A review of thermohydrodynamic aspects of gas foil bearings

2021 ◽  
pp. 135065012110625
Author(s):  
Jitesh Kumar ◽  
Debanshu S Khamari ◽  
Suraj K Behera ◽  
Ranjit K Sahoo
Keyword(s):  
Numerical Models ◽  
Operating Conditions ◽  
Current Paper ◽  
Foil Bearings ◽  
Free Zone ◽  
Turbine Generators ◽  
Space Industry ◽  
Foil Bearing ◽  
Reliability Characteristics ◽  
Work Done

In recent times, gas foil bearings have become popular for commercial use in the aircraft and space industry, turbocompressors, turbine generators and in the more complex fields of turbochargers and turboexpanders. The gain in popularity for gas foil bearings is due to their features such as contamination-free zone, wide temperature range, higher stability and higher reliability characteristics as compared to other types of bearings. However, several challenges have come across while analysing the gas foil bearing behaviour at different working conditions. The current paper presents an overview of the work done in the past few decades for developing numerical models and listing the efforts of several researchers around the world to conduct the experimental investigation for predicting and analysing thermohydrodynamic behaviour of gas foil bearings at different operating conditions. It is expected that the current paper will help readers to thoroughly understand the hydrodynamic and thermal aspects of gas foil bearings.

Hybrid Air Foil Bearings With External Pressurization

Tribology ◽  
2006 ◽  
Author(s):  
Daejong Kim ◽  
Soonkuk Park
Keyword(s):  
Load Capacity ◽  
Experimental Studies ◽  
Axial Flow ◽  
Steel Tube ◽  
Operating Conditions ◽  
Drag Torque ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Hybrid Operation ◽  
Lift Off

Foil bearings are widely used for oil-free microturbomachinery. One of the critical technical issues related to reliability of the foil bearings is a coating wear on the top foil and rotor during start/stops. Especially for heavily loaded foil bearings, large start torque requires a large drive motor. Bearing cooling is also mandatory for certain applications because the foil bearings can generate significant amount of heat depending on operating conditions. Usually axial flow is used through the space between the top foil and bearing sleeve. In this paper, a hybrid air foil bearing with external pressurization is introduced. A flexible steel tube is attached to the backside of the top foil with orifice holes, and externally pressurized air is directly supplied to the bearing clearance to lift off the rotor before rotor spins. The hybrid operation eliminates the coating wear during start/stop cycles, reduces drag torque during starts, and eliminates axial flow cooling. The hybrid foil gas bearing was constructed using a multiple compression springs to demonstrate a feasibility of the concept. A simple analytical model to calculate top foil deflection under hydrostatic pressurization has been developed. Predictions via orbit simulations indicate the hybrid air foil bearings can have much higher critical speed and onset speed of instability than hydrodynamic counter part. Measured load capacity was slightly higher than hydrodynamic bearing even under smaller amount of air flow. In addition, the hybrid operation was very effective for bearing cooling even if the cooling flow rate was lower than hydrodynamic counterpart. The measured very small drag torque during the start/stop demonstrates the hybrid foil bearing can have near-infinite life time without wear of the bearing and rotor surface. The experimental studies show high potential of the hybrid air foil bearings for various oil-free turbomachinery, especially for heavily loaded high temperature applications.

scholarly journals Compliant Foil Journal Bearing Performance at Alternate Pressures and Temperatures

2008 ◽  
Author(s):  
Robert J. Bruckner ◽  
Bernadette J. Puleo
Keyword(s):  
Journal Bearing ◽  
Load Capacity ◽  
Ambient Pressure ◽  
Operating Conditions ◽  
Test Program ◽  
Foil Bearings ◽  
Current Test ◽  
Foil Bearing ◽  
Development Risk ◽  
Highly Loaded

