Low pressure drop radial inflow air-oil separating arrangement and separator employed therein

An air-oil separating arrangement in a gas turbine engine having a sump with a rotatable annular wall structure includes an annular section of the sump wall structure having a plurality of circumferentially spaced air metering orifices defined therein, and an air-oil separator having a circular plate attached to the annular section of the sump wall structure and rotatable therewith. The circular plate has a pair of opposite faces and a plurality of separator fins attached to and extending from one face of the plate. The separator fins are circumferentially spaced from one another and extend radially from the center of the plate and define spaces therebetween which are in flow communication with the orifices through the annular section of the sump wall structure. The engine also includes a center vent passage aligned with the center of the separator plate such that when oil particle-laden pressurized air flows from the sump through the metering orifices and radially inwardly through the radial spaces between the separator fins into the center vent passage, the oil particles carried by the air will be impacted by the fins and centrifugally ejected in an outward radial direction back outwardly through the metering orifices and thereby separated from the air flow through the separator and returned to the sump.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to gas turbine engines and, more 
particularly, to a lower pressure drop radial inflow air-oil separating 
arrangement in the engine and an air-oil separator employed in the 
arrangement. 
2. Description of the Prior Art 
Gas turbine engines typically include a core engine having a compressor for 
compressing air entering the core engine, a combustor where fuel is mixed 
with the compressed air and then burned to create a high energy gas 
stream, and a first or high pressure turbine which extracts energy from 
the gas stream to drive the compressor. In aircraft turbofan engines, a 
second turbine or low pressure turbine located downstream from the core 
engine extracts more energy from the gas stream for driving a fan. The fan 
provides the main propulsive thrust generated by the engine. 
Bearings are used in the engine to accurately locate and rotatably mount 
rotors with respect to stators in the compressor and high and low pressure 
turbines of the engine. The temperature capability of the bearings is, 
however, quite limited compared to the temperatures of many areas of the 
engine flowpath through the compressor, combustor and high and low 
pressure turbines, which flowpath areas are located in close proximity to 
the bearing. For example, bearings can operate up to 600.degree. F., 
whereas compressor exit temperature often exceeds 1100.degree. F. and 
turbine inlet temperature often exceeds 2000.degree. F. 
In order to prevent overheating of the bearings, lubricating oil and seals 
must be provided to prevent the hot air in the engine flowpath from 
reaching the bearing sumps, and lubricating oil flows must be sufficient 
to carry away heat generated internally by the bearings because of their 
high relative speed of rotation. Non-contacting or labyrinth seals are one 
type of seals that are employed at the sites of many bearings. A labyrinth 
seal includes one or more pointed teeth usually mounted on a rotating seal 
member and running in close proximity to a cylindrical or stepped 
cylindrical stationary stator with air or gas flow between the two 
members. 
Labyrinth seals require air pressurization to prevent leaking of oil 
through the seals. Pressurization of the seals, in turn, pressurizes the 
oil sump. However, the sump pressure must be maintained at a proper 
balance for the lubricating system to function properly. On the one hand, 
if the sump is over-pressurized, oil will be forced out through the oil 
seals. On the other hand, if the sump is under-pressurized, the 
performance of the oil pump of the lubricating system will be adversely 
affected. 
The pressurized air must be vented from the sump in a controlled manner in 
order to maintain sump pressure at the proper balance. However, the 
pressurized air is mixed with particles of the oil in the sump. Therefore, 
the oil must be separated from the air before venting of the air in order 
to minimize the amount of oil carried overboard by the venting air. An 
air-oil separator device is typically employed between the oil sump and a 
center vent passage through the inner drive shaft of the engine to achieve 
the desired separation. Air-oil separator devices utilized heretofore have 
several shortcomings which adversely affect seal effectiveness and oil 
consumption. 
One prior art air-oil separator device employs a concentric arrangement of 
cylindrical plates having staggered air holes which define a tortuous path 
for the flow of air through the apparatus. This separator device produces 
a large pressure drop which contributes to the sump pressure being too 
high and causes oil to backflow the sump labyrinth seals. One reason for 
the high pressure drop is the free vortex flow of the air once it exits 
the separator device and travels to the center vent passage. Another 
reason for the high pressure drop is that the tortuous path of air flow 
through the separator devices produces a non-determinable pressure drop 
which cannot be controlled. 
