Wet Critical Speeds Of Multi-stage Centrifugal Pump:Theory And Testing Technology

Nowadays many plants are developing super critical power generations for thermal power stations and nuclear power stations, multistage pump is one of the most important equipments of these power generations. The structure of pump rotor is complex and consists of many annular clearance components such as annular seal, balance piston, wearing ring and impeller, etc. Significant fluid-structure force will generate when fluid pass through these small clearances. With the fluid-structure force acting on rotor, dynamic characteristic of rotor will be changed. Critical speed of centrifugal pump rotor with water in pump is significantly different from that without water, which correspondingly account for the "dry" and "wet" critical speed. Due to the complex structure of multi-stage centrifugal pump rotor, the calculation of its critical speed is one of important research issues in turbomachinery. Up to now researchers at home and abroad have already made quantitative analysis on this issue, however, the accuracy of these analysis needs further improvement. Meanwhile, the lack of effective testing technology makes it difficult to measure "wet" critical speed of centrifugal pump. Considering the shortness of present research, this paper presents a systematic research on wet critical speed of centrifugal pump, including numerical and experimental investigation. A completed analysis method is present for analyzing one mulit-stage centrifugal pump. Testing technology is developed and used to measure the real wet critical speed of this pump. Numerical results fit well with experimental ones. Such systematic method is important for analyzing wet critical speed of centrifugal pump. The main work of this paper is as follows:1. Computational Fluid Dynamic (CFD) commercial code-Fluent is used to calculate dynamic coefficient of non-contact seal. The influence of pressure gap on dynamic coefficient is discussed.2. Finite Element Method(FEM) software-Ansys is used to model the pump rotor. The influence of seal is considered and wet critical speed in different pressure gap is calculated. 3. A vibration testing platform is developed for investigation on dynamic characteristic of multi-stage pump rotor, which includes an innovative electromagnetic vibration exciter and vibration testing software developed by using VC++MFC. This platform could exert non-contact periodical impulse on rotating object and is tried on lab rotor rig. The result shows that the platform could effectively identify the critical speed of rotor.4. Test rig is established to measure wet critical speed of multi-stage centrifugal pump. Dynamic testing is performed in different pump head. Testing results fit well with the previous numerical ones, which proves the reliability of the proposed analyzing method for wet critical speed of centrifugal pump.