Analysis Of The Flow Resistance Effect Of The Safety Barrier And Its Influence On The Hydraulic Performance Of The Axial Flow Pump Unit

The safety barrier is mainly arranged at the inlet of the inlet conduit of large and mediumsized pump stations,which plays a role in blocking floating objects and ensuring personnel safety,however,when the safety barrier is blocked,it will increase the head loss,leading to a decrease in the efficiency of the pump device,severe blockage can easily induce vibration and noise in the unit.This article uses numerical simulation combined with physical model experiments to analyze the flow resistance effect of safety barriers and their impact on the hydraulic performance of axial flow pump devices,the main research work and achievements are as follows:(1)The numerical simulation method was used to analyze the influence of the crosssectional form and net spacing of the safety barrier on the head loss,when the cross-sectional form of the barrier is circular,the head loss is minimized;Analyzed the impact of 8 different net spacing of grid bars on head loss,when the net spacing of grid bars is 2/15D(D is the nominal diameter of the impeller),the head loss is small and the proportion of flow area is ensured to be consistent with the actual engineering;A comparative analysis was conducted on the effects of different blockage ratios of safety barriers on head loss and flow characteristics in elbow shaped inlet conduit,when the blockage ratio is 0.3,timely cleaning of the safety barrier should be carried out.(2)A comparative analysis was conducted on the internal flow differences between the flow components of the vertical axial flow pump device under different flow conditions,with and without obstruction of the safety barrier,under different flow conditions,the areas with high vorticity are mainly concentrated near the impeller and guide vane body,as the flow rate increases,the distribution of vorticity in the impeller and guide vane body is significantly improved;Based on the entropy generation theory,the impact of the flow resistance effect of safety barriers on the energy loss of various flow passage components of vertical axial flow pump equipment was analyzed,and it was clarified that the impeller and guide vane are the main sources of energy loss in the pump equipment.(3)Based on the Fast Fourier Transform(FFT)analysis of pressure pulsation in axial flow pumps,it was determined that the resistance flow effect of safety barriers has the greatest impact on the frequency spectrum characteristics of internal pressure pulsation in axial flow pumps at a flow rate of 0.6 Qbep,at this time,the pressure pulsation at the impeller inlet and guide vane outlet is most significantly affected by the resistance flow effect of safety barriers;The sound pressure level distribution of the hydraulic noise of the axial flow pump under different flow conditions during the flow resistance of the safety barrier was clarified,the main frequency of the hydraulic noise at the impeller inlet was the blade passing frequency,and the main and secondary main frequencies of the hydraulic noise at the outlet of the guide vane did not show an integer multiple relationship with the shaft frequency as the flow increased;The coherence theory is used to analyze the pressure fluctuation and hydraulic noise of axial flow pump.