CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. provisional application no. 62/622,438 filed 26 January 2018 in the United States Patent and Trademark Office, the content of which is herein incorporated by reference in its entirety.

BACKGROUND

1. Field

[0002] Aspects of the present disclosure generally relate to the technical field of journal bearings which may be utilized in connection with turbomachines, such as for example gas turbines or steam turbines. Specifically, the present disclosure relates to a sumpless high kinetic energy journal bearing housing utilized in connection with for example a gas turbine.

2. Description of the Related Art

[0003] Turbomachines with large and heavy rotors, such as for example gas turbines or steam turbines, typically use journal bearings which utilize a thin hydrodynamic oil film to maintain a gap between a rotor shaft of the turbomachine and the bearing material. Lubricating fluid, such as lube oil, is continuously fed at a high rate to maintain the oil film and to take away heat from the bearing and the shaft.

[0004] The rotor shaft imparts high rotational velocities to the oil as it passes through the bearing. Due to high kinetic energy of oil leaving the bearing, bearing housings generally have a lubrication sump, e.g. oil sump, near a bottom dead center to collect and reduce the kinetic energy of the oil. The oil sump facilitates easy drain of oil back to an oil tank. A size of the sump is determined for example by an oil flow rate in a bearing housing which itself is a function of rotor load, rotor speed and rotor temperature. In absence of an oil sump, for example in applications where there is little or no room for a large bearing housing, swirling oil in the bearing housing does not have enough time to slow down and fails to drain out from for example one or more drain pipe(s) causing flooding and leakage through oil seals. Thus, drain flow gets restricted due to multiple reasons like air pressure fluctuation, oil vortex formation, oil frothing etc.

[0005] Currently, there is no solution for gravity drained bearings with small or no oil sumps. Additional vacuum suction systems (oil scavenging) may be needed to ensure continuous drainage. Thus, there may exist a need to provide an improved journal bearing, specifically an improved journal bearing in connection with small or no oil sumps.

SUMMARY

[0006] A first aspect of the present disclosure provides a journal bearing for use in a turbomachine comprising a bearing housing configured to receive a rotor shaft, the bearing housing comprising at least one drain outlet for draining lubricating fluid utilized during rotation of the rotor shaft, and a drainage facilitation element positioned on an inner surface of the bearing housing, wherein the drainage facilitation element is configured to obstruct and redirect the lubricating fluid towards the at least one drain outlet so that the lubricating fluid drains naturally due to loss of kinetic energy in the at least one drain outlet.

[0007] A second aspect of the present disclosure provides a turbomachine comprising a journal bearing as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 depicts a general schematic of a journal bearing in a turbine mid section in accordance with an exemplary embodiment of the present disclosure.

[0009] FIG. 2 depicts a cross-sectional view through a journal bearing in accordance with an exemplary embodiment of the present disclosure. [0010] FIG. 3 depicts a schematic of an overall test rig setup for a journal bearing with measurement system and auxiliaries in accordance with an exemplary embodiment of the present disclosure.

[0011] FIG. 4 depicts a cross-sectional view of a test rig setup in accordance with an exemplary embodiment of the present disclosure.

[0012] FIG. 5 depicts a section of a three dimensional view of a vertical wall(s) bearing housing configuration in accordance with an exemplary embodiment of the present disclosure.

[0013] FIG. 6 depicts a section of a three dimensional view of a wide scoop bearing housing configuration in accordance with an exemplary embodiment of the present disclosure.

[0014] FIG. 7 depicts a section of a cross-section view of vertical symmetry liner bearing housing configuration in accordance with an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

[0015] To facilitate an understanding of embodiments, principles, and features of the present disclosure, they are explained hereinafter with reference to implementation in illustrative embodiments. In particular, they are described in the context of being a sumpless high kinetic energy journal bearing housing utilized in connection with for example turbomachines. Embodiments of the present disclosure, however, are not limited to use in the described apparatus, systems or methods.

[0016] The components and materials described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components and materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of embodiments of the present disclosure.

[0017] FIG. 1 depicts a general schematic of a journal bearing 100 in a turbine mid section in accordance with an exemplary embodiment of the present disclosure.

[0018] Bearings are used to prevent friction between parts during relative movement. The primary function of a bearing is to carry load between a rotor (shaft) and the bearing with as little wear as possible. In machinery they fall into two primary categories, anti friction or rolling element bearings and hydrodynamic journal bearings.

