| The multistage centrifugal pump is a high-head centrifugal pump with at least two impellers connected in series.Frequent start-up is required due to changes in operating conditions.the operating parameters change sharply during the start-up process,and The unsteady flow of internal fluid includes the flow changes caused by the stageic change of relative position between the rotor and the stator and the change of pressure field boundary.The complex structure of multi-stage centrifugal pumps and the strong unsteady flow of internal fluids often result in complex force and vibration,even impact damage to equipment,which seriously affects the safety and life of multi-stage centrifugal pumps.In view of the current lack of research theory on the transient flow of multistage centrifugal pumps,the analysis of transient hydraulic and structural dynamic characteristics during the start-up process has important theoretical significance and engineering application value for the safety and reliability of multistage centrifugal pumpsIn this paper,the multistage segmental centrifugal pump of model TDM35-140×13 is taken as the research object.The start-up process is divided into two stages: closed valve transition and valve opening transition.Hydraulic optimization design and transient characteristics of the low-specific-speed multistage centrifugal pump during two start-up stages are studied.The main research content and results are as follows:(1)Based on the genetic algorithm,the optimal mathematical model is established taking the total power loss,reciprocal slope of theoretical Q-H curve and total hydraulic loss as sub-objective function.Constraints are set to determin the optimum combination of impeller geometric parameters by the relationship between performance parameters and impeller geometric parameters.compaerd with the hydraulic performance of the centrifugal pump designed by the velocity coefficient method,the hydraulic model of centrifugal pump meeting the design requirements is finally determined.(2)The complete fluid domain model of the multistage centrifugal pump is established,and the transient operation of the two start-up stages is numerically simulated to reveal the variation of the external characteristics with time and evolution characteristics of the internal flow field during the two transient start-up stages.By analyzing the external and internal flow characteristics between two start-up transient stages and steady state under the same speed or the same flow rate in the corresponding time,the difference of the flow characteristics between the start-up transient process and the corresponding steady-state state is explained,and the influence of transient effect on hydraulic performance during the two start-up stages is explored.(3)The modal analysis method is used to predict the natural frequency variation of multistage centrifugal pump rotor under three different conditions: free vibration in air,idle operation and design operation.Aiming at the phenomenon of temperature rise during start-up of closed valve stage and flow increase during start-up of valve opening stage,the effect of temperature and flow rate on impeller stress and deformation under steady operation condition are obtained by fluid-solid-thermal coupling method.(4)The transient impeller stress and deformation in the two start-up stages are obtained by loading the transient flow field pressure on the wet surface of the multistage centrifugal pump impeller during the start-up process.The transient dynamic analysis of pump shaft stability is carried out by loading the transient X-direction radial force Fx,and Y-direction radial force Fy on the cylinder contact surface between the pump shaft and the impeller during the start-up of the closed valve.The stress deformation variation and vibration speed is obtained with time at different nodes of the pump shaft during the start-up phase of the closed valve transition. |
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