Nicoleta M. Ene

A Dynamic Analysis of Hydrodynamic Wave Journal Bearings

The purpose of this paper is to study the dynamic behavior of a three-wave journal bearing using a transient approach. The transient analysis permits the determination of the rotor behavior after the fractional frequency whirl appears. The journal trajectory is determined by solving a set of nonlinear equations of motion using the Runge-Katta method. The fluid film forces are computed by integrating the transient Reynolds equation at each time step location of the shaft with respect to the bearing. Because of the large values of the rotational speeds, turbulent effects were included in the computations. The influence of the temperature on the viscosity was also considered. Numerical results were compared to experimental results obtained at the NASA Glenn Research Center. Comparisons of the theoretical results with experimental data were found to be in good agreement. The numerical and experimental results showed that the fluid film of a three-wave journal bearing having a diameter of 30 mm, a length of 27 mm, and a wave amplitude ratio greater than 0.15 is stable even at rotational speeds of 60,000 RPM. For lower wave amplitude ratios, the threshold speed at which the fluid film becomes unstable depends on the wave amplitude and on the supply pocket pressure. Even if the fluid film is unstable, the wave bearing maintains the whirl orbit inside the bearing clearance.

The Influence of the Sleeve Elastic Deformations on the Wave Bearing Performance in Heavy Loaded Transmissions

The purpose of this paper is to study the influence of the elastic deformations of the planet/star gear on the performance of a wave bearing supporting an elastic planet/star gear. An iterative algorithm that takes into consideration the responses of both the wave bearing and gear was developed. The turbulence effects and the influence of the temperature on the oil viscosity were also introduced in the computations. The numerical simulations showed that the elastic sleeve deformations have an important effect on the bearing performance by increasing the minimum film thickness and the safety limit margins.

An Investigation of the Steady-State Performance of a Wave Aerodynamic Thrust Bearing for High Speed Applications

The steady-state performance of an aerodynamic double thrust wave bearing was investigated. The investigation showed that a double thrust wave bearing with an inner diameter of 15 mm and an outer diameter of 45 mm can support axial loads of 200 N at 100,000 rpm for a minimum film thickness of 3 microns. The influence of the wave bearing parameters on the bearing performance was also analyzed. The theoretical analysis was validated by experimentally testing one side of the thrust bearing. A special test rig was built for this purpose. The experimental data were close to the numerical predictions, validating the computer codes.Copyright

The Influence of the Stiffness and Damping Properties of the Elastic Support on a Wave Journal Bearing Sleeve Motion

The motion of a wave bearing sleeve exposed at a differential pressure at the axial ends and supported by an elastic element is considered in this paper. The influence of the stiffness and damping properties of the elastic element and of the wave amplitude on the sleeve motion is analyzed. It was found that the wave amplitude ratio and the damping of the elastic element support have an important influence on the dynamic behavior of the wave bearing. The stiffness of the elastic support does not significantly affect the bearing behavior.Copyright

A Dynamic Analysis of a Dual Clearance Squeeze Film Damper

Squeeze film dampers (SFD) are devices utilized to control the shafts of high-speed rotating machinery. A dual squeeze film damper (DSFD) consists of two squeeze film bearings that are separated by a sleeve, which is released when the rotor experiences abnormal operating conditions. In this part of our study of DSFD we analyze the case when both the inner and the outer oil films are active. We present computed and measured unbalance responses of a shaft supported in DSFD. The oil forces which are utilized in the calculation of the unbalance response are obtained from numerical solutions of the Reynolds equation. A finite-difference algorithm is utilized for solving the pressure equation within the calculation of the dynamic response of the shaft.Copyright

Effect of the Wave Amplitude on the Dynamic Behavior of a Wave Journal Bearing

The effect of the wave amplitude on the dynamic behavior of a three-wave journal bearing is analyzed. A transient method was used to predict the wave bearing behavior after Fractional Whirl Frequency (FFW) occurs. Dynamic trajectories, Poincare maps, and FFT analyses are used to study the dynamic behavior of the journal bearing. It was found that the threshold of stability is strongly influenced by the wave amplitude. However, even when FFW occurs, the journal maintains its trajectory inside the bearing clearance. The predicted data were found to be in good agreement with the experimental results obtained at the NASA GRC.

