平行化之三維直接模擬蒙地卡羅法的發展及其應用

Abstract

中文摘要 發展一個三維非結構性之平行化直接蒙地卡羅(Direct Simulation Monte Carlo, DSMC)程式。利用VHS (Variable Hard Sphere) 分子模型、NTC (No Time Counter) 碰撞取樣法以及利用CELL-BY-CELL的粒子追蹤法來完成分子的移動。這個單機程式(尚未平行化前)藉由模擬一超音速流場流經兩相互垂直之平板並比較Bird之三維結構性直接蒙地卡羅程式的結果而得到驗證。更進一步，以孔洞擴散流場模擬作為另一個測試，藉由比較以往的實驗結果證明此三維非結構性之平行化直接蒙地卡羅程式是正確的。本論文對於各處理器之間工作量的分配是根據估計粒子密度分布，採用靜態區域切割，切割的方法則式使用Multi-level graph切割法。此程式接下來用來模擬超高音速流場流經一圓球並比較以往之模擬和實驗，結果亦相當吻合。最後，再將此程式應用在螺紋拖曳式真空幫浦之流場模擬。為了合適於幫浦實驗狀況，本論文提出一個用來處理與壓力相關(pressure-related)邊界條件的疊代過程，而模擬結果亦與以往的數值模擬的結果相符

The development of a parallel three-dimensional direct simulation Monte Carol (DSMC) method using unstructured cells is reported. VHS (Variable Hard Sphere) molecular model and NTC (No Time Counter) method are used for the molecular collision kinetics, while the cell-by-cell ray-tracing technique is implemented for particle movement. Developed serial code has been verified by comparing the results of a supersonic corner flow with those of Bird’s three-dimensional structured DSMC code. In addition, a benchmark test is performed for an orifice expanding flow to verify the parallel implementation of DSMC method by comparing with available experimental data. Static physical domain decomposition is used to distribute the workload among multiple processors by considering the estimated particle weighting distribution. Multi-level graph technique is used to perform the required domain decomposition. Completed code is applied to compute a hypersonic flow over a sphere. Results are good agreement with previous numerical result using axisymmetric DSMC method and experimental data. Finally, the developed code is applied to compute the flow field of a spiral drag pump. An iteration process treating pressure-related boundary condition is proposed to adapt to experimental condition. Results also agree well work previous numerical results.