Strength Analysis And Life Prediction Of A Turbofan Engine Fan Disk

As the main powerplant of most military aeroplane and civil aircraft, turbofan engine’s performance directly determines the working stability and reliability in the term of service. The thrust of secondary air stream is completely obtained from the fan in turbofan engine. As the key force bearing component, fan disc directly affects on the engine performance. With the great increasing of aero engine performance and thrust weight ratio, higher working reliability is required for discs. Therefore, in order to ensure the working safety of the engine, this paper carries out research work aming to solve the problem of the structure strength and fatigue life of a turbofan engine fan disc.First of all, the structure analysis of 1st fan disc and 2nd and 3rd stage fan disc perform is performed in this paper. Then 3-D cyclic symmetry finite elment models of the 1st fan disc and 2nd and 3 rd stage fan disc are built using ANSYS Workbench FEA software. Thermal analysis and thermal elastic analysis within mechanical load and temperature load are carried out and stress distribution of discs is obtained. Results indicate that the maximum stress point of 1st stage fan disc locate at the centre hole, and the maximum stress point of 2nd and 3rd stage fan disc locate at the bolt hole. 1st stage fan disc and 2nd and 3rd stage fan disc meet the requirment of the strength design. Vibration of 1st stage fan disc and 2nd and three 3rd fan discs is analyzed, and first 6 order natural frequency and vibration type is obtained in this paper. Resonance analysis of the 1st stage fan disc is studied, and results indicate that the disc has a tendency to form a resonance with the one and two order vibration in the " idling" state. The results provide a reference for the optimal design of disc structure.Secondly, disc-pin catact stress of the 1st, 2nd and 3rd stage fan disc is analyzed. The effect of different contact types on contact stress level is compared and studied. The effect of the friction coefficient and initial gap on disc-pin contact stress and distribution is discussed in this paper, and the relationship between contact stress level with the friction coefficient and the initial gap is investigated. Combining computing results of thermal elastic analysis of the 1st, 2nd and 3rd stage fan disc, dangerous position of three discs is confirmed. The nominal stress and theoretical stress concentration coefficient of the dangerous position are calculated, which prepared the condition for the assessment of the the disc’s fatigue life.Finally, fatigue life of 1st stage fan disc and 2nd and three 3rd stage fan disc is calculated and analyzed based on nominal stress method and local stress-strain method. A life prediction model considering stress gradient for 1st stage fan disc is developed based on Walker equation by introducing the effect of stress gradient on fatigue life. The comparison with nominal stress method and other life prediction models is showed that this model considering stress gradient has better prediction accuracy and applicability for the fatigue analysis in the condition of little plastic deformation.