[0019] The present disclosure relates to hydrodynamic journal bearings used for example in turbomachines. A journal bearing assembly 100 is configured and arranged to receive a rotating shaft 130 of a gas turbine or a steam turbine. The journal bearing assembly 100 can be arranged between a compressor end 140 and a turbine end 150 of a turbomachine. The turbomachine can comprise one or multiple journal bearing assemblies 100.

[0020] It should be noted that one of ordinary skill in the art is familiar with components and function of a journal bearing. Generally, the journal bearing assembly 100 comprises an inner bearing component 110 and bearing housing 120. The inner bearing component 110 is positioned inside the bearing housing 120 and may be referred to as for example bearing liner and may comprise a steel base material overlaid with a babbitt material and bored to a circular diameter equal to a shaft diameter plus desired clearance. The inner bearing component 110 further comprises openings or cutouts, such as for scallops, to admit lubricating fluid, such as for example oil.

[0021] Further, one or more oil seals 160 are typically arranged on either side of the bearing assembly 100 to prevent leakage of the lubricating fluid, e.g. oil, out of the clearance between the shaft 130 and the housing 120 and further to prevent outside materials such as dirt from entering the bearing assembly 100.

[0022] FIG. 2 depicts a cross-sectional view through a journal bearing, such as journal bearing assembly 100, in accordance with an exemplary embodiment of the present disclosure. Journal bearing assembly 100 comprises bearing housing 120 with one or more bearing housing support struts 122. The bearing assembly 100 further comprises oil supply 170 and oil drain 180 configured to supply or drain oil to or from the bearing housing 120.

[0023] The bearing housing 120 can be considered as a small oil tank. Oil enters through the inner bearing component 110 and exits through an outlet, e.g. oil drain 180, near bottom dead center (BDC) 190 of the housing 110 where one or more pipe(s) may be connected for drainage. The bottom dead center 190 is the location where the shaft 130 rests on the bearing component 110 at zero speed.

[0024] For a bearing housing 120 configured as a regular oil tank with gravity drained oil outlet, i.e. low energy flow, a steady state oil level can be estimated analytically. In such a case the steady state oil level is proportional to an inlet flow rate and inversely proportional to a cross sectional area of an outlet drain pipe. In bearing housings 120 with traditional sumps (oil tank) there is a cavity at the BDC to collect and reduce the kinetic energy of the oil prior to its drainage.

[0025] But for high energy journal bearings with large oil flow rate and negligible or no sump, for example due to a small bearing housing diameter and/or absence of a cavity at BDC, it is difficult to analytically estimate the steady state oil level or film thickness, because the flow is a combination of highly rotating multiphase and free surface fluid. Computational fluid dynamics (CFD) models using volume of fluid (VOF) models have been utilized to solve similar problems but require a very fine mesh with several million elements.

[0026] FIG. 3 depicts a schematic of an overall test rig setup 300 for a journal bearing with measurement system and auxiliaries in accordance with an exemplary embodiment of the present disclosure.

[0027] Rig tests are generally performed to test performance of a system or a subsystem before it is put into actual operation. But when the system is not fully designed, the rig needs to have flexibility to change design features until desired results are achieved. An objective of the rig tests is to determine which design feature or combination of features would leave a lowest liquid level of lubricating fluid at a bottom of the rig (a simulated journal bearing housing) or a minimum residence volume. Residence volume is the amount of liquid instantaneously present in the chamber/housing at any time. A high residence volume leads to poor performance caused by heat generation from windage or churning. The heat must be removed to prevent oil coking and thus represents a parasitic loss to an engine, e.g. turbomachine.

[0028] A desirable bearing housing configuration is a configuration with a sump region where liquid, e.g. lubricating fluid, and gas, e.g. air or air/fuel mixture, undergo minimal mixing and from which the liquid is quickly drained out thereby minimizing the residence volume. Another key benefit of the rig tests is to be able to test sensitivity of a design to various design variables like different oil and air flows which helps designers to restrict engine operating parameters within acceptable limits and to increase reliability of the engine. It is further important that a liquid level does not reach the seals (see oil seals 160 in FIG. 1) as the liquid would leak outside of the bearing housing 120.

[0029] Test rig setup

[0030] Test rig setup 300 comprises a stationary test rig 310. In the stationary test rig 310, the lubricating fluid, e.g. oil, flowing out of a bearing is simulated by multiple nozzles and has no rotating parts. Rig components are designed to simulate the journal bearing assembly 100 with bearing housing 120 as shown in FIG. 1 and FIG. 2.

[0031] During testing, the test rig 310 is supplied with a glycerol-water mixture (representing the lubricating fluid of the bearing) from a liquid tank 312 equipped with copper coolers 314 fed with water from regular tap water supply. From the liquid tank 312, the fluid is fed to multiple nozzles of the test rig 310 by a low pressure system 316 comprising a multistage centrifugal pump (variable flow) and a high pressure system 318 comprising multiple pump units that were switched on and off as per flow requirements.