An Analysis of Cavitated Wave Journal Bearings

A numerical investigation of the two dimensional flow in cavitated wave journal bearings is presented in this paper. An algorithm based on an upwind differencing scheme combined with a Rosenbrock integrator was used to simulate bearing cavitation. The algorithm, which conserves mass throughout the bearing, automatically implements JFO boundary conditions at rupture and at reformation. The numerical predictions are compared with numerical results obtained with other algorithms.Copyright

New Tendencies in the Design of the Modern Aerospace Transmissions

The modern aerospace transmissions require an increased power density while their weight, fabrication and maintenance costs should be as low as possible. In addition, the future helicopter transmissions should generate less noise and vibration then the actual transmissions. The fluid film bearings, and particularly the wave bearings, could help approaching these goals. In this paper, the aspects implied by using these bearings to support transmission rotating parts are discussed from two points of view: (1) the capacity of the wave bearings to support the bearing sleeve distortions under similar loads as rolling element bearings: and (2) the capacity of the wave bearings to attenuate the noise/vibration generated by the gear mesh compared to the rolling element bearings due to the increased damping properties of the wave bearings.

No Conventional Fluid Film Bearings with Waved Surface

A new type of fluid film bearings called “wave bearing” has been developed since 1990’s by Dimofte (Dimofte, 1995 a; Dimofte, 1995 b). The main characteristic of the wave bearings is that they have a continuous wave profile on the stationary part of the bearing. The wave bearings can be designed as journal bearings to support radial loads or as thrust bearings for axial loads. One of the main advantages of the wave bearings is that they are very simple and easy to manufacture. In most cases they have only two parts. A journal bearing consists of a shaft and a sleeve while a thrust bearing consists of a stationary and a rotating disk. One of the bearing parts is sometimes incorporated into the machine part that is supported by the bearing. For example, the wave bearing can be used to support the gear of a planetary transmission, the bearing sleeve being incorporated into the gear (Dimofte et al., 2000). Compressible (gases) or incompressible (liquids) fluids can be used as lubricants for both the journal and thrust wave bearings. Tests were conducted with liquid lubricants (synthetic turbine oil, perfluoropolyethers –PFPE-K) and air on dedicated test rigs installed in NASA Glenn Research Centre in Cleveland, OH USA (Dimofte et al., 2000; Dimofte et al., 2005). In this chapter, the wave bearings lubricated with incompressible fluids, commonly known as fluid film wave bearings, are analysed. The performance of both journal and thrust bearings is examined. Because one of the most important properties of the wave journal bearings compared to other types of journal bearings is their improved stability, the first part of the chapter is dedicated to the study of the dynamic behaviour of the journal wave bearings. The wave thrust bearings can be used for axially positioning the rotor or to carry a thrust load. For this reason, the steady-state performance of the thrust wave bearings is analysed in the second part of the chapter.

An Analysis of a Journal Bearing Sleeve Motion With a Transient Approach

The purpose of this paper is to study the dynamic behavior of a journal bearing sleeve center by using a transient approach. Unlike other papers presenting the motion of the shaft inside the bearing sleeve, in this paper the rotor is considered rigid having only a small unbalance and the motion of the sleeve center is analyzed. The sleeve is supported by elastic elements. In addition, the axial ends of the bearing are exposed at two different pressures. To the authors’ knowledge, this paper is the first study of such a bearing configuration. Moreover, the influence of the stiffness and damping properties of the elastic element on the sleeve dynamic behavior (trajectories, motion frequencies, etc.) is also analyzed. Relative and absolute trajectories of the sleeve center and FFT analysis of the motion are presented.Copyright