Shemiao Qi

An investigation on the static performance of hydrodynamic wave journal bearings

The wave journal bearing was first reported by Dimofte In the early 1990s. The static behavior of a hydrodynamic wave journal bearing is present in this paper. It is found that the static performance is related to the design parameters including eccentricity ratio, wave number, wave amplitude ratio and wave position angle. It is shown by the numerical results that the influence of the wave number to the load capacity and attitude angle is significant. The load capacity of the wave bearing decreases with the rise of wave number when the wave amplitude ratio is lower than 0.1 under the assumption that the load is applying on the sleeve between the two groove. The wave bearing has a larger load capacity than the plain one in general, except that the wave amplitude ratio is less than 0.15 and the wave position angle is smaller than 20 degree. There is a minimum value of the load capacity as the increasing of wave position angle with wave amplitude ratio smaller than 0.15, while in the larger wave amplitude ratio situation, the load capacity rises as first and then decreases in the end as an increasing wave position angle.

Study on Load Capacity and Dynamic Characteristics of the Wave Bearing at Infinite Compressibility Number

The wave bearing developed by Dimofte in the 1990’s features a continuous wave profile and presents numerous advantages compared to plain journal bearings. One of the main advantages of the wave bearing is that it has a higher degree of stability than the plain journal bearing and this load capacity is close to the load capacity of the plain journal bearing. Predicting these coefficients for the wave bearing with high bearing numbers is difficult, although there are many studies on the aerodynamic bearing. This paper presents an analytical method for calculating the limiting values of load capacity, dynamic stiffness and damping coefficients of the wave bearing for compressible fluids by simplifying the compressible Reynolds equation at high journal operation speed. A computational method is submitted which is derived from simple algebraic equations combined with infinitesimal perturbation method. The limiting characters of the wave bearing are compared with the plain journal bearing for all eccentricity ratios. Special emphasis is placed on investigating the effects of wave number, wave eccentricity ratio and wave starting angle on the limiting characteristics. Numerical results obtained indicate that the load capacity and stiffness of the wave bearing is better than the plain journal bearing at the same eccentricity ratio.Copyright

An experimental investigation of a microturbine simulated rotor supported on multileaf gas foil bearings with backing bump foils

Two multileaf gas foil journal bearings with backing bump foils and one set of gas foil thrust bearings were designed, fabricated, and used in a 100 kW class microturbine simulated rotor system to ensure stability of the system. Meanwhile, a preliminary test rig had been built to verify the simulated system stability. The rotor synchronous and subsynchronous responses were well controlled by using of the gas foil bearings. It is on the multileaf gas foil bearings with backing bump foils that the test was conducted and verified for the first time in open literatures. The success in the experiments shows that the design and fabrication of the rotor and the gas foil bearings can provide a useful guide to the development of the advanced high speed rotating machinery.

Testing of a simulated rotor system supported on gas foil bearings for a Microturbine

The rotordynamic characteristics of a simulated rotor system supported on gas foil bearings was investigated, which has a rated speed of 24 krpm. A test rig was established and assembled to simulate the operating performance of the rotor system for a microturbine. The compliant gas foil journal and thrust bearings were designed to support the rotor. The rotor system was driven by high pressure gas pushing on the impellers. As the rotor speed was accelerated to the rated speed of 24 krpm, the rotor response was mostly synchronous. The rotor system was unstable at the speed decreasing to 18 krpm. The paper presents the design, the operational procedures, and preliminary test results for a simulated rotor supported on gas foil bearigs test rig.

Study on numerical solution of the contact mechanics in gas foil bearings

In spite of the successful application of this oil-free supporting technology in engineering, theoretical researches on static, especially dynamic performances of compliant foil bearing seem rather difficult and far behind experimental investigations because of complexity. One of the most difficult problems to deal with is, odelling of contact mechanics problem between bump foil and top foil. The goal of this study is to find the most suitable numerical solution method for the contact mechanics problems between the bump foil and top foil in gas foil bearing. By comparing the characteristics, Lagrange Multiplier Method, Multi-Point Constraint Method and Direct Constraint Method, Direct Constraint Method is considered the most appropriate numerical algorithm for the contact mechanics in gas foil bearings. In solving the contact problem, this algorithm has a good accuracy, and micro-contact status between the bump foil and top foil in gas foil bearing, it has the important significance Of the elastic for the design of the foil bearing.

Numerical Calculation of the Structural Stiffness of Gas Foil Bearings

The dynamics of a rotor supported in Gas Foil Bearings is strongly influenced by stiffness and damping properties of the bearings. In order to obtain the structural stiffness properties of Gas Foil Bearings, a coupled finite element method (FEM) is developed in this paper. The compressible gas lubricated Reynolds equation is transformed into a typical elliptic partial differential equation and solved by FEM. The elastic deformation equation and the contact boundary conditions between foils are solved by nonlinear contact finite method. A generalized numerical solving method for the elasto-aerodynamically coupled lubrication problem in the foil bearing is given with mesh mapping relationship between the two kind of finite element solving process above mentioned. The structural stiffness of the foil bearings with different parameters is estimated by using the numerical method. It is helpful to decide the structural parameters of the foil bearing.Copyright

Theoretical Prediction of the Lift-Off Speed in Aerodynamic Compliant Foil Journal Bearings

In aerodynamic bearings, since the supporting air film is generated by rotor motion, there is no support at the start of motion. As in all such bearings, there is dry rubbing until the rotor achieves sufficient speed to lift-off. Thus, the lower the lift-off speed, the less will be the rubbing and so the greater will be the life of the bearing. This paper focuses on the theoretical prediction of lift-off speed in aerodynamic compliant foil journal bearings based on a generalized solution of elasto-aerodynamically coupled lubrication for compliant foil bearings. A computational method is presented which is used to predict the lift-off speed in aerodynamic foil journal bearings with eccentricity ratio greater than or equal to 1.0. Special emphasis is placed on investigating the effects of the load imposed on the bearing, the nominal radial clearance and the bearing radius on the lift-off speed. The numerical results obtained indicate that lift-off speed decreases with the decrease of load and nominal radial clearance, but with an increase in bearing radius. The eccentricity ratios are all greater than 1.0 at the lift-off speed for the aerodynamic compliant foil journal bearings used in this study.Copyright

Advances in Investigation of Elasto-Aerodynamic Lubrication in Compliant Foil Bearings

Advances in theoretical researches of the compliant foil bearing are introduced, and emphasis is placed on the generalized solution of elasto-aerodynamic lubrication, the computation of the dynamic characteristics of compliant foil bearings and the stability analysis of related rotor systems. Systematical theories and methods are presented for purpose of the prediction of dynamic behavior of a rotor system equipped with compliant foil bearings.