本文係以直接模擬蒙地卡羅(Direct Simulation Monte Carlo, DSMC)法，計算兩種不同流速之平行流的首闊結構。自由流乃模擬距海平面109.75km高度下之大氣狀態：氧分率0.217，氮分率0.783，密度，溫度249(K)，分子暈27.23(g/mol)，自由徑0.649(m)。較大之自由流流速分別取爲12、16、20Mach而速度比爲0.3（即如8Mach與8*0.3Mach）及0.6。計算域則爲高自公尺（兩種流速之流體也左方邊界進入，各佔一半高度），長12公尺之矩形區域。分子模型探氧氮混合之雙原子分子模式。
計算結果發現，混合區的成長(Mixing layer growth)，與下游距離成線性關係；且在高超音速(Hypersonic flow)下及平行流同一速度比時，自由流馬赫數愈來高則混合區愈狹長。這些現象與連流高雷諾數平行流混合層類似。對混合區中速度、溫度、壓力、及密度的分佈情形亦加以分析討論。溫度與壓力在混合區中呈增加的趨勢，密度則在中心(core)部份呈減小，而在自由流與混合層交接附近呈增加的淚象。吾人更進一步探討自由剪力層中各階動量脈動相關函數(correlation functions of momentum fluctuations)，等分佈情形，以初探在稀薄氣體自由混合層中物理量（動量）的“紊性”。動量傳遞中，由速度脈動所形成之傳遞量約爲分子黏滯性所形成之動量傳遞量的七成左右，此現象顯然比連性紊流中者爲低。 The direct simulation of Monte Carlo method was employed to calculate the flow structures, such as mean velocities, temperatures, pressures and mean quantities of various order of momentum fluctuations correlations of a free shear layer at hypersonic speed. The free stream temperature was kept as 273 K for all cares of calculations. The free stream velocities (of the higher one stream) cons: dered were M(subscript ∞) 10.15 and 20. The free stream densities considered were 10^20, 10^21 and 10^22 per m^3. The velocity ratio chosen as r=0.3, 0.45 and 0.6 for the present calculations. From the comparisons of above mentioned conditions of the rarefied parallel flow structures it is found that the effect of the changes of free stream density on the various flow properties was monotonously as the length scale nondimensionalized by the mean free path of the free stream. For different M(subscript ∞) with the same velocity ratio r the calculated shear layer growth were almost the same for M(subscript ∞). The tendency of the distributions of various order of fluctuation correlations in the mixing layer was the same as that of the continuum one. The momentum transfer due to mean fluctation correlations was about 70% of that due to molecular viscosity. This is obviously lower that in the case of continuum shear layer
Relation:
中國航空太空學會學刊=Transactions of the Aeronautical and Astronautical Society of the Republic of China 30(1)，頁77-86
