| Compressor is one of the three core components of gas turbine,its design and selection is very significance for the performance improvement of gas turbine.Centrifugal compressor is widely used in small and micro gas turbines because of its high pressure ratio,and wide operation margin.However,an investigation shows that in gas turbines with power above 1.75 MW,multi-stage axial or axial/centrifugal combination structure is generally adopted for compressors,the advantage of centrifugal compressor have not been fully applied in MW gas turbines.The layout of centrifugal compressor in gas turbine or aero engine mainly adopts singlestage or two-stages connection.If a two-stages compressor are used,there must be a return channel to connect the two impellers,which will limit the reduction of the axial size of the gas turbine and lead to more energy loss in the compressor stages.Based on the design of a 4 MW gas turbine,the design and flow control mechanism of two-stages centrifugal compressor were studied.Starting from the overall design of gas turbine,the general layout selection demonstration and aerodynamic designare carried out.The flow control research was based on the structure improve and performance experiments.The main work of this study is as the following:1)Starting form the overall design of gas turbine,the performance requirements of the compressor for the gas turbine cycle and various technical parameters and limiting conditions for the compressor were discussed.The theoretical feasibility and technical advantage of two-stages centrifugal compressor for the 4MW gas turbine were demonstrated;2)In the process of compressor design,the theoretical and empirical basis for the selection of design parameters were summarized.The design process and the method used for the centrifugal compressor were introduced.The flow control methods inside the impeller,such as the control of the Mach number at the impeller shrouding inlet region,the dynamic control of the impeller tip clearance and the axial thrust control of the impeller,were discussed;3)A new cross sectional through-flow passage design for the two-stages centrifugal compressor was preposed to solve the problem for the reverse inlet design of the twostages compressor.This structure design can not only balance the axial force between the two impellers,but also avoid the problems of staggered interstage of the flow channels and the destruction of flow field uniformity.The computational result showsthat the flow loss of the new flow path is equivalent to that of the traditional return channel,and the uniformity of the inlet flow of the secondary stage is significantly improved;4)Tandem cascade diffuser with three different inlet setting angle were designed and analyzed to explore the flow mechanism in the tandem cascade diffuser.Results show that the change of the inlet setting angle has a significant impact on the performance of the compressor.Studies for the tip gaps on tandem diffuser show that a proper tip gap can broaden the operation range of a centrifugal compressor,the surge margin of the compressor may be increased by 15%,with a small efficiency loss by about 1%.;5)Experiment schemes for the two centrifugal compressors are designed.The experiment verification of the compressor involved in the research were carried out to ensure the reliability of numerical calculation.This study provides a new idea for the application of two-stages centrifugal compressor for the MW gas turbine,supplements a material for the design and flow control of centrifugal compressor.The tandem cascades diffuser and new flow path not only show great value for the gas turbine,but also can be transplanted to the aeroengine to realize the further compactness of the engine structure. |
