流量测量结构.矩形、梯形和U形水槽

[中文适用范围]： 本文件规定了在稳定或缓慢变化的流动条件下，使用某些类型的临界深度水槽（也称为“驻波水槽”）测量河流和人工渠道流量的方法。已经开发了各种各样的水槽，但本文仅考虑那些经过充分研究和现场测试而得到普遍认可的临界深度水槽，因此不需要现场校准。所考虑的流动条件唯一地取决于上游水头，即水槽上游必须存在亚临界流，此后流动通过收缩加速并通过其临界深度（见图 1）。结构下游的水位足够低，不会影响其性能。本文件适用于三种常用类型的水槽，涵盖广泛的应用，即矩形喉口、梯形喉口和 U 型喉口。本文件背后的水力学理论已在参考文献 [7] 中提出。本文件不适用于文献中提到的一种水槽（有时称为“文丘里”水槽），其中的流体始终处于亚临界状态。注意：文丘里水槽基于与封闭管道系统中使用的文丘里流量计相同的原理，依靠在两个位置测量水头和应用伯努利能量公式。 [外文原描述]： This document specifies methods for the measurement of flow in rivers and artificial channels under steady or slowly varying flow conditions, using certain types of critical-depth flumes (also known as “standing-wave flumes”). A wide variety of flumes has been developed, but only those critical-depth flumes which have received general acceptance after adequate research and field testing, and which therefore do not require in situ calibration, are considered herein. The flow conditions considered are uniquely dependent on the upstream head, i.e. subcritical flow must exist upstream of the flume, after which the flow accelerates through the contraction and passes through its critical depth (see Figure 1 ). The water level downstream of the structure is low enough to have no influence upon its performance. This document is applicable to three commonly used types of flumes, covering a wide range of applications, namely rectangular-throated, trapezoidal-throated and U-throated. The hydraulic theory behind this document was presented in Reference [ 7 ]. This document is not applicable to a form of flume referred to in the literature (sometimes called a “Venturi” flume) in which the flow remains subcritical throughout. NOTE The Venturi form of flume is based on the same principle as a Venturi meter used within a closed conduit system and relies upon gauging the head at two locations and the application of Bernoulli’s energy formula.