Study On The Effect Of Blade Perforation On Cavitation Performance Of Axial Flow Pump

The operating environment of an axial flow pump is complex,and during its operation,cavitation can occur due to the low local pressure,which can lead to high-temperature and high-pressure micro-jets when the cavitation bubbles collapse.This can cause damage to the blades and other components,as well as vibration and noise.Severe cavitation can also affect the normal operation of the pump and reduce its service life.Therefore,it is of great value and significance to suppress the development of cavitation inside the axial flow pump and explore the means of cavitation suppression.In this study,a axial flow pump with a specific speed of 700was selected as the research object,and a rectangular hole was opened on the blade to suppress cavitation.The numerical simulation method was used to investigate the effects of the location and cross-sectional dimensions of the hole on the cavitation performance of the axial flow pump and the internal flow field structure.The main research content and conclusions are as follows:(1)An introduction to commonly used turbulence models and cavitation models was provided,and the modified SST k-ωturbulence model and Zwart cavitation model were selected.The reliability of numerical calculations was verified by comparing experimental and numerical simulation results.An analysis of the flow field in the impeller revealed that cavitation first occurs at the inlet edge of the blade’s back surface.As cavitation develops,the cavitation gradually expands towards the outlet direction,and the cavitation expansion speed on the blade’s rim is much faster than that on the hub.During the cavitation rupture stage,the cavitation gradually covers the entire blade surface,blocks the flow passage,and affects the normal operation of the pump.Comparing the pressure and cavitation volume fraction distribution maps,it was found that the distribution of the cavitation volume fraction corresponds to the low-pressure region.In the initial stage of cavitation,the flow field structure is relatively uniform,but as cavitation develops,the streamlines deviate towards the rim side,and the flow field exhibits recirculation and vortex generation,becoming turbulent.(2)Coefficients K_aand K_rare defined to describe the position of rectangular holes.Keeping the cross-sectional size of the rectangular hole and K_rconstant,three rectangular hole schemes with chordwise coefficients K_aof 0.15,0.25,and 0.55 were set up to analyze the effect of chordwise coefficient on cavitation performance of axial flow pumps.Simulation results show that opening rectangular holes on the blade introduces high-pressure flow from the working surface to the back surface,compensating for the low-pressure region on the back surface and reducing the low-pressure distribution.There is backflow on the downstream side of the rectangular hole,forming a local low-pressure area.A convex-shaped cavitation bubble forms on the back surface of the blade,and the shedding of the cavitation bubble occurs earlier.The chordwise coefficient has a significant effect on the initial stage of cavitation.When K_ais 0.15,the effect of inhibiting cavitation is the best in the initial stage of cavitation,and the volume fraction of cavitation decreases by up to18%,and the high-turbulence kinetic energy area decreases the most significantly.(3)Under the premise that the optimal effect of inhibiting cavitation is achieved when the chordwise position coefficient of the rectangular hole is K_a=0.15,the radial position coefficient K_ris changed to 0.965,0.930,and 0.865 to study the effect of the radial coefficient of the rectangular hole on cavitation performance of axial flow pumps.After opening the rectangular hole,the pressure distribution on the back surface of each scheme is consistent,and the low-pressure area on the back surface is cut into two parts by the high-pressure flow.In the cavitation rupture stage,the flow field at the outlet of the blade is combed to improve the flow state.When the radial coefficient of the rectangular hole is larger,the effect of inhibiting cavitation is better.When K_ris 0.865,the effect of inhibiting cavitation is not obvious,and its effect on the main flow disturbance is more pronounced.When K_ris 0.93,the high-turbulence kinetic energy area on the back surface of the blade decreases the most significantly,the cavitation bubble becomes more stable,and the energy dissipation is reduced.Compared with the other two schemes,the distribution of flow lines is more uniform.(4)Further research was conducted on the size of the rectangular hole section,with the position coefficients K_a=0.15 and K_r=0.93 kept constant.Three hole size schemes were set:3mm×3mm,6mm×3mm,and 9mm×3mm.It was found that there exists an optimal length parameter for the suppression of cavitation in the early stage,and the cavity volume decreased most significantly when the rectangular hole size was 6mm×3mm.In all stages of cavitation development,the low turbulent energy area increased,and energy dissipation decreased when the rectangular hole size was6mm×3mm.As cavitation developed and entered the cavitation rupture stage,the larger the hole size,the more effective the control of cavitation.When the rectangular hole size was 9mm×3mm,the low-pressure area on the back of the blade decreased significantly,and the volume fraction of cavitation decreased the most.