Computation And Analysis On Hydrodynamics And Rotors Critical Rotational Speeds Of The Partial Emission Pump

Nowadays, the power and speed of the pump rotor is higher and higher. Open impeller pump is mainly applied to the field of high speed pumps. The high speed pump will inevitably across the first-order even two or three first-order critical speed, so it is obviousiy about the resonance of its rotor when the operating speed approaches the critical one. To avoid this influence and ensure the stable running of the open impeller pump rotors, the critical rotational speeds must be calculated accurately in wet state respectively in the design course. The common algorithms to get the critical rotational speeds of the rotors are FEM (Finite Element Method) and Transfer Matrix Method. Here, the FEM is employed in the calculation of this paper.In this paper, the main model is a partical emission pump, and the overall flow model is established. The three-dimensional flow through the whole flow passage model of the partical emission pump is simulated using CFD technology. The predicted performance of the partical emission pump is obtained through the numerical results. Internal flow conditions of the pump are got. The velocity and pressure distributions within the impellers, volute are analyzed so that the later calculation on the critical speed can be continued. To the critical rotational speeds of the rotor on complete immersion, it is necessary to considering the fluid-solid coupling reaction. The entity model of the partical emission pump rotor is built. Then the static and modal analysis are finished, so that the influence of the fluid-solid coupling reaction and spin softening on the critical rotational speeds calculation can be discussed based on the model. Furthermore, the first-order critical rotational speed of the rotor with rigid support is got separately using Dunkerley Method and FEM by comparison. Also, the influence of the cantilever length, the number of the impeller and supporting stiffness on the natural frequency of the rotor is analyzed respectively using the finite element model consisted of beam, mass and spring. In addition, the wet critical rotational speed of the rotor is calculated. The results show that:1) The numerical simulation results agree well with the design requirements, and the flow states in thepartical emission pump can be revealed correctly. It proved that the simulation method which is adopted in this paper is feasible.2) Generally, the rotor's critical rotational speeds are incresed by the fluid-solid coupling reaction. 3) The supporting stiffness has great influence on the rotor's critical rotational speed. The preconditions of the calculation are not only simplifying the supporting system accurately but also determining the stiffness and damping matrix reasonably.4) For the fluid-solid coupling reaction, there are great differences between the dry critical rotational speeds and the wet ones for the partical emission pump rotor.The calculation of the wet critical rotational speeds in partical emission pump rotors is a complicated process. We must take the knowledge which refers to the classic rotor dynamics, hydrodynamic lubrication theory and seal dynamics into account synthetically. The research in this paper will provide evidence for the structural checking of the multistage centrifugal pumps.