Research On The Influence Of Balancing Hole Geometrical Parameters On Performance Of High-speed Centrifugal Pump

High-speed centrifugal pump with small axial size and compact structure is mainly used in aerospace field.With the help of ultra-high working speed,the linear velocity of fluid at the outlet of impeller is increased,which makes the high-speed centrifugal pump obtain high head.It is precisely because of the high head of the high-speed centrifugal pump,the pressure difference between the high-pressure area and the low-pressure area in the pump chamber is very large,which leads to the huge axial force on the pump rotor and seriously affects the safe and stable operation of the high-speed centrifugal pump.The high-pressure fluid in the balance chamber is introduced into the inlet of the centrifugal impeller through reasonable balancing holes designed on the back cover plate of the centrifugal impeller,which can balance the axial force of the rotor,but the internal flow characteristics of the pump can be changed at the same time,which has a certain impact on the performance of the high-speed centrifugal pump.Therefore,it is of great significance for the design and operation of high-speed centrifugal pump to study the influence of geometric parameters of balance hole on its performance.The specific area of the balancing hole determines its cross-section area,and its meridional angle determines its inflow direction.In this paper,the numerical method is used to study the influence of these two key geometric parameters of balance hole on the performance of high-speed centrifugal pump.The main research contents and results are as follows:1.Influence of specific area of balancing hole on performance of high-speed centrifugal pumpThe influence of balancing hole on the performance of high-speed centrifugal pump was studied under four schemes of specific area k= 0.5,1,3 and 5.The results show that with the increase of specific area,the head of high-speed centrifugal pump decreases by 2.4% of the highest head,the efficiency decreases by 3.4%,and the shaft power increases by 3.8% of the its minimum.When the specific area is 3?k?5,the flow in the balancing hole of the high-speed centrifugal pump will produce vortex,which has a great influence on the main flow.With the increase of the specific area,the leakage of the balancing hole increases to a certain value and remains unchanged,and the maximum leakage can reach 23% of the design flow of the pump.The change of specific area has a significant effect on the magnitude and direction of the axial force of the rotor of high-speed centrifugal pump.When the specific area is k<1,the axial force direction of the rotor points to the inlet of the centrifugal impeller,but when the specific area is k?1,the axial force of the rotor deviates from the inlet of the centrifugal impeller;when the specific area is k=1,the balancing hole can effectively balance the axial force of the rotor.2.Influence of specific area of balancing hole on cavitation performance of high-speed centrifugal pumpThe research includes the variation laws of external characteristics,internal flow field,rotor axial force and cavitation performance of high-speed centrifugal pump under the four schemes of specific area k= 0.5,1,3 and 5.The results show that with the increase of specific area,the critical cavitation number increases and the anti-cavitation performance of the pump decreases.With the decrease of cavitation number,the head,efficiency,shaft power and rotor axial force of high-speed centrifugal pump all reduce.With the increase of specific area,the pressure in the balancing chamber of high-speed centrifugal pump decreases.When the specific area is k?3,cavitation occurs in the balancing chamber.3.Influence of balancing hole meridional angle on performance of high speed centrifugal pumpThe influence of balancing hole on the performance of high-speed centrifugal pump was studied under the six schemes of balancing hole meridional angle ?=-30°,-20°,-10°,0°,10° and 20°.The results show that there is a certain angle between the inflow direction of the balancing hole and the inlet direction of the centrifugal impeller,and the pump head will be improved.With the increase of meridional angle,the pump shaft power decreases,but the pump efficiency increases.When the high-pressure jet enters the flow passage of the centrifugal impeller,a local low-pressure area is generated near the back cover plate,and its range increases with the increase of the meridional angle.With the change of the meridional angle,the leakage of the balancing hole is consistent with the rotor axial force.Compared with the traditional balancing hole with meridional angle of ?=0°,the balancing hole with meridional angle of ?=20° can effectively balance the rotor axial force of high-speed centrifugal pump.