Study On Fluid-solid Coupling For Dynamic Characteristics Of The Multistage Centrifugal Pump

Multistage centrifugal pump is widely used in urban water supply and drainage, irrigation, oil chemical industry, mine drainage, forest fire control, high-rise building and other industries of national economy because of its high efficiency and high head. Multistage centrifugal pump structure becomes more complex and the impellers are added in the series connection in order to meet the needs of higher head, which results inevitably in the increase of vibration amplitude of rotor system. In the operational process, the interplay between the internal flow field in the pump and the impeller structure easily leads to the fatigue rupture of the impeller. Especially when the rotation frequency and inherent frequency are similar or identical, it will lead to resonance, and seriously affect the safe and reliable operation of the multistage centrifugal pump. Therefore, it has not only important theoretical significance, but also more important engineering practical value to carry out the study of dynamic characteristics of multistage centrifugal pump rotor system based on the fluid-structure interaction.The softwares of TurboGrid, UG, ICEM were employed to create numerical model, and numerically simulate on a certain type D multistage centrifugal pump. On such a basis, the co-simulation platform of ANSYS Workbench was utilized to study the dynamic characteristics of rotor structure of multistage centrifugal pump under the fluid-structure interaction of the unidirectional flow. The main research contents and results are as follows:(1) The standard k-s turbulent model was used to simulate the flow field in the multistage centrifugal pump under different flow rates; pressure distribution of flow field was analyzed, and the feasibility and reliability of numerical simulation was tested against the results of model test in external characteristics.(2) The linear static force calculation of multistage centrifugal pump rotor structure was carried out based on unidirectional flow fluid-structure interaction, in order to do research on equivalent stress and deformation of the impeller, obtain its maximum stress deformation and its location, and conduct the intensity check of the impeller. It was found out that the fluid pressure load played a main role in the structure stress and deformation; and the maximum equivalent stress decreased with the increase of flow rate; the total deformation increased with increasing flow. It was further found out in design conditions, the equivalent stress has the tendency of first increased and then decreased according to the impeller blade stages:the maximum equivalent stress was in the second stage and there existed stress concentration; in the first stage the maximum equivalent stress of the impeller blade was in the joint of inlet blade leading edge and wheel hub and while in other stages it was in the joint of inlet blade leading edge and front shroud. It was also found out that the deformation increased step by step:the maximum deformation occurred in the outer edge of the last stage impeller blade; at the same impeller, the deformation was mainly uneven along the circumferential direction, and increased gradually along the radial direction. The structure minimum safety factor was3.75under different flow rate conditions, which can meet the strength requirements.(3) In the Workbench Modal analysis module, the rotor structure modes of stage3～15impellers were respectively calculated in the air; the natural frequency of different impeller were analyzed and compared with1,2,3times of rated speed rotation frequency of multistage centrifugal pump to predict the possibility of multistage centrifugal pump resonance occurring at all stages. It was showed that the rotor structure vibration modes mainly were swinging, twisting vibration, bending vibration and longitudinal vibration; the vibration characteristics of5-stage centrifugal pump were good under given conditions and there was no resonance; the increase of the number of impellers may cause the structure resonance; at stage15, it was prone to resonance when rotation frequency was close to the first and second order natural frequency under the rated speed.