Research On Internal Stall Characteristics And Pressure Pulsation Of Centrifugal Pump Under Flow Transient Conditions

The transient nature of the internal state and the complexity of pressure pulsation make centrifugal pump operation under transient conditions a dynamic and complex process.With a change in flow rate,the centrifugal pump’s internal flow shows obvious hysteresis characteristics.At the same time,the impeller’s internal stall is a dynamic development process,and it’s difficult to describe the entire stall process using stall characteristics under stable conditions.The change rate of pressure and velocity inside the impeller will be affected by the difference in flow transient frequency,causing the stall and hysteresis characteristics of the flow inside the impeller to change.The flow pulsation and static and dynamic interference affect the pulsation field of a centrifugal pump,and its specific pulsation characteristics are related to time and space.Therefore,it is urgent to carry out in-depth research on the internal stall characteristics and pressure pulsation of centrifugal pump under flow transient conditions.This paper takes the centrifugal pump(impeller)as the research object and uses the large eddy simulation method to obtain the calculation results of the indeterminate constant value.First,under stable conditions,the comparison between the numerical results and the existing experimental data verifies the reliability of the numerical method.Then,according to the working conditions of sinusoidal flow change(0.25Q_dto 0.75Q_d),the centrifugal pump(impeller)and its internal unsteady flow law with different transient frequencies are studied,and the stall characteristics and pressure pulsation are analyzed.The main conclusions are as follows:1.Under sinusoidal flow conditions,the transient flow characteristics and evolution laws in the impeller of centrifugal pumps are investigated.The centrifugal pump impeller has gone through a process of"stability-flow separation-stall-flow separation-stability"during a period of transient operating conditions.Under the same transient flow,the flow characteristics of the impeller in the descending phase are closer to the state of large flow,while the flow characteristics of the impeller in the rising phase are closer to the state of small flow.The pressure pulsation of impeller flow channel has both low and high frequency characteristics.The low-frequency component corresponds to the impeller’s flow frequency,while the high-frequency component is related to the flow channel’s stall.The stalled flow channel’s pressure pulsation phase is one-tenth of the period of the non-stalled flow channel.Simultaneously,as the impeller flow channel develops,the lag effect of the low-frequency pressure pulsation phase becomes more apparent.The size of the stall area and the average stall intensity of an impeller stall during transient operation are described.2.The effect of transient flow frequency on the centrifugal pump impeller’s unsteady characteristics is investigated.During the operation of transient conditions,the flow transient frequency has a significant impact on the centrifugal pump impeller.The centrifugal pump impeller has a harder time getting rid of the stall state in the ascending phase but enters the stall state faster in the descending phase as the frequency of flow transients decreases.Simultaneously,as the flow transient frequency decreases,the phase difference of the pressure pulsation between adjacent channels gradually increases,as does the pulsation amplitude difference.The flow transient frequency is negatively correlated with the range of centrifugal pump impeller stall conditions and the average stall intensity.In terms of external characteristics,the pulsation of the head of the centrifugal pump impeller is more severe the lower the frequency of flow transients,but the average value of the head is nearly equal.At the same time,the higher the hysteresis of the centrifugal pump impeller head,the lower the frequency of flow transients.3.The characteristics of centrifugal pump pressure pulsation are investigated when flow pulsation is combined with static and dynamic interference.The pressure inside the impeller is found to be more sensitive to changes in flow rate during transient conditions,and the intensity of pressure pulsation caused by static and dynamic interference is related to time and space position,while the influence of flow and speed on the impeller speed is of the same magnitude.The change law of pressure and speed on the volute,on the other hand,shows an opposite trend.The flow rate is the first factor that affects the flow in the volute.The pulsation is amplified by the dynamic and static interference,as well as the shedding vortex,and the stronger the dynamic and static interference,the greater the enhancement effect.The interference of movement and static determines the amplitude of velocity pulsation.The greater the amplitude of the pulsation of the monitoring point,the stronger the interference of movement and static,and the frequency of the velocity pulsation of the monitoring point is closely related to the shedding vortex of the flow channel.