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研究生： Million Asfaw Belay
Million - Asfaw Belay
論文名稱： Large Eddy Simulation Applied on the Analysis of Vortex Tube
Large Eddy Simulation Applied on the Analysis of Vortex Tube
指導教授： 林顯群
Sheam-Chyun Lin
口試委員: 楊旭光
S.K. Yang
郭振華
Guo, Zhen-Hua
莊福盛
Fu-Sheng Chuang
學位類別： 碩士
Master
系所名稱： 工程學院 - 機械工程系
Department of Mechanical Engineering
論文出版年： 2014
畢業學年度： 102
語文別： 英文
論文頁數： 154
中文關鍵詞： Vortex tube 、CFD code Fluent 、sk-ɛ 、RNG k-ɛ 、k-ω 、RSM 、LES
外文關鍵詞： Vortex tube, CFD code Fluent, sk-ɛ, RNG k-ɛ, k-ω, RSM, LES
相關次數： 點閱：369  下載：17 
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    • 渦流管也被稱為Ranque-Hilsch渦流管，是將氣體分離為熱氣流與冷氣流的機械裝置，它沒有任何移動部件，只是將高壓氣體由切線方向經噴嘴注入腔室產生高度的旋流，因此空氣會沿著管壁周圍往熱端進行螺旋式運動；當位於熱出口氣閥附近的空氣壓力高於外側(藉由關閉部分氣閥)，將於此高壓區域產生壹軸向逆流通往另一冷端，而從渦流管之另一端(即冷端)流出。在此過程中，往熱端流體在管壁而逆流則在管中央部分流動，由於兩者之溫度不同，故在逆向氣流與向前氣體之間發生產生巨幅能量交換，因此導致通過管子核心之逆流會進行冷卻(低於氣流的入口溫度)，而正向氣流之溫度則隨著往前的方向持續被加熱。
    本研究採用高解析的大渦流模擬(LES)方法，將之應用在三維的計算模型以求解其流體的分離和流動現象，以期能經由計算結果解釋渦流管內的溫度分離現象。本文採用計算流體力學軟體Fluent模擬流場，共使用了包括LES模型在內的五種湍流模型，FLUENT是用於模擬流體流動問題的通用軟體，係利用有限體積法求解流體的統御方程式，它提供了一個解決廣泛問題的方法。本文成功地模擬出隨著時間渦流管內的氣流溫度和壓力場分佈，在給定的進氣壓力下，取得了速度之切線分量、低溫分離點、與冷端出口質量等性能特性。同時，在模擬使用不同的湍流模型以及不同的進口壓力分析後，可清楚看出大渦漩模擬模型可得，到比起其它紊流模組更多的流場資訊，且更接近實驗數據的結果。

    Vortex tube (VT), also known as the Ranque-Hilsch vortex tube (RHVT), is a mechanical device with no moving parts that can separate a homogenous air flow into hot and cold streams. The gas is injected tangentially into a nozzle chamber with high degree of swirl velocity so that air travels in a spiral motion along the periphery of the hot side. When the pressure of the air near the valve (which is located at the hot exit) is higher than the ambient pressure by partly blocking the valve, thus a reversed axial flow through the pipe core region is generated from this high-pressure region near the hot-side exit. During this interacting process, energy transfer takes place between the reversed stream and the forward stream, therefore air stream through the core is cooled to a temperature below the inlet air while the air stream in the forward direction is heated. This simple devise can provide a significant temperature drop at the cold-end stream which has plenty engineering application; thus becomes the topic of this research.
    In this study, a three dimensional VT model is constructed and used to carry out the numerical computation in the framework of commercial CFD code Fluent for predicting the energy separation and flow phenomenon inside the tube. Moreover, five turbulence models including standard k-epsilon (sk-ɛ), renormalization group k-epsilon (RNG k-ɛ), k-omega (k-ω), Reynolds stress model (RSM) and large eddy simulation (LES) model are adopted in the calculating procedures for evaluating their outcomes. As a result, the numerical simulations clearly illustrate the temperature separation and flow phenomena within the vortex tube. Also, the CFD flow visualization on vortex tube can identify three regions, which are the incoming fluid at ambient temperature and high pressure, the cold exit and the hot exit where the temperatures are significant lower or higher than the inlet temperature, respectively. Also, performance curves (cold temperature separation versus cold outlet mass fraction) of vortex tube were obtained successfully under a given inlet pressure. Regards the comparison among turbulent models, CFD predictions from the large eddy simulation yields the best high-resolution flow pattern and provides more detailed information for understanding the physical mechanisms of this flow and energy separation. Also, its calculated results are in a better agreement with the available experimental measurements compared to other turbulent models.

    摘　要 I ABSTRACT III ACKNOWLEDGEMENTS V NOMENCLATURE VI TABLE OF CONTENT IX LIST OF TABLES XI LIST OF FIGURES XII Chapter 1 INTRODUCTION 1 1.1 Background 1 1.2 Components of vortex tube 2 1.3 Working principle of vortex tube 4 1.4 Theory of operation 6 1.5 Types of vortex tubes 9 1.6 Basic definitions 13 1.7 Fundamentals of vortex tube (VT) 16 1.8 Commercial vortex tubes 26 Chapter 2 LITERATURE REVIEW 33 2.1 Experimental studies 34 2.2 Analytical studies 36 2.3 Computational studies 37 2.4 Motivation and objective of the study 41 Chapter 3 COMPUTATIONAL FLUID DYNAMICS 43 3.1 History of CFD 44 3.2 CFD application 45 3.3 Governing equations 47 3.4 Turbulent modeling 52 3.5 Boundary conditions 64 3.6 CFD methodology 65 Chapter 4 NUMERICAL SIMULATION OF VORTEX TUBE 73 4.1 Utilized experimental results 74 4.2 RHVT CFD Model 78 4.3 Assumptions and boundary conditions 79 4.4 Mesh convergence study/Grid independence test 80 4.5 Solution procedure 83 4.6 Result and discussion 85 4.6.1 Thermal performance 85 4.6.1.1 High pressure inlet boundary condition 85 4.6.1.2 Low pressure inlet boundary condition 105 4.6.2 Flow field 115 4.7 Summary 126 Chapter 5 CONCLUSIONS 129 5.1 Conclusions 129 5.2 Future work 130 References 131

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