An experimental test program has been conducted to determine the highly loaded performance of current generation gas foil bearings at alternate pressures and temperature. Typically foil bearing performance has been reported at temperatures relevant to turbomachinery applications but only at an ambient pressure of one atmosphere. This dearth of data at alternate pressures has motivated the current test program. Two facilities were used in the test program, the ambient pressure rig and the high pressure rig. The test program utilized a 35 mm diameter by 27 mm long foil journal bearing having an uncoated Inconel X-750 top foil running against a shaft with a PS304 coated journal. Load capacity tests were conducted at 3, 6, 9, 12, 15, 18, and 21 krpm at temperatures from 25°C to 500°C and at pressures from 0.1 to 2.5 atmospheres. Results show an increase in load capacity with increased ambient pressure and a reduction in load capacity with increased ambient temperature. Below one-half atmosphere of ambient pressure a dramatic loss of load capacity is experienced. Additional lightly loaded foil bearing performance in nitrogen at 25°C and up to 48 atmospheres of ambient pressure has also been reported. In the lightly loaded region of operation the power loss increases for increasing pressure at a fixed load. Knowledge of foil bearing performance at operating conditions found within potential machine applications will reduce program development risk of future foil bearing supported turbomachines.

Experimental Evaluation of Foil Bearing Performance: Steady-State and Dynamic Results

2009 ◽  
Author(s):  
M. J. Conlon ◽  
A. Dadouche ◽  
W. M. Dmochowski ◽  
R. Payette ◽  
J.-P. Be´dard ◽  
...  
Keyword(s):  
Steady State ◽  
High Speed ◽  
First Generation ◽  
Dynamic Properties ◽  
Operating Conditions ◽  
Pneumatic Cylinder ◽  
Test Procedures ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Stepped Shaft

An experimental facility dedicated to measuring both the steady-state and dynamic properties of foil bearings, under a variety of operating conditions, has been designed and commissioned. The bearing under test is placed at the midspan of a horizontal, simply-supported, stepped shaft which rotates at up to 60 krpm. Static and dynamic loads of up to 3500 N and 450 N (respectively) can be applied by means of a pneumatic cylinder and two electrodynamic shakers. This paper outlines the test procedures and data analysis methods pertaining to the operation of the high-speed, oil-free bearing test rig, and presents steady-state and dynamic results for a first-generation foil bearing. The test bearing, which was fabricated in-house, is 0.07 m diameter and has an aspect ratio of 1; bearing manufacturing details are provided.

Low-Friction Wear Resistant Coatings for High-Temperature Foil Bearings

2005 ◽  
Author(s):  
Hooshang Heshmat ◽  
Piotr Hryniewicz ◽  
James F. Walton ◽  
John P. Willis ◽  
Said Jahanmir
Keyword(s):  
High Temperature ◽  
High Speed ◽  
Tribological Behavior ◽  
Operating Conditions ◽  
Hard Coatings ◽  
Wear Resistant Coatings ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Chrome Coating ◽  
Maximum Coefficient

Compliant foil bearings offer many advantages over rolling element bearings in high-speed and high-temperature applications. However, implementation of foil bearings in these applications requires development of solid lubricant coatings that can survive the severe operating conditions encountered at high speeds and high temperatures. The objective of this paper is to present results on development of an advanced coating system for use with compliant foil bearings that permits higher operating speeds and temperatures. In order to evaluate the coating performance and to select the best coating combination for implementation, a number tests were conducted using a high-temperature, high-speed tribometer up to 810 °C. Inconel test substrates, representative of a portion of a foil bearing, were coated with several different Korolon™ coatings. The counterface disks were coated with four different hard coatings. The test results confirmed the excellent tribological behavior of Korolon™ coatings for high-speed high-temperature foil bearing applications. While the tribological behavior of Korolon™ coatings were determined to be a function of temperature, in most cases a maximum coefficient of friction less than 0.1 was observed during startup/shutdown periods. Subsequently, a foil journal bearing was designed and a composite Korolon™ coating was applied to the bearing top foil; and a dense chrome coating was applied to the journal surface. The foil bearing was installed in a turbojet engine and operated successfully to 54,000 rpm for over 70 start-stop cycles.

