Abstract
The annular seal between stator and rotor substantively acts as a bearing that affects the rotordynamic characteristic of the turbomachinery rotor system. The rotor wake turbulence in a canned motor Reactor Coolant Pump (RCP) will lead to inflow pressure distortion at the annular seal entrance, thus further affecting the seal rotordynamic characteristics and threatening the stable operation of RCP. In order to obtain the seal rotordynamic coefficients, a transient numerical method applies the mesh deformation technique to simulate the multiple-frequency elliptical rotor whirling orbit model. The transient solutions were proposed to solve the unsteady reaction forces of annular seals at five excitation frequencies for each case. The inflow pressure distortion patterns were simplified as harmonic functions, including two important influence parameters that are impeller blades number m and pressure fluctuation ratio λ. The numerical results showed that with nonuniform time-averaged pressure distribution at the entrance of the annular seal in Case 2, the inflow distortion significantly affects the seal rotordynamic coefficients, while the rotational spinning speed in Case 3 can weaken the time-averaged nonuniformity and accordingly make a dent in the influence. Increasing impeller blades number m and pressure fluctuation λ both result in a sharp diminution of the negative stiffness Keff, as well as an obvious increase in the effective damping Ceff, which will strengthen rotor misalignment and system stability. In addition, the larger impeller blades number m and higher pressure fluctuation λ will make the effective damping Ceff more independent of the whirling frequency. These results provide theoretical guidance for the operation safety of RCP.
Highlights
Turbomachinery has been commonly used in modern industry to meet stringent costeffectiveness, high energy conversion efficiency, high power to weight ratio, high reliability and rigid safety requirements
It is believed that the annular seal between the stator and rotor substantively acts as a bearing, which affects the rotordynamic characteristic of the turbomachinery rotor system [1,2]
The results focus on discussing rotordynamic coefficients for different inflow distoHrtieonncep, ainttethrniss pwaipther,twthoe mimapinorgtoaanlt iisntfoluiennvceestfiagcattoertsh(ebelaffdeectnoufminbfleorwanddistporretisosnuroen the flucturoattoiorndyrnataimo)i.c characteristics of a 1400-MW Reactor Coolant Pump (RCP) annular seal with a transient method
Summary
Turbomachinery has been commonly used in modern industry to meet stringent costeffectiveness, high energy conversion efficiency, high power to weight ratio, high reliability and rigid safety requirements. The numerical methods used by researchers to predict the dynamic characteristics of the sealed rotor are mainly divided into the bulk-flow model and the CFD method. Moore [14] adopted the steady-state CFD method, which applies a transformation of coordinative systems to solve the transient problem in stationary frames to predict the rotordynamic coefficients of artificially roughened stator gas annular seals. For predicting a series of the frequency-dependent rotordynamic coefficients of the nuclear coolant pump annular seal, the multiple-frequency elliptical rotor whirling orbit motion was utilized as the motion model in the present numerical analysis. FigXur=e 4b i llusctroastes tihte ,mYult=ipale -freqsiunen cyitelliptical whirling or(2b)it with a maximum peak vibration ia=m1 plitude 3.2 × 10−5 mi=1, which is 10% of the annular seal clearance In this way, the solutions will capture the linear motion characteristics based on the small motion theory.
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