本研究旨在針對IDDES於車輛超車之空氣動力學分析時所產生的數值問題及應對策略。由於傳統的RANS模型在處理兩車併行或尾流交互作用等複雜情境時，其預測結果與實驗數據存在顯著差異，本研究採用SST-IDDES此一混合式RANS-LES模型，以期更精確地捕捉大尺度紊流結構。然而，在使用高解析度網格對具有非平滑邊緣的鈍體進行模擬時，會因幾何尖角處物理量的不可微分性而引發Gibbs現象，導致數值結果產生非物理性的震盪。為此，本研究提出針對幾何奇異點與線附近進行局部網格加密的應對方式。結果顯示，此方法能有效抑制抖動，並將阻力係數（C_D）的預測誤差從約14%大幅降低至3%以內。儘管如此，所有模型對側向力係數（C_Y）的預測仍存在相對可觀的誤差 (>10%)，其原因為模型對紊流黏滯係數採用等向性假設所致。總結而言，DES紊流模型雖然能更真實地呈現流場，但是其高解析度的需求使其在非平滑幾何上易觸發Gibbs現象，而局部網格加密為一有效的抑制手段。

This study investigates the numerical issues when applying Detached Eddy Simulation (DES) to the aerodynamic analysis of vehicle overtaking maneuvers. Traditional Reynolds-averaged Navier-Stokes (RANS) models show significant discrepancies between predicted results and experimental data, especially in complex scenarios like two vehicles driving side-by-side or interacting in wakes. To address this, this research employs IDDES, a hybrid RANS-LES (Large Eddy Simulation) model, aiming at more accurate capture of large-scale turbulent structures.
However, simulating bluff bodies with non-smooth edges using the spectral method, like LES, can trigger the Gibbs phenomenon. This occurs due to the non-differentiability of velocity at sharp edges, leading to non-physical, severe oscillations in the numerical results. To overcome this, the study proposes a strategy of local mesh refinement near geometric singularities and lines.The results demonstrate that this method effectively suppresses oscillations, significantly reducing the prediction error for the drag coefficient (C_D) from approximately 14% to within 3%. Despite this improvement, a substantial discrepancy in predicting the side force coefficient (C_Y) is still observed. It may be attributed to the model's assumption of isotropic turbulent viscosity.
In conclusion, while DES-type model offers a more realistic representation of flow field, its requirement for high resolution makes them susceptible to the Gibbs phenomenon on non-smooth geometries. Local mesh refinement is an effective suppression technique.

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