Investigation on the transient characteristics of the pump system using MOC-CFD coupled method

The security and stability of the pump system have received extensive attention in hydraulic engineering, especially in nuclear system. Transient operations, such as the rapid closure of a valve, a sudden switch over and start procedure of pumps and pump failure will cause sudden flow variation in the pipe system. This phenomenon, known as water hammer, will cause transient effects on the pump. So it is essential to study the transient characteristics of pump during the hydraulic transition process. Up to now, one dimensional MOC (Method of Characteristic) and three dimensional CFD (Computational Fluid Dynamics) analyses have been two relatively independent ‘‘modeling cultures’’. MOC is commonly used in solving the hydraulic transients in pipe and giving important information at system levels[1][2]. CFD is increasingly being used to capture complex local 3D features inside the fluid machinery[3]. During the traditional analysis, when analyzing transient characteristics of the system, the pump is often described by a simple one-dimensional(1D) model, and when analyzing transient characteristics of the pump, a three-dimensional(3D) independent analysis is done for the pump without considering the outer pipe system. Therefore, it is difficult to get the pump transient characteristics in the transient events and the pump transient effects on system characteristic. That is to say, it failed to fully consider the interaction of pump and system. However, the two simulations methods are to be seen as complementary. Thus, a multi-scale modeling approach, namely MOC-CFD, can be proposed by combining both models together to utilize the strengths of both approaches.