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Instability of stratified two-phase flows in inclined rectangular ducts
International Journal of Multiphase Flow ( IF 3.6 ) Pub Date : 2021-02-07 , DOI: 10.1016/j.ijmultiphaseflow.2021.103586
Alexander Gelfgat , Ilya Barmak , Neima Brauner

The effect of inclination on instability of two-phase stratified flow in inclined rectangular ducts is studied for the first time via a rigorous linear stability analysis that accounts for all possible infinitesimal three-dimensional disturbances. The results of stability analysis of concurrent downward, concurrent upward, and countercurrent air-water flows are presented in the form of stability diagrams in the coordinates of critical superficial velocities for each of the cases at a characteristic set of other governing parameters. The multiplicity of base-flow solutions predicted for inclined flows is addressed. This study is the first to show that within the rigorous formulation of the stability problem in a realistic duct geometry, the concurrent upward two-phase flows allow for multiple stable flow states. While the main bulk of results is obtained for ducts with a square cross-section, the effect of the duct aspect ratio on the onset of instability is studied for several representative examples. It is shown that in most cases the flow becomes unstable due to different modes of long-wave disturbances that are associated with either interface or shear instability mechanisms. The latter arises mainly due to the duct bottom and top walls. The results substantiate the premise that the simpler two-plate geometry can be used to estimate the effect of the system parameters on the flow stability. The three-dimensional finite-wavelength critical disturbances are visualized by a novel approach of divergence-free projections on the coordinate planes.



中文翻译:

倾斜矩形管道中分层两相流的不稳定性

首次通过严格的线性稳定性分析,分析了倾斜对矩形矩形管道中两相分层流不稳定性的影响,该分析考虑了所有可能的最小的三维扰动。并发向下,并发向上和逆流空气-水流的稳定性分析结果以稳定性图的形式呈现在每种情况下在其他控制参数特征下的临界表观速度坐标中。解决了针对倾斜流预测的多种基础流解决方案。这项研究首次表明,在现实的管道几何形状中对稳定性问题的严格表述中,并发的向上两相流动允许多个稳定的流动状态。对于横截面为正方形的风管,虽然获得了大部分结果,但仍通过几个代表性示例研究了风管纵横比对不稳定性的影响。结果表明,在大多数情况下,由于与界面或剪切不稳定性机制相关的不同模式的长波扰动,流动变得不稳定。后者的产生主要是由于管道的底壁和顶壁。结果证实了这样一个前提,即可以使用更简单的两板几何形状来估计系统参数对流动稳定性的影响。三维有限波长临界扰动通过坐标平面上无散度投影的新颖方法可视化。对于几个代表性的例子,研究了管道长宽比对不稳定性的影响。结果表明,在大多数情况下,由于与界面或剪切不稳定性机制相关的不同模式的长波扰动,流动变得不稳定。后者的产生主要是由于管道的底壁和顶壁。结果证实了这样一个前提,即可以使用更简单的两板几何形状来估计系统参数对流动稳定性的影响。通过一种在坐标平面上无散度投影的新颖方法,可以看到三维有限波长临界扰动。对于几个代表性的例子,研究了管道长宽比对不稳定性的影响。结果表明,在大多数情况下,由于与界面或剪切不稳定性机制相关的不同模式的长波扰动,流动变得不稳定。后者的产生主要是由于管道的底壁和顶壁。结果证实了这样一个前提,即可以使用更简单的两板几何形状来估计系统参数对流动稳定性的影响。通过一种在坐标平面上无散度投影的新颖方法,可以看到三维有限波长临界扰动。结果表明,在大多数情况下,由于与界面或剪切不稳定性机制相关的不同模式的长波扰动,流动变得不稳定。后者的产生主要是由于管道的底壁和顶壁。结果证实了这样一个前提,即可以使用更简单的两板几何形状来估计系统参数对流动稳定性的影响。三维有限波长临界扰动通过坐标平面上无散度投影的新颖方法可视化。结果表明,在大多数情况下,由于与界面或剪切不稳定性机制相关的不同模式的长波扰动,流动变得不稳定。后者的产生主要是由于管道的底壁和顶壁。结果证实了这样一个前提,即可以使用更简单的两板几何形状来估计系统参数对流动稳定性的影响。三维有限波长临界扰动通过坐标平面上无散度投影的新颖方法可视化。

更新日期:2021-02-21
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