Analysis of Thermal Damage in the High-Speed Foil Bearing

2017 ◽  
Vol 260 ◽  
pp. 266-277 ◽  
Author(s):  
Grzegorz Żywica ◽  
Paweł Bagiński ◽  
Artur Andrearczyk
Keyword(s):  
High Speed ◽  
Thermal Analyses ◽  
Experimental Tests ◽  
Significant Rise ◽  
Operating Conditions ◽  
Factors Affecting ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Wide Range ◽  
Heavy Loads

The article discusses experimental research and simulation testing on prototypical foil bearings. All experimental tests were conducted on a special test rig which makes it possible to operate in various conditions and within a wide range of speeds. As a result of the study, it turned out that adverse operating conditions caused almost instant bearing damage, accompanied by a significant rise in temperature. The main factors affecting the durability of foil bearings were material covering mating surfaces, bearing geometry, way of assembling the bearing, rotational speed and load. To better understand the physical phenomena occurring in foil bearings, a numerical model has been developed which allowed carrying out thermal analyses. The analysis of heat flow in the bearing's structure showed that, because of the system geometry, significant problems with proper removal of large amounts of heat continued to be experienced, which may have led to an accelerated rate of fatigue damage and shorter bearing life. This phenomenon can occur in bearings operating under tough conditions (e.g. at low speeds or under heavy loads). The research showed that the development of a new foil bearing is a very difficult task and requires many aspects to be taken into account, including the aspects directly related to the operation of the bearing itself, as well as those related to the rotor's operation and characteristics of the machine.

EXPERIMENTAL INVESTIGATION OF A FOIL BEARING STRUCTURE WITH A POLYMER COATING UNDER STATIC LOADS

Tribologia ◽  
2018 ◽  
Vol 278 (2) ◽  
pp. 153-158 ◽  
Author(s):  
Grzegorz ŻYWICA ◽  
Paweł BAGIŃSKI
Keyword(s):  
Numerical Models ◽  
Static Characteristics ◽  
Static Loads ◽  
Foil Bearings ◽  
Metal Foils ◽  
Foil Bearing ◽  
Supporting Layer ◽  
Bearing Design ◽  
Bearing Structure ◽  
Very High

Gas foil bearings can operate at very high temperatures and rotational speeds. The operation under such conditions requires developing an appropriate bearing design, including the use of advanced material solutions. This article presents one of the basic stages of work on a new foil bearing, namely, experimental research on the structural supporting layer of such a bearing regarding its static loads. Tests of the bearing were carried out on a test rig specially prepared for this purpose. Changing the magnitude and direction of the load was possible. The elasto-damping elements of the bearing were made of thin metal foils. In addition, a layer of carefully selected polymer was applied onto one side of the top foil in order to protect the surface and reduce friction. Characteristics of the structure of the foil bearing were determined at various load variants after taking a series of measurements upon it. The conducted research has yielded much information about static characteristics of the structural supporting layer of a new foil bearing in which the top foil’s surface is covered with a layer of polymer. These results can be used, among other things, to optimise the bearing design and to verify numerical models.

Magne´li-Type Phases for Dry High-Speed Sliding Applications Up to 800°C

2005 ◽  
Author(s):  
M. Woydt ◽  
N. Ko¨hler ◽  
N. Kelling
Keyword(s):  
Boundary Lubrication ◽  
High Speed ◽  
Mixed Boundary ◽  
Operating Conditions ◽  
Thermal Cycles ◽  
Wear Rates ◽  
Foil Bearings ◽  
Foil Bearing

The wear rates established up to 800°C and 7,5 m/s qualify the new and non-commercial available metallurgical concepts (Ti,Mo)(C,N) and Tin-2Cr2O2n-1 qualify both metallurgical concepts for radial and axial air foil bearings in small jet turbines, APUs and turbochargers, but are not limited to these, as well as the values of wear rates are comparable to those typically attributed under mixed/boundary lubrication of liquid lubricated tribosystems. The selection between (Ti,Mo)(C,N) and Tin-2Cr2O2n-1 under tribological considerations depends from the operating conditions and thermal cycles of the regarded foil bearing.

scholarly journals Experimental Research on Foil Vibrations in a Gas Foil Bearing Carried Out Using an Ultra-High-Speed Camera

2021 ◽  
Vol 11 (2) ◽  
pp. 878
Author(s):  
Łukasz Breńkacz ◽  
Paweł Bagiński ◽  
Grzegorz Żywica
Keyword(s):  
High Speed ◽  
Numerical Models ◽  
Digital Camera ◽  
New Approach ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Ultra High Speed ◽  
Supporting Layer ◽  
First Time ◽  
Further Development

