利用平行化直接模擬蒙地卡羅法進行多超音速噴流流場模擬之研究

Abstract

利用三維、混合非結構性網格、平行化之直接蒙地卡羅法進行多超音速噴流流場之模擬。分別計算一個、二個、三個及四個噴口，將氬氣噴向低壓環境的模擬。利用流續流體的假設計算出喉管口的出口流場，並帶入直接蒙地卡羅法來模擬。在這個模擬中，上游的停滯壓力跟下游腔體的壓力比值固定為50。以喉管為基礎的Knudsen number 範圍為0.001~0.1，其流場特徵為近流續流到過渡流。結果顯示流場Knudsen number為0.001時可以清楚的描述出barrel shock及Mach disk shock，隨著Knudsen number的增加而消失而成為可壓縮的膨脹流。而具有多噴管流場的流場也會被詳細的討論。在不同稀薄程度的流場也會因不同的理由產生不平衡現象。

Flow fields of multiple underexpanded supersonic jets are simulated using the three-dimensional, parallel direct simulation Monte Carlo (DSMC) method employing an unstructured mesh incorporating static domain decomposition. One, two, three and four jets of argon gas issuing from the orifice(s) into a lower-pressure environment are considered, respectively. Inflow conditions at the orifice outlet (throat) required for the DSMC computation are calculated using the continuum approach. Ratio of upstream stagnation pressure to downstream chamber pressure remains fixed at 50 in the current study. Rarefaction parameter characterized by Knudsen numbers (based on throat conditions) is varied in the range of 0.001~0.1, which corresponds to the flow from near-continuum to transitional regimes. Results show that a distinct barrel shock and Mach disk structure is clearly captured for a single jet flow at Knudsen number of 0.001, while it is diminished to a purely compressible, expanding flow with increasing Knudsen number. Interaction between multiple jets is discussed in detail. Strong thermal non-equilibrium in translational degree of freedoms appears for both high and low Knudsen-number flows due to different reasons.