Aerodynamic Analysis And Optimum Design Of Two-Stage Centrifugal Compressor

Centrifugal compressors are widely used in micro gas turbine. With the continuous development of power demand, single-stage centrifugal compressor can no longer meet the requirement of high cycle pressure ratio. Compared to the multi-stage axial compressor, two-stage centrifugal compressor has the advantages of light weight, small size and high power density. Although the two-stage centrifugal compressor’s research has been done in some developed countries for a long time, and some high-performance two-stage centrifugal compressor has been put into application, our research on two-stage centrifugal compressor was still in its infancy because of its complex structure and difficult design.The numerical simulation was carried out to do the aerodynamic analysis and optimization design of a closed two-stage centrifugal compressor which was used in a micro gas turbine, and then two sets of design were obtained. In addition, the numerical simulation of three-dimensional viscous flow was carried out to investigate the effects of different diffuser stagger angle and tip clearance width on flow field and performance of a high-speed centrifugal compressor. The main research contents are as follows:1. The two-stage centrifugal compressor’s performance and off-design performance of low and high pressure stage were investigated in detail. Then we studied the flow characteristics and analyzed the impact of the two-stage centrifugal compressor’s efficiency and surge margin.2. Because of the great flow loss of the prototype’s vaned diffuser, the numerical simulation was carried out to research the effects of different diffuser stagger angle on flow field and performance of a high-speed centrifugal compressor.3. Under the premise without changing the hub and shroud, optimization was done focus on the vaned diffuser. The performance of optimized compressor was better than the prototype. The efficiency of the design point condition was increased by2percent. It was concluded that the optimization achieved the target very well.4. Based on aerodynamic analysis and optimization of the prototype and fully reference to its characteristics and advantages, a new closed two-stage centrifugal compressor was done. Compared to the prototype, it had a wider flow range, larger surge margin and higher efficiency at the design point conditions. It was concluded that the design fully achieved the design goals.5. Tip clearance leakage flow can highly influence the performance of centrifugal compressor, as a result, before the semi-open design, the numerical simulation was carried out to research the effects of different tip clearance width on flow field and performance of a high-speed centrifugal compressor.6. Based on the two-stage centrifugal compressor of closed design, a semi-open design was done taking into account the impact of the gap. Compared to the prototype, the design of semi-open two-stage centrifugal compressor had a lower efficiency, but its total pressure ratio and surge margin was larger. It was concluded that the design basically achieve the design goals.