Another prior art air-oil separator device employs a series of aligned air 
flow orifices of different diameters which makes it impossible to predict 
the pressure drop across the device and thus to determine the efficiency 
of the separator device. Also, the air flow has a higher pressure drop due 
to combined forced and free vortex flow. 
Consequently, a need exists for improvement of air-oil separation in a 
manner that will increase separator efficiency and improve sump pressure 
control. 
SUMMARY OF THE INVENTION 
The present invention provides an air-oil separator and separating 
arrangement designed to satisfy the aforementioned need. The air-oil 
separating arrangement of the present invention provides radial inflow of 
the air-oil mixture and produces a low pressure drop between the oil sump 
and center vent passage of the engine in such manner that separator 
efficiency is substantially uncoupled from sump pressure control. 
Accordingly, the present invention is directed to an air-oil separator for 
an air-oil separating arrangement in a gas turbine engine. The air-oil 
separator comprises a circular plate having a center and a pair of 
opposite faces, and a plurality of separator fins attached to and 
extending from one of the opposite faces of the plate. The separator fins 
are spaced circumferentially from one another and extend radially from the 
center of the plate. The separator further comprises a removal hub 
connected to the center of the plate and extending outwardly from the one 
face of the plate. The separator fins have generally planar configurations 
and extend substantially perpendicular to the one face of the plate. The 
separator fins also have opposite outer and inner edges. The inner edges 
are radially spaced from one another relative to the center of the plate 
and also spaced from the hub of the plate. 
The present invention is also directed to an air-oil separating arrangement 
in a gas turbine engine having a sump with a rotatable annular wall 
structure. The air-oil separating arrangement comprises an annular section 
of the sump wall structure having a plurality of circumferentially spaced 
air metering orifices defined therein, and an air-oil separator as defined 
above. The circular plate of the separator is attached to the annular 
section of the sump wall structure such that the separator is rotatable 
therewith. The separator fins of the separator being spaced 
circumferentially from one another and extending radially from the hub of 
the plate define spaces therebetween which are in flow communication with 
the metering orifices through the annular section of the sump wall 
structure. 
The engine also includes a center vent passage aligned with the center hub 
of separator plate. The center vent passage is vented to ambient to 
establish a lower air pressure in the center vent passage than in the sump 
such that oil particle-laden pressurized air in the sump will flow from 
the sump through the metering orifices radially inwardly toward the center 
of the separator plate through the radial spaces between the separator 
fins and therefrom into the center vent passage. As the oil particles 
carried by the air traverse through the radial spaces between the 
separator fins, they will be impacted by the separator fins of the 
rotatable separator and centrifugally ejected in an outward radial 
direction back outwardly through the metering orifices and thereby 
separated from the air flow through the separator and returned to the 
sump. 
These and other features and advantages and attainments of the present 
invention will become apparent to those skilled in the art upon a reading 
of the following detailed description when taken in conjunction with the 
drawings wherein there is shown and described an illustrative embodiment 
of the invention.

DETAILED DESCRIPTION OF THE INVENTION 
In the following description, like reference characters designate like or 
corresponding parts throughout the several views. Also in the following 
description, it is to be understood that such terms as "forward", 
"rearward", "left", "right", "upwardly", "downwardly", and the like, are 
words of convenience and are not to be construed as limiting terms. 
Gas Turbine Engine 
Referring now to the drawings, and particularly to FIG. 1, there is 
illustrated a gas turbine engine, generally designated 10, in which is 
incorporated an air-oil separating arrangement 12 of the present 
invention, as shown in detail in FIGS. 2-4. The engine 10 has a 
longitudinal center line or axis A and an outer stationary annular casing 
14 disposed concentrically about and coaxially along the axis A. The 
engine 10 includes a core gas generator engine 16 which is composed of a 
multi-stage compressor 18, a combustor 20, and a high pressure turbine 22, 
either single or multiple stage, all arranged coaxially about the 
longitudinal axis or center line A of the engine 10 in a serial, axial 
flow relationship. An annular outer drive shaft 24 fixedly interconnects 
the compressor 18 and high pressure turbine 22. 
