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United States Department of Agriculture

Agricultural Research Service

Research Project: Technologies for Managing Water and Sediment Movement in Agricultural Watersheds

Location: Watershed Physical Processes Research Unit

Title: Performance assessment and calibration of a profiling lab-scale acoustic Doppler velocimeter for application over mixed sand-gravel beds

Authors
item Ursic, Michael
item Langendoen, Eddy
item Wren, Daniel
item Kuhnle, Roger
item Pellachini, Corrado -

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 13, 2012
Publication Date: August 13, 2012
Citation: Ursic, M., Langendoen, E. J., Wren, D. G., Kuhnle, R. A., and Pellachini, C. Performance assessment and calibration of a profiling lab-scale acoustic Doppler velocimeter for application over mixed sand-gravel beds. Hydraulic Measurements and Experimental Methods Conference, Snowbird, Utah. 6 pp. 2012. CD-ROM.

Interpretive Summary: Advances in sediment transport research are dependent on the ability to measure rapid changes in water velocity that are responsible for moving particles. Acoustic Doppler velocimetry has made high-resolution turbulence measurements in sediment-laden flows possible. New instruments must be tested before their results can be trusted for research. Towards this end, the Vectrino-II was towed at known speeds in a tank at the National sedimentation laboratory. Results of the tow experiments indicate that the vertical extent of acceptable turbulence statistics may be reduced as the mean velocity is increased, possibly due to probe head wake effects. Application over coarse gravel beds filled with different percentages of sand shows that the quality of the measured data may be dependent on both bed roughness and suspended particle concentration.

Technical Abstract: Acoustic Doppler velocimetry has made high-resolution turbulence measurements in sediment-laden flows possible. Recent developments have resulted in a commercially available lab-scale acoustic Doppler profiling device, a Nortek Vectrino II, that allows for three-dimensional velocity data to be collected at a rate of 100 Hz at 1 mm increments over a 3.5 cm range centered at 5 cm from the face of the instrument. The new instrument was evaluated through tow-tests conducted at the USDA-ARS-National Sedimentation Laboratory in a 30.48 m (L) x 1.22 m (W) x 0.61 m (H) flume. The instrument was used to record velocity data while being towed over a 10 m section of the quiescent flume at known velocities (23.8 cm/s, 47.6 cm/s, 71.3 cm/s, and 95.1 cm/s) and at 0, 90, 180, and 270 degree orientations relative to the tow direction. Results of the tow experiments indicate that the vertical extent of acceptable turbulence statistics may be reduced as the mean velocity is increased, possibly due to probe head wake effects. Application over coarse gravel beds filled with different percentages of sand shows that the quality of the measured data may be dependent on both bed roughness and suspended particle concentration.

Last Modified: 7/28/2014
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