Research On Cylinder Dynamic Modeling Method Of Heavy Gas Turbine

Gas turbine technology is honored as "the crown jewel of advanced manufacturing industry" and is one of the important symbols of a country’s science and technology level and overall national strength.Gas turbine engine and rotor dynamics modeling analysis are one of the key technologies in heavy-duty gas turbine design.Gas turbine cylinder,as the main structure of the gas turbine,provides support for the rotor;its dynamics and coupling characteristics with the rotor are important contents of engine dynamics design.Due to the complicated structure and multiple connection interfaces of the heavy-duty gas cylinder,it is difficult to achieve uniform,rapid and effective dynamic modeling.In this paper,according to the practical problems and needs in the design of gas turbine dynamics,the cylinder dynamics modeling of gas turbine combining with the structure of typical heavy gas turbine cylinders is studied to provide support for the design of gas turbine dynamics.The major work of the paper is as follows:In light of the complex structure of a heavy-duty cylinder,the compressor bearing support,compressor blade carrier,and combustor are simplified based on the approximation principle of modal frequency and mode shape.Aiming at the simplified model,a modeling method is proposed based on the consistency rule that the cylinder mass,stiffness and pole moment of inertia are not changed before and after modeling.The complicated cylinder structure is modeled as several ring structures and modal analyses are conducted to verify its feasibility,which provides an effective method for modeling and optimizing the dynamics of gas turbine rotor dynamics.Considering the interfacial bolt connection between the cylinder face and cylinder,two modeling methods for the joint plane of the mock bolt connection are proposed.Firstly,finite element modeling for the bolt structure is adopted to simulate the actual bolt connection,and its effectiveness is verified by comparing the theoretical and experimental results.Due to the limitations of solid bolt modeling for overall dynamics analysis,a dynamic modeling method for equivalent joint surfaces is proposed.The interactions between the normal and tangential features at the joint surfaces are considered.A set of analytical solutions for mechanical parameters such as equivalent elastic modulus,Poisson’s ratio and density are given based on the Hertz contact theory and fractal theory.The finite element dynamic modeling method is used to establish the dynamic model of cylinder with equivalent joint surfaces using the obtained equivalent mechanical parameters.Then,the consistency of the two methods is verified by modal analysis.According to the combustor cylinder of a certain type gas turbine,a prototype of shrinkage ratio is fabricated.The influence of the preload forces of the middle-faceted flange bolt on the modal frequency and vibration mode of the cylinder is studied.The effectiveness of the proposed modeling method is verified by comparing its results with those of the experiment.The influence of bolt preload forces and friction coefficients on the modes of the cylinder’s overall structure is studied by the proposed method.Based on the proposed cylinder modeling method,the finite element model of the complete machine,including the compressor support,turbine support,compressor bearing and turbine bearing is established.The influence law of the preload forces on the dynamic stiffness of the cylinder bearing is explored.The rotor dynamic model of the gas turbine is established,and the influence of dynamic stiffness of the cylinder on the rotor dynamic characteristics is analyzed.