| This work is supported by the National Outstanding Young Scientists Funds of China （Grant No.50825902）, National Science&Technology Pillar Program （Grant No.2011BAF14B04） and Jiangsu Provincial Project for Innovative Postgraduates of China （Grant No. CX10B262Z）.Pumps, of which70%are centrifugal pumps, are important energy conversion devices and fluid delivery equipment. Centrifugal pump is widely used not only in all industrial and agricultural applications like petroleum, chemistry, water resources and irrigation, but also in high-tech applications as key equipment like nuclear industry, aviation, ships and submarine, et al. As the society develops and technology advances, the reliability of centrifugal pump has been paid more and more attention. Unsteady flow-induced vibration is one of the most important reasons that cause negative effect on pump reliability. The fluid-structure interaction （FSI）, which can lead to increased potential for flow-induced vibration, exists between complex inner flow and structures of centrifugal pumps. That means hydraulic excitation will change dynamic characteristics of structures and lead to deformation, meanwhile the distribution of pump inner flow field will be affected by the deformation as well. Based on numerical and experimental methods, two different kinds of centrifugal pumps were systematically studied in the aspects of unsteady flow-induced impeller oscillations, fluid-structure interaction effects and inner flow unsteadiness behaviors. The main work and creative achievements of this dissertation were:1. Advances and development trends of research on3D fluid-structure coupling methods have been systematically summarized and analyzed. Based on rotor vibration behaviors and unsteady flow characteristics, considering the applicability of coupling methods for different fluid-structure systems, the final coupling strategy, partitioned coupling method with external load transfer between fluid and structure fields, for unsteady flow-induced impeller oscillation with FSI effect has been selected for centrifugal pumps.2. Experiment scheme and data acquisition method of transient flow-induced impeller oscillation measurement of centrifugal pump were established for the first time, and the test rig based on non-contact rotor vibration measurement chain under eddy current principle has been built. Data processing method, which can exclude the vibration induced by non-fluid phenomenon, was put forward. The orbit curve results of impeller deflection induced only by periodically unsteady flow have been successfully obtained considering different rotating speeds and flow rates, and primary factors that can influence the accuracy of the measurement results have been studied.3. A conversion formula between the results in stationary and rotating coordinate frames, which lays a foundation for analyzing the vibration results in different expression forms, was derived. The key parameters influencing the accuracy of transient fluid-structure coupling results for centrifugal pump impeller were analyzed based on the measurement results initially. The results showed that the mapping methods on the fluid-structure interfaces, damping coefficients in the FSI solving procedure, fluid mesh stiffness, under relaxation factor for the load transfer procedure and load transfer convergence target were main factors that can influence the FSI solving results, and a parameter combination for FSI solution with high accuracy has been primarily obtained.4. The transient FSI calculation results for centrifugal pump was validated by the measured vibration results firstly, and the comparison between numerical and experimental results showed that good agreements in both aspects of vibration magnitude and phase, can be observed for all examined rotating speeds and flow rates. Some deviations, however, can also be found, especially for low flow rate. In addition, hydrodynamic force results based on two-way coupling effect for the single-blade centrifugal pump were quantitively analyzed for every rotating speed and flow rate condition, and the force components acting on different part of the impeller were studied. Equivalent stresses in the pump impeller for multi-condition were analyzed, and the time-variant equivalent stresses were studied.5. The periodic flow unsteadiness in single-blade pump has been quantitatively investigated in detail by defining pressure fluctuation intensity, velocity unsteadiness intensity and turbulence intensity based on solving URANS equations. To validate the reliability of the CFD calculation, transient pressure measurement for the model pump has been carried out using transient pressure sensor with high-precision. Periodic pressure results for one impeller revolution were obtained, and good agreements can be observed between numerical and measured pressure results for different rotating speeds and flow rates.6. FSI simulation under partitioned coupling strategy for a centrifugal pump with multi-blade impeller was done to analyze impeller periodical oscillation, stress distribution and hydrodynamic force results for different operational conditions, and FSI effects for multi-blade impeller has been initially revealed.3D flow unsteadiness analysis method for centrifugal pump with twisted blades was established. Based on the unsteady flow calculation results within whole flow passage for the centrifugal pump, the3D velocity unsteadiness intensity and3D turbulence intensity were defined to study the unsteady flow from a new point of view. The magnitude and location of the pressure fluctuation intensity,3D velocity unsteadiness intensity and turbulence intensity have been obtained.Through this study, the flow-induced vibration behaviors with FSI effect were preliminary obtained, and numerical and experimental methods used can be a reference for FSI analysis in centrifugal pump. The proposed analysis method for flow unsteadiness can determine the periodic flow unsteadiness strength distribution, and can provide basis for optimization of pump on unsteady flow behaviors. |
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