Subcritical Contraction for Improved Open-Channel Flow Measurement Accuracy with an Upward-Looking ADVM

by Daniel J. Howes, (corresponding author), (M.ASCE), Senior Irrigation Engineer; Irrigation Training and Research Center, California Polytechnic State Univ., San Luis Obispo, CA 93407, djhowes@calpoly.edu,
Charles M. Burt, (M.ASCE), Professor; Dept. of BioResource and Agricultural Engineering, and Chair, Irrigation Training and Research Center, California Polytechnic State Univ., San Luis Obispo, CA 93407., cburt@calpoly.edu,
Brett F. Sanders, (M.ASCE), Professor; Dept. of Civil and Environmental Engineering, Univ. of California, Irvine, CA 92697., bsanders@uci.edu,


Serial Information: Issue 9, Pg. 617-626


Document Type: Journal Paper

Abstract: Acoustic Doppler velocity meters (ADVMs) 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 three-dimensional computational fluid dynamics (CFD) model was used to design a subcritical rapidly varied flow contraction that provides 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.

Subject Headings: Flow measurement | Subcritical flow | Open channel flow | Hydraulic contraction | Computational fluid dynamics technique | Open channels | Fluid velocity | Calibration | Laboratory tests |

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