Flow-induced noise on pressure gradient hydrophones
- Penn State University, Graduate Program in Acoustics and Applied Research Laboratory, P.O. Box 30, State College, Pennsylvania 16804 (United States)
- Naval Air Warfare Center, Aircraft Div., Code 45C, Warminster, Pennsylvania 18974 (United States)
Moored or drifting hydrophones are subject to a variety of potential self-noise sources. Flow-induced self noise arises when the sensors are subjected to oceanic currents such as those due to wave motion and changing tides. Research at Penn State, in cooperation with the Naval Air Warfare Center (NAWC), has been concerned with the basic mechanisms of flow-induced self noise on velocity gradient hydrophones of various shapes and sizes. These sensors are configured as finite-length cylinders in cross flow and as spheres. The sensors are sensitive to acoustic particle velocity, and one of the sensors is sensitive to acoustic intensity. With the diameter of the sensor as the characteristic dimension, and for operational flow velocities in the 0.5 to 2.0 knot range, the Reynolds number range of interest is from values less than 100 (for some miniature sensors) to about 27,000 (for standard-size sonobuoy hydrophones). Experiments are conducted for the higher ranges of Reynolds number by towing the sensors over the given range of speeds in quiet basins of water (9 meter tow tank at Penn State and a flooded quarry at the NAWC). To achieve the lower range of Reynolds numbers over the same range of velocities, but without having in hand actual miniature sensors, some of the experiments are performed in glycerine. Glycerine has a kinematic viscosity some three orders of magnitude greater than that of water; therefore, a large sensor can be subjected to a velocity in the range of interest but yield an operational Reynolds number that is three orders of magnitude smaller. In this paper, we will show the broadband spectral characteristics of finite-length cylindrical sensors in cross flow, as well as spherical-shaped sensors. The Reynolds number of the flow is the independent variable. The threshold of velocity-dependent noise increase is found to correlate with the occurrence of turbulent flow not necessarily in the wake, but on the surface of the body itself.
- OSTI ID:
- 288870
- Report Number(s):
- CONF-9509298-; ISSN 0094-243X; TRN: 9615M0129
- Journal Information:
- AIP Conference Proceedings, Vol. 368, Issue 1; Conference: Acoustic velocity sensor focused workshop, Mystic, CT (United States), 12-13 Sep 1995; Other Information: PBD: Apr 1996
- Country of Publication:
- United States
- Language:
- English
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