Research On Influence Of Pre-inducer On High-speed Centrifugal Pump Cavitation And Pressure Fluctuation

High-speed centrifugal pumps have high speed and unique impeller design to achieve low flow and high head that only multi-stage centrifugal pumps or positive displacement pumps can achieve.With the rapid development of the petrochemical industry and the advancement of aerospace,theoretical research on high-speed pumps has progressed rapidly.However,in the case of high speed,high pressure,etc.,cavitation is likely to occur in the pump,and cavitation will seriously affect the performance of the pump and destroy its stability.At present,it is more extensive to add an inducer to the centrifugal pump to suppress the diffusion of cavitation.Because the inducer itself also has a certain cavitation phenomenon,the inducer structure,structural parameters or setting parameters will affect the performance of the inducer and thus affect the hydraulic performance of the pump.Domestic and foreign scholars have not yet perfected the theoretical study of the inducer.In particular,there have been few reports on the cavitation performance of the high-speed centrifugal pump by the front inducer.Therefore,there is still an important research significance in the inducer to improve the anti-cavitation performance of high-speed centrifugal pumps and to predict the generation and development of cavitation through pressure pulsation.In this paper,by optimizing equals pitch inducer and after a lot of numerical calculations,the flow characteristics of the inducer with different structure parameters and the improvement of the performance of the high-speed centrifugal pump were analyzed.The optimum total wrap angle inducer for improving the cavitation performance of the high-speed centrifugal pump impeller was determined,and the optimal relative circumferential position between the inducer blade and the impeller blade is explored.Next,for further pressure pulsation analysis was performed of full flow path of a high-speed pump and the influence of the pre-inducer on the sensitivity of high-speed centrifugal pumps to cavitation explored.The main research contents and results are as follows:(1)In order to improve the cavitation performance of high-speed centrifugal pumps,a design plan was worked out for optimizing the inducer,including the number of blades,the wrap angle of the blade(that is,the total wrap angle of the blade)and the relative position of the inducer blade outlet and the impeller blade,etc.And its impact on the cavitation performance was explored of the high-speed centrifugal pump.(2)The calculation model in this paper is based on CFturbo and UG software for the establishment of three-dimensional physical model,and the use of ICEM software for meshing the model.Due to the large degree of distortion of the model structure,a non-structural meshing calculation model grid with adaptability is adopted.Finally,mesh was imported to the Ansys CFD to begin numerical simulation analysis.(3)Through the numerical calculation of the two-blade inducer,the three-blade inducer and the four-blade inducer,five kinds of working conditions including the optimal total wrap angle were selected for each structure of the inducer,and comparative analysis of the different structures was made.The best inducer for anti-cavitation performance was identified.Finally,influence of the optimal inducer and impeller on the blade circumferential angle was analyzed.(4)The degree of cavitation in the impeller is closely related to its static pressure.Therefore,for the high-speed centrifugal pump with three kinds of front structure inducer,the impeller static pressure analysis under different working conditions is carried out.It is found that the optimal total wrap angle of the two-blade inducer is about 480°,the optimal total wrap angle of the three-blade inducer is about 720°,and the optimal total wrap angle of the four-blade inducer is about 654.8°.At the same time,the optimal total wrap angles of the three structures are compared with each other.The highest overall static pressure distribution is the three-blade inducer,followed by the two-blade inducer,and the lowest is the four-blade inducer.Then,the angle matching analysis of the three-blade inducer with the optimal wrap angle and the impeller blades is performed.The results showed that the static pressure in the impeller with the circumferential angle of 48° is the highest.(5)The numerical simulation of the two-phase flow of gas and liquid was carried out for different working conditions of the three types of structural inducer.At the same inlet pressure,the total wrap angle of the inducer with the best cavitation performance is consistent with the static pressure analysis result.The lowest vacuole volume fraction is the three-blade inducer,followed by the two-blade inducer,and more often the four-blade inducer.When the relative circumferential angle between the target blade of the inducer and the target blade of the impeller is 48°,the volume fraction of the vacuole is the smallest.(6)The numerical results can be used to verify the performance of the high speed centrifugal pump.It was found that the outlet pressure pulsation of the high-speed pump is most sensitive to the change of cavitation,followed by the tongue and finally the volute.At the same time,the state of cavitation in the impeller of the high-speed centrifugal pump can be determined based on the variation of the pressure coefficient and the magnitude of the pressure value.The analysis shows that the stability of the high-speed centrifugal pump of the front inducer is obviously better than that of the high-speed centrifugal pump without the inducer.