Research On The Dynamic Characteristics Of Blades With Vibration-impact-friction Effects

In the filed of rotating machine, aircraft engine which belongs to high-speed impeller machinery is a typical part. Unfortunately, due to its working conditions the engine is influ-enced by varied fault and especially vibrate fault which is a significant one. Aircraft engine vibration belongs to the issue described as a multi-component, multilevel coupled vibration system. Thus an important indicator to measure the engine’s performance is vibration restrain. As one of the core parts of engine, work capability of blades directly affects the safety and stability of the engine. According to literature, blade failure takes about at least70%of en-gine vibration fault. Especially during the development stage of a new engine, the blade fault is common occurance. Such as oversize vibration amplitude leads to blades fatigue failure, rotating blade tips against the stationary outer casing caused by imbalance of the rotators or thermal deformation of the casing, which can result in blades fatigue failure. What’s worse, outer casing may be punched by broken blades and this will cause a tremendously loss.In this paper, emphasis will be in the dynamic characteristics of engine blades with vi-bration-impact-friction effects. At the beginning of the study, it makes a qualitative analysis of mathematic expression between dynamic frequency, static frequency and rotating fre-quency of blades based on analytical model of continuous body, and dynamic frequency coef-ficient is included. The analytic solution of stiffness matrix due to centrifugal stiffening effect is worked out with the usual Euler-Bernoulli beam finite element which has no shear defor-mation. Considering the methods mentioned above, including Timoshenko beam finite ele-ment of ANSYS, the dynamic frequency of rotating blades is explored according to numerical calculation.Then, a rotating blade with tip-rub is considered to be a uniform and initially straight cantilever. Both finite element method(FEM) and analytic method are introduced to research the dynamic characteristics of blade with impact and fiction among shrouds. And in this foun-dation, carrying on the annotation to the damping mechanism that the friction damper absorbs vibration energy through the friction between the adjacent shrouded blades. The parameters which have significant effects on the dynamical responses of blades, such as the rotational speed of blades, gap of the tip and elastic stiffness, are introduced into the models so that ef-fects of dry friction damper on vibration suppression is discussed via changing the parameter.Finally, consideration is given to a very specific structural model interaction phenome-non that may occur in turbo-machines due to radial rub between a bladed disk and surround-ing casing(between the stator and the rotor), so called "modal interaction". A very simple two-dimensional model of outer casing and bladed disk is introduced. The dynamic differen-tial equation is established onto their modal coordinates, and two special coordinate trans-formation and their matrices are given. Subsequently, the unified equation of casing and bladed disk system is derived by Hamilton variational principle, and equations of motion are solved using an explicit central differences scheme.