The foil bearing consists of parts made of very thin, properly shaped foils. Usually, it is very difficult or even impossible to measure the vibrations of these elements during the bearing operation using traditional sensors. Therefore, the authors of this article have proposed an entirely new approach to this issue. This article discusses the analysis of vibrations of the structural supporting layer of a gas foil bearing at high rotational speeds. Instead of using a traditional method to measure the bearing journal movement, the measurement was performed using an ultra-high-speed digital camera. This type of measurement was used for the first time to analyse foil bearing displacement. It turned out that doing so can give a far more vibrant picture of what is happening in gas foil bearings during their operation. The article includes an analysis of foil vibrations. This phenomenon has already been analysed numerically, and this is the first time it has been analysed experimentally. The registered motion of the foils can be compared with the results obtained from numerical models, thus allowing their further development. One such comparison is shown in this article.

scholarly journals Investigation of Gas Foil Bearings With an Adaptive and Non-Linear Structure

2019 ◽  
Vol 13 (1) ◽  
pp. 5-10 ◽  
Author(s):  
Grzegorz Żywica ◽  
Paweł Bagiński
Keyword(s):  
Experimental Research ◽  
Numerical Models ◽  
Dynamic Performance ◽  
Linear Structure ◽  
Operating Conditions ◽  
Vibration Level ◽  
High Rotational Speed ◽  
Foil Bearings ◽  
Thin Foils ◽  
Operational Characteristics

Abstract The article discusses the results of simulation-based and experimental research carried out on gas foil bearings. Owing to the use of a set of flexible thin foils in such bearings, they exhibit certain beneficial features that cannot be found in other types of bearings. They have nonlinear operational characteristics and allow the dissipation of excess energy, thus reducing the vibration level. Moreover, gas foil bearings can self-adapt themselves to the current operating conditions by changing the shape of the lubrication gap. Therefore, they can be used to improve the dynamic performance of rotors, in particular, those operating at very high rotational speeds. This article explains the mechanisms for changes of stiffness and vibration damping in compliant components of a foil bearing. The results of the analysis of the bearing’s subassemblies using advanced numerical models are presented. They are followed by conclusions that were drawn not only from these results but also from the results of the experimental research. It has been proven that the rotor supported on carefully designed foil bearings is capable of maintaining a low vibration level, even if it operates at a high rotational speed.

Dynamic analysis of a helical gear reduction by experimental and numerical methods

2020 ◽  
Vol 68 (1) ◽  
pp. 48-58
Author(s):  
Chao Liu ◽  
Zongde Fang ◽  
Fang Guo ◽  
Long Xiang ◽  
Yabin Guan ◽  
...  
Keyword(s):  
Numerical Methods ◽  
Dynamic Analysis ◽  
Dynamic Behavior ◽  
Fourth Order ◽  
Numerical Models ◽  
Helical Gear ◽  
Operating Conditions ◽  
Dynamic Responses ◽  
Lumped Mass ◽  
Gear Mesh

Presented in this study is investigation of dynamic behavior of a helical gear reduction by experimental and numerical methods. A closed-loop test rig is designed to measure vibrations of the example system, and the basic principle as well as relevant signal processing method is introduced. A hybrid user-defined element model is established to predict relative vibration acceleration at the gear mesh in a direction normal to contact surfaces. The other two numerical models are also constructed by lumped mass method and contact FEM to compare with the previous model in terms of dynamic responses of the system. First, the experiment data demonstrate that the loaded transmission error calculated by LTCA method is generally acceptable and that the assumption ignoring the tooth backlash is valid under the conditions of large loads. Second, under the common operating conditions, the system vibrations obtained by the experimental and numerical methods primarily occur at the first fourth-order meshing frequencies and that the maximum vibration amplitude, for each method, appears on the fourth-order meshing frequency. Moreover, root-mean-square (RMS) value of the acceleration increases with the increasing loads. Finally, according to the comparison of the simulation results, the variation tendencies of the RMS value along with input rotational speed agree well and that the frequencies where the resonances occur keep coincident generally. With summaries of merit and demerit, application of each numerical method is suggested for dynamic analysis of cylindrical gear system, which aids designers for desirable dynamic behavior of the system and better solutions to engineering problems.

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