Dynamic mechanism and parametric analysis of shrouded blades in aircraft engines

A mathematical model for the shrouded blades in aircraft engines is developed under the consideration of the friction and impact to study the dynamic mechanism and the effect of parameters for the system on responses. Aircraft engine blades experience excessive vibrations due to the gas excitation forces during operation. The blade vibrations lead to high dynamic stress that may cause high cyclic fatigue failure (HCF). A model which is made up of springs, damping and a beam carrying a concentrated mass is established to simulate the cyclic symmetry structure of the shrouded blades. The independent mass effect of the shrouds is taken into account in this model. It is closer to the reality that the shroud is regarded as a mass instead of only a part of the beam and the centrifugal force is accounted for in the equation of motion. The Euler-Bernoulli beam theory is adopted to obtain the equation of motion with consideration of the gas excitation forces, the rotational speed effect and the combined effect of the impact and friction between shrouds. The parametric analysis is carried out to study the influence of the contact angle, the friction coefficient, the stiffness and the gap between the shrouds on the responses. Numerical results show that there exists an optimum value of the contact angle for a better damping effect. The nonlinear characteristic, which is derived from the impact and contact, is briefly showed in this paper.