Design guidelines for bump-type compliant conical foil bearing

2021 ◽  
pp. 095440622110127
Author(s):  
Hongyang Hu ◽  
Ming Feng
Keyword(s):  
Load Capacity ◽  
Design Guidelines ◽  
Foil Thickness ◽  
Axial Stiffness ◽  
Structural Stiffness ◽  
Foil Bearing ◽  
Stiffness Model ◽  
Opposite Position ◽  
Stiffness Distribution ◽  
Half Length

The integral bump foil strip cannot optimize the performance for the compliant conical foil bearing (CFB) as the uneven distribution of structural stiffness. To maximize the bearing characteristics, this paper proposed different bump foil schemes. Firstly, the anisotropy of CFB was studied based on the nonlinear bump stiffness model, and the circumferentially separated foil structure was proposed. Moreover, an axially separated bump foil structure with the variable bump length was introduced to make the axial stiffness distribution more compliant with the gas pressure. In addition, the effect of foil thickness was also discussed. The results show that CFB with integral bump foil exhibits obvious anisotropy, and the suggested installation angle for largest load capacity and best dynamic stability are in the opposite position. Fortunately, a circumferential separated bump foil can improve this defect. The characteristics of CFB with axial separated foil structure can be improved significantly, especially for that with more strips and the variable bump half-length design. The suitable bump and top foil thickness should be set considering the improved supporting performance and proper flexibility. The results can give some guidelines for the design of CFB.

Study on the performance of gas foil journal bearings with bump-type shim foil

2020 ◽  
pp. 135065012096900
Author(s):  
Hongyang Hu ◽  
Ming Feng ◽  
Tianming Ren
Keyword(s):  
Dynamic Stability ◽  
Load Capacity ◽  
Practical Interest ◽  
Journal Bearings ◽  
Working Environment ◽  
Foil Thickness ◽  
The Novel ◽  
Improvement Potential ◽  
Stiffness Model ◽  
The Stability

The upscaling of turbomachinery using gas foil journal bearings (GFJBs) is limited because of their limited load capacity and dynamic stability. The improvement potential of shim foil inserted under the bump foil of such bearings is investigated in terms of better bearing performance. The arch height difference Δ hb between the shim foil and bump foil can be zero or not to attain the different effect. By considering the local hardening structural stiffness and an Initial installation clearance due to the shim foil, the static and dynamic characteristics of the novel bearing were calculated through the finite difference method (FDM) and perturbation method, respectively. In the analysis, a modified bump stiffness model considering the variable foil thickness was established, and a 2 D thick plate model was adopted for the top foil. The characteristics of novel GFJB with and without preload were compared with the traditional bearing. The results indicate that the load capacity and direct stiffness of the novel GFJB with shim foil can be increased largely, especially when there is a preload (Δ hb≠0). And the improvement is reinforced as the increment of Δ hb. Moreover, the stability threshold speed ( STS) of rotor supported by the novel GFJBs is enhanced by the preload, which means better stability. In addition, an air compressor test has also been conducted to verify the improved supporting performance of novel bearings. Based on this study it is convinced that the addition of shim foil under a GFJB's bump foil can be of practical interest in the quest of enhanced load capacity and dynamic stability. Moreover, the installation of shim foil is not affected by the working environment and could even be retrofited on the existing GFJBs.

Experiments and predictions on the performance of double-bump foil bearings: Effects of bearing loads and height difference between bumps

2017 ◽  
Vol 231 (11) ◽  
pp. 1474-1485 ◽  
Author(s):  
Kai Feng ◽  
Tao Zhang ◽  
Xueyuan Zhao
Keyword(s):  
Load Capacity ◽  
Load Test ◽  
Underlying Structure ◽  
Viscous Damping ◽  
Structural Stiffness ◽  
Static Load Test ◽  
Height Difference ◽  
Equivalent Viscous Damping ◽  
Foil Bearings ◽  
Foil Bearing

The concept of multilayer bump foils was introduced in the design of bump foil bearings to produce a double-bump foil bearing, which can provide increased load capacity and damping by adding another bump foil in the underlying structure. The height difference between the upper and lower bumps is a crucial parameter in the design and application of such structure. In this study, two double-bump foil bearings with various height differences between bumps are designed and fabricated to compare with an ordinary bump foil bearing. Three bearings are examined via static and dynamic load tests to estimate the structural stiffness and equivalent viscous damping. Test results indicate that lower bumps can enhance both the structural stiffness and equivalent viscous damping. A theoretical link-spring model, which exhibits good agreement with the data obtained from the static load test, is adopted to analyze the effect of height difference between bumps on gas film thickness and gas pressure of double-bump foil bearings. Results show that lower bumps of the double-bump foil bearing with a smaller height difference become active more easily and are more likely to form a stable double-bump supporting structure.

