Adaptation of the Rotor Design of Expander-Compressor Unit for the Installation of Magnetic Bearings Based on Dynamic Analysis Using Integrated Computer Systems

The article discusses the issues of studying the possibilities of modernizing components and elements of rotary machines by static and dynamic analyzes of structures using integrated computer systems. Such machines include gas turbine and turbojet engines, turbocompressors, and turboexpanders. The main goal of the work is to select a modified rotor design for installing a different type of support. In this case, the search of rational design of expander-compressor rotor unit is considered to use a combination of passive and active bearings instead of plain bearings. Since these types of supports have different levels of support rigidity, topological rationalization of the structure is carried out using static structural analysis (for the estimation of rotor static equilibrium position) and dynamic analysis (for the estimation of the critical rotation speeds). The last one makes it possible to detune critical speeds from the range of operating rotation speeds. For the rotor of an expander-compressor unit with the impellers of the expander and compressor cantilevered on a single shaft, multivariate calculation studies made it possible to find a rational rotor design for the installation of magnetic bearings. The following parameters varied within certain limits, when changing the design: locations of support sections, diameters and lengths of shaft sections. Analyzes were carried out using a numerical finite element method. The results are presented for the final design in the form of displacement distributions, corresponding to the static equilibrium position, as well as the values of natural frequencies and critical rotation speeds and the shapes corresponding to them. The accuracy of the numerical simulation results was assessed using traditional finite element methods and was confirmed by comparison with the results of model numerical experiments. The presented approach to searching for a rational design made it possible to prove the possibility of using a combination of passive and active magnetic bearings as rotor supports for small and medium-sized rotors. That reduces friction losses in the system and provides all the other advantages of this combination of this type of support.