Flow Mechanisms And Improved Designof Multistage Axial Compressors

Aero engine is an important manifestation of comprehensive national strength as well as the national technology level and innovation ability.Being a key component of aero engine,multistage axial compressor has extremely complicated flow mechanisms and designing difficulties,which makes ita bottleneck that restricts the development of aero engine.In this thesis,the 5-stage axial compressor of a turboshaft aero engine was utilized to do the detailed research.Based on the research results,the improved design of the investigated compressor was performed to improve its performance.The efficiency loss coefficient was defined with the entropy generation to analyze the loss distribution of multistage axial compressor.The results showed that in front stage,the loss in rotor is higher than that in stator while in middle stage they are of the same magnitude.In rear stage,the loss in stator is higher than that in rotor.The shroud loss of front rotor is higher than that of embedded rotors.However,the hub loss increases from front to rear stator.At off-design speeds,the efficiency loss coefficients increase with the increase of rotational speed and the increased magnitude decreased from front to rear stage.Based on the analyses,front rotors and rear stators are of much higher influence on the performance of multistage axial compressors.The endwall boundary layer and blockage of multistage axial compressorwere investigated.At design point,hub displacement thickness increases from front to rear stage while shroud displacement thickness keeps almost the same,which results in the increase of blockage from 2.4% at first stage to 14.7% at last stage.Therefore,the endwall treatment would be more effective for rear stages.At design speed from near choke to near surge condition,the displacement thickness as well as the blockage increases with an increasing magnitude from front to rear stage.Comparing the results at design and off-design speeds,the blockage keeps almost the same,which means the correction factor at design speed is still effective for a range of off-design speeds.The influence of tip clearance on the performance and matching of multistage axial compressors is also investigated.As the tip clearance increases from 0 to 5.0%,the choked mass flow decreases by 21.8%,pressure ratio decreases by 43.1% and efficiency decreases 14.3 percents.Front stage and rear stage contribute more to the whole compressor's efficiency deficit than middle stage,which means more attentions should be paid on them.This thesis defined a new parameter named Peak Efficiency Deviation(PED)to quantify the magnitude that each stage deviates from its peak efficiency.This parameter varies little in the commonly used range of tip clearance.So,the matching could be good within a wide range of tip clearances if the matching of the compressor is good at design tip clearance.Based on the flow mechanisms,the improved design of the investigated compressor was performed.Three-dimensional sweep and bend were introduced to R1,R2,S3,S4 and S5.Ultimately at design speed the efficiency increases by 1.1 percents,mass flow increases by 1.2% and pressure ratio increases by 1.1%.At off-design speeds the performance also improves which indicates the optimal design is available for off-design speeds.The reliability was validated by stress and modal analyses,which showed that the stress of improved compressor is better than the datum and the modal is almost the same.