Assessment of Porous Type Gas Bearings: Measurements of Bearing Performance and Rotor Vibrations

Gas bearings are an attractive means of load support for rotating machinery due to their low mechanical power losses and dispensing of expensive lubrication systems. A subset of gas bearing technology, porous type gas bearings utilize a porous material as a means of feeding externally pressurized gas (typically air) to the bearing clearance region. When compared to typical orifice type hydrostatic bearings, porous bearings distribute pressurized gas more uniformly into the film clearance, thus resulting in a higher load capacity for similar flow rates [1]. The majority of the literature on porous type gas bearings focuses on the numerical evaluation of cylindrical bushings, yet experimental data on their performance is scant. As a follow up to Ref. [2], the paper presents an analysis of measurements of flow, drag torque and rotordynamic response of a large (100 mm OD, ∼275 N) rotor supported on two tilting pad (five-pad) porous journal bearings (specific load∼19 kPa). Measurements of air mass flow into the bearings, with and without the rotor in place, show that the film clearance offers little restriction. The mass flow rate is proportional to the supply pressure and lead to an estimated permeability coefficient. In operation with various levels of supply pressure and with the rotor spinning to 8 krpm (133 Hz, surface speed ∼42 m/s), several rotordynamic response tests (masses up to 6.9 gram) show the rotor amplitude of synchronous response is proportional to the mass imbalance; hence demonstrating the system is linear. Finally, rotor speed coast down tests from 8 krpm show that the bearings offer little drag friction; and increasing the supply pressure gives to lesser drag. The measurements verify the pair of gas bearings support effectively the rigid rotor with little expense in mass flow rate delivered to them. Most importantly, while operating at 10 krpm with a large added imbalance, the system survived a seizure event with little damage to the rotor and bearings, both restored to a near pristine condition after a simple cleaning procedure.

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Behavior of Thermal Effects and Velocity-Slip on Performance of Externally Pressurized Porous Incompressible Gas Thrust Bearing

Journal of Applied Mechanics ◽

10.1115/1.3424577 ◽

1979 ◽

Vol 46 (2) ◽

pp. 465-468 ◽

Cited By ~ 3

Author(s):

V. K. Kapur ◽

J. S. Yadav

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Thermal Effects ◽

Thrust Bearing ◽

Load Capacity ◽

Velocity Slip ◽

Experimental Results ◽

Slip Condition ◽

Static Stiffness

In the present analysis, the interactions of thermal effects and velocity slip on the performance of externally pressurized porous incompressible gas thrust bearing have been studied. Numerical results for load capacity, mass flow rate, and static stiffness have been obtained and their behavior is illustrated in figures. The results for slip as well as no-slip condition have also been compared with the experimental results of Gargiulo and Gilmour [7].

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Study of Hybrid Lubrication at the Tooth Contact of a Wormgear Transmission: Part 2—Results and Discussion

Journal of Tribology ◽

10.1115/1.2834173 ◽

1998 ◽

Vol 120 (1) ◽

pp. 112-118

Author(s):

Qin Yuan ◽

D. C. Sun ◽

D. E. Brewe

Keyword(s):

Temperature Distribution ◽

Film Thickness ◽

Numerical Solution ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Power Loss ◽

Oil Film ◽

Supply Pressure ◽

Transmission Part

Part 2 begins by describing the numerical solution procedures of the hybrid lubrication problem. Results of the computation are then presented that include the detailed pressure and temperature distribution in the oil film, the required supply pressure for maintaining the prescribed minimum oil film thickness, the fluid friction acting on the worm coil surface, the mass flow rate of supply oil, and the power loss associated with the restrictor flow. The feasibility of the hydrostatically lubricated wormgear transmission is discussed in light of these results.

