Compliant Foil Journal Bearing Research Articles

Experimental study of the aircraft air cycle machine rotor dynamics on gas foil bearings

In this paper the results of the experimental research of the dynamics of the rotor of a four-wheeled aircraft air cycle machine on gas foil supports under conditions of vibration. The description of the experimental unit, measuring system, and methods of results processing is given. The rotor of the turbomachine is mounted on compliant gas foil journal bearings of the second generation. The rotor speed varied from 20000 to 32000 rpm. The cooling turbine was exposed to broadband random vibration with a mean square value of Vibro-acceleration up to 5 g. The influence of vibration load level, air supply temperature, amplitude-frequency characteristics of the turbine cooler case, and vibration equipment on the rotor dynamics was assessed.

A fully coupled 3D thermo-elastohydrodynamics model for a bump-type compliant foil journal bearing

Coupled thermo-elastohydrodynamics model has been developed to predict three-dimensional thermal, structural and hydrodynamic performance of foil bearings. Bearing deformation and film pressure has been coupled in FEM considering thermal/centrifugal growths, and thermo-mechanical material properties. Energy equation has been solved for film temperature using FDM, which is also coupled to FEM via successive iterations. Augmented-Lagrangian method and thermal contact models have been applied to solve for mechanical and thermal contacts. The predicted values have been benchmarked against published measurements, which indicated reasonable correlation. A parametric study has been conducted for various shaft speeds and load conditions to visualize bearing performance.

Simulation of Compliant Bump Foil Journal Bearing Using Coupled Reynolds Equation and Finite Element Model Method

Based on a “1st generation” compliant foil journal bearing, the performance of foil bearing was simulated according to the model base on Reynolds equation coupled the finite element method. Model considers the bending of top foil, elastic deformation of bump foil, the friction between top foil and bump foil and the interaction between bumps. After compared analysis results to test data, the result of simulation was more accurate than other models, thus this model establish a basis for further study of the compliant foil bearing.

Experimental study on a small Brayton air refrigerator under −120 °C

A small Brayton air refrigerator with high-speed gas bearing turbo-expander and compact plate-fin heat exchanger was designed and fabricated. Performances of the two key components (turbo-expander and heat exchanger) and the refrigerator as a whole were investigated. The bearings used in the refrigerator were compliant foil journal bearings with elastic support, and stability inspection was conducted on them. The results indicate that the refrigerator had a high cooling capability, and that the gas bearings used here achieved good performance in a wide speed region up to 250,000 rpm. While the expander operated at its design speed (220,000 rpm), the refrigerator had a cooling capacity of 1500 W at −80 °C, and the lowest no-load refrigeration temperature of −124.5 °C was obtained. Moreover, the influence of nozzle number and velocity ratio on the turbo-expander and the effect of flow rate and cold inlet temperature on the heat exchanger are discussed in detail.

공기 포일 베어링으로 지지되는 초고속 마이크로 터보차져의 구동 안정성 향상에 관한 연구

To improve the operational stability of the 100 Watts class Micro Gas Turbine, the air foil bearing with additional damping material has been investigated. The key of structure is that a viscoelastic material is coated under the top foil. The compliant foil journal bearing and thrust bearing are designed to withstand high load of vibrations at the operational speed 870,000 rpm. Test is executed in room temperature. Rotor has stably operated above 480,000 rpm. It is over 55% of the designed speed 870,000 rpm. Synchronous and subsynchronous vibrations are both well controlled. Vibration amplitude diminished over 50%. With the help of increased damping resulting from the viscoelasticity, the rotor stability of Micro turbocharger has been improved.

Durability and Stability Analysis of Compliant Foil Journal Bearings with Elastic Support Using Different Surface Treatments

The durability and stability characteristics of compliant foil journal bearings with elastic support are discussed in this paper. Using different choices for surface treatment of foil materials and foil element geometry parameters, the start-stop cycle and the rotor-bearing system dynamic characteristics of a compliant foil bearing (CFB) were experimentally studied. This CFB with elastic support can steadily run the turbo expander with a 25.0-mm-diameter rotor revolving at 14.8 × 10 4 rpm and has excellent performance in terms of stability and durability. The test results indicate that with suitable bearing structure parameters, foil materials and application of the surface treatment of this type of CFB is appropriate for high-speed turbo machinery.

A Thermohydrodynamic Analysis of Foil Journal Bearings

A thermohydrodynamic model is developed for predicting the three-dimensional (3D) temperature field in an air-lubricated, compliant foil journal bearing. The model accounts for the compressibility and the viscosity-temperature characteristic of air and the compliance of the bearing surface. The results of numerical solutions are compared to published experimental measurements and reasonable agreement has been attained. Parametric studies covering a fairly wide range of operating speeds and load conditions were carried out to illustrate the usefulness of the model in terms of predicting the thermal performance of foil journal bearings.

Operation of a Mesoscopic Gas Turbine Simulator at Speeds in Excess of 700,000rpm on Foil Bearings

A small mesoscopic gas turbine engine (MGTE) simulator was tested at speeds over 700,000rpm. The MGTE was operated with specially designed miniature compliant foil journal and thrust air bearings. The operation of the simulator rotor and foil bearing system is a precursor to development of turbine powered micro-aerial vehicles and mesoscopic power generators. The foil bearings use a new fabrication technology in which each bearing is split. This feature permits the use of these bearings in highly advanced engines where single piece ceramic rotors may be required. The simulator weighed 56g (including the 9g rotor) and included two non-aerodynamic wheels to simulate the compressor and turbine wheels. Each compliant foil journal bearing had a diameter of 6mm and was located equidistant from each end of the rotor. Experimental work included operation of the simulator at speeds above 700,000rpm and at several different orientations including having the spin axis vertical. Results of the rotor bearing system dynamics are presented along with experimentally measured natural frequencies at many operating speeds. Good correlation between measurement and analysis is observed indicating the scalability of the analysis tools and hardware used. The rotor was very stable and well controlled throughout all testing conducted. Based on this successful testing it is expected that the goal of operating the rotor at speeds exceeding 1 million rpm will be achieved.