The core engine 16 is effective for generating combustion gases. 
Pressurized air from the compressor 18 is mixed with fuel in the combustor 
20 and ignited, thereby generating combustion gases. Some work is 
extracted from these gases by the high pressure turbine 22 which drives 
the compressor 18. The remainder of the combustion gases are discharged 
from the core engine 16 into a low pressure power turbine 26. 
The low pressure turbine 26 includes an annular drum rotor 28 and a stator 
30. The rotor 28 is rotatably mounted by suitable rear bearings 32 and 
includes a plurality of turbine blade rows 34 extending radially outwardly 
therefrom and axially spaced. The stator 30 is disposed radially outwardly 
of the rotor 28 and has a plurality of stator vane rows 36 fixedly 
attached to and extending radially inwardly from the outer stationary 
casing 14. The stator vane rows 36 are axially spaced so as to alternate 
with the turbine blade rows 34. The rotor 28 is fixedly attached to an 
inner drive shaft 38 being mounted for rotation relative to the outer 
drive shaft 24 via differential bearings 40 and via suitable forward 
bearings 42 interconnected to the outer stationary casing 14. 
The inner drive shaft 38, in turn, rotatably drives a forward fan 
disk/booster rotor 44 which forms part of a booster compressor 46. The 
rotor 44 also supports forward fan blades 48 that are housed within a 
nacelle 50 supported about the stationary outer casing 14 by a plurality 
of struts 52. The booster compressor 46 is comprised of a plurality of 
booster blade rows 54 fixedly attached to and extending radially outwardly 
from the booster rotor 44 for rotation therewith and a plurality of 
booster stator vane rows 56 fixedly attached to and extending radially 
inwardly from the stationary outer casing 14. Both the booster blade rows 
54 and the stator vane rows 56 are axially spaced and so arranged to 
alternate with one another. 
Air-Oil Separating Arrangement of Present Invention 
Referring now to FIG. 2, there is illustrated the region of the gas turbine 
engine 10 where a conventional bearing sump 58 is defined about the 
forward bearings 42 of the inner drive shaft 38 and where the air-oil 
separating arrangement 12 of the present invention is located in 
communication with the bearing oil sump 58. The bearing sump 58 is 
generally defined by an outer annular structure 60 which is interconnected 
to the outer casing 14 and an inner annular structure 62 which rigidly 
interconnects the forward end of the inner drive shaft 38 to the forward 
fan disk/booster rotor 44. The inner annular structure 62 of the bearing 
sump 58 being connected with an inner annular race 42A of the forward 
bearings 42 rotates with the inner drive shaft 38 relative to the 
stationarily mounted outer annular structure 60 of the bearing sump 58 
being connected to an outer annular race 42B of the forward bearings 42. 
Conventional labyrinth air and oil seals 64, 66 are provided adjacent to 
the forward bearings 42 and between the forward ends of the relatively 
rotating outer and inner annular structures 60, 62 to seal the forward end 
of the bearing sump 58. Oil is pumped to the forward bearings 42 and 
therefore into the sump 58 through an oil supply conduit 68. Pressurized 
air is injected to the labyrinth air seal 64 through an air supply conduit 
70 in order to prevent oil from leaking through the labyrinth oil seal 66. 
A portion of the injected pressurized air which enters the bearing sump 58 
must be vented from the sump in a controlled manner in order to maintain 
sump pressure at a proper balance. However, the pressurized air becomes 
mixed with particles of the oil in the sump 58. Therefore, the particles 
of oil must be separated from the air before venting of the air in order 
to minimize the amount of oil carried overboard by the venting air. The 
air-oil separating arrangement 12 of the present invention is provided in 
communication with the bearing sump 58 for this purpose. 
