偏工况下气液两相离心泵喘振特性

当离心泵在小流量工况运行且传输介质为气液两相流时,含气率达到某一值时,会发生喘振现象,导致泵的扬程突降。本文采用计算流体动力学分析方法对一气液两相流离心泵进行了研究,通过对外特性曲线进行分析,发现了学者们所提到的喘振现象。为了提高离心泵在气液两相小流量工况下的水力特性,引入一种空腔结构,分析其对气液两相离心泵内部流场的影响及喘振的改善作用。结果表明:在气液两相喘振工况下,空腔结构可以改善叶片正背面的压力分布,均匀气液两相在叶轮流道中的分布,有效减轻离心泵的气堵现象。因此,空腔结构不仅在结构上可以平衡叶轮、减轻泵的整体质量,还可以减轻流场中气液分离现象,避免喘振的发生,提高泵的水力性能。

Surge characteristics of gas-liquid two-phase centrifugal pumps under part-load conditions

Gas-liquid two-phase centrifugal pumps are widely used in agriculture, water environment, nuclear industry, and petroleum industry. Centrifugal pumps perform most efficiently when operating under single-phase flow conditions. However, the presence of gas causes head degradation, low efficiency, and low hydraulic performance; and surge is one of the most serious problems faced by gas-liquid two-phase centrifugal pumps. In this work, the commercial software ANSYS CFX 16.0 is adopted to calculate the three-dimensional turbulent flows in a centrifugal pump with a mid-low specific speed impeller. From the results, we can find out that at the pump inlet, gas gathering becomes increasingly obvious and the gathering area is growing larger with the increasing gas volume fraction at the inlet until a surge occurs. Subsequently, a large amount of gas gathers in the impeller channel and even blocks its passages completely, which is known as surge. To improve the hydraulic performance of the pump under surging conditions, we apply a cavity structure to the pump, and examine in detail its effects on the external characteristics and internal flow field. The results show that under low flow rates, the cavity structure can improve blade pressure distribution and uniform gas phase distribution in the impeller channel, effectively reducing the gas blockage of the pump. This study shows that the cavity structure cannot only balance the pump impeller and reduce the pump weight, but reduce the phenomenon of gas-liquid separation in the flow field.