| A boiler-feeding-water pump is a multistage centrifugal pump havingCharacteristics of high pressure and rotational speed with higher requirements instability and safety, it is necessary to calculate the critical rotational speed, wet-statecritical rotational speed,of the rotor rotating in operating condition accurately toensure the rotor runs smoothly and avoid the influence, caused by the resonanceproduced while the rotating speed of the rotor is close to the critical rotational speedof the one, of the pump life.Transfer matrix and finite element methods are usuallyused to calculate the critical rotational speed of the rotor.So the flow passages in the boiler-feeding-water pump powered by agas-turbine used in the supercritical unit in a600megawatt power plant wereestablished in a whole geometrical model, the entire flow passage was split into15zones in tetrahedron mesh by adopting block grid technique by means of GAMBITsoftware, and the inner flow in the pump was computed and analyzed using thecomputational fluid dynamics (CFD) approach by means of a parallel computer. Thefinite element method is chosen to compute the critical rotational speed of the rotor ofthe boiler-feeding-water pump in this paper and the finite element modal analysis ofthe rotor was carried on by ANSYS Workbench12software, the critical rotationalspeed of the rotor was respectively computed by the software with the conditions ofno-load, rigid supports、seal clearances in the spaces in rotor, seals in the mouth of theimpellers, seals between stages the tensile axial force taken into account，some resultsas follows:1) Compared with the internal flow in a single-stage centrifugal pump, somespecial phenomena are found in the flow channels in the boiler-feeding-water pump，the internal flow in the pump is complicated having obvious flow characteristics.There is a bigger change of the pressure in the near-wall zones of the internal casecompared with that of the external case; The pressure distribution are clearlyasymmetrical in the flow channel between the cases, which enlarges the force of thecases；The high pressure and velocity regions with large area are found near the exitof the impeller in the flow passages in the ones；The vortex flow exists in the suctionchambers from the first stage to the sixth one；These features will provide theevidence for the improvement of the pump.2) If the same dynamic characteristics are given, the stiffening effect produced by the seals in the stages is greater than that of the seals in the mouth of the impellers,at the same time, the tensile axial force having strong stiffening effect on the criticalrotational speed of the rotor, therefore, it is necessary to compute the wet-state criticalrotational speed of the rotor, rotating in liquid, of the centrifugal pump taking thetensile axial force into consideration.It is important to take various factors and various theories, including traditionalrotor dynamics and hydrodynamic lubrication theory and the knowledge of sealdynamics， into account while calculating the wet-state, rotating in liquid, criticalrotational speed of the rotor of a multistage centrifugal pump with complicatedcomputational process, the results provides references for further research as well asthe evidence for checking up the structure of the rotor of the multistage centrifugalpump. |
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