本文研究的目的在發展重疊式網格及計算流力程式，模擬三維不可壓縮的流場。重疊式網格是採用Chimera網格系統來產生模擬三維複雜外型流場所需要的網格。透過Chimera網格系統將兩個或是多個計算區域連接在一起，以便簡化結構性的網格產生之複雜性。而本文基本上是以向風有限體積法(Upwind Finite Volume Method)計算三維不可壓縮那威爾-史拖克方程式(Navier-Stokes Equation)。本程式用三階的向風有限體積法計算對流項(Convection Terms)，用二階的中央體積法計算黏滯項(Viscous Terms)。
對於Chimera網格，本文歸納出四點注意事項：
(1)主網格必須蓋住所有的次網格，(2)次網格只要有足夠的網格數來計算影響範圍即可，(3)各個重疊區域的格點儘量不要有交錯或太靠近的情形出現，(4)遇到固邊邊界儘可能繞過並保持一定距離，以上都會影響到計算的準確度。
本文在物理模型方面，先以單一圓柱驗證程式，再以兩個圓柱做測試，大的圓柱固定位置，小的圓柱由外面往裡面接近，小圓落在大圓的渦流範圍之內，以Chimera網格來計算流場，觀察小圓在不同的位置及大小比例對於大圓的影響，例如會增加或是降低流場的穩定性。再以不同方式取適當的重疊區域，來做交互疊代運算，在不同方法下以相同的雷諾數，加上不同的距離下比較計算結果的差異。測試結果在兩個重疊區未發生交錯時且有一定的距離時，流場都有一定的準確度，各個方法並無明顯的差異。一旦兩個重疊區距離靠近或是有交錯情形發生，流場以不同的方法計算，結果差異性相當大，因此，目前本文所提之方法的極限在於重疊的網格不能太過靠近或是有交錯情形發生。

This work develops the Chimera grids and numerical method for simulating of three–dimensional incompressible flows. It can simulate 3-D complex flows over complex configurations. The Chimera-grid system simplifies difficulties of the structured-grid generation by connecting the computation of the two-zone or the multi-zone together.
The method solves the 3-D incompressible Navier-Stokes Equations by using a upwind finite volume method. This program handles the convection terms with the third-order upwind finite volume method. Then it deals the viscous terms with the second-order central volume method.
For chimera grid, four important rules are addressed. (1) The main-grid must contain all the sub-grids. (2)The sub-grid should be smaller, but it needs to capture its ph. (3) All the blank regions may not be overlapped to each other. (4) The blank regions should bypass the solid wall.
The flow over two cylinders with one large and one smaller is tested. At first, the larger cylinder is fixed in the position. Then we applied the chimera-grid system with moving the smaller closer to the larger. The smaller is placed in the wake region of the larger to stabilize the flow fields. Finally, we compare the results with different distances under the same Reynolds number. The numerical results indicate that if the blank regions are overlapped each other, then the solutions are not acceptable in accuracy.

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