Simulations of Nonhomogeneous Terrain Flows

微氣候中，大部分的地表層分析假定均勻地形流況和水平均勻流動。然而，一個均勻的環境系統在自然界中的存在是相當少見的。一個更有物理意義的有限體積法被用來考慮當流動受地表粗糙度影響時之變化。所以我們使用雷諾應力紊流模式，以了解大氣紊流結構如何被不同地表影響。 地表粗糙度對風速有相當深刻的影響。越粗糙的地表，則越易使大氣邊界層內的風速減速。此研究顯示從粗糙到平滑的紊流邊界層的變化小於平滑到粗糙。紊流強度的分佈也描述了邊界層的變化。地形變化越大則風速變化越大。In microclimate, most surface layer analyses assume uniform terrain conditions and a horizontally-homogeneous flow. However, a homogeneous environmental system rarely exists in the nature. A finite volume method with more reasonable physical meanings is introduced to consider a flow field over a changed roughness surface. In order to know how various types of surface affect the atmospheric turbulence structure, RSM (Reynolds Stress Model) is used. Surface roughness has a profound effect on wind speed. The rougher a terrain is, the more it retards the wind in the atmospheric boundary layer. This study reveals that the variation of turbulent boundary layer due to rough-to-smooth is less than that in the smooth-to-rough. The distribution of the turbulence intensities also depicts the variations of the internal boundary layer. The higher height a terrain surface has, the more variation it exhibit near the step change.Contents Acknowledgements i Chinese Abstract ii Abstract iii Contents iv List of Tables vii List of Figures viii Nomenclature xii Chapter 1 Introduction 1 1.1 Motivations 1 1.2 Objectives 2 1.3 Literature review 2 1.4 Synopsis 5 Chapter 2 Mathematical Formulae and Numerical Model 7 2.1 Governing equations 7 2.2 Turbulence model (Reynolds Stress Model, RSM) 8 2.2.1 Modeling of - equation 10 2.3 Numerical Methods 16 2.3.1 Grid generation 16 2.3.2 Finite volume method 16 2.4 SOLA method 17 2.5 Summary 18 Chapter 3 Validation of Proposed Numerical Model 19 3.1 Cavity flow 19 3.2 Turbulent channel flow passes a square cylinder 19 3.2.1 The experimental setup and procedure 20 3.2.2 Grid-independence studies 21 3.2.3 Mean velocities and turbulent intensity 21 3.3 Summary 23 Chapter 4 Simulations of Nonhomogeneous Terrain Flow 24 4.1 The experimental setup and procedure 24 4.2 Flow from a smooth terrain to a rough terrain 26 4.2.1 Mean Velocities 26 4.2.2 Turbulent kinetic energy and turbulent stresses 27 4.2.3 Growth of the internal boundary layer 27 4.2.4 Discussion 27 4.3 Flow from a rough terrain to a smooth terrain 28 4.3.1 Mean velocities 28 4.3.2 Turbulent kinetic energy and turbulent stresses 28 4.3.3 Growth of the internal boundary layer 29 4.3.4 Discussion 29 4.4 Summary 30 Chapter 5 Conclusions 31 References 78 Curriculum vitae 8