水躍明渠試驗

Abstract

中文摘要 在水利工程領域中，明渠水力學的應用相當重要，一般的河川、灌溉圳道皆屬明渠流。 試驗以簡易的矩形渠道、坡度 ，藉由實驗數值來證明渠流中利用動量方程式、能量方程式或連續方程式所推導出的公式，並比對兩者間誤差。 試驗步驟一開始開啟循環馬達，固定馬達轉速致水流穩定，調整下射式閘門開度造成阻水，造成迴水現象產生水躍，量測臥箕型溢洪道上游水深、臥箕下游水深、水躍後水深與水躍長度，以蓄水槽進行流量率定並記錄，再將數值代入理論公式比較誤差大小。 從實驗中觀察流況由超臨界流(Fr>1.0)轉變為亞臨界流(Fr<1.0)，渠流中之能量於此變化過程中，因水流之混亂、渦動而有大量之損失現象為水躍，在工程中可運用此現象達到消能的功用，保護河道不被急流所破壞。

Abstract In the field of water conservancy projects, the application of open channel hydraulics is very important. Ordinary rivers and irrigated townships are open channels.

The experiments had started with the premise with simple rectangular channels, and slope equal zero. We prove the formula which is derived from momentum flow equation, energy equation, and continuous equation via experimental values. Next, we compared the error between theoretical value and actual value.

The test procedure begins by turning on the circulating motor. Second, fixed the speed of motor let water flow stay stability. Third, adjust the firing gate opening caused by water blocking, then in phenomenon produces hydraulic jump. Measure the water depth of the upper side of the spillway, the water depth of the down-stream, the water depth after the hydraulic jump and the length of the hydraulic jump, set the flow rate in the water tank and record it. Finally, take the value into the theoretical formula to compare the error.

From the experiment, it was observed that the flow conditions changed from supercritical flow (Fr> 1.0) to subcritical flow (Fr <1.0). During the change of energy in the flow, there was a large amount of loss due to confusion and vortex hydraulic jump. In the project, this phenomenon can be used to achieve the function of energy dissipation, and it protect the river from damaged by the rapids.