深入探討運動型自行車之空氣動力行為

Investigation into sport bicycles aerodynamics

羅鈺棋(Yu-Chi Lo)

指導教授 ： 許文翰

共同指導教授 ： 蔡順峯

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201904301

摘要

本研究透過CFD分析工具深入探討運動自行車的空氣動力學，所使用的方法是基於有限體積法的CFD開源工具OpenFOAM來進行數值模擬。為了瞭解單一自行車者在迎風條件下騎乘時，探討不同類型的空氣動力套件對阻力面積的影響。採用的空氣動力套件包含不同形式的輪組、整流罩以及車架，並比較了九種運動自行車幾何配置與減阻百分比的關係。此外，選擇球體、 $65^{circ}$三角翼和$25^{circ}$艾哈邁德體三個基準問題，在與實驗相同的條件安排下進行特徵流場的驗證。當前模擬中的實體模型使用SolidWorks建立，網格由Pointwise和snappyHexMesh所生成。為建立一個有效率且具備一定準確性的穩態計算模型，選擇求解三維雷諾平均納維爾－斯托克斯方程，並採用傳統的SST $k$ - $omega$紊流模型和SIMPLEC算法。基準問題的數值結果與現有的實驗數據具有良好的一致性。自行車的模擬結果表明在適當的配置下，所考慮的三種形式空力套件都能有效地減少阻力，其中尾錐形式的整流罩給予了將近15\%的減阻百分比。最後，本研究統整出騎乘自行車時，人體後方主要渦流結構的成因及其對阻力的影響，並以視覺化的方式呈現，藉此幫助人們更清楚地了解自行車運動的空氣動力行為。

關鍵字

計算流體力學 ； OpenFOAM ； 球體 ； 三角翼 ； 艾哈邁德體 ； 運動自行車 ； 自行車空氣動力學

並列摘要

In the present study, the aerodynamic details of sport bicycles were explored by conducting CFD analysis. The numerical simulations were performed based on the finite-volume method by using the CFD open-source package OpenFOAM. To understand how different types of aerodynamic kits affect the drag area ($c_{mathrm {d}}A$) when a single cyclist is riding in windward conditions. The relationship between the geometry of nine sport bikes and the percentage of the drag reduction is compared. The aerodynamic kits under consideration used include different types of wheel sets, fairings, and frames. Also, benchmark studies on a sphere, the $65^{circ}$ delta wing, and the $25^{circ}$ Ahmed body have been carried out under the same arrangement of experiments. The solid models in this study are built using SolidWorks, and the meshes are generated by Pointwise and snappyHexMesh. In order to establish an efficient and accurate steady-state calculation model, we choose to solve the three dimensional Reynolds averaged Navier-Stokes equations. A conventional SST $k$ - $omega$ turbulence model and SIMPLEC solution algorithm were adopted. The numerical results of the benchmark studies were all found to have good agreements with the existing experimental data. The bicycle simulation results show that these three forms of aerodynamic kits can effectively affect the drag area in proper geometric shapes; among the kits under investigation, the form of a tail cone fairing gives a nearly 15\% reduction in drag area. This study integrates the causes of the eddy currents and their effect on drag area when a cyclist cycling in a dropped position. Moreover, the main vortex structures behind the human body have been visualized for aiding us to understand the aerodynamic behavior of cycling more clearly.

並列關鍵字

Computational Fluid Dynamics (CFD) ； OpenFOAM ； Sphere ； delta wing ； Ahmed body ； Sport bicycle ； Cycling aerodynamics

參考文獻

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