- 學位論文
單階與多階渠道跌水消能之研究
A study on energy dissipation of free falling of unit-step and multi-step channels
摘要
本研究利用數值模擬方法探討三個主題，一為單階跌水消能工的各項水利參數模擬及迴歸分析；二為多階垂直跌水消能率探討；最後將模式應用於3-D消能池尾檻設置對消能率的影響。本文所利用套裝軟體Fluent，為有限體積法模式，求解Navier-Stokes Equation。利用單階垂直跌水消能工之水墊區內迴水深度、撞擊水平床底位置兩者和入流狀態找出相互關係進行整理，並運用迴歸分析整理模擬結果之資料；多階垂直跌水消能率探討，藉由改變不同之階長比探討相同流量在不同階長比時之消能率；3-D消能池尾檻設置之消能率，將消能池加上間隔尾檻和設置連續尾檻相互比較其消能率。 驗證的部分是設置的不同展弦比實驗資料和本文所模擬之自由液面明渠流水面流線和水深變化比對。另外驗證模型中所利用的二相流模型及紊流模型，透過五階跌水實驗改變不同之流況，流況分為水舌流、過度流、平滑流探討三者之消能率，透過消能率相互比對得到良好的驗證。 透過多階垂直跌水之消能模擬結果，得知階長比為1/1時之消能效果最差，階長比為1/3之後消能效果隨著降低階長比而變佳，階長比為1/6時消能效果最佳；透過消能池不同之後方尾檻設計，得知消能尾檻具有開口消能效果較佳，消能池後方尾檻為間隔尾檻設計比連續尾檻設計消能率來的高且間隔越多越好，具有兩個間隔之尾檻比一個間隔之尾檻提升7%之消能率。
並列摘要
There are three parts of study in this thesis. First is the investigation of the hydraulic parameters and linear regression analysis of energy dissipation of unit-step free fall. The relation of simulation data for the depth in the circulation zone, , critical depth, , and distance from the drop wall, , were analyzed by regression analysis. Second is investigation of energy dissipation rate of free falling on multi-step open channels, Discussion on the energy dissipation in multi-stage free fall by changing different ladder length ratio were conducted. The last one is the effects of energy dissipation rate by spacing end block placed across the channel. Using 3-D model to investigate energy dissipation by simulating the stilling basin with spacing end- block in comparison with the basin with continuous end-block. This study uses the software package, Fluent, which is finite volume method numerical model, for solving the Navier-Stokes Equations. The simulation by using the open-channel flow downstream of drop structure created within different aspect ratios were compare with the measured data. That compares energy dissipation causing napped, transition, and skimming flows by changing flow in different Froude number. The verification of the two-phase flow model and turbulence model in the model used is appropriate. Simulation results through dissipation rate of multi-step free fall concluded that the worst effect of energy dissipation is the depth/height aspect ratio of 1/1. Effect of energy dissipation gets better with the aspect ratio decrease after aspect ratio of 1/3. The best energy dissipation effect is reached at the aspect ratio of 1/6. Through the study by spacing end block of energy dissipation pool, a better effect of energy dissipation was found out. That with opening end block and more intervals used, the better dissipation effect was reached. By using two intervals of opening, under the condition with the same volume of spacing, the energy dissipation rate increases 7% than just using one. Therefore, the energy dissipation design with spacing end-block is better than continuous block.