstrated for the geometries evaluated. Keywords Turbulent boundary layer Acoustic propagation Background noise reduction Wall pressure measurement Noise cancellation.
- Test Facilities, Equipment and Methods
- Fluid Mechanics