The Numerical Investigation Of Blade Tip's Stall In A Transonic Compressor Rotor

The unsteady flow of compressor in tip clearance is very significance to broaden compressor stable operation scope and improve active control to stall.But so far researchers have had no common perspective with the flow mechanism.Former researchers are focusing on the relationship between the tip leakage vortex and the stall to transonic rotor,which is aimed to explain some unsteadiness phenomenon and obtain stall inception signal.A transonic rotor is treated as the study object.And the flow field is more complicated in tip clearance of transonic rotor duo to the existing of shock wave.Because of these factors,the influence on the stall inception and the process of the stall are mostly focused.In this thesis,through an axial flow low pressure compressor numerical simulation,the changes of the flow field and its internal flow mechanism in the rotor tip area have been analyzed.The contents contained explaining the whole process of a stall at the big axial distance and results of the axial distance affects the performance of the transonic rotor;how the interference between stator and rotor would change the type of the tall process;with the tip clearance size increasing,the characteristics of the low energy fluid group would be varied.The distribution characteristics of the disturbance frequency have been calculated,near the stall flow field condition.By calculating the Multi-channel rotors,the circumferential speed of low energy group and its radial development process have been explained clearly.Through the single channel numerical simulation,some conclusions have been gotten.Reducing the axial distance would improve the efficiency of the transonic stage,and cut its losses,at the same time,its' increase has caused the more instability of flow field,and blade aerodynamic force has been also enhanced.Approaching to the stall condition,the warning of unsteady flow pre-stall has happened.Due to the shock in the rotor passage,the tip leakage vortex have occurred periodic breakdown.The blockage region in the rotor tip field has mainly come from the blade tip leakage vortex and boundary layer separation.The stator wake would reduce the boundary layer separation,but would strengthen the blockage from the tip leakage vortex brokedown.Under the bigger gap size,the instability of disturbance cycle has been extended.Low energy disturbances would gradually move forward to the leading edge and be developed along the radial direction.Near stall condition,the differentaxial distances have not the same number of the low energy groups.The disturbance frequency was also varied from the distance.Multi-channel and the whole passage calculation have shown the changes from uniformity to non-uniformity in the tip flow fluid area near stall condition.The low speed disturbance circumferential transmission speed has been received,the region is 74%~82%rpm and 56%~88%rpm.Its development in the radial direction has been described in the whole passage case.After the first small to big,low speed group from a wide range of tip distribution has gradually developed to the obvious four partition structure.The monitoring points about static pressure in the leading edge have been transformed by FFT to get the frequency distribution of the circumferential disturbances.The frequency ranged from 0.1 to0.35 BPF.