Advancements in the Structural Stiffness and Damping of a Large Compliant Foil Journal Bearing: An Experimental Study

This paper presents the results of an experimental investigation into the dynamic structural stiffness and damping characteristics of a 21.6‐cm(8.5in.)-diameter compliant surface foil journal bearing. The goal of this development was to achieve high levels of damping without the use of oil, as is used in squeeze film dampers, while maintaining a nearly constant dynamic stiffness over a range of frequencies and amplitudes of motion. In the experimental work described herein, a full compliant foil bearing was designed, fabricated, and tested. The test facility included a non-rotating journal located inside the bearing. The journal was connected to an electrodynamic shaker so that dynamic forces simulating expected operating conditions could be applied to the structurally compliant bump foil elements. Excitation test frequencies to a maximum of 400Hz at amplitudes of motion between 25.4 and 102μm were applied to the damper assembly. During testing, both compressive preload and unidirectional static loads of up to 1335 and 445N, respectively, were applied to the damper assembly. The experimental data from these tests were analyzed using both a single degree of freedom model and an energy method. These methods of data analysis are reviewed here and results are compared. Excellent agreement in results obtained from the two methods was achieved. Equivalent viscous damping coefficients as high as 1050N.s∕cm(600lbf.s∕in) were obtained at low frequencies. Dynamic stiffness was shown to be fairly constant with frequency.

Effects of Static Load on Dynamic Structural Properties in a Flexible Supported Foil Journal Bearing

This paper describes an experimental investigation into the structural dynamic characteristics of corrugated foil (bump foil) strips used in one type of compliant surface foil journal bearings and dampers. The nonrotating journal was supported by a compliant foil journal bearing and driven by two shakers which were used to simulate dynamic forces acting on the bump foil strips. The dynamic structural stiffness and equivalent viscous damping coefficients were calculated based on the experimental measurements for a wide range of operating conditions. The results were compared to the analytical predictions obtained by a theoretical model developed earlier, and the agreement is considered reasonably well. Both experimental and theoretical results show that the direct structural stiffness and damping coefficients increase with increasing bearing static load.

Structural Stiffness and Coulomb Damping in Compliant Foil Journal Bearings: Parametric Studies

This paper presents the results of the second part of the investigation on structural stiffness and Coulomb damping in compliant foil journal bearings. In the first part, a theoretical model was developed to calculate equivalent viscous damping coefficients and structural stiffness of a bump foil strip in a journal bearing or damper. A computer program was also developed to compute the eccentricity and attitude angle of the journal static equilibrium position as well as the deflections, displacements, reacting forces, and equivalent friction coefficient of each bump on the strip. This model and program enabled further parametric studies to be conducted in the second part of the investigation, the results of which are the subject of this paper. The design parameters studied were static eccentricity (bearing load), pad angle (load angle), sliding friction coefficients, and perturbation amplitude (dynamic load). In addition, more effective methods of achieving both Coulomb damping and optimum structural stif...

Structural Stiffness and Coulomb Damping in Compliant Foil Journal Bearings: Theoretical Considerations

Compliant foil bearings operate on either gas or liquid, which makes them very attractive for use in extreme environments such as in high-temperature aircraft turbine engines and cryogenic turbopumps. However, a lack of analytical models to predict the dynamic characteristics of foil bearings forces the bearing designer to rely on prototype testing, which is time-consuming and expensive. In this paper, the authors present a theoretical model to predict the structural stiffness and damping coefficients of the bump foil strip in a journal bearing or damper. Stiffness is calculated based on the perturbation of the journal center with respect to its static equilibrium position. The equivalent viscous damping coefficients are determined based on the area of a closed hysteresis loop of the journal center motion. The authors found, theoretically, that the energy dissipated from this loop was mostly contributed by the frictional motion between contact surfaces. In addition, the source and mechanism of the nonline...

Structural Damping of Self-Acting Compliant Foil Journal Bearings

This paper describes an experimental investigation into the dynamic characteristics of corrugated foil (bump foil) strips used in compliant surface foil journal bearings and dampers. In the experimental method described herein, a test facility with a journal supported by a compliant foil journal bearing was built. The nonrotating journal was driven by two shakers which were used to simulate dynamic forces acting on bump foil strips. The dynamic structural stiffness and equivalent viscous damping coefficients are calculated based on the experimental measurements for a wide range of operating conditions. The results are compared to the analytical predictions obtained by a theoretical model developed earlier.

Self-Alignment Systems for Heavily Loaded, Compliant, Hydrodynamic Air Bearings

Internal and external self-alignment system for compliant-foil journal bearings have been developed and tested at 35000 rpm in ambient air. These system have been shown to substantially improve the self-alignment capabilities of the compliant-foil bearings. The standard bearings with center-split bump have a misaligned capacity of 0.07 degrees at 55 kPa and 0.03 degrees at 83 kPa. Bearings with an internal self-alignment system were shown to have 0.15-degree misalignment capability at 55-kPa loading and 0.06 degrees at 90 kPa. A bearing with an external self-alignment system tolerated 0.43 degrees of misalignment at 69 kPa and 0.37 degrees at 110 kPa. Self-alignment capabilities of the bearings were improved at higher speed. Limited testing at 288°C showed that the temperature had no influence on the bearing performance. Presented at the 35th Annual Meeting in Anaheim, California, May 5–8, 1980