Aerodynamic Design And Flow Control Investigation Of High Pressure Ratio Centrifugal Compressors

Centrifugal compressors are core components of gas turbine engines.High pressure ratio centrifugal compressors(HPCC)can further improve the power-toweight ratio,the fuel consumption and the reliability of engines,which is the essential technology for the next generation of low/middle power series of turboshaft engines.Developing the HPCC is meaningful to the economy and the defense.The thesis applied an approach combing theoretical analysis,numerical simulations and experiments to investigate the aerodynamic design and flow control methods,which aim to increase the efficiency and the stable flow range of HPCCs.The aerodynamic design of a single-stage,pressure-ratio-8.0,and highperformance centrifugal compressor has been completed.The thesis proposes an aerodynamic design methodology for HPCCs.Based on the compressor design requirement of a turboshaft engine,the aerodynamic design for the relevant HPCC has been completed.From three-dimensional CFD simulations,the designed HPCC has a pressure ratio of 8.0 and an efficiency of 79.9% at design conditions.The finite element analysis has verified the structural reliability of the designed HPCC.Flow control methods in increasing efficiencies of HPCCs have been investigated.The thesis built an optimization platform that couples the genetic algorithm,the artificial neural network,and the three-dimensional CFD simulation to explore the potential of complex three-dimensional features in increasing the compressor efficiency.Through the individual optimization of the blade angle distributions,the sweep feature and the lean feature,the optimal geometry of each group has increased the efficiency by 1.0%,0.5%,and 0.2%,respectively.Geometry parameters that are close to both the leading edge and the endwalls are found most influential on the efficiency.The dominant mechanism of performance improvement by optimizing the blade angle distribution is the decreased shock strength,and that by optimizing the sweep feature is the reduced wake region.Since their mechanisms differ from each other,their potential for efficiency improvement can be added up.The final round of optimization considers both the blade angle distribution and the sweep feature.The optimal geometry improves the efficiency and the choke mass flow rate by 2.2% and 8.1%,respectively.It presents an end-bend feature at hub section and an S-shaped forward-swept leading edge.Flow control methods in improving stabilities of HPCCs have been investigated.The thesis conducted rig tests and dynamic pressure measurements to capture the flow instability evolution process of HPCCs across scales,including the small-scale rotating instability,the middle-scale stall,and the large-scale deep and mild surge.Flow mechanisms of self-recirculation casing treatment on constraining flow instabilities with different scales have been studied: because the injection flow from the upstream slot and the suction flow from the rear slot restrain the formation of passage radial vortices,the small-scale rotating instability and the middle-scale rotating stall at the impeller inlet in low speeds and middles speeds are eliminated;because the flow recirculation process inside the recirculation device changed the slope of both the impeller and the stage pressure rise characteristics,the compression system have been stabilized,and the large-scale deep and mild surge in middle speeds and high speeds have been suppressed.