Influence Of Volute Outlet Position On Hydraulic Performance Of Low Specific Speed Centrifugal Pump

Volute as one of the main flow passage parts of centrifugal pump,its hydraulic structure has important influence on the efficiency of centrifugal pumps.Previous studies on volute mainly focused on the area and shape of the first eight sections,the area of throat and the angle of tongue insertion.In this paper,three types of centrifugal pumps with 46 specific speed of IS80-50-180,IS100-80-290 and IS200-150-550 were studied,the volute structure was based on the conventional central outlet A and lateral straight outlet E,divide the horizontal distance between the two outlets into four equal parts,keep the base circle,the area and shape of the first eight sections,the outlet diameter and the center height of the volute exactly the same,each type of centrifugal pump had five types volutes of A、B、C、D and E,the influence of outlet position of volute on the external characteristics,internal flow field in steady state,pressure fluctuation and internal flow characteristics in unsteady state of centrifugal pump were studied.1、The heads of C、E-type volutes are higher than that of A、B、D-type volutes,and the change trend of heads is more reasonable;The shaft powers of A、E-type volutes are larger than that of B、C、D-type volutes;The hydraulic efficiency depends on the amplitude change of head and shaft power,it is the result of comprehensive influence of head and shaft power.The C-type volute structure has the best hydraulic efficiency performance among the three types of centrifugal pumps.In IS80-50-180 centrifugal pump,the efficiency of C-type volute in rated working condition is 3.47% higher than that of A-type volute,the efficiency of C-type volute is 2.35% higher than that of A-type volute at each working point on average;In IS100-80-290 centrifugal pump,the efficiency of C-type volute in rated working condition is 2.68% higher than that of A-type volute,the efficiency of C-type volute is 3.57% higher than that of A-type volute at each working point on average;In IS200-150-550 centrifugal pump,the efficiency of C-type volute in rated working condition is 4.85% higher than that of A-type volute,the efficiency of C-type volute is 4.02% higher than that of A-type volute at each working point on average.2、 The static pressure distribution,streamline distribution and turbulent kinetic energy distribution at the impeller inlet are basically the same in different volute structures of the same centrifugal pump in steady flow,it shows that the change of volute outlet position has little effect on the flow field inside the impeller inlet;The static pressure distribution,streamline distribution and turbulent kinetic energy distribution in impeller outlet and volute passage are quite different,it shows that the change of volute outlet position mainly affects the flow field at impeller outlet and volute passage,especially in volute diffusion section.Overall,the distribution of internal flow field in C-type volute is the best,followed by B、D、E-type volutes,and A-type volute is the worst in steady flow.3、In unsteady flow,the pressure fluctuation amplitude of each monitoring point in the flow passage of centrifugal pump with C-type volute is the smallest,and the amplitude of main frequency of pressure fluctuation is particularly obvious,B-type volute followed,A、D、E-type volutes are the largest.At different moments of a cycle,comparing C-type structure with A-type structure,the pressure gradient in each impeller passages of the same impeller is smaller,the diffusivity of fluid to the impeller passage passing through the tongue at that time is weaker after fluid collided the tongue,the sudden drop of fluid velocity near the eighth section is smaller,the angle between the direction of fluid flow in the volute diffusion section and the profile line the volute diffusion section is smaller,more fluid can flow smoothly along the tangent direction of the volute inner wall,therefore,the impact loss of C-type structure is smaller,it shows that the influence of C-type structure on the flow instability of impeller passage caused by the asymmetry of volute geometry is smaller,and the influence of C-type structure on the flow direction change of centrifugal pump passage,especially the volute diffusion section caused by the change of outlet position of volute,is less significant.