Prediction Of Cavitation Flow And Pressure Fluctuation Characteristics Of Double Volute Centrifugal Pumps

Cavitation is one of the important factors affecting the stable operation of centrifugal pumps.When cavitation occurs in the pump,the performance of the unit will be degraded,and the vibration of the unit will be intensified,which will affect the service life of the unit.With the development of economy and technology,higher requirements are put forward for the efficiency and stability of centrifugal pump unit operation.Therefore,the cavitation characteristics of centrifugal pump and its induced unstable flow are studied to improve the centrifugal pump cavitation performance,to prevent of cavitation in the pump,and to monitor the cavitation status of the unit of great significance.In this paper,the double volute centrifugal pump is used as the research object.Using the numerical calculation method,the flow field parameters of the single-phase pump are used as the contrast to analyze the cavitation performance,cavitation flow characteristics and the pressure fluctuation state under cavitation state,thus to investigate the effect on cavitation and pressure fluctuation in the pump under different operation condition.The main research contents of this paper are as follows:1.Single-phase steady and unsteady calculations were performed on the model pump in Ansys-CFX.The pump internal pressure fluctuation signal is extracted in the unsteady calculation,and the flow characteristics in the steady state and unsteady state are analyzed,which provides a reference for the flow field analysis under cavitation.The simulation results show that the unstable flow in the centrifugal pump is intensified under the low flow condition,and the double volute structure has a certain inhibitory effect on the unstable flow in the centrifugal pump.2.The cavitation numerical simulation of the model pump under design conditions is carried out.According to the calculation results,the critical Net Positive Suction Head(_?8?is predicted,and the cavitation distribution and pressure distribution in the pump under different NPSH conditions are analyzed.The pressure fluctuation signal in the cavitation state is extracted.The simulation results show that when the NPSH_a is reduced below the NPSH_c,the head reduced sharply,and the bubble is captured at the inlet of the suction surface of the blade.The cavitation is mainly attached to the inlet from the suction surface of the blade to the exit and 1/3 length of the blade,the form of the bubble is affected by the pressure distribution of the suction surface of the blade.3.The cavitation numerical simulation was carried out under the off design conditions of the centrifugal pump,such as 0.8and 1.2.Predict the NPSHc under the corresponding flow rate and perform unsteady calculation to provide the pressure fluctuation signal in the cavitation state.The results show that the cavitation performance of centrifugal pump decreases with the increase of flow rate.The flow change has an important influence on the shape and distribution position of the bubble in the pump.4.The time domain data of the pressure fluctuation of different states in the unsteady calculation is compared with the frequency domain data obtained by Fast Fourier Transform?FFT?.The main analysis of the suction and pressure surfaces of the blade along different axial conditions is carried out.Pressure fluctuation characteristics in the direction of the streamline and different axial sections in blade,pressure fluctuation in the volute and pressure fluctuation at the position of the double tongue are analyzed.The results show that the pressure fluctuations of the same axial section of the blade are consistent,and the pressure fluctuation from the inlet to the outlet of the blade increases gradually along the stream line direction.The pressure fluctuation has a periodic characteristic.The main frequency of the pressure fluctuation in the circumferential direction of the volute is the blade pass frequency.The cross-sectional area of the volute has an important influence on the pressure fluctuation intensity.