Title

應用PIV於固床工下游沖刷坑紊流特性參數時空變化之量測

Translated Titles

Temporal and Spatial variations of Turbulent Flow over a Scour Hole Downstream of a Grade-Control Structure with a PIV System

Authors

曾威甯

Key Words

固床工 ; 沖刷坑 ; PIV ; 超越機率 ; 紊流特性 ; groundsill ; scour ; PIV ; exceeding probability ; turbulent characteristics

PublicationName

中興大學土木工程學系所學位論文

Volume or Term/Year and Month of Publication

2016年

Academic Degree Category

碩士

Advisor

盧昭堯

Content Language

繁體中文

Chinese Abstract

臺灣地理環境特殊加上近年來降雨過度集中,使得河床泥砂沖刷顯著,故常使用固床工穩定河床。惟固床工下游沖刷坑常隨時間逐漸變大,甚至造成基礎易被掏空而破壞。因此,本研究乃針對固床工下游沖刷坑隨時間與空間的變化做深入之研究。 本研究利用質點影像測速儀於室內動床輸砂渠槽試驗進行量測,分析項目包含不同時程(15 mins、1 hr、5 hrs)、單寬流量(0.0167、0.0283、0.0475 ㎡/s)、坡度(1%、1.5%)之平均速度、紊流強度及雷諾應力等紊流特性參數。此外,將底床剪應力與希爾茲圖之臨界剪應力比較,並計算全剖面底床沖刷超越機率。 實驗結果顯示,水流以潛沒式射流(submerged jet)進入沖刷坑,於各時程紊流流場變化最急劇的地方大多發生在高速水舌區及水躍區,且流速剖面於第一個底床坡度折點後至垂直斷面最大水深位置之間,因擴散現象局部地區會逐漸發展成近似常態分佈曲線。除大流量組次(M-3、S-3)外,其餘組次之最大沖刷深度處及爬升處於t= 5 hrs已接近平衡狀態,全剖面底床超越機率隨時間而降低,並隨流量及坡度增加而增加。結果顯示,大流量組次於5 hrs後沖刷坑仍有繼續拉長之趨勢。

English Abstract

Due to Taiwan’s special geographical environment and the excessive concentration of rainfall in recent years, groundsills are frequently used to reduce scouring and stabilize the riverbed. However, the local scour downstream of the groundsill may grow with time, even causing the collapse of the structure. In order to increase our understanding of the temporal and spatial variations of the scour hole downstream of a grade-control structure, this study uses a PIV system to measure the mean velocity, turbulence intensity and Reynolds stress etc. for the movable bed tests in an indoor flume. The independent variables include the experimental duration(15 mins,1 hr, and 5 hrs), unit discharge(0.0167, 0.0283 and 0.0475 ㎡/s), and channel bed slope(1% and 1.5%). In addition, the measured bed shear stresses are compared with critical shear stresses calculated from the Shields diagram, and the exceeding probabilities are calculated along the whole scour hole surface. According to the experiment results, the flow enters the scour hole with a submerged jet, and the most violent variation of the turbulent flow occurs in the areas of the high-speed nappe and the hydraulic jump. Because of the diffusion phenomenon, velocity profiles will gradually develop into approximate normal distribution curves between the section with maximum scour depth and that with maximum water depth. The reach between the maximum scour depth and the maximum flow depth have almost reached equilibrium at t= 5 hrs except the large unit discharge (M-2 and M-3) cases. Besides, the exceeding probability decreases with time, and increases with the unit discharge and slope. The results also reveal that the scour hole still continuously stretches after 5 hrs for the large unit discharge cases.

Topic Category 工學院 > 土木工程學系所
工程學 > 土木與建築工程
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Times Cited
  1. 蕭國廷(2017)。固床工下游側流場之PIV量測-猝發現象之初探。中興大學土木工程學系所學位論文。2017。1-104。