The occurrence of sub-atmospheric pressure in the drainage of pipelines containing an air pocket has been known as a major cause of several serious problems. Accordingly, some system malfunction and pipe buckling events have been reported in the literature. This case has been studied experimentally and numerically in the current research considering objectives for a better understanding of: (i) the emptying process, (ii) the main parameters influencing the drainage, and (iii) the air-water interface deformation. Also, this research demonstrates the ability of a computational fluid dynamic (CFD) model in the simulation of this event. The effects of the air pocket size, the percentage and the time of valve opening on the pressure variation have been studied. Results show the pipeline drainage mostly occurs due to backflow air intrusion. The worst case scenario is associated with a fast valve opening when a tiny air pocket exists in the pipeline.

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管道排水中亚大气压分析的计算流体动力学

已知在含有气穴的管道排水中出现低于大气压的压力是导致若干严重问题的主要原因。因此，文献中已经报道了一些系统故障和管道屈曲事件。在当前的研究中已经对这种情况进行了实验和数值研究，目的是为了更好地理解：(i) 排空过程，(ii) 影响排水的主要参数，以及 (iii) 空气-水界面变形。此外，这项研究证明了计算流体动力学 (CFD) 模型在模拟该事件中的能力。已经研究了气穴大小、阀门打开的百分比和时间对压力变化的影响。结果表明，管道排水主要是由于回流空气侵入。