Reports & Papers > Subcritical Contraction Design
ITRC Paper No. P 10-005. Daniel J. Howes, Charles Burt, and Brett F. Sanders
Subcritical Contraction Design for Improved Open Channel Flow Measurement Accuracy with an Upward-Looking Acoustic Doppler Velocity Meter
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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.
Howes, D.J., C.M. Burt, and B.F. Sanders. 2010. Subcritical Contraction Design for Improved Open Channel Flow Measurement Accuracy with an Upward-Looking Acoutsic Doppler Velocity Meter. ASCE Journal of Irrigation and Drainage. September 2010. 17 pp.
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