Dynamic Modeling of Tie-bolt Rotors via Fractal Contact Theory and Virtual Material Method

Tie-bolt rotors, comprised of multiple stages of discs fastened by tie bolts, are commonly used in heavy-duty gas turbines. The contact interfaces between adjacent discs have considerable influence on the dynamic characteristics of tie-bolt rotors. Although many studies on the modeling of tie-bolt rotors have been reported, it is still a challenge to develop a relatively simple, efficient, and accurate model for such a kind of complex rotors. In this article, a new virtual material modeling method is proposed to analyze the dynamic characteristics of tie-bolt rotors. The elastic modulus and Poisson ratio of the virtual material are determined from the interface contact stiffness, which is derived based on the three-dimensional fractal contact theory. To verify the modeling approach proposed here, modal tests are conducted on a tie-bolt rotor specimen, of which the measured natural frequencies are compared with the simulation results. Finally, by using the verified modeling approach, the dynamic behaviors of tie-bolt rotors are investigated comprehensively, where the effects of fractal dimension parameters and preload level on rotor dynamics are evaluated.