Investigation On The Influence Mechanism Of Wake Vortex Migrating On The Tip Clearance Flow In A Counter-rotating Compressor

In high-load counter-rotating axial flow compressors,the flow structure in the tip region is very complex.The upstream rotor wake vortex and leakage vortex interact with the downstream rotor bow shock wave and tip leakage flow,which has a significant effect on aerodynamic performance and stability in the downstream rotor tip region.Establishing a method to estimate the migration trajectories of the upstream rotor wake vortex in the design stage and clarifying the mechanism of the effect of the trailing vortex stage migration characteristics on the downstream rotor tip leakage flow are conducive to the selection of design parameters,thereby improving aerodynamic performance and stability with significantly shortening the design cycle.Therefore,aiming at the foundation of parameters selection for a high load counter-rotating compressor in the design stage,a dimensionless criterion has been established to model the migration trajectories of the upstream rotor wake vortex and the tip leakage vortex.And the mechanism of the influence of upstream wake vortex on the loss and the unsteady fluctuating caused by the downstream rotor tip leakage flow has been clarified.Firstly,in order to estimate the migrating trajectories of wake vortex at the design stage,the unsteady numerical simulation on the S1 stream surface has been conducted.The mechanism of upstream rotor wake vortex shedding and its relationship with the frequency of downstream rotor bow shock wave sweeping the upstream rotor trailing edge have been clarified.The influencing factors of upstream rotor wake vortex migrating at the axial gap between the rotors have also been clarified.Based on this,the dimensionless criterion to model the wake vortex migration trajectories has been established.Combining one-dimensional estimation,through-flow calculation and shock wave model,the method of estimating the migration trajectories of wake vortex migrating at the axial gap between rotors in the design stage has been explored.The deviation between the estimated value and the numerical simulation value is 3.5%,which can provide a theory for the selection of axial gap between rotors in compressor design.Secondly,the migration characteristics of the upstream rotor wake vortex in the tip region were explored to clarify the effect of the downstream rotor bow shock wave on the upstream rotor blade loading,and when the wake vortex shedding,the impact of upstream rotor tip leakage flow on the circumferential distance between the reference blade and downstream rotor has been revealed.In addition,the influence mechanism of the upstream rotor tip leakage flow on the wake vortex pattern and migration trajectories have been explained,and the applicability of the dimensionless criterion used to model the migration trajectory of wake vortex by numerical simulation on S1 stream surface in the tip region has been evaluated.Thirdly,from the perspective of the wake vortex migration trajectories,the mechanism of the upstream rotor wake vortex on the downstream rotor tip leakage flow loss was revealed,and the effect of the wake vortex and tip leakage vortex migration trajectories on the tip leakage flow loss was studied to clarify the influence mechanism.The conclusion shows that the wake vortex reduces the secondary leakage flow loss and when the leakage vortex migrates along the downstream rotor channel,the loss resulted from the passage shock wave and the secondary leakage flow have been reduced and the aerodynamic performance in the tip region has been significantly improved.Finally,the mechanism of the influence of wake vortex on the unsteady fluctuation of the tip leakage flow was studied.The mechanism of unsteady fluctuation resulted from the tip leakage flow and wake vortex suppressed the unsteady fluctuation at the small tip clearance were clarified.The results show that at the small tip clearance,the breakdown of tip leakage vortex accounted for unsteady fluctuations in the tip region and a higher tip leakage flow to mainstream momentum ratio was required to judge the unsteady fluctuation by tip leakage flow due to the effect of wake vortex.