臺灣博碩士論文加值系統

本研究主要目的在於同時利用計算流體力學之數值模擬與縮小模型阻力係數之風洞量測兩種技術，探討小型競賽車輛之外流場與阻力係數，以作為外形改善之依據。首先利用1比8縮小模型在風洞內作阻力係數測試及流動觀察，再採用不同紊流模型，對風洞實驗的縮小模型狀況做數值模擬，將模擬結果與實驗結果做比較，以選定較適當的紊流模型。最後利用選定的紊流模型與數值計算程序，探討影響小型競賽車輛風阻係數之重要參數，例如雷諾數、前擋板之設計、底板傾斜角度、與駕駛者姿態等。
實驗與數值模擬結果比較顯示，數值計算採用 紊流模型所得結果與風洞實驗數據最相吻合。利用此紊流模型做高雷諾數之延伸，由數值計算結果提出涵蓋實際應用範圍的風阻係數曲線。對整車外型，尤其是前擋板與前整流罩，作減低風阻之設計後，新設計原型車之風阻比市售車有明顯的降低。參數探討的結果顯示，前擋板角度之設計以及跟車距離影響風阻較為明顯，駕駛者姿態對風阻的影響決定於最後形成的壓力場分布情形。

The main objective of this study is to investigate the external flow field and drag coefficient for Go-karts, by using both numerical modeling with a computational fluid dynamics package and the measurement of the drag coefficient with a scaled model in a wind tunnel. At first, a 1:8 scale model was used in a wind tunnel test to measure its drag coefficient and to conduct flow visualization. The experimental data was then used to select the most suitable turbulence model for the simulation of Go-kart aerodynamics. Finally, the chosen turbulence model and the computational procedure were used to investigate important factors that influence the drag coefficient of a Go-kart, such as the Reynolds number, the design of the front panel, the orientation angle of the chassis, and the pose of the driver.
Comparisons of the experimental and numerical results show that turbulence model gives the best agreement with the measured data. By extending this turbulence model to higher Reynolds numbers, complete curves of drag coefficient were presented which cover the parameter range for real applications. New phase designs with the consideration of drag, especially the change of the front fairing and the front panel, showed obvious reduction in the drag when compared to a commercially available Go-kart. Among the investigated parameters, both the angle of the front panel and the distance between two carts have significant influence on the drag. The influence of the driver’s pose is uncertain, depending on the resulting pressure distribution.

第一章 緒論　　　　　　　　　　　　　　　　　　　
1.1研究背景　　　　　　　　 　　　 　　　　
1.2研究動機　　　　　　　　 　　　 　　　　
第二章 文獻回顧
2.1空氣動力學與造型探討
2.2 CFD數值模擬應用於車輛
第三章 研究方法
3.1 風洞實驗
3.2數值分析程序
3.3數值分析程序
3.4統御方程式
3.5 紊流方程式
3.6 數值求界方法
3.7收斂條件
3.8 鬆弛因子
3.9 網格數量測試
3.10 動力相似驗證
3.11 計算區域驗證
第四章 結果與討論
4.1風洞條件下實驗與模擬比較結果
4.1.1 SI模型實驗與模擬結果
4.1.2 PhaseI模型實驗與模擬結果
4.1.3 PhaseII模型實驗與模擬結果
4.1.4 三種車型之模擬結果比較
4.2.改變駕駛姿勢支實驗與模擬結果
4.3.跟車實驗與模擬結
4.4.三種車型於自由區域下之模擬結果
4.5自由區域下改變front panel角度模擬結果
4.6自由區域下各零組件模擬結果
4.7與自由區域下加底板之模擬結果
第五章 結論與建議
5.1 結論
5.2 建議
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