A NEW TRAPEZOIDAL FLUME FOR OPEN CHANNEL FLOW MEASUREMENT DESIGN, THEORY, AND EXPERIMENT

B. ACHOUR, D. MEHTA, H.M. AZAMATHULLA

Abstract


Several means are used for flow measurement, including the flumes that are of interest to the present study. The operating principle of the flume is based on the lateral contraction of the walls of a trapezoidal channel that ends in a triangular section extended by a throat of the same section. The convergent part of the flume accelerates the flow from a subcritical state to a critical state in the throat where a control section is created. Thus, the flow can be determined by taking a single depth reading in the inlet cross-section of the flume.

The recommended device is simple and compact in shape, requiring a minimum of space compared to known trapezoidal flumes. Furthermore, the device has been designed to be used in open channels regardless of the shape. Therefore, the flume has the property of being of a universal range.

A rigorous theoretical development led to the derivation of the governing discharge coefficient Cd relationship, solely depending on the dimensionless parameter M1 = mh1/b1, where m is the side slope of the flume, h1 is the upstream flow depth, and b1 is the inlet cross-section width of the converging part of the flume.

Based on 1023 pairs of values Q-h1 collected from twelve tested flumes of different practical dimensions, the in-depth analysis of laboratory observations corroborated the validity and reliability of the theoretical relationship governing Cd within the wide range 0.10 £ M1 £ 0.95, since the maximum deviation is only 0.215% when compared to observations.

Among the twelve tested devices, only the results of the observations carried out on one device will be presented herein. The observations collected on this device are considered the most unfavourable compared with those carried out on the eleven other tested devices, especially regarding the deviation affecting the discharge coefficient Cd.


Keywords


Trapezoidal flume, Discharge coefficient, Discharge, Stage-discharge relationship, Flow measurement

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References


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