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中文摘要：
采用低雷诺数k-ε模型对输气管道气体置换过程进行二维数值模拟。研究结果表明：混合区浓度在轴向呈非对称分布，呈“头短尾长”特征；流速、管径、管道长度是混合长度的主要影响因素。混合初始，混合长度增长速率大，随着主流向下游流动距离的增加，增长速率减小；流速是混合长度的重要控制参数，湍流时的混合长度小于层流，流速对混合长度的影响在高雷诺数湍流时比较小；同一湍流流速下，混合长度随管径增加而增加；管径对混合长度的影响随湍流度的降低而增大；氮气-天然气混合长度比氮气-空气混合长度大1％—2％。
英文摘要：
The low Reynolds number k-ε turbulence model was applied for the 2-dimensional numerical simulation of the length of mixed region of the gas purging in natural gas pipeline conveying. The result indicates that the concentration distribution profile in the mixed region appears asymmetric along the axial direction, which has such a characteristic called ＂short head and long tail＂. Purging velocity, pipe diameter and length of purged pipe are three key factors to the length of mixed region. The mixture length increases very fast in the initial purging state and then changes slowly with the increasing of length of purged pipe. Purging velocity is one of the key parameters of control in the process of the purging. The length of mixed region is shorter during the turbulent flow than that during the laminar flow. Increasing the velocity of turbulent flow has less effect on shortening the length of mixed region. Under the same turbulent velocity, the length of mixed region increases with the increasing of the pipe diameter. But the impact of the pipe diameter on the length of mixed region is weakening while the turbulent intensity is high. The gas mixing length of nitrogen-natural gas is 1% -2% more than that of nitrogen-air.
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