不同汽車外形在大雨下之氣動力研究

An Aerodynamic Study on Different Automobile Configurations under Severe Rain Conditions

江亦穎(I-Ying Chiang)

指導教授 ： 宛同

淡江大學/工學院/航空太空工程學系碩士班/碩士(2018年)

https://doi.org/10.6846/TKU.2018.00705

摘要

近代汽車的外形設計與操作性能息息相關，而空氣動力學更是影響汽車性能的重要因子。在本論文中，吾人初步探討汽車空氣動力學和幾種不同降雨量之傾盆大雨，及其對汽車空氣動力學的影響與相關物理現象。在工業設計上對於汽車空氣動力學已有許多標準的驗證模型，例如Ahmed body、SAE reference model和DrivAer model，本研究選擇Ahmed body及DrivAer model兩種模型來進行相關空氣動力學的研究，前者為汽車空氣動力學中較經典且簡單的實驗模型，後者為近年較現代且真實的汽車實驗模型。吾人使用基於有限體積法(FVM)的計算流體力學軟體ANSYS Fluent v16.0來模擬Ahmed body和DrivAer model周圍的流場現象，計算域網格則使用CutCell法來進行生成，此外，傾盆大雨的二相流模式使用結合Eulerian-Lagrangian approach的Discrete Phase Model (DPM)來建構。在成功的對兩種汽車模型進行驗證後，針對傾盆大雨之模擬，吾人考慮三種汽車行進速度與三種大雨量，結果發現在不同車速時，流經車體表面的流體加速性均有變小的趨勢，使得流場內壓力有著顯著的變化，此結果將造成兩種外形汽車的阻力各有不同的改變量，而負升力則有類似的變小趨勢。期待本研究結果能夠成為未來汽車工業的參考，甚或能增進汽車之行駛安全。

關鍵字

汽車空氣動力學 ； 二項流 ； 大雨 ； DrivAer model

並列摘要

Automobile configuration design is closely related to its operational performance, and aerodynamics is one of the most influential factors for modern automobile maneuverability. In this thesis, we not only investigate on the preliminary aerodynamics of automobiles, but also deal with some physical phenomenon of automotive aerodynamic behavior under some severe rain conditions. There are several major benchmark models for the aerodynamic study on automobiles, such as Ahmed body, SAE reference model, and DrivAer model. The Ahmed body and the DrivAer model are chosen for our automotive aerodynamics research. The first model is a classical reference model with a simple shape, and the second model is a more realistic and newer model created by Technical University of Munich. The Finite Volume Method (FVM) code ANSYS Fluent v16.0 was implemented to simulate the flow field of Ahmed body and DrivAer model, and their grids are generated by cutcell assembly meshing method. In addition, we used the Discrete Phase Model (DPM) which is the combined Eulerian-Lagrangian approach to modeling the two-phase flow for the heavy rain condition. In the case of heavy rain, it is found that the acceleration of fluid flow through the body surface becomes smaller, and the pressure distribution of the flow field will also change significantly. According to our result, the drag of these two models has different effects due to their different degree of bluntness, and the negative lift of both configurations will be reduced.

並列關鍵字

Automotive aerodynamics ； two-phase flow ； Heavy Rain ； DrivAer model

參考文獻

References

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