Calculated-experimental analysis of the natural and critical frequencies and mode shapes high-speed of rotors micro gas turbine unit

The Micro gas turbine plant (MGTP) is used as power plant to decentralized supply of external electric power consumers. Its nominal capacity is 100 kW and its heat capacity is 200 kW. Rotor is a critical part of the MGTP, the operating speed of which is 65 000 min-1. It consists of two subsystems - the turbocharger rotor (TCR) and the rotor of the starter-generator (SGR) connected by elastic coupling. One of the requirements for the design of the rotor, it is the absence of critical frequencies in the range of ± 30 % of the operating speed. This article is devoted to the analysis of the natural and critical frequencies of the MGTP rotor. The natural frequencies evaluated for the system as a whole and for each of the two subsystems separately. For the TCR such an assessment was obtained by finite element method (FEM) calculation. Due to the complexity of the SGR's design, its natural frequencies were estimated and confirmed experimentally using LMS modal analysis technology. A study on the natural frequencies of the MGTP rotor was conducted at different rigidity of bearings and its acceptable range was specified. The study on the critical frequencies of the MGTP was performed by calculation in two stages. At the first stage, an analytical and numerical solution of the test problem obtained in order to confirm the accuracy and correctness of the determination of the critical frequencies in the Ansys Workbench FEM-package. At the second stage, critical frequencies of the MGTP rotor evaluated by FEM calculation on solid model. Based on the obtained results, some recommendations on the rotor's elements designs are given to ensure the natural frequencies in the restrained region.