以二相流離散元素電腦模擬與物理實驗探討液體中顆粒體崩塌行為

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Title:	以二相流離散元素電腦模擬與物理實驗探討液體中顆粒體崩塌行為
Authors:	陳定偉;Chen, Ting-Wei
Contributors:	機械工程學系
Keywords:	液體中顆粒體;崩塌行為分析;CFD-DEM模擬技術;實驗驗證;黏滯效應;傳輸性質;granular column in fluid;collapsing behavior;combined CFD-DEM model;experimental validation;viscosity effect;transport property
Date:	2017-11-29
Issue Date:	2018-01-16 11:07:42 (UTC+8)
Publisher:	國立中央大學
Abstract:	本論文以二相流離散元素電腦模擬與物理實驗探討液體中顆粒體崩塌行為，在物理實驗中進行水中顆粒體崩塌實驗，使用影像處理技術量測水中顆粒體的速度分佈與顆粒流的表面輪廓，並分析流量與時間的關係。同時本文提出二相流離散元素模型，並考慮背景阻尼用以消散二相流顆粒系統中過多的能量，模擬對應的水中顆粒體崩塌實驗。研究結果顯示，該二相流離散元素模型配合適當的背景阻尼，其電腦模擬結果與實驗結果相當吻合，吻合的物理量包括壁面沿深度方向的流速分佈，出口處的流量分佈，顆粒流平移速度向量場及歷時表面輪廓分佈。接著分析驗證合理的二相流離散元素電腦模擬結果，進一步探討二相流顆粒系統中的內部物理量，同時並比較乾顆粒系統中的內部物理量，最後探討液體黏滯係數對液體中顆粒體崩塌行為的影響。本研究考慮顆粒體在四種液體(空氣，水，橄欖油及蓖麻油)中的崩塌行為，得知邊璧處平移速度剖面皆為SSH (Sidewall Stabilized Heap) 流態，但顆粒體在空氣，水，橄欖油及蓖麻油中，其中心處的平移速度剖面皆為混合型態，而顆粒體在空氣中較其他三種介質更快速地演化成SSH流態。顆粒體在四種液體中，其旋轉速度剖面皆呈現SSH流態，水平方向的旋轉速度均甚小於厚度及垂直方向的旋轉速度，且在邊璧處的垂直方向旋轉速度均大於中心處的旋轉速度。研究結果亦顯示顆粒體的平移速度及旋轉速度隨著液體黏滯係數增加而減少，流量變化也隨著黏滯係數增加而下降。 ;The purpose of the study is to investigate granular column collapse in fluid experimentally and numerically. Experiments on granular column collapse in the water environment were conducted, and image processing technique was employed to measure velocity profile and surface profile of granular flow in the water as well as the flow rate at the outlet. In addition, a two-phase flow discrete element method (combined CFD-DEM modeling) was proposed to simulate the corresponding experiments. In the combined CFD-DEM simulation, a background damping mechanism was incorporated to dissipate excessive energy of particulate system. The study shows that the simulations produce reasonable agreement with experiments for the velocity profiles, flow rate at the outlet, translational velocity field and surface profiles. The validated numerical model was further used to explore internal physical properties of granular assembly. Four kinds of fluid, including air, water, olive oil and castor oil, were also used to explore the effect of fluid viscosity on granular column collapse. The results show that all of the translational velocities at the sidewall exhibit the SSH (Sidewall Stabilized Heap) rheology. However, the translational velocities at the center of the chute show a mixed profile in the air, water, olive oil and castor oil, and the velocity profile in the air evolves to the SSH rheology more quickly than those in other conditions. The angular velocities in the four kinds of fluid all exhibit the SSH rheology. The angular velocities in the horizontal direction are much smaller than those in the vertical and depth directions. In addition, the angular velocities in the vertical direction at the sidewalls are larger than those at the center of the chute. The results also indicate that the translational and angular velocities and the flow rate decline with the increase of viscosity.
Appears in Collections:	[Graduate Institute of Mechanical Engineering] Electronic Thesis & Dissertation

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