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Open-Channel Flow and Turbulence Measurement by High-Resolution Doppler Sonar

R. LhermitteUniversity of Miami, Miami, Florida

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U. LemminEcole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland

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Abstract

Measurements of water velocity and turbulence in a water flume using a Doppler sonar operating at 1 MHz are presented. Analysis of the results shows that the instrument qualifies as a very useful tool for nonintrusive and accurate measurement of vertical profiles of water horizontal velocity u and vertical velocity w as well as water turbulence parameters including the ¯u′w′ Reynold's stress component.

The water circulating in the flume is well filtered, so that the backscattering signal relates primarily to temperature microstructure occurring at λ/2, with λ=0.15 cm being the sonar wavelength. Quantitative measurements of backscattering intensity show that the backscattering signal disappears if the water turbulence intensity is below a certain value. This relates to the fact that the high-wavenumber end of the temperature turbulence spectrum no longer reaches the λ/2 scale. Application of the method to measurement of oceanic turbulence is discussed.

Abstract

Measurements of water velocity and turbulence in a water flume using a Doppler sonar operating at 1 MHz are presented. Analysis of the results shows that the instrument qualifies as a very useful tool for nonintrusive and accurate measurement of vertical profiles of water horizontal velocity u and vertical velocity w as well as water turbulence parameters including the ¯u′w′ Reynold's stress component.

The water circulating in the flume is well filtered, so that the backscattering signal relates primarily to temperature microstructure occurring at λ/2, with λ=0.15 cm being the sonar wavelength. Quantitative measurements of backscattering intensity show that the backscattering signal disappears if the water turbulence intensity is below a certain value. This relates to the fact that the high-wavenumber end of the temperature turbulence spectrum no longer reaches the λ/2 scale. Application of the method to measurement of oceanic turbulence is discussed.

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