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建工学院土木系 Autumn 2007 Dept. of Civil Engineering Fluid Mechanics Lecture 10 Weir Flow Dr. Shao Weiyun Dept. of Civil Engineering Email:shaowy@zju.edu.cn 1/29 建工学院土木系 Autumn 2007 Dept. of Civil Engineering Outline ? 1 General Characteristics of Weir Flow ? 2 Basic Formula of Weir Flow ? 3 Sharp-crested Weir ? 4 Ogee-crested Weir ? 5 Broad-crested Weir ? 6 Summary 2/29 1 建工学院土木系 Autumn 2007 Dept. of Civil Engineering 1 General Characteristics of Weir Flow ? Weirs(堰): Weirs are elevated structures in the subcritical flow in open channels that are used to measure flow and/or control outflow elevations from basins and channels. ? Weir Flow(堰流)： a local hydraulic phenomenon appearing when the subcritical flow overflows the weir wall. ? There are three types of weirs in common use: Sharp-crested weirs, ogee-crested weirs and the broad-crested weirs. ? The sharp-crested weirs are commonly used in irrigation practice Aim: Study the relationships between the discharge Q through the weir and the characteristic quantities corresponding to the weir flow. 3/29 建工学院土木系 Autumn 2007 Dept. of Civil Engineering Quantities of Weir Flow L=(3~5)H 1.Head above crest H(堰顶水头)； 2.Weir width b (堰宽)； H nappe 3.Upstream weir height P (堰高) and Z δ downstream weir height P1； P w v0