臺灣博碩士論文加值系統

本文主要的焦點是檢測動態次格點模型在大窩數值模擬上應用的效果。將採用動態次格點模型的大渦數值模擬來模擬完全發展的管流和旋轉圓盤內的流場模擬。首先，將大渦數值模擬的動態次格點模型應用在完全發展的管流模型中，在雷諾數等於180的情況下，發現所採用的動態次格點模型比Van Driest damping模型對網格的大小更敏感。所採用的動態次格點模型和Van Driest damping 模型在網格大小是96X96X96的情況下，的數值計算結果和直接數值計算(DNS)的結果非常符合。從平均流速來看，在viscous sub-layer的區域，動態次格點模型預測的效果不錯，但在中心流動的區域，所採用的動態次格點模型和Van Driest damping 模型相比較看來，有低估的現象。第二，在旋轉圓盤方面，在圓盤內流場的結構主要是由切線方向的動量油旋轉面到圓盤內部的擴散傳輸所造成的，而且在圓盤內部會產生二次流的現象。順時的切線方向的漩渦在切線方向可以看見被拉長了。在靠近旋轉面的地方，漩渦的結構比較有一置性，但是在靠近固定面的地方，相比較起來，漩渦的結構看起來就比較混亂，最後也將採用的動態次格點模型和Van Driest damoing 模型比較，兩種所使用的模型和實驗值比較起來都有不錯的效果，除了在Ekmann layers 的區域之外。

The main focus of the present work is to explore the effects of the dynamic model in large eddy simulations. Application is first applied to the fully developed channel flow with Reynolds number at . It was found that the dynamic model is more sensitive to the grid density compared to that using the van Driest damping. Both the sub-grid models with van Direst damping and the dynamic model predict the mean and turbulence quantities well by comparisons with the DNS data. The viscous sub-layer is adequately resolved by the models. However, the dynamic model does predict a lower level of turbulence intensity at the central core of the channel. For rotor-stator flow, the internal structure is induced by the diffusive transport of the tangential momentum from the rotor into interior. A secondary flow exits within the rotor-stator cavity. The instantaneous azimuthal vorticity contours show stretching and elongated structure in the tangential direction. Near the rotor, the vorticity structure is more coherent; but near the stator the vorticity structure is more chaotic. Comparisons with the available measured data, both models show good results, though there are some discrepancies across the Ekmann layers.

Contents
Abstract.......................................1
Nomenclature...................................2
Chapter 1 Introduction
1.1 Introduction...............................7
1.1.1 Large eddy simulation.................7
1.1.2 rotor-stator cavity flow..............8
1.2 Literature survey..........................9
1.2.1 Large eddy simulation.................9
1.2.2 Rotor-stator flow.....................11
1.3 Objectives.................................12
Chapter 2 Mathematical Model
2.1 Governing equation ........................13
2.1.1 The filtering operation...............13
2.1.2 Filtered Navier-Stokes equations......14
2.2 Sub-grid scale modeling....................15
2.2.1 Smagorinsky model.....................16
2.2.2 Scale-similar and mixed models........17
2.2.3 Dynamic model.........................18
Chapter 3 Numerical algorithm
3.1 Fractional-step Method.....................20
3.2 How to get the Smagorinsky coefficient C...27
Chapter 4 Result and Discussion
4.1 Fully develop channel flow.................28
4.2 Rotor-stator cavity flow...................30
Chapter 5 Conclusion and Future Works
5.1 Conclusion.................................33
5.2 Future work................................34
Bibliography...................................35
Figures........................................38

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