Investigations Of Rotor Dynamic Of Pump Subjected To Base Movement And Fluid-Solid Interaction

Pump is a device that converts mechanical energy into potential energy and kinetic energy. Pump is widely used. It is the important equipment in energy, electric power, petrochemical, aerospace and other fields. Most pumps are rotating machinery. Rotor system, which consists of rotor, bearing, seal and base, is the core of the rotating machinery. With further research of the rotor dynamics, design of the rotor system has not only pursue efficiency of the whole system, but also considers the nonlinear characteristics of the rotor system. Only by fully understanding of the nonlinear characteristics of the rotor system, safe operation speed range of the rotor can be designed more accurately, as well as running state of the rotor can be identified better. Different from the traditional linear research, the bearing force and the sealing force no longer be simplify into eight linear coefficients during investigation of nonlinear rotor system. The effect of inertia force of fluid in small gap and the effect of cyclic force caused by external damping are taken into account in the nonlinear model. Moreover, rotor interacts with fluid as rotating machinery running which has distinct characteristics of fluid-structure interaction. Viscous fluid act on the solid surface in the form of pressure, and movement of the solid changes boundary of the flow field during the running of machinery. In consideration of complexity of response of the rotor system subjected to nonlinear force action, although people have been studied for several decades, there are still many nonlinear problems worthy of further research. The results of the research can not only provide theoretical basis for interpretation of the rotor dynamics, but also provide reference for design of the rotor system.Rotor system of pump is investigated in this paper. The motion equations are proposed for rotor system with multi-degree of freedom. The Runge-Kutta-Fehlberg, which is adaptive time step method, is applied to solve the differential equations of motion. The first critical frequency of the rotor system is investigated; the running speed range of the rotor system is calculated; the respondes when the rotor system subjected to base movements are studied. Furthermore, based on the Computational Fluid Dynamics (CFD) and Radial Basis Function (RBF) method, the respond surfaces of dynamics parameters of the seal which are closely relevant to fluid field are obtained and the rotordynamic analysis is completed. The analysis of the Fluid Solid Interaction (FSI) as a rotor which has blades rotated in fluid is accomplished. The major contents are as follows:1. The differential motion equations of rotor-bearing system of pump with nonlinear oil film force are proposed. The software of Matlab is used to program and solve the equations. The nonlinear methods, such as bifurcation maps, Poincare maps, phase diagrams, etc, are employed to investigate dynamics behaviors of horizontal and vertical rotor. The first critical frequency of the system is found by observing the amplitude of the system vs. variation of rotation speed. Based on the results of amplitude frequency curves, axis trajectories and cascade diagrams, oil film instability of the bearing is gained. The phenomena of "oil whirl" and "oil whip"'are identified and the speed of oil film instability is achieved. The results proved the modeling approach is "robust". The proposed method can be applied to the case of a symmetric rotor, and also to the case of mass bias. The results of critical speed, bifurcation point and speed of instability provide a theoretical basis to designs of both operation speed range and separation margin of pump.2. The differential equations of motion of rotor-bearing system of pump which subjected to base movements are build. The seismic wave and sinusoidal wave are used as base movements by time history analysis method. The nonlinear responses of horizontal rotor and vertical rotor are investigated, separately. Due to the critical frequency of the horizontal rotor is lower, the first critical frequency in the frequency domain is observed when the seismic wave happened. While the first critical frequency of the vertical rotor is higher, there is not exist the critical frequency in the frequency domain. Nevertheless, the lowest speed when the peak of half frequency of rotational speed emerged for the vertical rotor becomes lower. The phenomena of combination resonance of multi-degree of freedom system are obtained when the nonlinear system subjected to both centrifugal force and sinusoidal base movements. There are several peaks which have relevances in the results of the FFT. These peaks include not only the two peaks of the rotational speed and the frequency of base movements, but also the the peaks of algebraic sum of integer multiple of both the rotational speed and the frequency of base movements. The results proved the phenomena of combination resonance of multi-degree of freedom system may happen at some cases, as well as provide a theoretical basis to identify status of the rotor system subjected to base movements.3. Nonlinear characteristics of rotor-bearing-seal system of pump with varying coefficients based on CFD and RBF is investigated. Approximate function surfaces of coefficients which are relevant to fluid of the seal are obtained. The Muszynska nonlinear seal force model has been widely applied because of its simple form, clear physical meaning and so on. The coefficients of the model, such as inlet loss coefficient, axial velocity and fluid average circumferential velocity ratio, are closely related to status of the flow field. In the former researches, these coefficients often replaced by constants or emprical formula. The fluid field is decided by rotational speed and relative eccentric rate in case of the conditions both of inlet and outlet are given. The CFD method is applied to compute the coefficients of fluid field as different rotational speed and different relative eccentric rate. The RBF method is employed to fit the approximate function surfaces of the coefficients. According to the values of rotational speed and relative eccentric rate, call the corresponding data of the approximate function surfaces in each steps during solving process of motion equations. This method of transient analysis is more accurate than the formers. The approach in this paper provides a new way to investigate the nonlinear characteristics of the rotor-bearing-seal system.4. The rotordynamics of an axial flow pump considering the effect of FSI are numerically investigated using finite element software ADINA. The non-slip condition is applied on the fluid solid interaction surface. The iterative method is adopted in computation of coupled fields of displacement and fluid. What distinguishes the present study from previous ones is the use of moving meshes and the FSI interface that separates the rotor surface from its surrounding fluid. The rotor"s center orbit and frequency response as well as the transient fluid dynamics are obtained with various axial flow speeds. The "wet" critical frequency is obtained. The change of the FSI interface affects the pressure of fluid field. This can be approved by comparing with the results of rotor as it never whirls around Z axis. Moreover, by comparing with the traditional method, it is proved that the method of simulation in this paper is effective. By including real rotating motion of the rotor, this paper presents a better way to solve complicated rotordynamic problems of rotating mechinary that are operated in FSI circumstances.