The effect of curvic coupling joints on the roto rdynamic characteristics of gas turbines with tie-shaft

The importance and use of curvic coupling joints are garnering interest in many aero-engine rotordynamics applications thanks to their benefits such as lower stress, higher service life, reliable positioning, precise centering and strong loading capability. Their predominant application is in the assembly of the rotating elements such as shafts, impellers and turbine discs in order to mainly provide torque transmission in high-speed rotating machines. In order to predict rotor dynamic behavior of the rotor systems, specialized one dimensional (1D) finite element codes are generally preferred due to their computational efficiency. However, the effect of the curvic couplings is usually ignored in traditional rotor dynamics analysis due to their complex geometry. This approach may lead to inaccurate calculations especially at higher speeds. In this study we compare the dynamic characteristics of continuous and discontinuous curvic coupling joints on a single stage compressor-turbine rotor system with tie-bolt design. The first four lateral natural frequencies are calculated and compared for each case by using three dimensional (3D) finite element models considering the contact effect via modal analysis with linear perturbation method. Results show that curvic couplings reduce the natural frequencies of rotor system at all rotating speeds under preload and centrifugal forces. Finally, a sensitivity analysis under separation loading is examined in which higher frequency shifting and mode shape changes are observed.