The Influence of Injection Pockets on the Performance of Tilting-Pad Thrust Bearings—Part II: Comparison Between Theory and Experiment

[+] Author and Article Information
Niels Heinrichson

Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmarknhe@mek.dtu.dk

Axel Fuerst

Hydrogenerator Technology Centre, Alstom(Switzerland) Ltd., CH-5242 Birr, Switzerlandaxel.fuerst@power.alstom.com

Ilmar Ferreira Santos

Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmarkifs@mek.dtu.dk

J. Tribol 129(4), 904-912 (Jun 19, 2007) (9 pages) doi:10.1115/1.2768610 History: Received June 14, 2006; Revised June 19, 2007

This is Part II of a two-part series of papers describing the effects of high-pressure injection pockets on the operating conditions of tilting-pad thrust bearings. The paper has two main objectives. One is an experimental investigation of the influence of an oil injection pocket on the pressure distribution and oil film thickness. Two situations are analyzed: (i) when the high-pressure oil injection is turned off and (ii) when the high-pressure injection is turned on. The other objective is to validate a numerical model with respect to its ability to predict the influence of such a pocket (with and without oil injection) on the pressure distribution and oil film thickness. Measurements of the distribution of pressure and oil film thickness are presented for tilting-pad thrust bearing pads of 100cm2 surface area. Two pads are measured in a laboratory test rig at loads of 1.5MPa and 4.0MPa and velocities of up to 33ms. One pad has a plain surface. The other pad has a conical injection pocket at the pivot point and a leading-edge taper. The measurements are compared to theoretical values obtained using a three-dimensional thermoelastohydrodynamic (TEHD) numerical model. At the low load, the theoretical pressure distribution corresponds well with the measured values for both pads, although the influence of the pocket is slightly underestimated. At the high load, large discrepancies exist for the pad with an injection pocket. It is argued that the discrepancies are due mainly to geometric inaccuracies of the collar surface, although they may to some extent be due to the simplifications employed in a Reynolds equation description of the pocket flow. The measured and theoretical values of oil film thickness compare well at low loads and velocities. At high loads and velocities, discrepancies grow to up to 25%. This is due to the accuracy of the measurements. When using hydrostatic jacking the model predicts the start-up behavior well.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 3

Left: pad shown in a dismounted pad holder. Right: view of the trailing edge. The distance sensors and the oil injection pipe are seen.

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Figure 4

Pictures of the tested pads taken after the measurements. Measurements and calculations are stated for the two first pads (a) and (b). The pad in (c) is used only for the comparison of pressure profiles in Fig. 8.

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Figure 5

Top: example of trailing-edge film thickness measurements (sensors h3 and h4). There are 2048 sampling points for one turn of the rotor. The position for the pressure measurements and the position for calibration of the distance sensors are stated. Bottom: distance from collar to sensor h4 at 143 evenly spaced points on the collar circumference. The pad is pressed against the collar. Offset measurement 123 is used for calibration of the distance sensors.

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Figure 6

Illustration of the forces acting on the pad. The pressure distribution in the oil film and the Hertzian pressure distribution between the spherical support and the pad are indicated. The centers of the pressure distributions are shown as Fz. The centers are offset by xoffset. A resulting moment Mres in the pivot is therefore necessary.

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Figure 7

Comparison of measured (red lines) and calculated (blue lines) pressure profiles for selected operating conditions. The line legend for all figures is stated in (a). (a), (b): The plain pad operated at 15kN, 600rpm. Calculations in (a) are performed with nominal operating conditions. In (b), the pivot point is moved and the load reduced to give force and moment equilibrium with the measurements. The input conditions in (c)–(i) are similarly adjusted. (c)–(f): pad with injection pocket but no oil injection operated at two different speeds (400rpm and 1000rpm) and two different loads (15kN and 40kN). (g)–(i): pad with injection pocket operated with oil injected at a flow rate of 400cm3∕min. The load is 15kN, and the speed is varied (20rpm,200rpm, and 400rpm). The pocket stretches from approximately θ=10deg to approximately θ=14deg on the curves for p2 and p3.

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Figure 8

Comparison of measured pressure profiles for pad without taper or injection pocket (dashed lines), pad with taper but no injection pocket (solid lines), and pad with taper and injection pocket (dotted lines) operating without oil injection at 39kN, 400rpm. Pictures of the three pads are shown in Fig. 4.

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Figure 10

Input data for the calculations in which the pivot point and the load are adjusted for moment and force equilibrium with the measurements. Nomenclature is defined in (d). (a) illustrates the loads used when the nominal condition is a load of 15kN. Data for various collar speeds and three bearing configurations are given: pad without pocket ×, pad with pocket but without high-pressure injection ◻, and pad with pocket and 400cm3∕min oil injection 엯. (b) illustrates the same data for a nominal load of 40kN. (c) presents the pivot offsets resulting in moment equilibrium with the measurements. (d) shows the leading-edge pressures determined from measurements and used in the calculations. (e) shows the measured collar temperatures used as a boundary condition in the calculations.

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Figure 12

Measured (×, 엯, +, and ◇) and calculated (lines) liftoff oil film thickness for different loads and zero velocity. The calculated values are obtained at a speed of 0.01rpm. Eight measurements are performed at each load at various positions of the collar.

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Figure 1

Operational principle: collar diameter is 0.72m

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Figure 2

Left: position of sensors and the dimensions of the pad with an injection pocket are shown. All edges have a 1mm chamfer. Top right: positions of the pressure sensors in the collar. They are positioned ∼0.1mm below the surface. Bottom right: cross section of the injection pocket. A brass insert provides the injection piping.

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Figure 9

Comparison of measured and calculated oil film thicknesses (full lines: measurements; dashed lines: calculations using nominal values of Fz and θpiv; dotted lines: the pivot point is moved and the load reduced to give force and moment equilibrium with the measurements). (a)–(c) show leading-edge film thicknesses. (d)–(f) present trailing-edge values. (a) and (d): Results for the plain pad. (b) and (e): results for the pad with a pocket. The oil injection is turned off. (c) and (f): Results with oil injected at a flow rate of 400cm3∕min. ×, 엯, +, and ◇ represent measured values. Additionally, measurements are performed with intervals of 10rpm from the minimum possible of 20–120rpm for the pad operated with oil injection.

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Figure 11

Comparison of measured oil film thicknesses with (solid lines) and without (dashed lines) 400cm3∕min oil injection. Left: leading-edge film thicknesses. Right: trailing-edge values.




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