The steady-state thermal effect on dynamic characteristics of gas turbine rotor considering contact effect

Gas turbine rotor works at high temperature, especially the turbine used to expand hot gas and generate power. Temperature may change the elastic modulus of the material as well as cause thermal stress of the gas turbine rotor. Both of these two factors can cause a local stiffness variation of the rotor assembly and thus have an influence on the dynamic characteristics of the rotor. The rotor investigated in this paper is an annular tie rod-fastened rotor which is made of several discs bolted together. The 3-D model of the combined rotor is established considering contact effects. First, a thermal analysis is carried out to evaluate steady-state thermal map which also provided as thermal loads. Then a static structural analysis is performed to obtain the thermal stress state due to restrained expansion of the components of gas turbine. Next, the contact effect of the combined rotor is validated to decrease the stiffness through a modal analysis at room temperature by comparison with results from continuous rotor. Finally, a pre-stressed modal analysis of combined rotor under steady-state thermal loads is calculated to obtain the natural frequencies of transverse vibrating. In the structural and pre-stressed modal analyses, two types of elastic modulus are considered, i.e., the constant elastic modulus and the temperature-dependent elastic modulus. The constant elastic modulus case determines the effect of thermal stress alone and the variable elastic modulus corresponds to the cooperation effect of both thermal stress and elastic modulus degradation in changing the natural frequencies of the rod-fastened rotor.