Tilting Pad Gas Bearings

2013 ◽  
pp. 3691-3692
Author(s):  
Daejong Kim
Keyword(s):  
Gas Bearings ◽  
Tilting Pad

Experimental and Analytical Studies on Flexure Pivot Tilting Pad Gas Bearings With Dampers Applied to Radially Compliant Pads

2009 ◽  
Author(s):  
Daejong Kim ◽  
Aaron Rimpel
Keyword(s):  
Simulation Method ◽  
Analysis Tool ◽  
Primary Analysis ◽  
Successful Operation ◽  
Gas Bearings ◽  
Viscoelastic Dampers ◽  
Thermal Growth ◽  
Tilting Pad ◽  
Rotor Bearing ◽  
First Time

Hydrodynamic flexure pivot tilting pad gas bearings (FPTPGBs) can enable successful operation of oil-free microturbomachinery, and FPTPGBs with radially compliant pads (FPTPGB-Cs) permit rotor centrifugal and/or thermal growth to exceed original bearing clearances and achieve higher speeds. This work presents the experimental and analytical study of such bearings and the application of dampers behind the pad radial compliance structure. A time domain orbit simulation method was implemented as the primary analysis tool to predict rotor-bearing response to imbalance, the presence and location of critical speeds, etc., and compare with test results. Experiments demonstrate the stable hydrodynamic operation of FPTPGBs with a ∼28.6 mm, 0.8 kg rotor above 120 krpm for the first time. The rotor-bearing system was intentionally destabilized in tests by increasing bearing clearances, and viscoelastic dampers added behind the FPTPGB pads delayed the onset of subsynchronous vibrations (from 43 krpm without damper to above 50 krpm with damper). Midrange subsynchronous vibrations of the destabilized system initiated at ∼20 krpm were suppressed by ∼25 krpm due to the stabilizing effect of rotor centrifugal growth. The viscoelastic dampers had a negligible effect on suppressing these midrange subsynchronous vibrations in experiments, but this was not demonstrated in simulations, presumed to be due to much lower stiffness contribution of the damper at lower frequencies.

Experimental and Analytical Studies on Flexure Pivot Tilting Pad Gas Bearings With Dampers Applied to Radially Compliant Pads

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Aaron Rimpel ◽  
Daejong Kim
Keyword(s):  
Simulation Method ◽  
Analysis Tool ◽  
Primary Analysis ◽  
Successful Operation ◽  
Gas Bearings ◽  
Viscoelastic Dampers ◽  
Thermal Growth ◽  
Tilting Pad ◽  
Rotor Bearing ◽  
First Time

Hydrodynamic flexure pivot tilting pad gas bearings (FPTPGBs) can enable successful operation of oil-free microturbomachinery and FPTPGBs with radially compliant pads permit rotor centrifugal and/or thermal growth to exceed original bearing clearances and achieve higher speeds. This work presents the experimental and analytical study of such bearings and the application of dampers behind the pad radial compliance structure. A time domain orbit simulation method was implemented as the primary analysis tool to predict the rotor-bearing response to imbalance, the presence and location of critical speeds, etc., and to compare with test results. Experiments demonstrate the stable hydrodynamic operation of FPTPGBs with an ∼28.6 mm, 0.8 kg rotor above 120 krpm, for the first time. The rotor-bearing system was intentionally destabilized in tests by increasing bearing clearances and the viscoelastic dampers added behind the FPTPGB pads delayed the onset of subsynchronous vibrations (from 43 krpm without damper to above 50 krpm with damper). Midrange subsynchronous vibrations of the destabilized system initiated at ∼20 krpm were suppressed by ∼25 krpm due to the stabilizing effect of rotor centrifugal growth. The viscoelastic dampers had a negligible effect on suppressing these midrange subsynchronous vibrations in experiments, but this was not demonstrated in simulations, presumed to be due to much lower stiffness contribution of the damper at lower frequencies.

