Gas Turbine Rotor Damper Lift-Off Study

Abstract

Gas turbine rotor system is subjected to vibratory stresses due to excitations caused by various excitation sources at varying energy levels. To dissipate the energy that occurs in the rotating system, damping is induced internally or externally. Damping is achieved by having damper at the appropriate location in the rotor system. The damper needs to have a provision to assemble in the rotor assembly, which is typically a split, facilitating the damper to wind and unwind in circumferential direction. The damper used in the rotating system needs to be axisymmetric with a suitable cross-section, to achieve the required level of damping. As the damper is used at the interior location of the rotor system, it needs to build necessary preloading by itself in such a way that the damper rotates with the rotor system during operation. Damper design study is very vital in deciding the shape of the damper in such a way that it provides efficient damping and minimizing the vibratory stress. At some vibrating condition, damper tends to detach from its supporting feature which is referred to as damper lift-off. The magnitude of this lift-off is expected to be higher at the split regions compared to other circumferential location of the damper, which makes the damper design very complex. When the damper split region passes through the maximum lobe and minimum lobe position of any nodal diameter, the region near the split tends to lift-off from its support and behaves like a simply supported beam and cantilever beam respectively. A careful consideration of this damper lift-off phenomenon in damper design is key towards achieving a robust damper design. Various types of simulation techniques using finite element analysis are followed in performing necessary design assessments. This paper is intended to describe the steps followed in performing damper design study to help achieving design robustness.