Characterization of Foil Bearing Structure for Increasing Shaft Temperatures: Part I—Static Load Performance

2008 ◽  
Author(s):  
Tae Ho Kim ◽  
Anthony W. Breedlove ◽  
Luis San Andre´s
Keyword(s):  
Material Properties ◽  
Static Load ◽  
Load Capacity ◽  
Dynamic Stiffness ◽  
Radial Clearance ◽  
Structural Stiffness ◽  
Test Configuration ◽  
Hollow Shaft ◽  
Foil Bearing ◽  
Simple Physical Model

Oil-free turbomachinery relies on gas bearing supports for reduced power losses and enhanced rotordynamic stability. Gas foil bearings (GFBs) with bump-strip compliant layers can sustain large loads, static and dynamic, and provide damping to reduce shaft vibrations. The ultimate load capacity of GFBs depends on the material properties and configuration of the underlying bump strips structure. In high temperature applications thermal effects changing operating clearances and material properties can affect considerably the performance of the FB structure. The paper presents experiments conducted to estimate the nonlinear structural stiffness of a test FB for increasing shaft temperatures. A 38.17 mm inner diameter FB is mounted on a non-rotating hollow shaft affixed to a rigid structure. A cartridge heater inserted into the shaft provides a controllable heat source and thermocouples record temperatures on the shaft and FB housing. For increasing shaft temperatures (up to 188°C) a static load (ranging from 0 N to 133 N) is applied to the bearing and the deflection recorded. Load versus deflection tests render the FB static structural stiffness coefficient. In the test configuration, thermal expansion of the FB housing, larger than that of the shaft, nets a significant increase in bearing radial clearance which produces a significant reduction in the foil bearing structural stiffness. A simple physical model assembling individual bump stiffnesses predicts well the measured FB structural stiffness when accounting for variations with temperature of the bump elastic modulus and the actual radial clearance affected by the thermal growth of the shaft and bearing cartridge. Further tests identifying the FB structure dynamic stiffness and its equivalent viscous damping follow in a companion paper (Part II) for a similar range of shaft temperatures.

Load Capacity Measurements of Hydrostatic Bump Foil Bearing

2009 ◽  
Author(s):  
Manish Kumar ◽  
Daejong Kim
Keyword(s):  
Load Capacity ◽  
Hydrodynamic Pressure ◽  
Structural Stiffness ◽  
Test Results ◽  
Test Rig ◽  
Comparative Tests ◽  
Noticeable Increase ◽  
High Speeds ◽  
Foil Bearing ◽  
Compression Springs

A few years ago, a hydrostatic air foil bearing using compression springs as elastic foundation was firstly introduced by Kim and Park [1]. This paper presents recent experimental results on load capacity of a new hydrostatic air foil bearing made of corrugated bump foils. The new hydrostatic air foil bearing was designed with higher structural stiffness than the first design by [1]. A new test rig was also designed and constructed to measure load capacity of the bearing at higher speeds. The new test results indicate the hybrid operation has similar load capacity to that of hydrodynamic operation at high speeds due to dominance of hydrodynamic pressure. However, comparative tests at low speed (10,000 rpm) showed noticeable increase of load capacity in hydrostatic air foil bearing, manifesting effective hydrostatic levitation feature at low speeds.

Performance of a novel foil journal bearing with surface micro-grooved top foil

2017 ◽  
Vol 232 (9) ◽  
pp. 1126-1139 ◽  
Author(s):  
Jiajia Yan ◽  
Guanghui Zhang ◽  
Zhansheng Liu ◽  
Jingming Zhao ◽  
Liang Xu
Keyword(s):  
Thick Plate ◽  
Journal Bearing ◽  
Dynamic Properties ◽  
Load Capacity ◽  
Groove Depth ◽  
Machining Process ◽  
Foil Thickness ◽  
Foil Bearing ◽  
Direct Stiffness ◽  
Groove Structure

