Dynamics And Multi-Field Characteristics Analysis Of Blisk-Shaft System In Aircraft Engine With Complex Faults

The blisk-shaft system is the crucial part of the aircraft engine. Harsh environment containing high temperature, high pressure and high speed often causees all kinds of faults, for example rubbing, blade cracks, mistuning and so on. This greatly affects the stability of the aircraft engine and limits the development of the new aircraft engine. Fault mechanism analysis of the blisk-shaft system is the key to realize reliable operation. In the last decade, rubbing beam models that ignore the differences between vibrations in the width direction of the blade have received considerable attention in the literature. Linear and geometry nonlinear theory of the rubbing model of a rotating plate need to be investigated for further research. Especially, the influence of thermal shock on the rubbing plate also needs further research. With the development of the blisk-shaft integrated rotor, research on dynamic characteristics and crack failure of this new structure with large scale finite elements becomes necessary. In addition, Kriging model carries out data transfer of the coupling interface between a flow field and a structure field. This provides a theoretical basis to. obtain multi-field characteristics of mistuned bladed disks.Since it has not been previously studied, this paper investigates dynamics and multi-field characteristic analysis of blisk-shaft system with complex coupling faults involving multidisciplinary theory for example structural vibration, flow field analysis. To solve above problems, this paper uses the analytical and numerical methods to carries out efficient study. The research content and achievements are given in detail as follows:1. The dynamic model of a cantilever plate attached to a rotating rigid hub is established. Based on Hamilton's principle and the composite beam function method, analytical solutions of the dynamic behavior of rubbing and the coupling of rubbing and thermal shock for the rotating cantilever plate are obtained. Compared with the experimental results, models and methods are proved to be accurate. The influence of rubbing and thermal shock on forced vibration of the plate is analyzed. The results show that the thin plate model which can fully reflect the dynamic characteristics of a blade in the case of various rubbing is more accurate and reliable than the beam. Tip-rub has the characteristics of multiple frequency vibrations, and high frequency vibrations are significant. On the contrary, thermal shock shows the low frequency vibrations. Because rub-induced vibrations are more complicated than these caused by thermal shock, tip-rub is easier to result in the destruction of the blade.2. A solution process is developed to obtain forced vibration responses of a rotating large deflection plate. The accuracy of the solution method is demonstrated through a comparison of modal characteristics found in literature. Special attention is given to bifurcation and chaos of rub-induced nonlinear vibrations. The results show the second order nonlinear terms result in softening-type nonlinearity. However, third-order nonlinear terms combining with second-order terms lead to hardening-type nonlinearity. And friction force is the main source of rub-induced nonlinear vibrations for the rotating large deflection plate. The increasing force amplitude gives a very rich and complex nonlinear dynamics of the rotating large deflection plate.3. A contact-impact model is developed for the rub-induced vibration analysis of a rotating geometric nonlinear plate under thermal shock. The proposed model is capable of adjusting the form of rubbing forces to different system parameters. A series of discussions are carried out to verify the present contact-impact model. And the effects of the friction coefficient, the contact stiffness and thermal transient are investigated. Numerical results show that Thermal shock results in the divergence of rub-induced vibrations for the geometric nonlinear plate with the increase of the time. This leads to an unstable motion of the geometric nonlinear plate with tip-rub. These phenomena are intensified by the larger thermal flow. Reducing the time interval before the thermal transient ceases can be an effective way to reduce thermal rub-induced damage.4. Due to the problem of large scale finite element mesh, a prestressed component mode synthesis method is proposed for the dynamics analysis of blisk-shaft integrated rotor. Modal analysis results verify the accuracy of this method. The principle to choose the number of modal truncation is obtained. And vibration response and dynamic stress are investigated. The results show that the number of modal truncation of each substructure needs to be far more than the number of its blades. Besides, due to the effect of the shaft, rotating frequency for blade modes is reduced. The coupling modes of blades, the disk and the shaft is found. The aerodynamic force mainly causes strong vibrations of the corresponding loading blades. The maximum dynamic stress is in the root of blades and the drum shaft.5. The theory of fracture mechanics which is suitable for the blisk-shaft integrated rotor is investigated. The accuracy of the notch model is demonstrated through the comparison of results obtained by different crack models. And the influence of blade cracks on dynamic characteristics of this rotor system is discussed. It is shown that the equivalent notch model with a small angle to establish the blade crack model is simple and accurate. Blade cracks intensify vibrations of this system. The pressure load on blades reduces the possibility of blade central crack growth to a certain extent. On the contrary, the growth of cracks in exhaust-gas side of the blade occurs more easily with the increase of the blade pressure load.6. Because the equivalent flow excitation cannot accurately describe loading characteristics of the mistuned bladed disks, the dynamic model of mistuned bladed disks with the coupling of multi-physics field is established. The interaction between the structure and the flow field is studied. The results show that the proposed Kriging model can be used to precisely solve data transfer problems in aerothermoelastic analysis. An increase of the degree of mismatch intensifies vibrations of this rotor system along with the significant increase of the vibration amplitude. And the difference of blade vibrations gradually increases.