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Subcritical Contraction Design for Improved Open Channel Flow Measurement Accuracy with an Upward-Looking Acoutsic Doppler Velocity Meter





ITRC Report No.

P 10-005



17 pages



Daniel J. Howes, Charles M. Burt, and Brett F. Sanders



ASCE Journal of Irrigation and Drainage.  September 2010.






Acoustic Doppler velocity meters (ADVM) provide an alternative to more traditional flow measurement devices and procedures such as flumes, weirs, and stage-rating for irrigation and drainage canals. However, the requirements for correct calibration are extensive and complex. A 3D computational fluid dynamics (CFD) model was used to establish design criteria of a subcritical rapidly varied flow (RVF) contraction that provides a constant cross section in addition to a consistent, linear relationship between the upward-looking ADVM sample velocity and the cross-sectional average velocity, in order to improve ADVM accuracy without the need for in situ calibration. CFD simulations validated the subcritical contraction in a rectangular and trapezoidal cross section by showing errors within +1.8% and -2.2%. Physical testing of the subcritical contraction coupled with an upward-looking ADVM in a large rectangular flume provided laboratory validation with measurement errors within +/-4% without calibration.



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