Transitional Flow Between Orifice and Non-orifice Regimes at a Rectangular Canal Gate
Abstract (Summary)The main objective of this research was to analyze the hydraulic transition between non-orifice and orifice flow regimes at a rectangular sluice gate through the calibration of various discharge equations, and determining the value of a coefficient, which defines the transition between orifice and non-orifice flow conditions. The second objective was to determine whether a single equation could be used to represent the stage-discharge relationship for both free and submerged non-orifice flow through a rectangular sluice gate. Several hundred data sets were collected in a hydraulic laboratory, each including the measurement of water upstream depth and downstream for five different gate openings, and 17 different steady-state discharges, from 0.02 to 0.166 m3/s. Three approaches were used to define the limits of the non-orifice-to-orifice regime transition: (1) using an empirical equation; (2) using the traditional submerged non-orifice equation; and (3) using the specific-energy equation for open-channel flow. Based on the results of this research, the latter approach was ultimately chosen to define the boundaries of the transition between orifice and non-orifice flow regimes. Once the transition limits were defined, the estimation of the non-orifice-to-orifice transition coefficient, Co , was made. The transition coefficient was defined as the ratio of gate opening to upstream water depth. The experimental results indicate that orifice flow always exists when Co is less than 0.83, and non-orifice flow always exists when Co is greater than 1.00. To identify the flow regime (orifice or non-orifice) within the range 0.83 < Co < 1.00, it is necessary to consider the submergence, S, which is the ratio of downstream to upstream water depth. With respect to the second objective, laboratory data for non-orifice flow regimes were used to test several different empirical equation forms that could potentially represent both free and submerged flow conditions. The strategy was to find a relationship among flow rate, upstream depth, downstream depth, and submergence. As a result of the analysis, one particular equation form was found to have a relatively high coefficient of determination and low standard error of the estimate. This equation fits the laboratory data for submergences up to 0.87 with a discharge error not exceeding +-10%.
School:Utah State University
School Location:USA - Utah
Source Type:Master's Thesis
Date of Publication:05/01/2008