Patent Application
20160237844
1. Field of the Invention
The present disclosure relates to vanes, and more particularly to variable vanes such as in variable vane systems.
2. Description of Related Art
Traditionally, a gas turbine engine for an aircraft includes multiple stages of variable vanes to condition and guide airflow through the compressor and/or turbine sections. Variable vanes are configured to be pivoted about their vane axes in order to optimize airflow characteristics for various operating conditions.
Variable vanes can be connected to a synchronization ring (sync ring), each by a respective vane arm connected to the stem of the vane. The sync ring can drive each vane counter-clockwise and/or clockwise around its respective longitudinal axis in order to set the optimal vane stage angle for a particular operating condition. Each vane stem is operatively connected to a respective platform. Between each vane stem and its respective platform is a bearing and/or a bushing. High engine temperatures and pressures can present challenges for bearings and bushings. It is expected that this will be exacerbated due to the ongoing trend of designing gas turbine engines to operate at even higher temperatures and pressures.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved variable vane systems.
A variable vane system includes an outer platform defining a centerline axis, an inner platform radially inward from the outer platform with respect to the centerline axis and a vane extending between the inner and outer platforms defining a vane axis. The vane has an inner vane stem and an opposed outer vane stem. The inner vane stem is engaged with the inner platform and the outer vane stem is engaged with the outer platform. The system includes a bearing gap defined radially with respect to the vane axis between each of the inner and outer platforms and respective vane stems for allowing the vane to rotate about the vane axis for varying angle of attack. The system includes a pressurized air supply inlet in fluid communication with at least one of the bearing gaps to form a stem air bearing to intermittently float at least one of the vane stems for controlled rotation about the vane axis.
In accordance with certain embodiments, an internal cavity of the vane is in fluid communication with the pressurized air supply inlet. The bearing gap can be a stem bearing gap. The internal cavity of the vane can be in fluid communication with at least one of the bearing gaps to supply pressurized air thereto. At least one of the vane stems can include an aperture in fluid communication between the internal cavity of the vane and one of the bearing gaps to supply pressurized air from the internal cavity of the vane to the bearing gap. The vane can include a platform portion radially outward with respect to the centerline axis from the outer platform. A platform bearing gap can be defined radially with respect to the centerline axis between the platform portion and the outer platform.
The internal cavity of the vane can be in fluid communication with the platform bearing gap to supply pressurized air thereto to form a platform air bearing to intermittently float at least one of the vane stems for controlled rotation of the vane about the vane axis. The platform portion can include an aperture in fluid communication between the internal cavity of the vane and the platform bearing gap to supply pressurized air to the platform bearing gap. The system can include a seal between a radially inboard surface of the platform portion of the vane and a radially outboard surface of the outer platform.
In accordance with another aspect, at least one of the inner platform or the outer platform can include a platform cavity in fluid communication with the pressurized air supply inlet. The platform cavity can be in fluid communication with at least one of the bearing gaps to supply pressurized air thereto. The platform cavity can include an aperture in fluid communication between the platform cavity and at least one of the bearing gaps to supply pressurized air from the platform cavity to the bearing gap. The platform cavity can be in fluid communication with the platform bearing gap to supply pressurized air thereto to form a platform air bearing to intermittently float at least one of the vane stems for controlled rotation of the vane about the vane axis. The platform cavity can include a radially outboard facing aperture to supply pressurized air to the platform bearing gap.
A gas turbine engine includes a pressurized air source and a variable vane system in fluid communication with the pressurized air source. The pressurized air supply inlet of the variable vane system is in fluid communication with the pressurized air source and at least one of the bearing gaps to provide pressurized air to the bearing gap to form a stem air bearing to intermittently float at least one of the vane stems for controlled rotation of the vane about the vane axis.
It is contemplated that the gas turbine engine can include a heat exchanger fluidly connected between the pressurized air source and the variable vane system to change the temperature of the air from the pressurized air source before entering the variable vane system. The gas turbine engine can include a booster pump in fluid communication between the pressurized air source and the variable vane system to increase air pressure in the pressurized air supply inlet. The gas turbine engine can include a valve in fluid communication between the pressurized air source and the variable vane system to control airflow from the pressurized air source to the variable vane system. The pressurized air source can be at least one of diverted turbine cooling air, a compressor air bleed, a pressurized air tank, or outside ambient air.
These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings.
So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein:
Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a cross-sectional view of an exemplary embodiment of a gas turbine engine constructed in accordance with the disclosure is shown in
As shown in
With continued reference to
The low speed spool 30 generally includes an inner shaft 40 that interconnects a fan 42, a low pressure compressor 44 and a low pressure turbine 46. The inner shaft 40 is connected to the fan 42 through a speed change mechanism, which in exemplary gas turbine engine 20 is illustrated as a geared architecture 48 to drive the fan 42 at a lower speed than the low speed spool 30. The high speed spool 32 includes an outer shaft 50 that interconnects a high pressure compressor 52 and high pressure turbine 54. A combustor 56 is arranged in exemplary gas turbine 20 between the high pressure compressor 52 and the high pressure turbine 54. A mid-turbine frame 58 of the engine static structure 36 is arranged generally between the high pressure turbine 54 and the low pressure turbine 46. Mid-turbine frame 58 includes an inner case 59 and supports bearing systems 38 in the turbine section 28. The inner shaft 40 and the outer shaft 50 are concentric and rotate via bearing systems 38 about the engine central longitudinal axis A which is collinear with their longitudinal axes. While described herein as a geared fan, embodiments of the present disclosure can be used in non-geared fan engines as well.
