Measurements and Analyses of Flow Field at Upstream Side of Weir
Date Issued
2006
Date
2006
Author(s)
Huang, Chiou-Yuan
DOI
zh-TW
Abstract
The main goal in this thesis is to measure the velocity profile at weir crest and then derive the relationship between water surface velocity and profile at crest. That relationship can be utilized to estimate velocity profile as flow over weir where only two kinds of information: water surface velocity and water dapth. Furthermore, the discharge will be carried out through the integration of velocity profile. In addition, the horizontal and vertical variations of velocity profile at upstream side will also be discussed. This thesis constructs three-dimensional flow field at crest and upstream side of sharp crest and Ogee weirs with height 20 cm using Acoustic Doppler Velocimetry at various water depth at weir crest. In this study, there are 6 different cases in water depth at crest and range of depths is from 12 to 17 cm.
There are three topics according to results of measurements. First, the maximum longitudinal velocity of vertical velocity profiles at weir crest occurs near the crest which differs from general velocity profile in open channel flow without structure. The distinct pattern therefore causes the traditional estimation of velocity profile invalid. Hence the second topic holds an algorithm how to create the velocity profile at crest based on information of velocity at water surface and water depth. Surface velocity and water depth as characteristic values normalize the velocity profile and elevation. Summarizing all normalized measured data, similar non-dimensional profiles are presented. Afterward the regression is carried out between velocity profile and elevation ( ). Some examinations are performed and these show good agreement of estimating real velocity profile only according to surface velocity and water depth. Furthermore, the discharge calculations are discussed here and some comparisons are also exhibited with other methods. The last topic is an observation at upstream side of weir. Concluding the velocity profiles, there is a pivot of equilibrium longitudinal velocity that locates at approximate elevation of weir height. Zone above the pivot means velocity acceleration, and whereas the velocity deceleration appears below the pivot.
Subjects
聲波都卜勒測速儀
流速剖面
堰流
ADV
velocity profile
weir flow
Type
thesis
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