| Cavitation is a very harmful phenomenon for hydraulic machinery,which will lead to internal flow field disorder and flow complexity.With the intensification of cavitation,cavitation will block the flow channel,increase the hydraulic loss,and further reduce the efficiency of hydraulic machinery.In severe cases,it may cause vibration and noise,and affect the normal operation of the unit.Therefore,avoiding or mitigating cavitation is of great significance in the field of hydraulic machinery.According to previous research on arranging obstacles on the blade,arranging obstacles on the blade surface has a certain cavitation suppression effect on centrifugal pumps.Taking a low specific speed centrifugal pump as the research object,this paper proposes a method of arranging obstacles at the back of the blade and the working surface of the blade simultaneously.The numerical simulation method was used to study the effect of obstacles on cavitation suppression of centrifugal pumps at different back posit ions,working surface positions,heights,and shapes,and to analyze the impact of obstacle structures on cavitation performance and internal flow field of centrifugal pumps.The main research contents and innovative results of this article are as follows:(1)Firstly,the basic theory and research methods of cavitation are introduced;Summarize and introduce the current research status of cavitation control for hydrofoils,centrifugal pumps,and axial pumps;Secondly,the basic equations,turbulence models,and cavitation models for numerical simulation are introduced.Finally,the centrifugal pump test platform is introduced in detail,and the external characteristic test and cavitation performance test are conducted on the centrifugal pump test platform;The simulated external characteristic curve and cavitation characteristics agree well with the experimental values,with a consistent trend of change.The error values of head and efficiency are small,which verifies the accuracy of the numerical simulation method.(2)Obstacles were placed at the back of cent rifugal pump blade and working face at the same time,and the dimensionless position parameter L_h of obstacles was defined to study the effect of different positions on the back of centrifugal pump cavitation suppression,and four schemes were designed.Th e results show that the four schemes reduce the volume of impeller cavitation in the development and severe stage of cavitation,but promote cavitation in the initial stage of cavitation,and the volume of cavitation is increased compared with the prototyp e pump.The placement of obstacles can increase the turbulence kinetic energy near the wall of the flow field,reduce the pressure differential resistance caused by flow separation,and increase the pressure gradient,so as to inhibit cavitation.The four schemes all improve the fracture head of the centrifugal pump.Comprehens ively analyzing the factors such as pressure distribution,turbulence kinetic energy and cavitation volume,the cavitation performance of the centrifugal pump is optimal when the posi tion on the back of the blade L_h=35%.(3)Based on the conclusion that placing obstacles in the position of L_h=35%on the back of the blade is better for improving the cavitation performance of the centrifugal pump,the effect of different positions of the blade working face on the cavitation suppression of the centrifugal pump is studied.Firstly,three schemes are designed.It is concluded that when L_h=45%,the cavitation suppression effect is the best.Secondly,an indepth study was carried out on the position of L_h=45%,and four different working face position schemes were d esigned.The results show that the change of the position of the obstacle face has less influence on the external characteristics of the centrifugal pump,and the critical cavitation margin is reduced.The obstacle improves the inlet low pressure area and effectively inhibits the expansion of the low pressure zone to the exit direction.Obstacles in different positions can inhibit the development of cavitation to export,too close to t he impeller inlet,will block the flow passage;It is too far from the impeller inlet to induce the relative high pressure of blade wall to suppress cavitation.Therefore,there is an excellent position that L_h=45%is optimal for cavitation suppression.(4)On the basis of the excellent cavitation suppression effect of the obstacles placed on the centrifugal pump on the side of the blade(L_h=35%and the L_h=45%of the blade face,the influence of the chan ge of the obstacle height on the cavitation performance of the centrifugal pump was analyzed,and the non-dimensional height parameters of the obstacle were defined.The results show that obstacles at different heights reduce the turbulent kinetic energy i ntensity of impeller and change the turbulent kinetic energy distribution.Cavitation volume has been reduced to varying degrees in cavitation development and severity.In general,the obstacle of K_h=1/12has the best effect on cavitation suppression of centrifugal pump,and the reduction of cavitation distribution from low pressure is the most obvious.(5)On the basis of the optimal position on the back of the blade,working face the position and height are obtained,that designing four shape schemes.The research shows that in the stage of cavitation development,the obstacle with trapezoidal section promotes cavitation,and the cavitation volume increases compared with the prototype pump.Other shape schemes are reduced in volume compared with the prototype pump cavitation;In the serious stage of cavitation,the cavitation volume of impeller is reduced by different shape schemes.The existence of obstacles reduces the dissipation degree of impeller,optimizes the flow field structure,and makes the flow line relatively uniform in the flow passage.Through comprehensive analysis,the obstacle with rectangular section shape is optimal to suppress cavitation,making the operation of the centrifugal pump more stable,and is of great significance for cavitation suppressing in the centrifugal pump. |
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