To improve the performance of foil bearing including load capacity and stability, the surface micro groove structure on top foil is proposed, which is possible with the development of surface micro machining process. The micro groove structure on top foil can be processed by laser surface process, chemical etching, mechanical grinding, etc. This paper proposes a novel bump-type gas foil journal bearing with surface micro-grooved top foil and investigates the influence of micro groove depth on bearing performance theoretically. A modified pressure governing equation is established with the consideration of gas rarefaction, and the performance of the bearing is analyzed based on numerical simulation. By considering the variation of top foil thickness for surface micro groove, the load capacities with and without gas rarefaction considered are obtained by finite difference method, where the 2D thick plate model is adopted for the top foil. By employing the perturbation method, the force coefficients of this type foil bearing are calculated. The results indicate this novel foil journal bearing with surface micro-grooved top foil can decrease the end leakage and increase pressure around load domain efficiently. The load capacity and dynamic properties are improved. Moreover, with the increment of micro groove depth, the load capacity and direct stiffness are reinforced further. For the foil journal bearing with a micro groove depth of 8 µm on top foil, the load capacity and direct stiffness increase by about 11.89% and 11.87%, respectively, compared with traditional foil journal bearing.

The Static Performance Analysis of Foil Journal Bearings Considering Three-Dimensional Shape of the Foil Structure

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Dong-Hyun Lee ◽  
Young-Cheol Kim ◽  
Kyung-Woong Kim
Keyword(s):  
Structural Model ◽  
Load Capacity ◽  
Three Dimensional ◽  
Structural Models ◽  
Foil Thickness ◽  
Foil Bearing ◽  
Proposed Model ◽  
Static Performance ◽  
Dimensional Shape ◽  
Three Dimensional Shape

To obtain the foil bearing characteristics, the fluid film pressure must be coupled with the elastic deformation of the foil structure. However, all of the structural models thus far have simplified the foil structure without consideration of its three-dimensional shape. In this study, a finite element foil structural model is proposed that takes into consideration the three-dimensional foil shape. Using the proposed model, the deflections of interconnected bumps are compared to those of separated bumps, and the minimum film thickness determined from the proposed structural models is compared to those of previous models. In addition, the effects of the top foil and bump foil thickness on the foil bearing static performance are evaluated. The results of the study show that the three-dimensional shape of the foil structure should be considered for accurate predictions of foil bearing performances and that too thin top foil or bump foil thickness may lead to a significant decrease in the load capacity. In addition, the foil stiffness variation does not increase the load capacity much under a simple foil structure.

Study on the performance of novel gas foil conical bearings

2020 ◽  
pp. 135065012092536
Author(s):  
Hongyang Hu ◽  
Ming Feng ◽  
Tianming Ren
Keyword(s):  
Load Capacity ◽  
Dynamic Stiffness ◽  
Dynamic Performance ◽  
Cone Angle ◽  
Foil Thickness ◽  
Structural Stiffness ◽  
Power Turbine ◽  
Conical Bearing ◽  
Radial Thrust ◽  
Stiffness And Damping

To reduce the mass and size of low-power turbine machinery, a new type of gas foil conical bearing was proposed, and its static and dynamic performance was systematically studied. Based on a nonlinear bump stiffness model considering rounding and friction, the structural stiffness distribution, load capacity, dynamic stiffness, and damping coefficients of gas foil conical bearing were calculated, and the influence of bearing parameters on its static and dynamic characteristics was studied. In addition, a pair of gas foil conical bearings was used to replace the traditional radial-thrust foil bearing support scheme on an air compressor to explore the practicability of the novel bearing. The results show that the new gas foil conical bearing has an excellent supporting performance and broad prospects for application. The bump radius, rounding radius, friction coefficients, and foil thickness will significantly influence the bump foil stiffness. The bearing parameters such as structural stiffness, nominal clearance, cone angle, and eccentricity have a large effect on its static and dynamic performance, and we can obtain the desired bearing characteristics by tailoring these parameters.

