采用熵产理论的离心泵断电过渡过程特性

该文对商业软件ANSYS CFX进行二次开发,通过自定义函数求解角动量方程获取实时转速,建立了模拟离心泵事故断电过渡过程的三维瞬态数值计算方法,获得了离心泵外特性参数瞬变规律以及内部流场的动态特性。进一步采用熵产理论获得了离心泵事故断电停机飞逸过程中过流部件流场能量损失分布情况,并对流场内随时间变化的能量损失进行定量评估。结果表明:在整个事故断电飞逸过程中,熵产与离心泵外特性之间存在着明显的相关性,能量损失的产生与流场内部的流动分离、回流、漩涡等不良流动现象相关;叶轮、导叶与引水管的主要损失均是由湍流耗散引起的,其壁面熵产占总熵产的10%~15%左右,不可以忽略,而蜗壳区的损失则主要是由近壁面处的强壁面效应引起的;通过分析各部件流场局部熵产率分布随时间的变化情况,可以得出在制动工况中内流场的高损失区域最大。

Transition process characteristics of centrifugal pump with power-off based on entropy production theory

Abstract: In this paper, a transient numerical calculation method is established based on ANSYS CFX software and user-defined program, which can simulate the power-off runaway transient characteristics of a centrifugal pump. The variation rule of external characteristic parameters with time can be obtained through numerical calculations and compared with experimental data. The comparison of results show that the simulation results agree well with experimental results, the proposed numerical method has been therefore validated. During the power-off runaway transient process, the centrifugal pump system will successively undergo the pump condition, braking condition, turbine condition and runaway condition, with external characteristic varying significantly during the process. Internal flow structure is closely related to external characteristic and affects each other. The hydraulic loss due to friction and unstable flow patterns in the pump causes a drop in hydraulic efficiency. The traditional method for analyzing the hydraulic loss is by evaluating the total pressure drop, which has certain limitations and cannot determine the exact locations at which the high hydraulic loss occurs. In this study, entropy production theory has been adopted to obtain a detailed distribution of the hydraulic loss in the centrifugal pump. Through the use of the entropy production theory, the variation of the entropy production was obtained. The distribution of energy loss of flow components during this process is obtained by using the entropy generation theory, and the energy loss is analyzed. The results show that there is a clear correlation between the entropy production and the external characteristics of the centrifugal pump during the entire runaway process. The entropy production also undergoes dramatic changes at the moment of sudden changes in flow rate, rotational speed and torque. The main losses of the impeller, guide vanes and suction pipe are caused by turbulent dissipation, and the wall entropy production accounts for about 10%-15% of this total entropy production, which means the wall effect could not be ignored. However, the loss of the volute is mainly due to the strong wall effect in the near wall region, which is different from other three flow components, denoting the main loss generation mechanism is different. In addition, it is found that both the energy loss and variation range of the impeller and guide vanes are relatively larger than those of other flow components in the whole process. By analyzing the distribution of the local entropy production of the impeller and the vanes at different stages, it is intuitively obtained from the energy point of view that the high loss region of the internal flow field is the largest in the braking condition, and the high loss area fills the entire impeller flow path when the rotational speed drops to 0. The results obtained in this paper can improve the understanding of transient characteristics of a centrifugal pump during the power-off transient condition.