Study On Internal Flow And Cavitation Characteristics Of Centrifugal Pump With Jetting Device

Centrifugal pumps are the heart of liquid delivery systems in aerospace,petrochemical and other fields.As a key device,the performance directly affects the overall operation of the system.Therefore,how to improve the stability of centrifugal pump operation has always been a hot topic for scholars.External characteristic and cavitation performance are important indicators to measure the performance of centrifugal pumps.Analysis of the internal flow and cavitation characteristics of centrifugal pumps is of great significance for the safe and stable operation of pumps.The use of a jetting device is one of the effective means to improve the cavitation performance of a centrifugal pump.In this paper,the jetting device is used to deliver a part of high pressure fluid from a centrifugal pump outlet to the inlet which can improve its cavitation performance.The influence of the jetting flow on the external characteristic and cavitation performance of the pump are obtained through experiments.The influence of the jetting flow on the internal flow of the pump is analyzed by numerical simulation,and the internal cavitation flow of the pump is analyzed under the jetting flow when the cavitation performance of the design condition is optimal.This study is of great significance to effectively improve the cavitation performance and operational stability of centrifugal pumps.The main research contents of this paper are as follows:(1)The full flow field model of the centrifugal pump with jetting device is modeled based on the three-dimensional modeling software UG.The ICEM software is used to mesh the pump's full flow field model.The computational fluid dynamics software CFX is used to simulate the single-phase flow and cavitation flow inside the pump.The numerical results are compared with the experimental results to verify the reliability of the numerical simulation method.(2)The external characteristic experiment and cavitation performance experiment of the pump are carried out.It is found that the head and efficiency of the pump decrease slightly and the NPSHc(critical net positive suction head)decreased first and then increased with the increase of the jetting flow.Back to 6% flow is the best jetting flow for pump cavitation performance.(3)The numerical simulation is performed on the centrifugal pump with jetting device by delivering 0~10% flow at the design condition.The distribution of velocity,entropy generation rate and turbulent kinetic energy of the jetting device and the inlet pipe are mainly analyzed.It is found that the velocity and turbulent kinetic energy are more unevenly distributed in the jetting device and the inlet pipe resulting from the jetting flow.The entropy generation rate in the jetting device and the inlet pipe increase gradually with the increase of the jetting flow,which indicates that the hydraulic loss increase gradually.It also mainly analyses the changes of pressure and turbulent kinetic energy in the impeller.It is found that the jetting flow make the pressure increase in the impeller inlet and make the turbulent kinetic energy decrease in the impeller inlet and outlet.(4)The internal cavitation flow of the centrifugal pump with jetting device is analyzed at the optimal jetting flow of the design condition.When the NPSHa(available net positive suction head)reduces to a certain extent,it is found that the low pressure region quickly occupy the most of the impeller flow passages and the leading edge of the suction blades appear vapours at the same time.Vapours diffuse gradually toward the outlet of the impeller and the impeller flow passage obviously appears eddy current.At low NPSHa conditions,the regularity of radial force of the impeller is destroyed by cavitation.It also makes the frequency of pressure pulsation at the impeller outlet from the blade passing frequency to a very small frequency(f <10 Hz),which is the main reason for the instability of flow in the pump.