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

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 ?/2, with ?=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 ?/2 scale. Application of the method to measurement of oceanic turbulence is discussed.