Mingjian Lu

Research on the Static and Dynamic Characteristics of Misaligned Journal Bearing Considering the Turbulent and Thermohydrodynamic Effects

Journal misalignment usually exists in journal bearings that affect nearly all the bearings static and dynamic characteristics including minimum oil film thickness, maximum oil film pressure, maximum oil film temperature, oil film stiffness, and damping. The main point in this study is to provide a comprehensive analysis on the oil film pressure, oil film temperature, oil film thickness, load-carrying capacity, oil film stiffness, and damping of journal bearing with different misalignment ratios and appropriately considering the turbulent and thermo effects based on solving the generalized Reynolds equation and energy equation. The results indicate that the oil thermo effects have a significant effect on the lubrication of misaligned journal bearings under large eccentricity ratio. The turbulent will obviously affect the lubrication of misaligned journal bearings when the eccentricity or misalignment ratio is large. In the present design of the journal bearing, the load and speed become higher and higher, and the eccentricity and misalignment ratio are usually large in the operating conditions. Therefore, it is necessary to take the effects of journal misalignment, turbulent, and thermal effect into account in the design and analysis of journal bearings.

Analytical and Experimental Study of Dynamic Characteristics of Rod Fastened Rotor-Bearing System Under Preload Saturation

This paper investigates the dynamic characteristics of a composite rotor fastened by rods. Contact stiffness and equivalent bending stiffness between discs with different rod preloads of the rotor are obtained respectively by using the elastic and elastic-plastic contact theory. The finite element model of rotor-bearing system is built with Timoshenko beam elements. Critical speeds are respectively calculated with and without the consideration of contact effect, including the changing bearing dynamic coefficients. A test rig of rod fastening rotor-bearing system has been constructed to verify the numerical model results. The results show that the critical speed increases with rod preload and it keeps almost constant when the rod preload reaches a certain value, called preload saturation. The experiments demonstrate that the rod fastening rotor under preload saturation has the similar dynamic characteristics as integral rotor, such as the critical speed and backward whirl with asymmetric support stiffnesses. This kind of rotors which are under preload saturation can be analyzed and designed as an integral one without considering the contact effect. The study gives referential recommendations for analysis and design of a class of composite rotors which contain discs and rods.© 2013 ASME

Unbalance response analysis of the circumferential tie-rod combined rotor considering different support

The combined circumferential tie rod rotor with the advantages of light weight, good cooling effect and easy assembly is widely used in gas turbines, especially in heavy-duty gas turbines. In this paper, a circumferential tie-rod combined rotor was investigated using two-dimensional finite element model and three-dimensional finite element model with ANSYS. The critical speed of the rotor were calculated by finite element method and compared with experiments. The dynamic characteristics and stability of rotor are closely related to the supporting performance of bearing. The unbalance response analysis of the tie-rod rotor supported by elliptical pad bearing and tilting pad bearings which are loads acting on the tile pad and loads acting between the tiling pads are investigated respectively. The results show that the critical speed calculates with two-dimensional finite element model is closer to the experimental value. Selecting different support bearing has a great influence on the critical speed and vibration amplitude of the rotor. In addition, the tie-rod rotor supporting by tilting-pad bearing have a better stability when the load is between the pads.

Supporting Structure Performances Analysis of Heavy-Duty Gas Turbine Based on Fluid-Solid Coupling Method

In order to achieve high working efficiency, modern gas turbines operate at high temperature which is close to the melting points of metal alloys. However, the support of turbine end suffers the thermal deformation. And the journal center position is also changed due to the effects of high temperature and shaft gravity. Tangential or radial supporting structures, which are composed of supporting struts, diffuser cones, hot and cooling fluid channel, are widely used in gas turbine hot end. Cooling technology is usually used to keep the bearing temperature in a reasonable range to meet requirements of strength and deformation of the supporting struts. In this paper, three major assumptions are proposed: (a) radiation is not considered, (b) cooling flow system is only partially modeled and analysis assumes significantly higher cooling flow that is not typical for current engines, and (c) only steady state heat transfer is considered. And a 3D fluid-solid coupled model based on finite-element method (FEM) is built to analyze the performances of both the tangential and the radial support. The temperature distribution, thermal deformation and stress of supports are obtained from CFD and strength analysis. The results show that either the tangential or radial support is used in a 270MW gas turbine; the thermal stress is about 90.3% of total stress which is produced by both thermal effects and shaft gravity. Comparing to the results from radial supports, it can be seen that the struts stress and position variation of journal center of tangential support are smaller. Due to a rotational effect of the bearing housing caused by the deformation of the tangential struts, the thermal stress in these tangential struts can be relieved to some extent. When both thermal effect and shaft gravity are considered, the stress of each tangential supporting strut is almost uniformly distributed, which is beneficial to the stability of rotor system in the gas turbine.Copyright

Strength analysis of disc rotor heavy-duty gas turbine considering bolt pretension load

In the last years, heavy-duty gas turbine has been increasingly used as high efficiency systems for heat and power generation. The typical size of these powerplants mainly consist compressor, turbine and combustor. And the rotor disc assembly structure is different from the single whole rotor structure. Several computer codes have been developed to analyse the strength of the rotor. In the present paper, a heavy-duty gas turbine rotor system consists of seventeen stages of a compressor and four stages of a gas turbine. The front three stages compressor discs are forged into one single part and the other compressors are individual discs. The gas turbines have four individual discs which having teeth of a bevel gear are juxtaposed to engage the teeth. With the central or circumferential tie-rods fastened, stages of gas turbine are combined as a single construction by jointing faces form teeth. The teeth correspond to bevel gears having an apex angle of 180 degrees and are engaged to transmit a torque and to align the discs. As the construction of the modern gas turbine sets is sufficiently complex, it was expedient to use approximation methods of computation. One of the most urgent problems during design and manufacturing of gas turbine units is the provision of reliability and durability of units joints by development and application of perspective turbo machines constructions with application of up-to-date CAD/CAE/CAM-technologies. This code is based on the simplified 3d-dimensional model of different types of rotor structure (central and circumferential). The effects due to bolt pretension load of the rotor are also taken into account in the model. And the code is based on Green-Lagrange strain from the bolt pretension load force to initial stress and strain to calculate the stress stiffness of the rotor. This paper is devoted to finite element overall strength analysis of rotors considering the bolt preload effect, and the principle of the axial preload force is determined. The geometry structure parameters which affect the rotor strength are investigated. Moreover, this work is very important in practical design of the heavy-duty gas turbine tie rod disc rotor.