Dynamics Modeling And Modal Analysis For The Rotor In Water Medium

Rotating machinery is widely used in production and daily customer life, and thevibration characteristics of the rotors are related to the safe of the equipment in operation.Modal analysis, as an efficient and accurate analysis method, is gradually applied toanalyzing the vibration characteristics of the rotors of rotating machinery. Although manyscholars at home and abroad have carried out a large amount of research on the dynamiccharacteristics of the rotors of fans and steam turbines, the working medium of the axial flowpump is water but not air. When the rotor of the axial flow pump starts vibration due to astimulus, the vibration of the pump rotor will be transmitted to the liquid surrounding thepump rotor while the vibration of the surrounding liquid in turn influences the vibrationcharacteristics of the pump rotor.Based on the lift method this paper proposes a design of the leaves and rotor of the axialflow pump as per the characteristics of the axial flow pump. The dynamics models of theleaves and rotor in air medium and in water medium were established, respectively. Themode of the leaves and rotor in air medium was calculated first, and then the mode in watermedium was calculated. Comparison of the modes of the leaves and rotor in air medium andin water medium reveals the influence of water medium on the vibration of the pump rotor.In practical applications the axial flow pump does not always operate under the ratedconditions. During the acceleration and deceleration of the pump rotor, the rotor and inparticular the leaves are subject to large centrifugal force. The effects of the rotor on thesurrounding liquid vary with its rotational speed, and the liquid in turn influences thevibration characteristics of the rotor. In this paper, the centrifugal force and water mediumare taken into account together to analyze their influences on the vibration characteristics ofthe pump rotor. The simulation results show that the centrifugal force mainly influences thelow frequency of the rotor, and that the influence of centrifugal force on the vibrationfrequency of the rotor in water medium is much smaller than that in the air.Rotor modal tests based on water medium were designed and carried out in order tostudy the influence of water further. The test result not only demonstrates that the watermedium surrounding the rotor influences the natural frequencies of the rotor but also revealsthat the influence changes with water boundary conditions.