Numerical simulation on modal of large submersible axial-flow pump rotor

Abstract: Based on method of fluid-solid coupling, a model of the large submersible axial-flow pump (1600QZ55-1100) rotating component which contains an impeller，axis and hub was studied by means of a second development of UDF and coupling WORKBENCH with APDL command. It obtained the natural frequencies and mode of vibration of a rotating component in a vacuum with pre-stress was considered, and pre-stress was not considered. Furthermore, it also achieved the natural frequencies and mode of vibration of a rotating component in water with pre-stress considered. All the above were studied in a steady condition. However, the axial-flow pump works in an unsteady condition in fact. This paper studied the effect of an unsteady condition on the structure mode too. The result showed that the natural frequencies of considering pre-stress in a steady condition are larger than those of not considering pre-stress, especially that the natural frequency corresponding to a longitudinal mode of vibration is 20% larger in a condition of considering pre-stress, and the natural frequencies of a structure in water decrease by about 10% compared with those in a vacuum. On the other hand, the first-order natural frequency in unsteady condition changes periodically with time, yet the range of that is so narrow that it could be regarded as steady. The narrow range of the first-order natural frequency that results from the range of the force on a structure in an unsteady condition is pretty narrow, compared with the huge axial force. It proved that the result in a steady condition was correct. The reason that caused the natural frequencies to increase with pre-stress considered in a vacuum is that the force on the structure results in the stress stiffening of structure, so that the stiffness of the structure in all directions is enhanced, especially the huge axial force on the structure lead to the natural frequencies increasing by 20% corresponding to a longitudinal mode of vibration. The effect of the damping of water was the main reason that makes the natural frequencies of a structure in water decrease, which also reduces the value of the amplitude of all modes of vibration at the same time. Thereby, the modal distribution consistent with the actual situation could be obtained, which can provide a theoretical basis for improving system performance and further study for more complicated dynamics analysis and fatigue analysis.