Abstract Flow characteristics for a wide range of Reynolds number up to turbulent gas flow regime, including flow choking were numerically investigated with a microtube discharged into the atmosphere. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The LB1 turbulence model was used in the turbulent flow case. Axis-symmetric compressible momentum and energy equations of an ideal gas are solved to obtain the flow characteristics. In order to calculate the underexpanded (choked) flow at the microtube outlet, the computational domain is extended to the downstream region of the hemisphere from the microtube outlet. The back pressure was given to the outside of the downstream region. The computations were performed for adiabatic microtubes whose diameter ranges from 10 to 500 μm and whose aspect ratio is 100 or 200. The stagnation pressure range is chosen in such a way that the flow becomes a fully underexpanded flow at the microtube outlet. The results in the wide range of Reynolds number and Mach number were obtained including the choked flow. With increasing the stagnation pressure, the flow at the microtube outlet is underexpanded and choked. Although the velocity is limited, the mass flow rate (Reynolds number) increases. In order to further validate the present numerical model, an experiment was also performed for nitrogen gas through a glass microtube with 397 μm in diameter and 120 mm in length. Three pressure tap holes were drilled on the glass microtube wall. The local pressures were measured to determine local values of Mach numbers and friction factors. Local friction factors were numerically and experimentally obtained and were compared with empirical correlations in the literature on Moody’s chart. The numerical results are also in excellent agreement with the experimental ones.

中文翻译：

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通过微管排放到大气中的气流的流动特性

摘要 使用排放到大气中的微管对大范围雷诺数到湍流气体流态的流动特性进行了数值研究，包括流动阻塞。数值方法基于任意-拉格朗日-欧拉 (ALE) 方法。LB1 湍流模型用于湍流情况。求解理想气体的轴对称可压缩动量和能量方程以获得流动特性。为了计算微管出口处的欠膨胀（阻塞）流，计算域从微管出口扩展到半球的下游区域。背压施加到下游区域的外部。对直径为 10 至 500 μm 且纵横比为 100 或 200 的绝热微管进行了计算。以这样一种方式选择停滞压力范围，使得流动在微管出口处变成完全膨胀不足的流动。获得了雷诺数和马赫数的广泛范围内的结果，包括阻塞流。随着滞流压力的增加，微管出口处的流量膨胀不足和阻塞。尽管速度受到限制，但质量流量（雷诺数）会增加。为了进一步验证当前的数值模型，还通过直径为 397 μm、长度为 120 mm 的玻璃微管对氮气进行了实验。在玻璃微管壁上钻三个测压孔。测量局部压力以确定马赫数和摩擦系数的局部值。局部摩擦系数通过数值和实验获得，并与穆迪图表文献中的经验相关性进行比较。数值结果也与实验结果非常吻合。