Pressure Pulsation Characteristic Analysis Of Low-specific-speed Centrifugal Pump Considering Cavitation

Pressure pulsation usually exists in the centrifugal pump which is a kind of rotary fluid machinery,it will be much more complicated influenced by the vapor-liquid flow when the cavitation occurs.In this thesis,the constant hydraulic and cavitation performance of IB50-32-250 low-specific-speed centrifugal pump are analyzed through the experiments and numerical simulation methods,and the study of unsteady cavitation flow and pressure pulsation including time domain,frequency domain and amplitude characteristics is conducted.According to research results,under small flow rate,the hydraulic performance curve of low-specific-speed centrifugal pump appears ‘hump',while the pump runs steadily at the rated and the large flow conditions.There is obvious vortex in impeller,and with the increasing of flow rate the vortex weakens;vapor distribution inside the impeller is asymmetry,and the vortex is increasing with the decreasing of the NPSHa(Net Positive Suction Head available).Under different flow rates and NPSHa conditions,cavitation development process inside impeller is similar,showing ‘growth – retraction-growth' cyclical evolution characteristic in the impeller rotation process.The pressure pulsation in impeller flow passage is mainly related to the impeller rotation frequency.While in the volute,because of the interference between impeller and volute tongue,the main dominant frequency of pressure pulsation is the blade pass frequency and its harmonic frequency,and the pressure pulsation near tongue is the strongest.The pressure pulsation in the centrifugal pump will be enhanced with the increase of flow rate,but along with the development of cavitation,different monitors show different changes.The amplitude of pressure pulsation in the adherent cavitation of impeller becomes lower,but in the margin of cavitation region,pressure pulsation amplitude increases.Affected by the cavitation flow,the pressure pulsation in volute strengthened with the flow disturbance intensified.In addition,the occurrence of cavitation can also induce low frequency pulsation,and increase the broadband pressure pulsation.The research results can not only help to understand the evolution of cavitation flow characteristics and pressure pulsation in the low-specific-speed centrifugal pump,but also provide necessary basis for further exploration of the cavitation flow vibration.