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Permeability and Inertial Coefficients of Porous Media for Air Bearing Feeding Systems

Journal of Tribology ◽

10.1115/1.2768068 ◽

2007 ◽

Vol 129 (4) ◽

pp. 705-711 ◽

Cited By ~ 16

Author(s):

G. Belforte ◽

T. Raparelli ◽

V. Viktorov ◽

A. Trivella

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Darcy’S Law ◽

Darcy's Law ◽

Flow Rates ◽

Mass Flow Rates ◽

Thrust Pad ◽

Gas Bearing ◽

Forchheimer’S Law

In porous resistances, Darcy’s law provides a good approximation of mass flow rate when the differences between upstream and downstream pressures are sufficiently small. In this range, the mass flow rates are proportional to the porous resistance’s permeability. For gas bearings, the pressure difference is normally higher, and it is known experimentally that the mass flow rates are lower than would result from Darcy’s law. Forchheimer’s law adds an inertial term to Darcy’s law and, when an appropriate coefficient is selected for this term, provides a good approximation of flow rates for the same applications even with the highest pressure differences. This paper presents an experimental and theoretical investigation of porous resistances used in gas bearing and thrust pad supply systems. The porous resistances considered in the investigation were made by sintering bronze powders with different grain sizes to produce cylindrical inserts that can be installed in bearing supply devices. The paper describes the test setup and experimental results obtained for: (i) mass flow rate through single porous resistances at different upstream and downstream pressures and (ii) mass flow rate and pressure distribution on a pneumatic pad featuring the same porous resistances. The theoretical permeability of the chosen porous resistances was calculated, and the results from setup (i) were then used to obtain experimental permeability and to determine the inertial coefficients. The results, which are expressed as a function of the Reynolds number, confirmed the validity of using Forchheimer’s law. The mass flow rates from setup (ii) were compared to those from setup (i) at the same pressure differentials across the resistance.

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2D Parametric Study Using CFD of a Circulation Control Inlet Guide Vane

Volume 6: Turbo Expo 2007, Parts A and B ◽

10.1115/gt2007-28058 ◽

2007 ◽

Cited By ~ 2

Author(s):

H. E. Hill ◽

W. F. Ng ◽

P. P. Vlachos ◽

S. A. Guillot ◽

D. Car

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Pressure Ratio ◽

Operating Conditions ◽

Circulation Control ◽

Trailing Edge ◽

Pressure Losses ◽

Supply Pressure ◽

Edge Radius

Circulation control inlet guide vanes (IGVs) may provide significant benefits over current IGVs that employ mechanical means for flow turning. This paper presents the results of a two-dimensional computational study on a circulation control IGV that takes advantage of the Coanda effect for flow vectoring. The IGV in this study is an uncambered airfoil that alters circulation around itself by means of a Coanda jet that exhausts along the IGV’s trailing edge surface. The IGV is designed for an axial inlet flow at a Mach number of 0.54 and an exit flow angle of 11 degrees. These conditions were selected to match the operating conditions of the 90% span section of the IGV of the TESCOM compressor rig at the Compressor Aero Research Laboratory (CARL) located at Wright-Patterson AFB, the hardware that is being used as the baseline in this study. The goal of the optimization was to determine the optimal jet height, trailing edge radius, and supply pressure that would meet the design criteria while minimizing the mass flow rate and pressure losses. The optimal geometry that was able to meet the design requirements had a jet height of h/Cn = 0.0057 and a trailing edge Radius R/Cn = 0.16. This geometry needed a jet to inflow total pressure ratio of 1.8 to meet the exit turning angle requirement. At this supply pressure ratio the mass flow rate required by the flow control system was 0.71 percent of the total mass flow rate through the engine. The optimal circulation control IGV had slightly lower pressure losses when compared with a reference cambered IGV.

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Feeding System of Aerostatic Bearings With Porous Media

Volume 3: Dynamic Systems and Controls, Symposium on Design and Analysis of Advanced Structures, and Tribology ◽

10.1115/esda2006-95810 ◽

2006 ◽

Cited By ~ 1

Author(s):

