Modified Particle Swarm Optimization Algorithm To Improve The Performance Of A Centrifugal Pump And Investigation Of Unsteady Flow

With increasing attention being paid on the development of renewable energy and energy conservation,a growing number of the construction projects like the nuclear power plants,pumped storage power plants and so on have been being carried out,and a centrifugal pump with vaned diffuser is applied in these projects widely.The high-efficiency and energy saving of pumping system is relative to pump's operating efficiency of pump,while the safe operation of the system is determined by the unsteady flow in the pump.Therefore,performance improvement of the pump based on optimization algorithm and complex unsteady flow characteristics induced by rotor-stator interaction have been carried out in recent years.Supported by National Science&Technology Pillar Program of China?Grant No.2011BAF14B04?and Jiangsu Provincial Project for Innovative Postgraduate of China?Grant No.KYLX15₁066?,the optimization on performance at design point and numerical and experimental investigation on the unsteady flow in vaned centrifugal pump was carried out with the theoretical analysis,numerical simulation and experimental measurement of pressure fluctuation.The main work and creative results of the dissertation include:?1?The hydraulic design and optimization methods of centrifugal pump are summarized in this dissertation from the current literatures.The advantages and disadvantages of five different optimization methods are compared.The improvement of pump performance and the number of optimized parameters are determined by the adopted optimization methods.The reasonable optimization method can make a balance between the optimization period and objectives that meet the minimum requirement of design.?2?Based on the basic principle of Particle Swarm Optimization?PSO?algorithm,the strategies of modification on the PSO is summarized and an adaptive and time-varying PSO is proposed creatively considering the time-consuming numerical simulation of pump and the low accuracy of optimized objective.Specifically,the inertia weight factor and cognition acceleration coefficient are decreasing with iterations,while social acceleration coefficient is increasing with iterations.At the same time,they are also associated with the current distance between each particle and the global best particle discovered so far.Six well-known benchmark functions are utilized to test the global search ability and convergence speed of five different PSO algorithms.Meanwhile,the adaptive and time-varying PSO is compared with the genetic algorithm,which is often applied in the performance optimization on pumps.The results show that the modified PSO can improve the convergence speed and enhance the calculation robustness.?3?An automatic optimization method based on adaptive and time-varying PSO is proposed to improve the efficiency of the vaned centrifugal pump at design point firstly.An optimization flowchart is built to combining the generation of three-dimensional impeller model with BladeGen,generation of structured mesh with TurboGrid and performance calculation with CFX based Workbench software.The pump efficiency obtained from the numerical simulation is set as the optimization objective with constraint of head that is within the range between 72.5m and 77m.Total ten design parameters of impeller that controlling Bézier curves of the impeller blade angle?four parameters?,leading edge position?2 parameters?and impeller blade thickness?2 parameters?are determined.MATLAB software is applied to call the functions to run the Workbench automatically and modified PSO to find the global best efficiency value.After PSO runs 50 iterations,corresponding to steady simulation of 1000 impeller cases,the pump efficiency improved to be 78.5%,2.1%higher than that of original pump and the head is 72.5m,meeting the design requirement.The comparison of velocity streamline in impeller and diffuser among the optimized impeller and original one,the optimization can improve the inner flow characteristics.?4?Numerical simulation is carried out to investigate the unsteady flow characteristics of the centrifugal pump with vaned diffuser.The flow rate coefficient in impeller channels and diffuser channels and unsteady pressure are captured.The pressure fluctuations characteristics are analyzed with methods of statistics and spectrum.The results show that the amplitudes of flow rate coefficients'fluctuations in impeller channels and diffuser channels are higher at off-design conditions than those at design point.With the increase of flow rate,the dominant frequency in spectral domain of flow rate in impeller channels changes from vane passing frequency to shaft rotating frequency,while the dominant frequency in spectral domain of flow rate in diffuser channels keeps blade passing frequency.The distribution of pressure fluctuation intensity is similar to that of amplitude of pressure fluctuation at vane passing frequency and its high harmonic frequencies,increasing from impeller inlet to outlet and reaching the highest at the pressure side of trailing edge.Pressure fluctuation intensity is the stronger in the throat area of diffuser than that in other area,achieving the highest at the leading edge of diffuser vane.The amplitude distribution of pressure fluctuation at blade passing frequency in both planes of diffuser and volute is similar to the distributions of pressure fluctuation intensity respectively.The distribution of pressure fluctuation intensity in volute is relative to the diffuser position.?5?An open test rig of the centrifugal pump with vaned diffuser is built to measure the pump performance and dynamic pressure at 12 monitors on the volute wall simultaneously.With the increase of flow rate,the pressure fluctuation intensity on the volute wall decreases and then increases,reaching the lowest between 0.7Q_d and 1.0Q_d.The frequency components of pressure fluctuations induced by rotor stator interaction consist of two fundamental frequency,namely blade passing frequency and vane passing frequency.Flow rates and monitor's positions have great influence on the main frequency and amplitude of pressure fluctuation.The pressure fluctuations are dominant by the blade passing frequency and vane passing frequency at part load and design conditions,while blade passing frequency is more obvious in frequency domain at overload condition.?6?Based on the open test rig of the centrifugal pump with vaned diffuser,the diffuser clocking effect on the pump performance and pressure fluctuations on the volute wall is investigated experimentally.The clocking effect on the performance curve grows with the flow rate increasing.The distribution of pressure fluctuation intensity on volute wall is independent of the relative position of diffuser to the volute.The relative position has significant influence on the dominant frequency and its amplitude of pressure fluctuation and can change the influence extent of rotor-stator interaction and stator-stator interaction on the pressure fluctuations.The transient pressure on the volute had the lowest fluctuations when the trailing edge of the diffuser reached the left corner of the volute outlet?position D?.