Guohui Xu

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.

Optimum design of ultra high speed hybrid rotor of PM machines

For the ultra high speed PM rotor, a metallic sleeve is usually interference fitted onto a cylinder or ring shaped PM to against the huge centrifugal force. The initial interference hinges not only on the loose of the rotor, but also strongly on the strength of the PM and the sleeve. In order to determinate the initial interference, this paper proposes an analytical model of stress/displacement field of the rotor which is verified by the Finite Element (FE) Method. Then, the initial interference which facilitates the optimal design of this type of rotor is deduced.

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

The Performance Comparison among Common Struts of Heavy-duty Gas Turbine

In order to study the performance differences among struts of a heavy-duty gas turbine, three-dimension finite-element models of several struts were established by Pro/Engineer. Firstly, the stresses of three struts were obtained only considering the rotor gravity. The magnitudes and distributions of stress and influences of the width and thickness for support plates on stiffness are studied. The results show that radial struts 2 are superior to radial struts 1 and tangential struts is superior to radial struts. The sensitivity of stiffness to the width of support plates is greater than the thickness. Then, the distribution of temperature was obtained by the thermo-fluid-solid coupled method in CFD software to calculate the thermal stress of radial and tangential struts. The results show that although the magnitudes and distributions of temperature are similar, the thermal stress of tangential struts is smaller than that of radial struts.