[0032] Drain fluid from the rig 310 drains through drain pipes 320, 322 into a receiving tank 324 and is pumped back to the liquid tank 312 by a return pump 330. The receiving tank comprises volumes 324A and 324B, wherein volume 324A is used for drainage with dummy oil supply pipe and volume 324B is used for drainage without dummy oil supply pipe. Bottom valves 332 between the volumes 324A and 324B provide flexibility and may be closed to measure a difference in flow between the drain volumes 324A, 324B. The setup 300 further comprises buffer air supply 340 with a maximum supply rate capability of 400 grams/second. Air is entering circular manifolds in end walls of the test rig 310 and then into the bearing housing volume through seals designed as actual oil seals of a turbine. The air is sucked from the receiving tank 324 to the atmosphere by a vacuum fan 342 mimicking a similar operation in an actual gas turbine.

[0033] The setup 300 further comprises multiple valves, such as for example safety valves 350, 352, 354 and other system valves 356, 358, 360, 362, 364, 366 arranged at appropriate/predefmed locations for example for fluid control purposes. Further, multiple mass flow meters 370, 372, 374 are arranged and utilized to measure fluid flow including lubricating fluid flow and buffer air flow.

[0034] FIG. 4 depicts a cross-sectional view of a test rig setup in accordance with an exemplary embodiment of the present disclosure. The test rig setup comprises test rig 400 manufactured with a combination of conventional and additive manufacturing methods. The test rig 400 comprises an inner (metal) part 410, that distributes liquid (simulating lubricating fluid) to a plurality of nozzles 420, 422. The inner part 410 sits in a printed plastic part. A circular outer mid-section 412 of the printed plastic part comprises a tube with inner diameter matching the journal bearing diameter (D). The printed plastic part further comprises end walls 414, 416 representing walls of a bearing housing. The test rig 400 further comprises radially adjustable seals 460 and air supplies 470. [0035] Fluid selection and nozzle arrangement

[0036] Viscosity, density and surface tension of the lubricating fluid, e.g. oil, are key drivers which determine drainage characteristics of the lubricating fluid. As noted before, the bearing lubricating fluid is simulated by a mixture of water and glycerin. A percentage of glycerin was altered to match viscosity, density and surface tension of oil at different operating temperatures. Fluid outflow from the bearing (test rig 400) is created by high pressure nozzles 420 directing fluid at an appropriate angle. An exit oil flow rate from the actual bearing are estimated using calculations. Specifically, axial and tangential components are calculated, and an initial oil flow path is estimated considering an impact of oil on a rotor shaft shoulder and subsequent flow acceleration. Thus, the simulated bearing comprises two sets of nozzles: 10 (ten) high pressure (HP) nozzles 420 and 10 (ten) low pressure (LP) nozzles 422 on each side of the simulated bearing 400, in total 40 nozzles 420, 422. The HP nozzles 420 have a tangential outflow, while the LP nozzles 422 have a small axial component. A low pressure oil supply pipe 419 (see low pressure pump 316 in FIG. 3) is connected to turbine side (TS) and high pressure oil supply pipe 418 (see high pressure pumps 318 in FIG. 3) are connected to the compressor side (CS). The oil supply pipes 418, 419 provide a bearing fluid supply via fluid supply line 402 to the multiple nozzles 420, 422 arranged at the inner part 410. The nozzles 420, 422 have a flat spray with a small broom angle. Numbers/parameters of nozzles 420, 422 and broom angle are chosen to ensure that all lubricating fluid low is provided to the bearing housing and wets bearing housing wall(s) 414, 416 uniformly.

[0037] Estimation of flow velocity and angle

[0038] An axial component of the lubricating fluid (oil) leaving tilting pads of the bearing (test rig 400), for example four tilting pads, is estimated using known calculations in journal bearing data books providing values for Sommerfield number S and side flow non-dimensional number Qs. Using bearing parameters (rotor diameter D, angular velocity co, machined radial clearance Cp and bearing length L), a side flow rate qs is calculated by: Qs = qs / (D/2 * co * Cp * L).

[0039] A side area per tilting pad Aps is calculated by:

Aps = Cp * D/2 * (p * b / 180),

wherein b is a pad angle.

[0040] Axial velocity Va is calculated by:

Va = (qs / (2*4)) / Aps.

[0041] Tangential velocity Vt is approximated to be same as rotor shaft tangential speed:

Vt = D/2 * co.

