單噴流及雙噴流於稀薄氣體流場之模擬

Abstract

利用三維非結構性調適網格、平行化之直接蒙地卡羅法進行單噴流及雙噴留再稀薄氣體流場模擬。在不同的 Knudsen number 及不同壓力比下觀察噴流的結構變化的超音速噴流流場之模擬。分別計算一個及二個噴口，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自50變化至真空。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。而隨著壓力比的增加，Mach disk shock 的位置也向下游推移。

Supersonic jets issuing from a sonic orifice over a wide range of the stagnation knudsen numbers，from a continuum to a near free molecular condition，and over a wide range of the pressure ratio are simulated by the DSMC method. single and twin jets of argon gas from the orifice(s) into a lower-pressure chamber are considered, in order to minimize the computational time and reduce CPU load. An adaptive mesh-embedding (h-refinement) scheme using unstructured grid and variable time step scheme in three-dimensional Direct Simulation Monte Carlo method is used. The result reproduces very well the jet structure including the Mach disk and the barrel shock for a near continuum flow condition as well as the jets in the transition regime.