Design And Numerical Simulation Of A Compact Two Stage Centrifugal Compressor

Centrifugal compressor has the advantages of high single-stage pressure ratio,wide stable operating range,compact structure,etc.It has been widely used in small and medium-sized aero-engines.For aero-engines,large windward area will increase the drag of the aircraft,hence the strict radial and axial size restrictions of the compressor are often accompanied in the process of aerodynamic design.Therefore,it is particularly important to explore the design of high performance two-stage centrifugal compressor with limited size.Based on this,this paper takes the two-stage centrifugal compressor with total pressure ratio of 10 as the research object,uses nrec software to design the components of the two-stage centrifugal compressor and analyze its flow field.(1)The factors affecting the performance of the impeller are studied.The performance difference between centrifugal impellers with and without splitter blade was compared.The results show that the centrifugal impeller with splitter blade can obviously improve the inlet blocking.Then the influence of hub diameter ratio on the performance of centrifugal impeller was investigated.The results show that the centrifugal impeller with small hub diameter ratio has certain advantages in improving isentropic efficiency and total pressure ratio.(2)A new type of static component is studied.In view of the strict restriction of radial size,a continuous type of return channel is proposed and is used in the first stage centrifugal compressor.The influences of the starting position and loading form of the continuous return channel on the performance of the compressor are studied.The results show that the performance of the continuous return channel is the best when the starting position is in the middle of the bend and the front loading or uniform loading is adopted.It is found that the compressor with continuous return channel has higher isentropic efficiency and total pressure ratio compared with the compressor with common return channel.(3)Tandem diffuser is studied.Flow from needs to be turned to meet the axial outlet flow condition.The design of tandem diffuser is adopted to reduce the load of axial diffuser.The results show that the flow of the first row diffuser is uniform and the performance is great.The second row of axial diffusers has a large separation in the diffuser due to the large turning angle.In order to improve the flow in the second row of diffuser,the axial diffuser with splitter blade is used.The results show that the flow at 10% and 50% of the blade height is improved,also,the efficiency at low flow rate is increased obviously.However,compared with the ordinary axial diffuser,the total stage pressure ratio of the axial diffuser with splitter blade is lower.(4)The off design calculation and flow analysis of the first and second stage centrifugal compressors are carried out respectively,and the combined calculation and flow analysis of the two-stage centrifugal compressor are carried out.The results show that the isentropic efficiency is 73.11%,the total pressure ratio is 11.24,the surge margin is 17%,and the size meets the requirements.Principles of two methods of calculating the axial thrust are introduced.Taking the two-stage centrifugal compressor designed in this paper as an example,the reliability of those two methods is compared.The results show that there is little difference between CFD calculation and 1D calculation.Within a acceptable error range,the results of two 1D calculation methods are equivalent.This paper provides some ideas for the design of multistage centrifugal compressor in micro turbojet engines.