[0042] Nozzle angle Q is estimated using the following ratio of axial velocity Va and tangential velocity Vt:

0 = Va / Vt.

[0043] FIG. 5, FIG. 6 and FIG. 7 depict sections of three dimensional views of multiple bearing housing configurations in accordance with exemplary embodiments of the present disclosure.

[0044] Bearing housing configurations

[0045] Different bearing housing configurations are provided in order to capture the lubricating fluid and to assist the lubricating fluid in draining into drain pipes. The different configurations are tested using the test rig setup (see FIG. 3 and FIG. 4). An objective of the configurations or concepts is to block and redirect high energy fluid flow (of the lubricating fluid) in the bearing housing towards drain pipes. [0046] Blocker configurations

[0047] An example configuration of a bearing housing comprises a hood blocker component, wherein the lubricating fluid is trapped near the oil drain using a flat plate protruding horizontally from 7 o'clock position obstructing the flow below it (see FIG. 2 with bearing housing 120 and oil drain 180). With the hood blocker component (horizontal flat plate), a lubricating fluid flow is stopped just downstream of the drain pipe so that the lubricating fluid may naturally drain in the drain pipe due to loss of kinetic energy. In another embodiment, the hood blocker configuration is enhanced by a curved vertical wall. This configuration comprises a horizontal flat plate and a curved vertical wall near the oil drain. Utilizing the flat plate and curved vertical wall, the lubricating fluid is not only blocked but also guided towards the oil drain holes/cavities using the curved vertical wall(s).

[0048] FIG. 5 depicts a section of a three dimensional view of a vertical wall(s) bearing housing configuration in accordance with an exemplary embodiment of the present disclosure.

[0049] Vertical walls configuration

[0050] In accordance with an exemplary embodiment of the present disclosure, the bearing housing configuration comprises bearing housing 500 comprising a drainage facilitation element, the drainage facilitation element comprising a plurality of vertical walls 520, 522 positioned on an inner bearing component 510. The inner bearing component 510 comprises a circular shape and is positioned inside the bearing housing 500 and may be referred to as for example bearing liner and bored to a circular diameter equal to a shaft diameter plus desired clearance (see also for example FIG. 1, component 110). The inner bearing component 510 further comprises openings or cutouts for lubricating fluid supply and drain holes 582, 584 configured to drain lubricating fluid from the bearing housing 500.

[0051] According to an exemplary embodiment, the drainage facilitation element comprising the vertical walls 520, 522 are arranged or located adjacent to the drain holes 582, 584, specifically on outer sides of the drain holes 582, 584. In this specific example, two vertical walls 520, 522 are provided and located adjacent to each drain hole 582, 584. The walls 520, 524 are parallel to an axial direction of a rotor shaft to be positioned inside the bearing component 510. The axial direction is represented by arrow 530.

[0052] A fluid flow of the lubricating fluid, e.g. oil, is obstructed by the vertical walls 520, 522 on both sides of the drain holes/pipes 582, 584. A small gap 590, which can be for example approximately 5mm, is left between each wall 520, 522 and the bearing housing's side walls to allow a limited amount of oil to flow down and get trapped near a bottom and drain in the drain holes 582, 584. Using this concept, a sump 592 is created between the vertical walls 520, 522 thereby trying to mimic a traditional bearing housing.

[0053] FIG. 6 depicts a section of a three dimensional view of a wide scoop bearing housing configuration in accordance with an exemplary embodiment of the present disclosure.

[0054] Wide scoop configuration

[0055] In accordance with an exemplary embodiment of the present disclosure, the bearing housing configuration comprises bearing housing 600 comprising a drainage facilitation element, the drainage facilitation element comprising a scoop element 620 positioned on an inner bearing component 610. The scoop element 620 is also referred to as wide scoop and is situated right above one of drain holes 682, 684, specifically drain hole 682, in direction of lubricating fluid flow. The fluid flow is obstructed by the scoop element 620 configured as scoop shaped wide blocker.

[0056] During testing of this configuration, multiple variations of the scoop with different heights were tested. The scoop concept was bom and optimized based on the concepts above, because simple blocking and encapsulation of the oil flow did not produce the desired results (the failures may be attributed to the high kinetic energy and the volume flow rate and the position of the drains). The scoop element 620 is designed to drain a required amount of lubricating fluid into the drain hole 682 by a combination of encapsulation and flow redirection. Height H and width W of the scoop component 620 are critical in determining a volume of the fluid that is to be encapsulated and drained. In an exemplary embodiment, an optimized width W to height H ratio of the scoop component 620 is 4 (W/H = 4). For example, when a width W of the scoop element 620 is approximately 10 cm, a height 624 is approximately 2.5 cm. This ratio ensures adequate drainage while not overwhelming the scoop element 620.

