數值與實驗探討明渠流在多階跌水底床運行之現象

Numerical and Experimental Studies of Free Overfall Flows in Open Channels with Multi-Stage Cascading Bottoms

丁琦瑋(Chi-Wei Ting)

指導教授 ： 鄧志浩

中原大學/工學院/土木工程研究所/碩士(2012年)

https://doi.org/10.6840/cycu201200687

摘要

本文內容是利用最小平方有限元素法(LSFEM)之二相流數值模式求解無因次三維不可壓縮流體之動量與質量守恆方程式，再配合流體體積法(VOF)以尤拉慣性座標描述自由液面的動力與邊界條件之連續函數 (Color Function)，藉以探討流體運行在渠道不規則底床變化中其流況與液面的變化關係。研究共分為三大研究類型，分別為雙階跌水、渠道邊壁突縮及底床組水擋板。經過多種模組案例的模擬分析及水工試驗的模場數據，成功歸納出雙階跌水其階層流體變化的關聯性；而在渠道突縮方面，藉由改變不同的邊壁突縮程度，探討其對於自由液面及流況現象的相關影響，發現當突縮截面積增大時，其水體碰撞擊及迴流之現象也會因此趨於顯著；為了能瞭解更多關於不規則底床變化的影響條件，本文調控了擋板個數、高度及設置地點等多種實驗因子，分別架設不同之計算流場進行分析，結果顯示其擋板個數的增加會與流體波能的消耗呈現一比例之變動關係，而相隔間距與障礙物高度的擴大亦會導致速率上下波動的現象。

關鍵字

二相流 ； 自由液面 ； 最小平方有限元素法 ； 數值模擬

並列摘要

In this study, the least-squares finite element method (LSFEM) is applied for solving the dimensionless three dimensional incompressible two-phase flow governed by the mass and momentum conservative equations. The dynamic variation of the free surface moving in a uneven or a suddenly width-reduced channel between both phases is expressed in terms of the color function of a volume of fluid (VOF) method in an Eulerian coordinate system.
There are three parts of study regarding the free surface distribution in this thesis, first is the dual-step free overfall flow, second is flow in a side-wall reduced channel, and the last one is the flow in a uneven channel with downstream blockage. From the numerical simulations and the experimental measurements, we can successfully classify the relationships for the free surface of the dual-step overfall and the channels with suddenly reduced width. The recirculation phenomena of the width reduced channel will be more significant with more section reduced. After the verification of the numerical and experiment for the first two cases, the energy dissipation for the channel with blockages settled downstream is also studied. The height, location and spacing of the blockages are carefully simulated. It is found that energy dissipation increases more when the blockage is higher. The increasing of the height and space of blocks will cause the oscillation of free surface more serious.

並列關鍵字

least-squares finite element method ； Two-phase flow ； numerical simulation ； free surface.

參考文獻

15.鄭雅允(2003)，”二相流模式探討明渠流在不規則底床運行之現象”， 私立中原大學土木工程學系碩士論文。

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