Performance Analysis of Oil Lubricated Foil Bearing With Flexible Supported Back Spring Structure—Part I: Model Development and Numerical Investigation

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Guanghui Zhang ◽  
Xie Liang ◽  
Yu Wang ◽  
Zhansheng Liu
Keyword(s):  
Reynolds Equation ◽  
Load Capacity ◽  
Model Development ◽  
Foil Thickness ◽  
Film Rupture ◽  
Finite Element Software ◽  
Flexibility Matrix ◽  
Foil Bearing ◽  
Deformation Equation ◽  
The Stability

A new type of multileaf oil lubricated foil bearing with flexible supported back spring structure was proposed to satisfy the requirement of high rotating velocity for turbo pump, where the rotor was submerged in the hydraulic oil. The numerical analysis was carried out in this paper. Based on the structure of oil foil bearing, the film thickness model was established without foil deformation. By employing Castigliano's theorem, the total flexibility matrix including the elastic back spring and cantilevered curved beam was calculated, and then compared with commercial finite element software to verify the accuracy of the proposed model. The obtained flexibility matrix was brought into the static and dynamic oil lubricated Reynolds equation. The Reynolds boundary condition was considered to simulate the oil film rupture effect. The deformation equation for the structure and the Reynolds equation were solved coupled by the successive over relaxation method. The static and dynamic characteristics of the oil lubricated multileaf foil bearing with supported back spring were acquired. The effect of the foil thickness on the load capacity was discussed. The variation of the dynamic coefficients with bearing load was acquired. By employing Routh–Hurwitz method, the stability of the bearing was analyzed. The results indicated that the load capacity of the foil bearing with back supported spring was bigger than that of the foil bearing without back supported spring. The stability characteristics of the foil bearing with back supported structure was better than traditional rigid self-acting bearing, particular for the high rotating speed case.

Foil Gas Bearing With Compression Springs: Analyses and Experiments

2007 ◽  
Vol 129 (3) ◽  
pp. 628-639 ◽  
Author(s):  
Ju-ho Song ◽  
Daejong Kim
Keyword(s):  
Loss Factor ◽  
Load Capacity ◽  
Underlying Structure ◽  
Equivalent Viscous Damping ◽  
Foil Bearings ◽  
Foil Bearing ◽  
Different Types ◽  
Structural Loss ◽  
Compression Springs ◽  
Gas Bearing

A new foil gas bearing with spring bumps was constructed, analyzed, and tested. The new foil gas bearing uses a series of compression springs as compliant underlying structures instead of corrugated bump foils. Experiments on the stiffness of the spring bumps show an excellent agreement with an analytical model developed for the spring bumps. Load capacity, structural stiffness, and equivalent viscous damping (and structural loss factor) were measured to demonstrate the feasibility of the new foil bearing. Orbit and coast-down simulations using the calculated stiffness and measured structural loss factor indicate that the damping of underlying structure can suppress the maximum peak at the critical speed very effectively but not the onset of hydrodynamic rotor-bearing instability. However, the damping plays an important role in suppressing the subsynchronous vibrations under limit cycles. The observation is believed to be true with any air foil bearings with different types of elastic foundations.

Static Performance of a Hydrostatic Thrust Foil Bearing for Large Scale Oil-Free Turbomachines

2020 ◽  
Author(s):  
Nguyen LaTray ◽  
Daejong Kim ◽  
Myongsok Song
Keyword(s):  
Large Scale ◽  
Load Capacity ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Outer Diameter ◽  
Frictional Loss ◽  
Foil Bearing ◽  
Foundation Model ◽  
Static Performance ◽  
High Load Capacity

Abstract This work presents a novel design of a hydrostatic thrust foil bearing (HSTFB) with an outer diameter of 154mm along with simulation and test results up to specific load capacity of 223kPa (32.3psi). The HSTFB incorporates a high pressure air/gas injection to the thrust foil bearing with a uniform clearance. This bearing has high load capacity, low power loss, and no friction/wear during startup and shutdown. In addition, the HSTFB allows for bidirectional operation. The paper also presents an advanced simulation model which adopts the exact locations of a tangentially arranged bumps to a cylindrical two-dimensional plate model of the top foil. This method predicts top foil deflection with better accuracy than the traditional independent elastic foundation model which distributes the bump locations over the nodal points in the cylindrical coordinates, and with less computational resource than the finite element method applied to the entire bump/top foils. The presented HSTFB, was designed for Organic Rankine Cycle (ORC) generators, but its performance was predicted and measured using air in this paper. The bearing static performance is compared analytically against the rigid counterpart, and presented at different supply pressures, speeds, and minimum film thicknesses. Experimental verification is conducted at 10, 15 and 20krpm. The measured load capacity and frictional loss agree well with the prediction. The measured film thickness also agrees with the prediction after the structural deflection of the thrust runner disc is compensated. Overall, the novel HSTFB demonstrates an excellent static performance and shows good potential for adoption to the intended ORC generators and other large oil-free turbomachines.

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