流體力學試驗報告第三章 銳緣堰流量試驗

Abstract

水堰在水利工程中，可以量測明渠控制斷面的流量。於自來水公司的淨水廠以及污水處理廠中也常用堰來估計水的處理量。本試驗乃人工渠道水堰的縮小版。通過量測上游水位，堰口高差等便可通過計算式得到其理論流量。通過比較不同形狀下的理論流量和實際流量，便可知流量係數的大致範圍。

本試驗必須配合水力試驗台，水自試驗台出水口流出，經儀器底下流入，堰口上游部分以一平板分爲兩個部分，堰口左邊為靜水箱，平板右方為進水箱。水自出水口流入后，沿管往上流入進水箱。在平板中央處有一孔口，以一透明軟塑料管與箱外透明量水桶底之孔口相連接，因連通管原理，靜水箱與量水桶保持在同一高度上。量水堰板以螺絲固定於支架板上，堰口下游為一底板略傾斜之集合水箱，自堰口溢流出水后，從箱底下之孔口，經一透明塑料軟管，自量水孔口流回堰口流量試驗而構成一循環。

通過對不同堰板的流量係數進行比較會發現，不同堰板流量係數不同，但正反方向的流量大致相同，后得知因爲本試驗儀器較小所以正反沒有產生較大差異，若如果在實際大型設備上，會有顯著的一個差異。同時我們將數據進行回歸分析會發現，梯形堰口的流量係數會介於矩形與三角形之間。

In a water conservancy project, a weir can measure the flow on the control section of an open channel.Weirs are also commonly used in water purification companies and sewage treatment plants of water companies to estimate the amount of water treated.This test is a reduced version of the artificial channel weir.By measuring the upstream water level,the height difference of the weir mouth,the theoretical flow can be obtained through calculation formulas.By comparing the theoretical flow and actual flow under different shapes, the approximate range of the flow coefficient can be known.

This test must be matched with a hydraulic test bench. Water flows from the test bench's water outlet and flows under the instrument.The upstream part of the weir is divided into two parts by a flat plate.The left of the weir is a static water tank and the right of the flat is an inlet tank. After the water flows from the water outlet,it flows up into the water tank along the pipe.At the center of the flat plate, there is an orifice, which is connected to the orifice of the bottom of the transparent measuring bucket outside the tank by a transparent soft plastic pipe. Due to the principle of the connecting pipe, the static water tank and the measuring bucket are kept at the same height.The water measuring weir plate is fixed to the support plate with screws. A weird water tank with a slightly inclined bottom plate is located downstream of the weir opening. After the water overflows from the weir opening, it flows from the opening under the tank through a transparent plastic hose to measure the water opening. Flow test to the weir mouth constitutes a cycle.

By comparing the flow coefficients of different weir plates,it will be found that the flow coefficients of different weir plates are different, but the flow in the forward and reverse directions is approximately the same.It was learned that because the test instrument is small,there is no large difference between the positive and negative.There is a significant difference in actual large equipment.At the same time,we perform regression analysis on the data to find that the flow coefficient of the trapezoidal weir will be between the rectangle and the triangle.