Stability Enhancement Mechanism Of Self-circulating Casing On The Supercritical Carbon Dioxide Centrifugal Compressor

In recent years,the energy shortage problem is becoming more and more serious.To improve the efficiency of energy conversion to electric energy,scholars around the world pay more and more attention to the high-performance power cycle.Supercritical carbon dioxide（S-CO₂）Brayton cycle power generation system is one of the most promising systems in the next generation,whose excellent characteristics and the possible subversion of power generation technology have been widely recognized by industry experts as the advanced power cycle in the future.As one of the core components of the power cycle,the performance of the S-CO₂ centrifugal compressor directly affects the operation of the whole system.In this paper,the S-CO₂centrifugal compressor is studied by using the CFD numerical simulation,and the influence on the compressor with a vane diffuser and a vaneless diffuser performance is analyzed.Meanwhile,the influence of inlet temperature and pressure on compressor stability margin is analyzed.Based on the previous research,the stability expansion design and numerical calculation are carried out.The following will elaborate on the main research content and some relevant conclusions:In this thesis,CFD numerical simulation method is adopted,and the relevant theory of NUMECA software used is described.The main compressor published by Sandia Laboratory in the United States was used to explore the influence of mesh and physical resolution of different accuracy levels on the numerical simulation results,and compared with the experimental data,so as to obtain the correct numerical simulation calculation method.A 10 MW S-CO₂ centrifugal compressor with vaned diffusers and vaneless diffusers was respectively simulated.By focusing on the analysis of the influence of different diffusers on the performance of the compressor and paying attention to the change of its stable operating range with different compressors,It is found that when the vane diffuser is matched,the stable operating range of the compressor decreases obviously,but the overall performance of the compressor is better.At the same time,the numerical simulation method is used to calculate the different inlet temperature and pressure conditions of the compressor with the vane diffuser.The influence of inlet temperature and pressure on the stable operating margin of the compressor is analyzed.It is found that the better the performance of the compressor is when the inlet fluid is closer to the supercritical liquids.And the range of condensing areas in the compressor under different inlet temperature and inlet pressure conditions is analyzed and compared.It is found that the lower the temperature or,the lower the pressure,the larger the condensing area at the leading edge of the compressor blade.Finally,in view of the above-mentioned facts,the compressor with a vane diffuser can improve performance and reduce stability margin.In addition,different inlet conditions also have an impact on the compressor stability margin.Therefore,by combining the air expansion application case,the self-circulating processor box is adopted in the study.The stability expansion design was carried out,and numerical simulation was performed.The influence of self-circulating processor casing on the flow field inside the compressor was analyzed,and its mechanism was explained.