Basically, the air-oil separating arrangement 12 is comprised of an air-oil 
separator 72 and an annular section 74 of the inner annular structure 62 
of the bearing sump 58 as best seen in FIGS. 2 and 3. Now referring to 
FIGS. 2-4, the air-oil separator 72 includes a circular plate 76 having a 
center C and a pair of opposite faces 76A, 76B, a plurality of separator 
fins 78 attached to and extending from one of the opposite faces 76A of 
the plate 76, and a removal hub 80 connected to the center C of the plate 
76 and extending outwardly from the one face 76A of the plate 76. The hub 
80 is internally threaded nd provides means for removing the separator 72 
from the annular structure 62 after it has been detached. The separator 
fins 78 are spaced circumferentially from one another and extend radially 
from the center C of the plate 76. The separator fins 78 have generally 
planar configurations and extend substantially perpendicular from the one 
face 76A of the plate 76. The separator fins 78 also have opposite outer 
and inner edges 78A, 78B and are so positioned such that adjacent fins 78 
converge from their outer edges 78A toward their inner edges 78B. The 
inner edges 78B are radially spaced from one another relative to the 
center C of the plate 76 and also spaced outwardly from the hub 80 of the 
plate 76. The outer and inner edges 78A, 78B of each separator fin 78 
extend to a radial edge 78C which is located at a greater height or 
distance from the plate 76 at the inner edge 78B than at the outer edge 
78A of the separator fin 78 so as to maintain a constant area. 
As best seen in FIG. 3, the annular section 74 of the inner annular 
structure 62 of the bearing sump 58 includes a plurality of tabs 82 
attached to the sump annular section 74 and extending radially inwardly a 
short distance therefrom and a plurality of circumferentially spaced air 
metering orifices 84 defined through the annular section 74. Bolts 86 
(only shown in FIG. 2) are installed through aligned holes 88 in the tabs 
82 and the peripheral portion of the plate 76 of the separator 72 to 
removably attach the separator 72 across a center vent passage 90 of the 
inner drive shaft 38. As best seen in FIG. 3, the metering orifices 84 are 
spaced from one another and are in flow communication with the narrow 
spaces 92 extending radially between the adjacent separator fins 78. 
Although the metering orifices 84 are shown as being aligned with the 
narrow spaces 92 extending between the adjacent separator fins 78, they 
need not be so aligned. Furthermore, the number of metering orifices 84 
need not equal the number of spaces 92. 
Since the center vent passage 90 is vented to the ambient environment, the 
air pressure is lower in the center vent passage 90 than in the bearing 
sump 58. Therefore, some of the oil particle-laden pressurized air in the 
sum 58 will flow through the annular row of metering orifices 84 radially 
inwardly toward the hub 80 of the separator 72 through the radial spaces 
92 between the separator fins 78 of the separator 72 and therefrom into 
the center vent passage 90. However, the spacing of the separator fins 78 
from one another is such that before a given oil particle carried by the 
air traverses the distance from the outer edge 78A to inner edge 78B of 
the fins 78 it will be impacted by the fin 78 and centrifugally ejected in 
an outward radial direction back outwardly through the metering orifice 
84. In such manner, the oil particles are separated from the air flow 
through the separator 72 and returned to the bearing sump 58. 
The advantages provided by the air-oil separating apparatus 12 are as 
follows: (1) a lower pressure drop separator for a given diameter due to 
totally forced vortex air flow and the separator fins extending down to 
the center vent passage diameter with no axial excursions producing 
minimum pressure losses; (2) a non-enclosed separator (no back cover 
plate) giving a lighter weight design, an internally inspectable part, and 
also a part that can be compression molded; (3) more predictable sump 
pressure due to standard orifice and forced vortex pressure losses which 
results in reduction in development time of components; and (4) uncoupling 
of sump pressure control and separator efficiency by making sump pressure 
mainly a function of the metering orifices and by making the separator 
efficiency mainly a function of the separator fins. 
It is thought that the present invention and many of its attendant 
advantages will be understood from the foregoing description and it will 
be apparent that various changes may be made in the form, construction and 
arrangement of the parts thereof without departing from the spirit and 
scope of the invention or sacrificing all of its material advantages, the 
forms hereinbefore described being merely preferred or exemplary 
embodiments thereof.