Effects Of Suction Chamber Nose Width And Guide Vane Thickness On Cavitation Performance Of Multi-Stage Centrifugal Pumps

In multi-stage centrifugal pumps,the reduction of hydraulic performance,shortened service life and vibration and noise problems due to cavitation have become important factors affecting the efficient and stable operation of multi-stage pumps.In order to improve the anti-cavitation performance of the multi-stage pump,the first-stage impeller of the pump is often different from the secondary stage,and the structure of the multi-stage pump suction chamber is mostly radial inflow and axial outflow.The cavitation performance has a certain effect,so the hydraulic pe rformance and cavitation performance of the multi-stage pump under different suction chamber nose widths are analyzed and studied to obtain the optimal performance of the suction chamber structure,in order to reveal the cavitation characteristics o f the first-stage impeller and optimizing the parameters of the suction chamber to provide a theoretical reference.In this paper,based on the consideration of the cavitation performance of the first-stage impeller of the multi-stage pump,the previous four-stage impeller was the research object.Through numerical calculation and theoretical analysis,the performance parameters of the multi-stage pump under different suction chamber nose widths and guide vane thicknesses were obtained.The unsteady pulsation characteristics of the first-stage impeller flow field under different nose and guide vane structures are studied.The main work includes the following:1.Performance analysis of the multi-stage centrifugal pumps at different flowsThrough numerical calculation,the relationship between the hydraulic performance and cavitation performance of the multi-stage pump under steady state with the flow rate is obtained,and compared with the test results.The research results show that with the increase of flow rate,the pump efficiency increases first and then Reduced change trend,there is a high efficiency zone ne ar the design conditions.Compared with small flow,the design flow and large flow of the multistage pump first-stage impeller internal flow line distribution is more uniform,and the test results are basically consistent with the numerical calculation res ults,and the error is within the allowable range.When the flow rate increases from 0.7Q_opt to 1.1Q_opt,the cavitation performance of the multi-stage pump gradually decreases.As the effective cavitation margin decreases,the average cavitation volume fraction of the first-stage impeller gradually increases.Under the same effective cavitation margin and as the flow rate increases,the average void volume fraction shows a decreasing trend.The main frequency of pulsation at each measuring point of the multistage centrifugal pump under different flow rates is the leaf frequency.Under the conditions of 0.9 Q_optpt to 1.1Q_opt,the pulsation amplitude and spectrum characteristics of each measuring point are similar.Under the 0.7Q_opt operating condition,the pulsation amplitude of each measuring point increases significantly.2.The influences of the suction chamber nose width on the performance of the multi-stage centrifugal pumpsThrough numerical calculations,the hydraulic performance and cavitation performance of four models with different nose widths are obtained.The research results show that compared with the original model,the model pump with a nose width of 10.30mm has the best overall hydraulic performance and its efficiency,the head is increased by 0.85%and 18.35m respectively,and the streamline distribution of the suction chamber is more uniform,the inlet pressure of the first-stage impeller is larger,and the critical effective cavitation margin is smaller.As the effective cavitation margin decreases,the internal flow of the first-stage impeller under the four model pumps gradually becomes turbulent and the pulsation intensity increas es.This is due to the effects of cavitation bubble generation,migration,collapse and dynamic and static interference during the development of cavitation.In the early stage of cavitation development,the pulsation characteristics of different model pum ps were basically similar.In the later period of cavitation,the model pump with a nose width of 10.30mm has a relatively weak pulsation intensity,and the volume fraction of cavitation is the smallest in a cycle.It shows that the proper increase of the nose width can weaken the pressure pulsation intensity of the first-stage impeller inlet in the later stage of cavitation and reduce the volume fraction of cavitation.3.Effect of suction chamber guide vane thicknesses on performance of the multi-stage centrifugal pumpOn the basis of the nose width of 10.30mm,change the guide vane thicknesses to obtain the hydraulic performance and cavitation performance of the multi-stage pump with different guide vane thicknesses.The results show that when the guide vane thicknesses is 3mm,the efficiency and head are reduced by 1.20%and 1.78m compared with the original guide vane,but its critical cavitation margin has been reduced,the volume fraction of cavitation volume of the model pump with a thickness of 3 mm in the guide vane are the smallest.The anti-cavitation performance of the multi-stage pump has been significantly improved,indicating that the hydraulic performance and cavitation performance of the pump under different guide vane thicknesses have a certain mutual suppression effect,that is,appropriately increasing the thickness of the guide vane can inhibit the development of cavitation,but the hydraulic performance of the centrifugal pump is reduced.In the initial stage of cavitation,the amplitude of the pressure pulsation of the model pump at each guide vane thicknesses is basically unchanged,and the main frequency is at twice the leaf frequency,and the secondary frequency is the leaf frequency.When cavitation progressed to the final stage,the pulsation amplitude of the original guide vane thicknesses was the smallest,while the pulsation amplitude of the model pump with a guide vane thicknesses of 4 mm increased by 3 times,and the main frequency also changed from the doubled frequency to the leaf frequency.It shows that increasing the guide vane thicknesses has a great influence on the pressure pulsation of the multi-stage pump.