[0057] FIG. 7 depicts a section of a cross-section view of vertical symmetry liner bearing housing configuration in accordance with an exemplary embodiment of the present disclosure. The view and components of FIG. 7 essentially correspond to the view and components of FIG. 4 showing the test rig 400.

[0058] Vertical symmetry liner configuration

[0059] The configuration comprises bearing housing 700 and inner component 710, that distributes liquid (simulating lubricating fluid) to a plurality of nozzles 720, 722. The bearing housing 700 comprises a circular outer mid-section 712 comprising a tube with inner diameter matching the journal bearing diameter (D). The housing 700 further comprises end walls 714, 716.

[0060] In an exemplary embodiment, the bearing housing 700 comprises a drainage facilitation element, the drainage facilitation element comprising a circular liner 730 attached or positioned inside the bearing housing 700 on an outer section of end wall 716. The liner 730 provides a‘vertical’ symmetry of both opposite end walls 714, 716 of the housing 700. Essentially, the liner 730 fills out a cavity (see cavity below end wall 416 in FIG. 4) thereby providing the symmetry of the end walls 714, 716.

[0061] Design variables

[0062] In addition to the different bearing housing configurations (see FIG. 5, FIG. 6 and FIG. 7), other design variables are investigated, such as for example drain pipe(s) diameter, lubricating fluid supply temperature, nozzle’s broom angle, fluid's swirl speed and fluid's flow rate increase.

[0063] Drain pipe(s) diameter: As part of sensitivity testing, drain pipe(s) with different inner diameter(s) were tested. A reduced pipe diameter made the lubrication fluid (oil) block an outlet for the air flow and a pressure inside the rig (simulated bearing housing) increased subsequently reducing the fluid supply to the bearing.

[0064] Lubrication fluid supply temperature variation: Oil temperature variations were simulated by changing fluid viscosities which was achieved by changing a percentage of glycerin in the mixture. The amount of fluid inside the bearing house was visually larger for hotter and colder simulated oil cases compared with a standard temperature simulated oil case.

[0065] Nozzle's broom angle: Tests with zero broom angle (a straight jet of liquid) and wider angles were performed. The zero broom angle test had a higher velocity when hitting the wall, making the liquid splashing around more at the wall. No other major difference was observed. The larger broom angle test looked a lot like the 15° spray. Based on these tests the 15° nozzle angle was chosen for all locations.

[0066] Fluid's swirl speed variation: The swirl speed is the average tangential speed of the fluid flow spinning within the bearing chamber. Larger nozzles were deployed which reduced the velocity to nearly half keeping the same volumetric flow rate. This resulted in a marked reduction in the resident swirling fluid volume.

[0067] Fluid's flow rate increase: The flow rate was nearly doubled keeping the swirl speed nearly the same (marginal increase). The result was similar to reduced drain pipe size, i.e. the air flow got blocked and the pressure inside the rig increased subsequently reducing the fluid supply to the bearing. This is due to the fact the bearing housing doesn't have a direct air venting system and the drain pipes are used to vent the air in addition to draining the oil. [0068] Film thickness assessment

[0069] As discussed earlier, an objective of the testing is to find out which design feature or combination of features may lead to the minimum residence volume in the journal bearing. A predictor of residence volume is film thickness along the bearing housing walls. Large film thickness may cause entrainment onto the shaft which may lead to increased leakage and increased power loss (excessive oil heat-up). Therefore, a maximum allowable oil film thickness on the housing walls may avoid oil entrainment onto shaft using the following Taylor-Couette flow equation with stationary outer cylinder: wherein:

Rs is a shaft outer radius,

R _H is a housing inner radius,

R is a local radius,

co is a shaft angular velocity,

u _f is a tangential velocity of gas (air) in chamber.

[0070] Average minimum air velocity in the housing was estimated at ~ 20m/s which resulted in maximum allowable film thickness to chamber height ratio of ~ 0.2.

[0071] Testing results

[0072] Testing proved that drainage of low volume high kinetic energy bearing housings is extremely difficult because the flow is highly three-dimensional and flows from each side of the bearing housing strongly interact. Further, testing of different bearing housing configurations suggests that certain design features improve the bearing housing drainage performance better than others. The vertical walls configuration (see FIG. 5), wide scoop configuration (see FIG. 6) and vertical symmetry liner configuration (see FIG. 7) assisted the most drainage using the described test rig setup (see FIG. 3 and FIG. 4)