Thermohydrodynamic Analysis of Compliant Flexure Pivot Tilting Pad Gas Bearings

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Kyuho Sim ◽  
Daejong Kim
Keyword(s):  
Boundary Conditions ◽  
Energy Equation ◽  
Numerical Procedure ◽  
Computational Method ◽  
Temperature Fields ◽  
Linear Perturbation ◽  
Gas Bearings ◽  
Thermal Boundary Conditions ◽  
Thermal Growth ◽  
Tilting Pad

A new thermohydrodynamic (THD) analysis for compliant flexure pivot tilting pad gas bearings is presented. Unlike many previous THD analyses on oil-lubricated bearings and gas bearings, the new THD analysis solves the rotor and bearing pad temperatures as well as the gas film temperature simultaneously upon adequate thermal boundary conditions on the bearing shell and rotor ends are given. All the previous studies assume that the rotor and bearing temperatures are given as thermal boundary conditions to solve 2D or 3D energy equation in the bearing film. The developed computational method is unique because these boundary conditions are found internally through global energy balance around the bearing. A numerical procedure involves solving the generalized Reynolds equation, 3D energy equation, and heat flux equations around the bearings simultaneously through iterative process. Furthermore, rotor thermal and centrifugal expansions are also considered during the iteration. Parametric studies were performed for the various temperature fields, i.e., rotor temperature, gas film temperature, and pad temperature as a function of nominal clearance, external load, and various thermal boundary conditions. Nominal clearance showed the most significant influence on overall THD behavior. The analyses also show that the rotor-bearing system can go to thermal runaway if adequate cooling mechanism does not exist. Linear perturbation analysis was also performed to investigate the thermal effects on the rotordynamic performance. Rotor thermal growth and increased viscosity increased direct stiffness and damping coefficients compared to the isothermal case.

Material Considerations for High Temperature Tilting Pad Gas Bearings

1968 ◽  
Vol 90 (4) ◽  
pp. 818-828 ◽  
Author(s):  
S. F. Murray ◽  
M. B. Peterson
Keyword(s):  
High Temperature ◽  
Contact Area ◽  
High Speed ◽  
Contact Problems ◽  
Sliding Contact ◽  
Gas Bearings ◽  
Hydrodynamic Bearing ◽  
Tilting Pad ◽  
Short Time

This paper is concerned with the sliding contact problems encountered in tilting pad gas bearings operating at temperatures up to 1400 deg F. Both the pivots and the bearing surfaces are considered. Short time experimental evaluations of pivot damage are summarized. The results of start-stop and high-speed rub tests on a single tilting pad hydrodynamic bearing are also described. Based on the results obtained to date, damage-resistant coatings are available for use on the bearing surfaces at high temperature. There are also suitable pivot materials, but the pivot must be properly designed to minimize slip in the contact area.

scholarly journals Hybrid Gas Bearings With Controlled Supply Pressure to Eliminate Rotor Vibrations While Crossing System Critical Speeds

2008 ◽  
Author(s):  
Luis San Andre´s ◽  
Keun Ryu
Keyword(s):  
Critical Speed ◽  
Pressure Control ◽  
Sudden Increase ◽  
Critical Speeds ◽  
Gas Bearings ◽  
Supply Pressure ◽  
Simple Strategy ◽  
Tilting Pad ◽  
Bearing Stiffness ◽  
Bearing Force

Micro-turbomachinery (MTM) implements gas bearings in compact units of enhanced mechanical reliability. Gas bearings, however, have little damping and wear quickly during transient rub events. Flexure pivot tilting pad bearings offer little or no cross-coupled stiffnesses with enhanced rotordynamic stability; and when modified for hydrostatic pressurization, demonstrate superior rotordynamic performance over other bearing types. External pressurization stiffens gas bearings thus increasing system critical speeds, albeit reducing system damping. Most importantly, measurements demonstrate that external pressurization is not needed for rotor super critical speed operation. In practice, the supply pressure could be shut off at high rotor speeds with substantial gains in efficiency. The paper introduces a simple strategy, employing an inexpensive air pressure regulator to control the supply pressure into the hybrid bearings, to reduce or even eliminate high amplitudes of rotor motion while crossing the system critical speeds. Rotor speed coast-down tests with the pressure controller demonstrate the effectiveness of the proposed approach. A simple on-off supply pressure control, i.e. a sudden increase in pressure while approaching a critical speed, is the best since it changes abruptly the bearing stiffness coefficients and moves the system critical speed to a higher speed. A rotordynamic analysis integrating predicted bearing force coefficients forwards critical speeds in agreement with the test results. Predicted rotor responses for the controlled supply conditions show an excellent correlation with measured data. The experiments validate the predictive tools and demonstrate the controllable rotordynamic characteristics of flexure pivot hybrid gas bearings.

Analysis on Dynamic Performance of Hydrodynamic Tilting-Pad Gas Bearings Using Partial Derivative Method

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Yang Lihua ◽  
Qi Shemiao ◽  
Yu Lie
Keyword(s):  
Analytical Method ◽  
Gas Turbines ◽  
High Speed ◽  
Dynamic Performance ◽  
Gas Bearings ◽  
Dynamic Coefficients ◽  
Tilting Pad ◽  
Dynamic Performances ◽  
Perturbation Frequency ◽  
San Andres

Tilting-pad gas bearings are widely used in high-speed rotating machines due to their inherent stability characteristics. This paper advances the analytical method for prediction of the dynamic performances of tilting-pad gas bearings. The main advantage of the analytical method is that the complete set of dynamic coefficients of tilting-pad gas bearings can be obtained. The predictions show that the perturbation frequency has the strong effects on the dynamic coefficients of gas bearings. In general, at lower perturbation frequency, the equivalent direct stiffness coefficients increase with frequency, whereas equivalent direct damping coefficients dramatically reduce. For higher perturbation frequency, the dynamic coefficients are nearly independent of the frequency. Moreover, the equivalent dynamic coefficients of four-pad tilting-pad gas bearing obtained by the method in this paper are in good agreement with those obtained by Zhu and San Andres [(2007), “Rotordynamic Performance of Flexure Pivot Hydrostatic Gas Bearings for Oil-Free Turbomachinery,” ASME J. Eng. Gas Turbines Power, 129(4), pp. 1020–1027] in the published paper. The results validate the feasibility of the method presented in this paper in calculating the dynamic coefficients of gas-lubricated tilting-pad bearings.

Rotordynamic Performance of Flexure Pivot Tilting Pad Gas Bearings With Vibration Damper

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Aaron Rimpel ◽  
Daejong Kim
Keyword(s):  
Gas Turbines ◽  
Dynamic Models ◽  
Natural Frequencies ◽  
Clean Energy ◽  
Design Guidelines ◽  
Vibration Damper ◽  
Shell Mass ◽  
Gas Bearings ◽  
Tilting Pad ◽  
Rotor Bearing

Recently, gas-lubricated bearings have drawn enormous attention for clean energy conversion/process systems such as fuel cells, micro-gas-turbines, gas compressors, etc. Among many different types of gas bearings, tilting pad gas bearings have many attractive features such as high rotor-bearing stability and less severe thermal issues (due to multipad configurations) than foil gas bearings. However, extension of the application of the tilting pad gas bearings to flexible rotors and harsh environments with external vibrations/impacts poses significant design challenges. The design problem addressed in this paper is the vibration damper to be integrated with the flexure pivot tilting pad gas bearing (FPTPGB) with and without pad radial compliance. Linear and nonlinear dynamic models of the FPTPGB with vibration damper were developed, and rotordynamic performance was evaluated to prescribe design guidelines for the selection of bearing shell mass and damper properties. Direct numerical integration (time-domain orbit simulations) and linear analyses were employed to predict rotordynamic responses and other interesting behaviors relevant of rotor-bearing systems with the vibration damper. Rotor-bearing systems showed better performance with larger damper stiffness for both with and without radial compliance. However, bearing shell mass showed different tendencies; lower bearing shell mass was shown to be ideal for bearings with radial compliance, while the opposite trend was observed for bearings without radial compliance. Although increasing the degrees of freedom of the system by allowing the bearing shell to move introduces additional natural frequencies, careful design considerations could allow the placement of the natural frequencies outside of the operating range.

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