Research On Mechanism Of Transonic Fan Flutter And Unsteady Flow-induced Vibration

In order to improve performance,reduce size,reduce weight,and reduce consumption,modern aero-engine and gas turbine compression system design(modern design)tends to use thinner and lighter blade,smaller blade axial spacing,and blisks,which makes the blade more prone to aeroelastic instability.In compression systems,especially fans,the problems of flutter and blade vibration induced by unsteady flow are particularly serious.Most of the existing studies only focus on the aeroelastic performance of isolated rotors,ignoring the reflection and interaction between the blade rows.Relying on the major national science and technology project,this thesis explores the mechanism of flutter considering the acoustic propagation characteristics,and analyzes the aeroelastic performance when there are blade rows downstream.The unsteady flow in the fan blade channel and the potential risk of aeroelastic instability are studied.The main content of this thesis are as follows:(1)Research on key parameters of flutter based on flat blade cascades.Taking the flat blade cascade as the research object,the research on the mechanism of the influence of different parameters on flutter are carried out.The key parameters studied in this part are as follows:reduced frequency,passage area(stagger angle and pitch),and incidence.The changes of aerodynamic damping with these key parameters are obtained,and the coupling effect mechanism of the incidence and stagger angle on aerodynamic damping is revealed.(2)Study on the flutter of a transonic fan considering the characteristics of acoustic propagation.Broaden the understanding of the mechanism of upstream and downstream acoustic propagation characteristics and flutter generation,proposed a new range of upstream acoustic propagation characteristics when flutter occurs,and explain why flutter is suppressed in the condition of upstream acoustic resonance.Clarified the mechanism of the "suction side separation flow driven flutter",and located the flow source that caused the flutter.A study on the flutter characteristics of transonic fans under different gap sizes was carried out,and the dual effects of tip clearance flow on blade load and local blade impact were clarified.The conclusion that the tip clearance effect on aerodynamic damping was proposed.The different changing mechanism of the amplitude and phase of the unsteady pressure with the tip clearance under the dual influence.(3)Research on flutter characteristics under the effect of downstream blades.The inter-row reflection mechanism when the acoustic propagation mode is cut-off is proposed.The mechanism of the downstream blades aerodynamic damping in different acoustic propagation characteristics is revealed.The difference between the upstream and downstream unsteady disturbance changes with frequency in the stage environment and the single rotor state is compared,and the aerodynamic damping changes with different numbers of stators are analyzed.(4)Research on high frequency unsteady flow and aeroelastic risk of blade tip.Aiming at the unsteady flow near the fan tip,the spectrum characteristics are analyzed,the evolution law of the three-dimensional vortex system inside the channel is clarified,the propagation mechanism of the flow of different frequencies in the channel and the blade surface is explained,and the flow and the inherent characteristics of the blade are explored.The lock-in phenomenon between frequencies analyzes the potential risk of aeroelastic instability of the blade under the action of unsteady flow.