Accession Number:

ADA199332

Title:

Developments in Hot-Film Anemometry Measurements of Hydroacoustic Particle Motion

Descriptive Note:

Final rept. Jan 1986-Sep 1987

Corporate Author:

NAVAL RESEARCH LAB WASHINGTON DC

Report Date:

1988-08-30

Pagination or Media Count:

25.0

Abstract:

Hot film anemometry may be used to measure particle motion in hydroacoustic fields. Since the cylindrical sensors used thus far are very fragile, the method is little suited for use outside the laboratory. The measurement of the response of a more rugged conical sensor is reported here. Another way of protecting the sensor consists of packaging the sensor in a rubber liquid filled boot. This also prevents fouling and bubble formation on the heated film. The response shows a resonance at low frequency, ascribed to the liquid filled boot, which may be used for enhanced response in a limited frequency region. The response of a hot film anemometer to vertical hydroacoustic particle motion is influenced by free convection, which acts as a bias flow. The output was shown to be proportional to particle displacement for a wide range of parameters. It was expected that an imposed bias flow would increase the output and remove the dependence on the direction of gravity. Therefore, a hot-film sensor diameter d was subjected to an underwater jet from a nozzle. The output showed a transition from being proportional to particle speed, to being proportional to particle displacement, depending on the angular frequency omega and imposed flow speed omega. The transition takes place when a dimensionless number Omega, defined as Omega omeganu is of order 1.

Subject Categories:

  • Test Facilities, Equipment and Methods
  • Acoustic Detection and Detectors
  • Fluid Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE