Erratum: “Static Performance Characteristics and Rotordynamic Coefficients for a Four-Pad Ball-in-Socket Tilting Pad Journal Bearing” [ASME J. Eng. Gas Turbines Power, 2009, 131(6), p. 062502; DOI: 10.1115/1.3098376]

2017 ◽  
Vol 140 (5) ◽  
Author(s):  
Joel Harris ◽  
Dara Childs
Keyword(s):  
Gas Turbines ◽  
Journal Bearing ◽  
Performance Characteristics ◽  
Rotordynamic Coefficients ◽  
Tilting Pad ◽  
Static Performance ◽  
Tilting Pad Journal Bearing

The following erratum has been written to alert readers to unreliable data contained in the referenced paper.

Static Performance Characteristics and Rotordynamic Coefficients for a Four-Pad Ball-in-Socket Tilting Pad Journal Bearing

2008 ◽  
Author(s):  
Joel Harris ◽  
Dara Childs
Keyword(s):  
Power Loss ◽  
Journal Bearing ◽  
Excitation Frequency ◽  
Performance Characteristics ◽  
Rotordynamic Coefficients ◽  
Test Conditions ◽  
Tilting Pad ◽  
Static Performance ◽  
Stiffness And Damping ◽  
Tilting Pad Journal Bearing

Static performance characteristics and rotordynamic coefficients were experimentally determined for a four-pad, spherical-seat, tilting-pad journal bearing in load-between-pad configuration. Measured static characteristics include journal static equilibrium position, estimated power loss, and trailing-edge pad temperatures. Rotordynamic coefficients were determined from curve fits of measured complex dynamic-stiffness coefficients as a functions of the excitation frequency. A frequency-independent [M]-[C]-[K] model did a good job of fitting the measurements. Test conditions included speeds from 4 to 12 krpm and unit loads from 0 to 1896 kPa (0 to 275 psi). The bearing uses cool inlet oil to decrease the pad operating temperatures and increase the bearing’s load and speed capacity. The bearing has a nominal diameter of 101.78 mm (4.0070 in). Measurements indicated significant bearing crush with a radial bearing clearance of 99.63 μm (3.92 mils) in the axis 45° counterclockwise from the loaded axis and 54.60 μm (2.15 mils) in the axis 45° clockwise from the loaded axis. The pad length is 101.60 mm (4.00 in), giving L/D = 1.00. The pad arc angle is 73°, and the pivot offset ratio is 65%. Testing was performed using a test rig described by Kaul [1], and rotordynamic coefficients were extracted using a procedure adapted from Childs and Hale [2]. A bulk-flow Navier-Stokes model was used for predictions, using adiabatic conditions for the fluid in the bearings. However, the model assumes constant nominal clearances at all pads, and an average clearance was used based on measured clearances. Measured static eccentricities and attitude angles were significantly lower than predicted. Attitude angles varied from 6° to 39° and decreased with load. Power loss was well-predicted, with a maximum value of 25 kW (34 hp). The maximum detected pad temperature was 71°C (160°C) while the temperature rise from inlet to exit was over-predicted by 8°C (14°F). Direct stiffness and damping coefficients were significantly over-predicted, but the addition of a simple pivot-stiffness in series with the measured stiffness and damping values vastly improved the agreement between theory and experiment. Direct added masses were negative to a higher degree for Myy (y load direction) at low speeds and increased with speed. With the exception of Myy at zero load, they became positive before reaching 8,000 rpm. Although significant cross-coupled stiffness terms were present, they always had the same sign, producing a whirl frequency ratio of zero and netting unconditional stability over all test conditions.

Static Performance Characteristics and Rotordynamic Coefficients for a Four-Pad Ball-in-Socket Tilting Pad Journal Bearing

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Dara Childs ◽  
Joel Harris
Keyword(s):  
Power Loss ◽  
Journal Bearing ◽  
Rotordynamic Coefficients ◽  
Damping Coefficients ◽  
Test Conditions ◽  
Tilting Pad ◽  
Frequency Independent ◽  
Static Performance ◽  
Stiffness And Damping ◽  
Tilting Pad Journal Bearing

Static performance characteristics and rotordynamic coefficients were experimentally determined for a four-pad, ball-in-socket, tilting-pad journal bearing in load-between-pad configuration. Measured static characteristics include journal static equilibrium position, estimated power loss, and trailing-edge pad temperatures. Rotordynamic coefficients were determined from curve-fits of measured complex dynamic-stiffness coefficients as a function of the excitation frequency. Aside from the cross-coupled damping coefficients, a frequency-independent [M]-[C]-[K] model did a good job of fitting the measurements. The added-mass coefficient was frequently dropped, leaving only a frequency-independent stiffness and damping coefficient. Test conditions included speeds from 4000 rpm to 12,000 rpm and unit loads from 0 kPa to 1896 kPa (0–275 psi). The bearing uses cool inlet oil to decrease the pad operating temperatures and increase the bearing’s load and speed capacity. The bearing has a nominal radial clearance of 95.3 μm (3.75 mils). However, measurements indicated significant bearing crush with a radial bearing clearance of 99.6 μm (3.92 mils) in the axis 45 deg counterclockwise from the loaded axis and 54.6 μm (2.15 mils) in the axis 45 deg clockwise from the loaded axis (assuming counterclockwise rotation). The pad length is 101.60 mm (4.00 in.), giving L/D=1.00. The pad arc angle is 73 deg, and the pivot offset ratio is 65%. Testing was performed using a test rig described by Kaul (1999, “Design and Development of a Test Setup for the Experimental Determination of the Rotordynamic and Leakage Characteristics of Annular Bushing Oil Seals,” MS thesis, Texas A&M University, College Station, TX), and rotordynamic coefficients were extracted using a procedure adapted from the work of Childs and Hale (1994, “A Test Apparatus and Facility to Identify the Rotordynamic Coefficients of High-Speed Hydrostatic Bearings,” ASME J. Tribol., 116, pp. 337–344). A bulk-flow Navier–Stokes model was used for predictions, using adiabatic conditions for the fluid in the bearing. However, the model assumes constant nominal clearances at all pads, and an average clearance was used based on measured clearances. Measured static eccentricities and attitude angles were significantly higher than predicted. Attitude angles varied from 6 deg to 39 deg and decreased with load. Power loss was underpredicted at low speeds and very well predicted at high speeds, with a maximum value of 25 kW (34 hp). The maximum detected pad temperature was 71°C(160°F) while the temperature increase from inlet to maximum pad temperature location was overpredicted by 10–40%. Direct stiffness and damping coefficients were significantly overpredicted, but the addition of a stiffness-in-series correction vastly improved the agreement between theory and experiment. Direct added masses were zero or negative at low speeds and increased with speed up to a maximum of about 50 kg; they were normally greater in the x (unloaded) direction. Although significant cross-coupled stiffness terms were present, they always had the same sign, and the bearing had a whirl frequency ratio of zero netting unconditional stability over all test conditions.

The Rolling-Pad Journal Bearing: A Promising Antiwhirl Configuration

1981 ◽  
Vol 23 (3) ◽  
pp. 131-141
Author(s):  
M. Malik ◽  
R. Sinhasan ◽  
D. V. Singh
Keyword(s):  
Journal Bearing ◽  
Dynamic Performance ◽  
Journal Bearings ◽  
Operating Conditions ◽  
Performance Characteristics ◽  
Tilting Pad ◽  
The Comparative Study ◽  
Tilting Pad Journal Bearing ◽  
Tilting Pad Journal Bearings ◽  
Theoretical Performance

The rolling-pad journal bearing is a kinematic variation of the well-known tilting-pad journal bearing. In rolling-pad bearings, the pads, instead of tilting about fixed pivots, roll at their back surfaces on the inside surface of a common sleeve to accommodate changes in the operating conditions of the bearing. This paper presents a comparison of the theoretical performance characteristics of rolling-pad journal bearings with those of tilting-pad journal bearings. The comparative study indicates that the dynamic performance characteristics of the rolling-pad bearing configuration are superior to those of the tilting-pad bearing.

scholarly journals Measurements Versus Predictions for the Static and Dynamic Characteristics of a Four-Pad, Rocker-Pivot, Tilting-Pad Journal Bearing

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
David P. Tschoepe ◽  
Dara W. Childs
Keyword(s):  
Dynamic Characteristics ◽  
Room Temperature ◽  
Journal Bearing ◽  
Dynamic Stiffness ◽  
Static And Dynamic Characteristics ◽  
Rotordynamic Coefficients ◽  
Stiffness Coefficients ◽  
Tilting Pad ◽  
Frequency Independent ◽  
Tilting Pad Journal Bearing

Measured and predicted static and dynamic characteristics are provided for a four-pad, rocker-pivot, tilting-pad journal bearing (TPJB) in the load-on-pad (LOP) and load-between-pad (LBP) orientations. The bearing has the following characteristics: pad-pivot offset = 0.57, L/D = 0.6, pad length = 60.33 mm. Unit loads ranged from 0 to 2903 kPa, and speeds ranged from 6.8 to 13.2 krpm. Nonrotating tests were carried out using a small rotating load to precess the test-bearing stator around the rotor shaft while measuring the clearances. These tests produced “clearance rectangles” for the LOP case and “clearance rhombuses” for the LBP cases. These tests defined the bearing clearances for facing bearing pads that were significantly different with a ratio between the larger and smaller clearances at approximately 1.6. Clearances were measured at room temperatures and immediately following tests to obtain room temperature and “hot” clearances. Hot-clearance measurements showed a 16%–25% decrease as compared to room-temperature clearances. Static load-deflection tests were carried out to determine the pad's flexibility characteristics with respect to the housing (pad-pivot flexibility). Detailed circumferential temperature measurements were made on the loaded pad(s) with only leading and trailing temperatures for the unloaded pads. The radial thermal gradient was examined in the loaded pad via embedded thermocouples on the rotor and outside of the pads. Results showed a 5–25 °C decrease from the rotor side of the pad to housing side. An FEM analysis predicted that the radial and circumferential temperature gradients caused an uneven thermal deflection in the pad, changing the pads' radii of curvature. (However, the changes made scant differences in predictions.) Dynamic-excitation tests were performed over a range of excitation frequencies Ω to obtain 2 × 2 complex dynamic-stiffness matrices [Hij] as a function of Ω. The Re(Hij) coefficients were readily fitted as a linear function of Ω2, producing frequency-independent stiffness and virtual-mass coefficients. The Im(Hij) coefficients were readily fitted as a linear function of Ω, producing frequency-independent damping coefficients and supporting the adequacy of a constant-frequency MCK model for bearings out to running speed. Measured (separate) pad clearances, pad-contact flexibility characteristics, and input temperatures were used as input for a recently-developed code to predict the static and dynamic characteristics of the bearing. The code used a Reynolds equation model plus an adiabatic energy equation. It also accounts for pad-contact flexibility. Measurements versus predictions were made for the temperature distributions, the dynamic-stiffness coefficients, and the direct rotordynamic coefficients (stiffness, damping, and virtual-mass). The measured cross-coupled stiffness and damping coefficients were insignificant, and are not presented. Generally, the code predicts the trends of the circumferential temperature distributions well; however, it predicted a continuing increase in temperature from leading to trailing edge, while the tests show an increase through the next-to-last temperature probe and then a drop to the last probe nearest the trailing edge. Generally speaking, the code does an adequate job of predicting rotordynamic coefficients for both LOP and LBP conditions. The input data (clearances, pad-flexibility, etc.) and output results (temperatures, dynamic stiffness coefficients, rotordynamic coefficients) presented allow other researchers to directly make predictions for these bearings using alternate models and codes.

Characteristics of a Spherical Seat TPJB With Four Methods of Directed Lubrication—Part II: Rotordynamic Performance

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
David M. Coghlan ◽  
Dara W. Childs
Keyword(s):  
Matrix Model ◽  
Journal Bearing ◽  
Leading Edge ◽  
Dynamic Data ◽  
Rotordynamic Coefficients ◽  
Test Conditions ◽  
Tilting Pad ◽  
Frequency Independent ◽  
In Series ◽  
Tilting Pad Journal Bearing

Measured and predicted rotordynamic characteristics are presented for a four-pad, spherical-seat, tilting-pad journal bearing (TPJB) with 0.5 pivot offset, 0.6 L/D, 101.6 mm nominal diameter, and 0.3 preload in the load-between-pivots orientation. One bearing is tested four separate times in the following four different lubrication configurations: (1) flooded single-orifice (SO) at the bearing shell, (2) evacuated leading edge groove (LEG), (3) evacuated spray-bar blocker (SBB), and (4) evacuated spray-bar (SB). The same set of pads is used for every test to maintain clearance and preload; each method of lubrication is added as an assembly to the bearing. Test conditions include surface speeds and unit loads up to 85 m/s and 2.9 MPa, respectively. Dynamic data includes four sets (one set for each bearing configuration) of direct and cross-coupled rotordynamic coefficients derived from measurements and fit to a frequency-independent stiffness-damping-mass (KCM) matrix model. The pivot stiffness (pad and pivot in series) is measured and incorporated into predictions.

Characteristics of a Spherical-Seat TPJB With Four Methods of Directed Lubrication—Part I: Thermal and Static Performance

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
David M. Coghlan ◽  
Dara W. Childs
Keyword(s):  
Journal Bearing ◽  
Thermal Characteristics ◽  
Leading Edge ◽  
Static Data ◽  
Axial Temperature ◽  
Tilting Pad ◽  
Thermal Data ◽  
In Series ◽  
Static Performance ◽  
Tilting Pad Journal Bearing

Static and thermal characteristics (measured and predicted) are presented for a four-pad, spherical-seat, tilting-pad journal bearing (TPJB) with 0.5 pivot offset, 0.6 L/D, 101.6 mm nominal diameter, and 0.3 preload in the load-between-pivots orientation. One bearing is tested four separate times in the following four different lubrication configurations: (1) flooded single-orifice (SO) at the bearing shell, (2) evacuated leading edge groove (LEG), (3) evacuated spray-bar blocker (SBB), and (4) evacuated spray-bar (SB). The LEG, SBB, and SB are all considered methods of “directed lubrication.” These methods rely on lubrication injected directly to the pad/rotor interface. The same set of pads is used for every test to maintain clearance and preload; each method of lubrication is added as an assembly to the bearing. Test conditions include surface speeds and unit loads up to 85 m/s and 2.9 MPa, respectively. Static data include rotor–bearing eccentricities and attitude angles. Thermal data include measured temperatures from 16 bearing thermocouples. Twelve of the bearing thermocouples are embedded in the babbitt layer of the pads, while the remaining four are oriented at the leading and trailing edge of the loaded pads exposed to the lubricant. Bearing thermocouples provide a circumferential and axial temperature gradient. The pivot stiffness (pad and pivot in series) is measured and incorporated into predictions.

scholarly journals Measurements Versus Predictions for the Static and Dynamic Characteristics of a Four-Pad, Rocker-Pivot, Tilting-Pad Journal Bearing

2013 ◽  
Author(s):  
David P. Tschoepe ◽  
Dara W. Childs
Keyword(s):  
Journal Bearing ◽  
Dynamic Stiffness ◽  
Radial Clearance ◽  
Static And Dynamic Characteristics ◽  
Rotordynamic Coefficients ◽  
Stiffness Coefficients ◽  
Bearing Clearance ◽  
Tilting Pad ◽  
Frequency Independent ◽  
Tilting Pad Journal Bearing

Measured and predicted static and dynamic characteristics are provided for a four-pad, rocker-pivot, tilting-pad journal bearing in the load-on-pad and load-between-pad orientations. The bearing has the following characteristics: 4 pads, .57 pad pivot offset, 0.6 L/D ratio, 60.33 mm (2.375in) pad axial length, 0.08255 mm (0.00325 in) radial clearance in the load-on-pad orientation, and 0.1189 mm (0.00468 in) radial clearance in the load-between-pad orientation. Tests were conducted on a floating test bearing design with unit loads ranging from 0 to 2903 kPa (421.1 psi) and speeds from 6.8 to 13.2 krpm. For all rotor speeds, hot-clearance measurements were taken to show the reduction in bearing clearance due to thermal expansion of the shaft and pads during testing. As the testing conditions get hotter, the rotor, pads, and bearing expand, decreasing radial bearing clearance. Hot-clearance measurements showed a 16–25% decrease in clearance compared to a clearance measurement at room temperature. To look at the radial thermal gradient in the loaded pad, embedded thermocouples were inserted inside the bearing pad near the bearing housing. Results showed a 5–25°C decrease in temperature from the rotor side of the pad to the temperatures near the bearing housing. This radial temperature gradient caused an uneven thermal deflection in the pad, changing the pads’ radii of curvature. For all test conditions, dynamic tests were performed over a range of excitation frequencies to obtain complex dynamic stiffness coefficients as a function of frequency. The direct real dynamic stiffness coefficients were then fitted with a quadratic function with respect to frequency. From the curve fit, the frequency dependence was captured by including a virtual-mass matrix [M] to produce a frequency independent [K][C][M] model. The direct dynamic stiffness coefficients for the load-on-pad orientation showed significant orthotropy, while the load-between-pad did not. The load-between-pad showed slight orthotropy as load increased. Experimental cross-coupled stiffness coefficients were measured in both load orientations, but were of the same sign and significantly less than direct stiffness coefficients. In both orientations the imaginary part of the measured dynamic stiffness increased linearly with increasing frequency, allowing for frequency-independent direct damping coefficients. Rotordynamic coefficients presented were compared to predictions from two Reynolds-based models. The models showed the importance of taking into account pivot contact flexibility and different pad geometries (due to the reduction in bearing clearance during testing) in predicting rotordynamic coefficients. If either of these two inputs were incorrect, then predictions for the bearings impedance coefficients were very inaccurate.

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