Investigation Of Unsteady Flow Mechanism Of Wear Ring Clearance In A Centrifugal Pump

Centrifugal pump is an important equipment with higher energy consumption in the national economy.It is of great theoretical and practical value to study the internal flow of the centrifugal pump and improve the performance of the centrifugal pump.Wear ring clearance flow has an important influence on the performance of the centrifugal pump.The interaction between the leakage flow of the wear ring and mainstream of the impeller inlet causes the variation of the inlet flow structure of the impeller,disrupting the orderly flow state.As a result,it affects the flow pattern and the stability of the centrifugal pump.Therefore,it is of great significance to thoroughly study the influence of the wear ring clearance flow on the internal and external characteristics of the pump.In this paper,the unsteady flow characteristics of the wear ring clearance flow of the centrifugal pump were studied.The numerical simulation,experimental research and theoretical analysis were combined to analyze the influence of the clearance flow in the pump.The unsteady flow characteristics of the wear ring clearance were described in detail.The interaction between the leakage flow of the wear ring and the mainstream of the impeller inlet was explored,and the influence of the flow of the wear ring on the internal flow and external characteristics of the centrifugal pump was preliminarily analyzed.The main work and innovation of this article are as follows:(1)A centrifugal pump wear ring clearance test platform was built to realize the synchronous acquisition of centrifugal pump external characteristics,pressure pulsation signals and vibration signals.The variation of the pump external characteristics caused by the change of the wear ring clearance was obtained,and the circumferential pressure of the volute and the radial pressure distribution of the pump chamber were analyzed.The results show that with the increase of the wear ring clearance,the head and the efficiency curves of the pump are reduced,the pressure at the measuring points of the pump are reduced to different extents.However,the pressure distribution trend remains unchanged.The rotating frequency and the blade passing frequency signals are found in the pressure fluctuation spectrum of the volute wall,and the dominate frequency is the blade passing frequency.In the vibration spectrum diagram,the rotating frequency and its harmonic frequencies and the blade passing frequency and its harmonic frequencies are captured.There are certain differences in the vibration energy of the pump in different directions.(2)The influence of the number of wear ring mesh nodes on the distribution of flow parameters in the clearance was discussed in detail.It is considered that the reasonable number of wear ring mesh nodes is crucial for obtaining accurate distribution of the flow parameters of the wear ring clearance flow.Based on the premise of both the computation time and the computation accuracy,the influence of the unsteady time step size on the precision of the numerical simulation of the centrifugal pump was systematically studied,and the difference caused by the time step was quantitatively analyzed.The experimental verification shows that the numerical solution strategy is correct and accurate.(3)The influence of the clearance flow in the centrifugal pump on the external performance of the pump was studied.By comparing the results of calculations considering the clearance and not considering the clearance centrifugal pump model,the cause of the large differences in the flow field and external characteristics of the pump caused by the clearance flow was revealed.That is,the differences in the flow loss in the pump caused by clearance flow in the gap region of the pump chamber,mouth ring,etc.The interaction between the leakage flow of the wear ring and the mainstream of the impeller inlet is preliminarily grasped and can be roughly divided into collision impact phase,reverse blending phase and assimilation phase.The effects of clearance flow on the evolution and orderly transition regulation of the separating vortex inside the impeller were described.The entropy production theory was used to analyze the important influence of the flow loss produced by the clearance flow on the flow inside the pump.The effect of the clearance flow on the pressure field is as follows: the pressure pulsation intensity between the impeller and the volute tongue is reduced,which affects the pressure distribution on the blades surfaces and causes the pressure fluctuation on the pressure side of the blade.(4)The numerical simulation of the unsteady flow in the centrifugal pump was carried out,and the main flow and clearance flow characteristics in the pump were studied.The influence of the leakage flow of the wear ring on the mainstream of the impeller inlet was analyzed.The entropy production theory was used to analyze the distribution characteristics of the flow loss in the pump and it was found that there is a close relationship between the flow behavior and energy loss in the pump.The energy gradient theory was used to predict the unstable flow region in the pump.The correlation between the functional force of the blade and the flow was concluded.The study of the clearance flow revealed the distribution of pressure and pressure pulsation in the pump chamber.The pressure at the low flow rate is highest,and the pressure pulsation at the inlet of the pump chamber is strong.The detailed flow distribution characteristics in the wear ring clearance were obtained.It is found that the inlet shrinkage loss is one of the main reasons of abrupt changes in the flow parameters of the clearance inlet,which represents a sudden increase in dynamic pressure and turbulent kinetic energy,a sharp drop in static pressure,and a gentle decrease in total pressure.The pressure fluctuation characteristics of the wear ring clearance are more complex and still affected by the interaction between the impeller and the volute tongue.The interaction between the wear ring leakage flow and the mainstream caused by flow rate variations was summarized.The collision,impact,blending,and assimilation are always present throughout the process,revealing the relationship between the leakage flow and the mainstream energy ratio.The increased flow leads to the increase of the energy of the mainstream of the impeller inlet,and continuously weakens the impact of the leakage flow on the mainstream.(5)The characteristics of the internal and external characteristics of the pump caused by variations of the wear ring clearance were studied preliminarily.The external characteristics of the centrifugal pump were verified by experiments and numerical simulation.It was found that when the wear ring clearance increases,the hydraulic efficiency and volumetric efficiency decrease,and the flow loss in the pump increases,thus leading to a reduction in head curve and efficiency curve.The reasons for the flow difference in the impeller resulted from the wear ring clearance were analyzed.It is found that the flow rate of the impeller is changed by the variation of the wear ring clearance,and there is a significant difference in the impeller flow pattern at low flow rates.The detailed flow distribution characteristics in the wear ring clearance were studied.It was found that the total pressure drop at the inlet of the wear ring is large.Due to the rotation of the impeller,the total pressure gradually increased to a maximum value along the flow direction of the clearance flow,and then gradually decreases until the wear ring clearance exit.The increase in the wear ring clearance leads to the static pressure decreases,the dynamic pressure increases,the total pressure of the fluid increases slightly.The variations of the wear ring have a slight effect on the pressure fluctuation intensity.The variations of the flow pattern at the impeller inlet caused by wear ring clearance changes was summarized.It is found that the with the increase of the wear ring clearance,the leakage and flow loss increase,and disturbs the flow behavior of the impeller inlet.(6)The effect of the wear ring clearance structure on the performance of the centrifugal pump was studied.It was found that under the same size and length of the wear ring clearance,the influence of the serrated and stepped wear ring clearance structure on the external characteristics of the centrifugal pump was approximately negligible,while the stepped wear ring clearance structure has a slight effect on the flow in the pump.The stepped wear ring clearance structure has an enhanced obstructure effect on the clearance flow,and reduces the interference of the wear ring clearance leakage on the impeller inlet mainstream.The variation of the wear ring sturcutre has a slight effect on the pressure pulsation intesnity in the wear ring clearance.