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Slug formation and frequency of slugging in gas-liquid flows.

机译：气-液流中团状形成和团状形成的频率。

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When gas and liquid flow concurrently in a pipe, a common flow pattern is slug flow, characterized by the presence of intermittent, aerated slugs of liquid that translate downstream at the local gas velocity. The prediction of flow conditions at which slugs flow are observed and the prediction of the frequency of slugging are a critical technological problems which have not been fully resolved. This thesis examines this problem by documenting how slugs are formed in horizontal and near--horizontal pipes. Experiments were conducted with air-water flow in a 0.0763 m pipeline at atmospheric pressure. Measurements of the variation of the interfacial displacement were made simultaneously at a number of locations in a 23 m pipeline. These yield information about how slugs evolve and how the liquid layer rebuilds after the formation of a slug. Results are obtained for horizontal flows ({dollar}theta = 90.0spcirc{dollar}) and for downwardly inclined flows ({dollar}theta = 89.8spcirc , 89.5spcirc ,{dollar} and {dollar}89.2spcirc{dollar}).; At low gas velocities, slugs evolve from small wavelength (16 to 20 cm), large amplitude waves in horizontal flows. The growth of this wave evolves into a slug when it reaches the top of the pipe. These waves obtain their energy from smaller wavelength waves (8 to 10 cm) through a non-linear growth mechanism. At high gas velocities, the liquid height is not thick enough for these small wavelength waves to reach the top of the pipe. Rather, the wave crests grow until they break, forming roll waves. Slugs are observed to evolve from the coalescence of roll waves at these flow conditions.; Surprisingly, the large amplitude small wavelength waves observed at the transition to slug flow at low gas velocities for horizontal flows are damped for inclined flows. The transition to slug flow for slightly inclined pipes is associated with long wavelength, small amplitude waves. A viscous long wavelength linear stability analysis predicts the appearance of these wave. A local Kelvin Helmholtz instability at the crest of a growing long wavelength wave is observed when a slug forms. At high gas velocities, the conditions at the onset to slug flow for inclined flows are similar to the horizontal case.; When a slug forms, the liquid level in a large length of pipe drops as the slug propagates downstream. Thus two time scales enter the slug frequency analysis: one characterizing wave evolution and one involving liquid buildup. When the Froude number of the stratified flow in a horizontal pipe at the onset of slug flow is less than unity, the frequency is related to the motion of upstream propagating gravity waves associated with the formation of slugs. A stochastic model is used to describe the frequency for supercritical flow conditions for which slugs form from roll wave coalescence far from the inlet, and also for conditions for which slugs are forming very close to the inlet. For stratified downflows in inclined pipes, the flow is supercritical. However, the frequency of slugging is observed to be periodic and equal to the frequency of long wavelength waves that are predicted by linear stability.
机译：当气体和液体同时在管道中流动时，常见的流型是段塞流，其特征在于存在间歇的充气的段塞，这些段塞以局部气体速度向下游平移。观察团状流的流动条件的预测和团状频率的预测是尚未完全解决的关键技术问题。本文通过记录在水平和近水平管道中如何形成团块来研究此问题。实验是在大气压下在0.0763 m的管道中以空气-水流进行的。在23 m管道中的多个位置同时进行界面位移变化的测量。这些产生了关于团块如何发展以及团块形成后液体层如何重建的信息。 ;水平流（{theta = 90.0spcirc {dollar}）和向下倾斜流（{dollar = 89.8spcirc，89.5spcirc，{dollar和and89.2spcirc {dollar}）获得了结果。在低气体速度下，弹头会从小波长（16至20厘米），大振幅波在水平流中演化。当到达管道顶部时，该波的增长演变为弹头。这些波通过非线性生长机制从较小波长的波（8至10 cm）获得能量。在高气体速度下，液体高度不够厚，不足以使这些小波长波到达管道顶部。相反，波峰会一直增长直至破裂，形成波状波。在这些流动条件下，观察到弹头是由卷波的聚结演变而来的。出乎意料的是，在水平流低气体速度下向团状流过渡时观察到的大振幅小波长波被倾斜流阻尼。稍微倾斜的管道向团状流的过渡与长波长，小振幅波有关。粘性长波长线性稳定性分析可以预测这些波的出现。当团状形成时，在长波长波的波峰处观察到局部的开尔文·亥姆霍兹不稳定性。在高气体速度下，倾斜流开始到团状流的条件类似于水平情况。当形成团块时，随着团块向下游传播，大段管道中的液位会下降。因此，两种时间尺度进入了弹头频率分析：一种表征波的演化，一种表征液体的堆积。当在段塞流开始时水平管中的分层流的弗洛德数小于1时，频率与段塞形成相关的上游传播重力波的运动有关。随机模型用于描述超临界流工况的频率，在超临界流工况下，卷波聚结会在远离入口的位置形成块，并且在其离入口很近的位置形成块。对于倾斜管道中的分层向下流动，流动是超临界的。但是，观察到的拍击频率是周期性的，并且等于通过线性稳定性预测的长波长波的频率。

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