American Society of Civil Engineers


Velocity Contour Weighting Method. I: Algorithm Development and Laboratory Testing


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

Journal of Hydraulic Engineering, Vol. 137, No. 11, November 2011, pp. 1359-1367, (doi:  http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000451)

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Document type: Journal Paper
Abstract: An algorithm is developed for real-time estimation of the cross-sectional average velocity of a channel flow by using an upward-looking pulsed wave acoustic Doppler velocity meters (ADVM). The Velocity Contour Weighting Method (VCWM) is applicable to gradually varied flows in prismatic channels and requires little to no calibration. VCWM estimates the average velocity as a weighted average of ADVM bin velocities. Weights are based on the velocity distribution sampled by the ADVM. Collectively, the VCWM is able to adapt to a wide range of channel geometry and roughness features. Expressions for the velocity weights are developed by first applying a validated 3D computation fluid dynamics (CFD) channel flow model to a wide range of flow scenarios including differing channel geometries, discharge rates, depths, and boundary roughness. CFD simulation data are then reduced empirically with the aid of dimensional analysis to obtain the velocity weight equation. Special attention is given to the first weight accounting for near-wall velocity where the ADVM does not measure. Application of the method to a large rectangular flume shows that the VCWM predicts the average velocity with an uncertainty less than ±5% and that this uncertainty can be reduced by minimizing the buffer distance between the channel bottom and the first velocity measurement. In a companion paper, the performance of the VCWM is examined in irrigation canals with trapezoidal cross sections.


ASCE Subject Headings:
Open channel flow
Gradually varied flow
Flow measurement
Laboratory tests
Velocity profile
Velocity distribution
Algorithms

Author Keywords:
Open channel flow
Gradually varied flow
Flow measurement
Acoustic Doppler profilers
Laboratory tests
Velocity profiles
Velocity distribution