Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
1999-11-18
2001-09-11
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
C415S110000, C415S111000, C415S112000, C415S175000, C415S176000, C415S177000, C415S180000, C415S229000
Reexamination Certificate
active
06286303
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to gas turbine engines and in particular to gas turbine engines that use foil or air bearings.
BACKGROUND OF THE INVENTION
Foil bearings are currently used in high-speed turbomachinery, and particularly in small air cycle machines where air is used as the lubricant. This eliminates the need for an oil lubrication system, lowering the cost and eliminating maintenance and reliability problems associated with oil systems. Compared to the small air cycle machines, gas turbine engines produce higher loads on the bearings, requiring larger bearings which generate more heat due to fluid friction. Yet the temperature limit for ‘state of the art’ foil bearings remains the same. The limit is set by the organic material used for coating the foils, which has the purpose of low rubbing friction and tolerance to foreign particles. When the temperature limit is exceeded, experience has shown that the coating material deteriorates and results in rubbing which ultimately produces bearing failure.
Foil bearings in small air cycle machines are cooled by conduction to relatively cool parts of the machine and by forcing cool air to flow through the bearings. In gas turbine engines, parts adjacent to the bearings are not always cooler than the bearings need to be. Also, the cooling air pressure required to force enough air through the bearings may be higher than the available pressure in the engine, especially during operation at high altitudes. Even in cases where enough pressure is available, this method of cooling is not very efficient because most of the air flow bypasses the bearing through the foil retaining slots. In gas turbine engines, cooling air must be used efficiently because of the associated performance penalty, which can increase engine weight and cost.
Heat generation in foil bearings is concentrated in the regions of smallest film thickness, i.e. where the air film separating the foil from the rotating component is less than 0.001 inch thick. Heat must be transferred away from these regions; radially in the case of journal bearings and axially in the case of thrust bearings. The foils are separated from the bearing housing by springs and air gaps to allow for dynamic motion and thermal expansion of the rotating part. This causes high resistance to heat transfer into the bearing housing. The rotating component, however, is always in intimate thermal contact with the air film where heat is generated by viscous shear, and the contact is distributed uniformly over the circumference due to its rotation. Therefore, to facilitate the heat transfer along the path of least resistance, i.e. into the rotating part and achieve the highest possible cooling effectiveness, the rotating part must be cooled directly.
Accordingly, a need exists for an apparatus for providing cooling air flow to the rotating components of journal and thrust foil bearings in gas turbine engines.
SUMMARY OF THE INVENTION
An object of this invention is to provide an apparatus for providing cooling air flow to the rotating components of journal and thrust foil bearings in gas turbine engine.
The present invention achieves this object by providing a gas turbine engine having a housing and a rotating assembly mounted for rotation to said housing on at least one foil journal bearing. The foil journal bearing comprises an annular bearing carrier mounted to the housing; an annular foil carrier disposed within the bearing carrier and attached thereto, a foil carrier carrying a plurality of overlapping foils; a journal mounted to the rotating assembly and having an outer surface that engage the foils; and a showerhead attached to the housing and disposed between said journal and the rotating assembly. The showerhead has an inlet for receiving cooling air and an outer wall with a plurality of orifices to create air jets for delivering impingement cooling air to the inner surface of said journal.
The engine may also have a foil thrust bearing assembly comprising a thrust disk mounted to the rotating assembly; a large thrust foil bearing on one side of the thrust disk; a small thrust foil bearing on the other side of the thrust disk; and a showerhead mounted to the housing and having a plurality of orifices to create air jets for delivering cooling air to the disk. This showerhead is shaped such that some of its jets are directed radially inward and others are directed normal to the backface of the thrust disk.
By use of these showerheads with these various foil bearing types, the rotating components of the foil bearings can be cooled without a substantial loss of performance of the gas turbine engine.
REFERENCES:
patent: 5450719 (1995-09-01), Marsh
patent: 5827040 (1998-10-01), Bosley et al.
patent: 6139269 (2000-10-01), Liang
Cunnington George R.
Larson Carl A.
Pfligler John J.
Allied Signal Inc.
Desmond, Esq. Robert
Freay Charles G.
Hayes Ed
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