The core airflow is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed and burned with fuel in the combustor 56, then expanded through the high pressure turbine 54 and low pressure turbine 46. The mid-turbine frame 58 includes airfoils 60 which are in the core airflow path C. It is also possible that the airfoils 60 can be variable vanes, similar to vanes 106 of variable vane stage 47, shown in
The engine 20 in one example is a high-bypass geared aircraft engine. In a further example, the engine 20 bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture 48 is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine 46 has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine 20 bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor 44, and the low pressure turbine 46 has a pressure ratio that is greater than about five (5:1). Low pressure turbine 46 pressure ratio is pressure measured prior to inlet of low pressure turbine 46 as related to the pressure at the outlet of the low pressure turbine 46 prior to an exhaust nozzle. The geared architecture 48 may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans.
A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section 22 of the engine 20 is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/(518.7° R)]0.5. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second.
Now with reference to
Vane 106 has opposed inner and outer vane stems 108 both engaged with respective inner and outer platforms 104 and 102, respectively, operatively connecting inner and outer platforms 104 and 102, respectively, to respective ends of vane 106. System 100 includes bearing gaps 110, e.g. stem bearing gaps, defined radially with respect to vane axis X between the inner and outer platforms, 104 and 102, respectively, and respective vane stems 108 for allowing vane 106 to rotate about vane axis X for varying angle of attack with respect to core airflow path C, shown in
An internal cavity 114 of vane 106 is in fluid communication with pressurized air supply inlet 112. Internal cavity 114 of vane 106 is in fluid communication with stem bearing gaps 110 to supply pressurized air thereto. Vane stems 108 include apertures 116 in fluid communication between internal cavity 114 of vane 106 and stem bearing gap 110 to supply pressurized air from internal cavity 114 of vane 106 to stem bearing gap 110. Variable vane system 100 is able to change the angle of attack and throat area of vane 106, for example, a first stage high pressure turbine (HPT) vane, while still maintaining high-temperature resistance and providing low-friction for ease of articulation. Those skilled in the art will readily appreciate that while vane system 100 is shown without bushings, bushings can be used in conjunction with vane system 100, for example circumferentially disposed around each vane stem 108. It is also contemplated that rolling element bearings can be used in conjunction with the bearing gaps described above. Rotation of vane 106 in variable vane system 100 is driven by actuation arm 130. Actuation arm 130 is part of an actuation mechanism.
With continued reference to
With reference now to
With continued reference to
During operation, a signal is sent indicating a need to change vane angle of attack of a vane, e.g. vane 106 and/or 206. Upon receiving the signal, pressurized air is directed to vane stems, e.g. a vane stem 108 and/or 208, of the vane. The release of pressurized air through apertures, e.g. apertures 116, 122, 216 and/or 222, to bearing gaps 110, 120, 210 and/or 220, provides a brief cushion of air within bearing gaps creating a momentary hydrostatic (air) bearing to lift vane stems, e.g. vane stems 108 and/or 208, off their respective resting points. Once lifted, the vane stems and the vane pivot under minimal load to the actuation mechanism, a portion of which is shown in
While variable vane systems 100 and 200 are described herein as having pressurized air supplied to bearing gaps 110, 120, 210 and/or 220 only when vane rotation is desired, it is also contemplated that pressurized air could also be provided to clear vane stems surfaces, e.g. surfaces of vane stems 108 and/or 208, and any bushing surfaces of foreign material, to provide cooling, and/or overcome any bonding that may have occurred during the period when the vane was in a stationary position. To the same end, the pressurized air can be provided intermittently for the purpose of maintaining reduced friction even when the vane is not being actuated.
As shown in
With continued reference to
Those skilled in the art will readily appreciate that the intermittency of the use of the pressurized air, described above, reduces the load on pressurized air source 300. It is also contemplated that pressurized air source 300 can be used to drive the actuation mechanism, discussed above, serving a dual purpose and further maximizing weight savings. Variable vane system 200, and variable vane system 100 can be used in the same vane or in the same vane stage. For example, vane cavity 114 and platform cavity 214 can be used in combination with one another within a single vane, and/or vanes having vane cavity 114, platform cavity 2014, or both, can be used in combination throughout a vane stage.
The methods and systems of the present disclosure, as described above and shown in the drawings, provide for variable vane systems with superior properties including improved temperature resistance and reduced weight. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and scope of the subject disclosure.
