隨著大跨度橋梁與高層建築的發展，結構物對風荷載的敏感度日益提升。傳統風洞試驗存在成本高昂與縮尺效應等限制，結合計算流體力學（CFD）的數值模擬已成為當今土木結構風工程研究的趨勢。然而，在解析複雜鈍體的三維瞬態氣動力行為時，傳統全六面體網格常面臨前處理耗時與運算資源龐大的瓶頸，而純二維模擬又因缺乏展向渦旋拉伸機制而嚴重高估阻力。為突破運算成本與物理精度的限制，本研究針對高寬比 7 之三維剛性矩形柱模型，導入「多面體-六面體核心網格（Poly-Hexcore）」技術與「擬三維週期性邊界條件」，並系統性地比較雷諾平均（RANS）SST 模型與壁面模型大渦模擬（WMLES）的預測精度與運算效能，並與風洞實驗及前人全六面體網格模擬結果進行對照分析。
研究結果顯示，嚴格控制近壁面網格正交性為消除低頻雜訊、穩定捕捉卡門渦街特徵的關鍵。Poly-Hexcore 網格不僅能展現出與傳統全六面體網格近乎一致的氣動力預測精度，更大幅降低了運算成本。此外，採用擬三維週期性邊界條件能有效保留三維渦漩在展向上的去相關特徵，並縮減約 60% 的網格總數。在擬三維架構下，WMLES 模型成功突破了傳統模型的過度耗散限制，精準解析出流場中的「雙重不穩定性」。最後透過紊流品質指標進行雙重檢驗，確證本研究所建置之數值模型真實深入了紊流的能量級聯機制，可為未來探討複雜結構雙向流固耦合與動態氣彈行為奠定可靠的數值解析基礎。

With the rapid development of long-span bridges and high-rise buildings, modern structures have become increasingly sensitive to wind-induced effects. Traditional wind tunnel testing remains a fundamental approach for evaluating structural aerodynamic behavior; however, it is often associated with high experimental costs, long preparation periods, and unavoidable scaling effects. Consequently, numerical simulations based on Computational Fluid Dynamics (CFD) have become an increasingly important tool in structural wind engineering. Nevertheless, accurately analyzing the three-dimensional (3D) transient aerodynamic behavior of complex bluff bodies remains computationally challenging. Traditional full-scale 3D simulations using full-hexahedral meshes often encounter bottlenecks associated with time-consuming preprocessing and substantial computational resource demands. To achieve a balance between computational efficiency and physical accuracy, this study introduces advanced Poly-Hexcore mesh technology and Quasi-3D periodic boundary conditions for a three-dimensional rigid rectangular cylinder model with an aspect ratio of 7. The proposed framework systematically compares the prediction accuracy and computational efficiency of the Reynolds-Averaged Navier-Stokes (RANS) SST k−ω model and Wall-Modeled Large Eddy Simulation (WMLES). The results demonstrate that the combination of Poly-Hexcore meshing and Quasi-3D periodic boundaries can significantly reduce computational requirements while retaining the essential three-dimensional characteristics of the wake. Furthermore, the proposed approach successfully captures the double-instability behavior of the flow field, including the interaction between Kelvin-Helmholtz instability and von Kármán vortex shedding. The findings provide an efficient and physically reliable numerical foundation for future investigations of aeroelastic behavior and fluid-structure interaction (FSI).

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