Flutter Analysis Of A Folding Rudder With Clearance

Nonlinear aircraft rudder/wing aeroelastic problems resulted mainly from the nonlinear factors instructural parts,pneumatic and servo systems.In order to meet the requirements of saving space during storage and transportation,the folding rudder/wing segment structure are adopted in some missiles and carrier-based aircrafts.The existence of unavoidable clearance sin the folding rudder hinge joints can change the stiffness and aeroelastic properties of the system.Generally,aerodynamic flutter occurs with a frequency which equals the natural frequency of the rudder,which can be significantly influenced by the structure gap.The periodic signal sweeping method in modal vibration test is often used to obtain the system natural frequency.The flutter of rudder/ring with structural gap is usually analyzed by using the numerical simulation method..In this thesis,influences of the gap on the main resonance and flutter of a folding rudder with hinge joint are investigated by the following three parts.1.For the periodic sweeping excitation was adopted in modal vibration test,the average method and numerical simulation were used to investigate the main resonance of the system under periodic exitation.Influence of the clearance,the external force and the fixed preload to rudder on the main resonance were analyzed.As the gap increased,nonlinear characteristics increasingly prominent,the overall main resonance response curve shifted to the left and amplitude jumping and hysteresis appeared.With the increase of the external force,the influence of nonlinear factor decreased,amplitude jumping gradually disappeared and the vibration characteristics of the system was nearly linear.With the increase of the fixed preload,resonance morphological changed great.2.The aeroelasticity equation of the rudder with clearance wass established using the piston theory.Incremental harmonic balance method was applied to obtain the formulas of flutter frequency of the system.The flutter law of the rudder was analysed.When the flow velocity was less than the flutter speed,vibration stabled at zero equilibrium point.With the increase of the flow velocity,vibration time required to reach steady increased.When the flow velocity reached flutter speed,stable vibration ring was generated and the flow speed was called VLC.When the flow velocity was larger than VLC,rudder fluttered divergent.With the increase of the flow speed,VLC increased.The area of the flow speed which could generate stable vibration ring was small,When the flow speed was larger than this area,flutter was almost immediately divergent.3.Based on the above analysis,the flutter of the rudder/wing with clearance was numerical simulated,and the influences of factors,such as Mach number and the clearance,the flutter frequency were investigated.Mach number and clearance had no effect on the flutter rule.With the increase of the Mach number,the critical flutter flow velocity increased and the flutter frequency increased.While clearance had little effect on the flutter frequency.At last,the influence of clearance to the main resonance frequency and the flutter frequency are compared,which provided a theoretical basis for ground modal experiment.