本文以直接模擬蒙地卡羅( Direct Simulation Monte Carlo )法計算極音速稀薄氣體中平行混合流之速度、壓力、溫度、密度之流場性質，另外本文亦計算混合層中速度、溫度脈動相關函數 、 、 、聯合機率密度函數 、 以對稀薄氣體混合之內在結構、動量、熱量傳輸有所了解。本文首先觀察其流場特性以及自由流(參考表2.1)分別為不同速度比,0.2,0.4,0,0.6時自由剪力流混合結構之差異，接著以各種機率密度函數探討流場特性，最後並與連性紊流混合層之結果相較，希望藉由這些函數的解析，對稀薄流場的”紊性”有更深一層的了解。

結果發現混合層紊性熱量的傳輸，x方向的熱量傳遞 (圖5.24)約為y方向的的熱量傳遞 (圖5.25)的二倍，且x方向的熱量傳遞趨勢和流場截面 的分佈類似，y方向的熱量傳遞( )的趨勢和能量項(圖5.17)相似，都是愈往下游愈小。

並藉由聯合機率密函數 、 與 、 截面分佈圖比較發現聯合機率密度函數形狀與混合層內在結構、動量、熱量傳輸相關性高，當 形狀愈偏離高斯分佈，其 值愈大，當 形狀愈接近高斯分佈，其 值愈小，而 的分佈趨勢和 相同，上層區偏向於正，下層區偏向於負。

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