G. Belforte ◽

T. Raparelli ◽

V. Viktorov ◽

A. Trivella

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Darcy’S Law ◽

Darcy's Law ◽

Flow Rates ◽

Gas Bearings ◽

Mass Flow Rates ◽

Set Up ◽

Forchheimer’S Law

In porous resistances, Darcy’s law provides a good approximation of mass flow rate when the differences between upstream and downstream pressures are sufficiently small. In this range, the mass flow rates are proportional to the porous resistance’s permeability. For gas bearings, the pressure difference is normally higher, and it is known experimentally that the mass flow rates are lower than would result from Darcy’s law. Forchheimer’s law adds an inertial term to Darcy’s law and, when an appropriate coefficient is selected for this term, provides a good approximation of flow rates for the same applications even with the highest pressure differences. This paper presents an experimental and theoretical investigation of porous resistances used in gas bearing supply systems. Cylindrical sintered bronze inserts featuring lengths, diameters and particle sizes commonly used in gas bearings and thrust pads were examined. The paper describes the test set-up and experimental results obtained for: a) Mass flow rate through single porous resistances at different upstream and downstream pressures; and b) Mass flow rate and pressure distribution on a pneumatic pad featuring the same porous resistances. The theoretical permeability of the chosen porous resistances was calculated, and the results from set-up a) were then used to obtain experimental permeability and to determine the inertial coefficients. The results, which are expressed as a function of the Reynolds number, confirmed the validity of using Forchheimer’s law. The mass flow rates from set-up b) were compared with those from set-up a) at the same pressure differentials across the insert.

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Magnetogasdynamic thrust bearing with an axial pinch

Journal of Fluid Mechanics ◽

10.1017/s0022112069002527 ◽

1969 ◽

Vol 38 (4) ◽

pp. 673-677 ◽

Cited By ~ 7

Author(s):

G. Ramanaiah

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Thrust Bearing ◽

Load Capacity ◽

Axial Current ◽

Pinch Effect ◽

Electrically Conducting ◽

Compressible Lubricant

An analysis of a hydrostatic thrust bearing with electrically conducting compressible lubricant under an axial-current-induced pinch is presented. It is shown that the load capacity of the bearing can be increased by the pinch effect and the magnitude of the pinch effect depends on the mass flow rate. It is also shown that a load proportional to the square of the axial current can be sustained even when there is no flow or external pressurization.

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Investigation into gas lubrication performance of porous gas bearing considering velocity slip boundary condition

Friction ◽

10.1007/s40544-021-0503-7 ◽

2021 ◽

Author(s):

Xiangbo Zhang ◽

Shuiting Ding ◽

Farong Du ◽

Fenzhu Ji ◽

Zheng Xu ◽

...

Keyword(s):

Mass Flow Rate ◽

Porous Layer ◽

Mass Flow ◽

Flow Rate ◽

Load Capacity ◽

Velocity Slip ◽

Slip Boundary ◽

Lubrication Performance ◽

Gas Lubrication ◽

Simulation Results

AbstractPorous gas bearings (PGBs) have a proactive application in aerospace and turbomachinery. This study investigates the gas lubrication performance of a PGB with the condition of velocity slip boundary (VSB) owing to the high Knudsen number in the gas film. The Darcy-Forchheimer laws and modified Navier-Stokes equations were adopted to describe the gas flow in the porous layer and gas film region, respectively. An improved bearing experimental platform was established to verify the accuracy of the derived theory and the reliability of the numerical analysis. The effects of various parameters on the pressure distribution, flow cycle, load capacity, mass flow rate, and velocity profile are demonstrated and discussed. The results show that the gas can flow in both directions, from the porous layer to the gas film region, or in reverse. The load capacity of the PGB increases with an increase in speed and inlet pressure and decreases with an increase in permeability. The mass flow rate increases as the inlet pressure and permeability increase. Furthermore, the simulation results using VSB are in agreement with the experimental results, with an average error of 3.4%, which indicates that the model using VSB achieves a high accuracy. The simulation results ignoring the VSB overrate the load capacity by 16.42% and undervalue the mass flow rate by 11.29%. This study may aid in understanding the gas lubrication mechanism in PGBs and the development of novel gas lubricants.

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A Self-Starting Hydrodynamic Gas Bearing

Journal of Engineering for Industry ◽

10.1115/1.3428265 ◽

1972 ◽

Vol 94 (3) ◽

pp. 876-882

Author(s):

D. Molnar ◽

T. Ranov

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

The Self ◽

Air Supply ◽

Gas Bearing

An experimental self-starting hydrodynamic gas bearing was designed, built, and tested. This bearing operates on the principle that the bearing is started and stopped hydrostatically by means of an air supply which is generated by the bearing itself. For this purpose, a portion of the self-starting bearing is executed as a herringbone grooved bearing, which performs as a pump, charging a reservoir during hydrodynamic operation of the bearing. The reservoir air supply generated by the herringbone bearing is used for hydrostatic operation of the bearing during starts and stops. Starting and stopping of the experimental bearing was demonstrated using the air supply generated by the herringbone bearing. An equation was derived for the mass flow rate of the herringbone bearing pump.

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