本研究利用兩種方法的結合，探討在低雷諾數的自由流下，流體流經球體後，計算球在不同雷諾數的阻力系數、尾流長度等數據，並將阻力係數的數值解與解析解和實驗結果比較誤差。而為了不讓邊界條件影響球體附近流場，在必須建構出大範圍的流場，同時又需要確保球體周圍網格的密集度情況下，本研究使用了區域分解法，建構非均勻網格，加密球體附近的流場網格，增加準確性。而最終結果驗證了，此兩種方法結合後，數值結果與實驗值的差異隨著網格數增加而大幅減少，但球體附近的網格也要夠密集才能地到更精準的數值解，因此必須使用區域分解法來提升其準確度。

Error analysis is performed for the pseudospectral element method (PSME) incorporated with direct-forcing immersed boundary (DFIB) method. The benchmark case – free flow past a sphere – is simulated by the proposed PSME-DFIB model to predict drag coefficient, wake length and relevant physical quantities at a variety of Reynolds numbers. The domain decomposition approach is utilized to generate non-uniform grids for a large flow field in comparison with the size of sphere. Grids in the vicinity of the sphere are locally re-fined to preserve accuracy of solutions. In terms of numerical results, it turns out that the discrepancy between numerical prediction by the proposed model and experimental results decreases with increasing grid number. It means that the spectral accuracy of PSME method is still retained despite the DFIB method is employed.