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研究生： 杜文冬
Do, Van Dong
論文名稱： 分析兩個Ahmed body模型之間超車過程
Analysis of the Overtaking Process between two Ahmed body models
指導教授： 張克勤
Chang, Keh-Chin
學位類別： 碩士
Master
系所名稱： 工學院 - 航空太空工程學系
Department of Aeronautics & Astronautics
論文出版年： 2019
畢業學年度： 107
語文別： 英文
論文頁數： 67
外文關鍵詞： Overtaking Process, CFD, Ahmed Body, Model Validation, Drag Force Coefficient, Side Force Coefficient
相關次數： 點閱：70  下載：6 
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    • The overtaking process is the common phenomena encountered in our daily life. It has significant effects on the stabilities of the moving vehicles. The study conducted the wind-tunnel tests with the Ahmed body models to provide available experimental data for validating the physical model and numerical method set for the simulation of the overtaking process. Three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations were applied to the simulation with ANSYS Fluent. The computational domain and the mesh size required for the accurate simulation are investigated by comparing with the experimental data. It is found that the outlet must be located sufficient far downstream such as x/L = - 10.91.
    The physical model employed in the simulation, such as the turbulence model, was also investigated through comparison with the experimental results. It is shown that the k-ω SST turbulence model can yield a satisfactory prediction of the flow field.
    Study of overtaking process pointed out that the drag force coefficient of the overtaken car reaches its maximum at the normalized relative distance between two cars (x/L) of around - 1, while the drag force coefficient of the overtaking car reaches its maximum at 1. This study also indicated that the side force coefficient of both overtaken and overtaking cars are changed greatly during the overtaking process of x/L from – 1.5 to 1.
    Effects of relative velocity and transverse spacing between the overtaken and overtaking cars on the drag force coefficient and side force coefficient are examined. It is appointed that greater relative velocity and narrower transverse spacing are, higher drag force and side force coefficients on both overtaken and overtaking cars are.

    ABSTRACT i ACKNOWLEDGEMENTS iii TABLE OF CONTENTS iv LIST OF TABLES vi LIST OF FIGURES vii NOMENCLATURE xi CHAPTER 1. INTRODUCTION 1 1.1. The Aerodynamic Characteristic on the Road of the Vehicle 1 1.2. The Overtaking Process between Two Vehicles 2 CHAPTER 2. LITERATURE REVIEW 3 2.1. Investigation in the Experimental Method 3 2.2. Investigation in the Numerical Method 5 CHAPTER 3. AND METHODOLOGY 7 3.1. Model Geometry 7 3.2. Experimental Method 8 3.2.1. Experimental Setup 8 3.2.2. Independence of Reynolds number 9 3.2.3. Pressure Surface and Aerodynamic Force Coefficients 11 3.2.4. Inlet and Outlet Flow Conditions 12 3.3. Physical Modeling and Numerical Analysis 13 3.3.1. Governing Equation 13 3.3.2. Computational Domain and Meshing 16 3.3.3. Modeling 17 CHAPTER 4. RESULTS AND DISCUSSION 19 4.1. Experimental Results 19 4.1.1. Reynolds-number Independent Test 19 4.1.2. Surface Pressure and Aerodynamic Force Coefficients 20 4.1.3. Inlet and Outlet Boundaries 22 4.2. Validation of the Simulation Results. 22 4.2.1. Turbulence Model 22 4.2.2. Mesh Independence Test 23 4.2.3. Computational Domain Test 24 4.3. Simulation of the overtaking process 24 4.3.1. Analysis of Aerodynamic Characteristics during the Overtaking Process 25 4.3.2. Effect of Relative Velocity 26 4.3.3. Effect of Transverse Spacing 27 CHAPTER 5. CONCLUSIONS 29 REFERENCES 30 TABLES 32 FIGURES 36

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