https://scholars.lib.ntu.edu.tw/handle/123456789/86195
標題: | 行政院國家科學委員會專題研究計畫期中進度報告:三維度自由液面沉澱池水理與懸浮微粒傳輸之數值研究(1/2) | 作者: | 張倉榮 | 關鍵字: | 自由液面沉澱池;懸浮微粒傳輸;計算流體力學;微粒軌跡追蹤;停留時間;Free surface sedimentation basin;Suspended particle transport;Computational fluid dynamics;Particle trajectory tracking;Particle detention time | 公開日期: | 2005 | 出版社: | 臺北市:國立臺灣大學生物環境系統工程學系暨研究所 | 摘要: | 本二年期研究計畫之主要目的在於以數 值模擬方式進行三維度自由液面沉澱池水理 與懸浮微粒傳輸之研究,以統合考量沉澱池 三維度流速分佈與紊流強度分佈、懸浮微粒 停留時間分佈、懸浮微粒濃度分佈與沉澱效 率、底床剪力分佈與微粒再懸浮機制探討及 自由液面對微粒傳輸之影響等因素。第一年 首先藉由計算流體動力學(CFD)發展三維度 自由液面沉澱池水理與尤拉觀點之懸浮微粒 濃度擴散對流模式,進行數值境況模擬,以 計算沉澱池在不同幾何形狀、入流口流量與 紊流強度、入流口微粒濃度分佈、底床啟動 剪應力沖刷機制、沉澱池隔艙板等條件下之 水理、濃度空間分佈與沉澱效果。三維度水 理模式係以不可壓縮黏性流體為模式之基本 架構,使用有限體積法(FVM)為數值模擬基 礎,以傳統的k-ε紊流模式及大漩渦模擬 (LES)等紊流模式模擬沉澱池內的紊流場,並 比較其異同。本研究所發展的數值模式也將 與前人水槽試驗量測結果進行驗證比對分 析。最後,本研究並根據氣流場通風理論, 提出利用微粒停留時間分析模式求得微粒在 沉澱池停留時間之計算方法。 本研究第二年繼而建立拉格蘭日觀點之 三維度微粒軌跡追蹤模式,以計算沉澱池中 懸浮微粒粒徑介於0.1 至1000 μm 間之運動 軌跡、停留時間分佈與濃度空間分佈。微粒 軌跡追蹤模式主要是以釋放符合統計顯著性 的大量微粒來追蹤其傳輸軌跡、沉降路徑、 停留時間及沉端沈積點,以期能了解沉澱池 在不同幾何形狀、邊界水理條件及邊界濃度 條件下之水理、濃度空間分佈與沉澱效果。 求解微粒軌跡追蹤方程式必須搭配第一年度 所得到的水流瞬時速度場,再使用4 階 Runge-Kutta 法來求解每個微粒在每個時間 的速度及其軌跡。軌跡的計算係從一開始釋 放時就追蹤,直到微粒碰到沉澱池邊界或流 出沉澱池方才停止。本研究亦將微粒軌跡追 蹤結果與前人水槽懸浮微粒濃度分佈試驗量 測結果進行驗證。此外,研究中將進一步比 較前一年度發展之濃度擴散對流方程式及本 年度所發展之微粒軌跡追蹤法,在相同起始 與邊界條件下,所計算而得的沉澱池微粒停 留時間、濃度空間分佈及沉澱效率等,以作 為模式修正與改進之參考。 The main objective of this two-year project is to numerically study water flow field and suspended particulate transport in 3-D free-surface sedimentation basins by interruptedly considering the effects of mean velocity and turbulence intensity distributions, particle detention time distributions, suspended load concentrations, sedimentation efficiencies, shear distributions on basin bed, and free surface. In the first year, a 3-D free-surface water flow model is established to investigate water flow field of sedimentation basins. The water flow field within a sedimentation basin is considered to be incompressible turbulent flow. The transport of the incompressible turbulent flow is herein simulated by the finite volume method (FVM) together with three kinds of commonly used turbulence models, i.e., the traditional k- εmodel and the large eddy simulation (LES). The difference of velocity distribution pattern among the three turbulence models is compared. A concentration convection diffusion model is developed as well. Numerical scenario simulations are carried out for various geometry configurations, inflow velocities, inflow turbulence intensities, inflow suspended particle concentration, erosion conditions on basin bed, and baffles. The water flow field model is verified with available water flume measurement. Finally, the particle detention time analysis is performed based on the building ventilation theory. In the second year, a 3-D Lagrangian particle tracking technique is developed to investigate particle transport trajectories, particle detention time, deposition patterns, and concentration distributions in sedimentation basins by releasing a large number of particles (at least 1000 particles per simulation) into the computational domain. The diameter of the particle released ranges from 0.1 to1000 μm. The particles released are tracked and recorded until they hit the basin boundaries or flow out of the basin. The particle tracking model, solved by the 4th order Runge-Kutta method, is next verified with available water flume measurement. Numerical scenario simulations are also carried out for various geometry configurations, hydraulic conditions, and concentration conditions. In addition, under the same boundary and initial conditions, the simulated results of particle detention time, deposition patterns, sedimentation efficiency, and concentration distributions by using the concentration convection-diffusion model and the particle tracking model are compared and discussed. Results obtained from this research are expected to offer engineers a design concept for sedimentation basins. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/10783 | 其他識別: | 932211E002023 | Rights: | 國立臺灣大學生物環境系統工程學系暨研究所 |
顯示於: | 生物環境系統工程學系 |
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