Patent Application
20130052021
The present disclosure is directed to an asymmetrical rotor assembly for use in a gas turbine engine.
Rotor wakes and bow waves impinge on the vanes of a stator in a compressor stage of a gas turbine engine. These rotor wakes and bow waves can result in unsteady forcing and high cycle fatigue response. When these unsteady forces couple with the stator structural modeshapes, modal work is performed and vibratory stresses result. The vibratory stresses can be significant enough to result in high cycle fatigue fractures of the vanes in the compressor stators.
In the past, quadrant mistuned rotor assemblies have been proposed to reduce vibratory stresses. These quadrant mistuned rotor assemblies had blades with different thicknesses in different quadrants of the rotor assembly. The mistuned rotor assemblies have been proposed to reduce the structural and aerodynamic coupling of the rotor airfoils within the stage.
It is desirable for the compressor section of a gas turbine engine to utilize one or more rotor assemblies which reduce the vibratory stresses on the stator vanes and thus reduce high cycle fatigue risk.
In accordance with the present disclosure, there is provided a gas turbine engine which broadly comprises a section having at least two spaced apart stator assemblies and an asymmetrical rotor assembly positioned between said spaced apart stator assemblies, wherein the asymmetrical rotor assembly has an array of airfoils which is asymmetric about at least one diameter of the rotor assembly.
Further in accordance with the present disclosure, a rotor assembly for use in a gas turbine engine is provided which broadly comprises a rotor array which is asymmetric about at least one diameter of the rotor assembly.
Other details of the rotor asymmetry for stator stress reduction are set forth in the following detailed description and the accompanying drawings, wherein like reference numerals depict like elements.
Referring to
The compressor 14 may be a single unit or may be sectioned into a low-pressure compressor 24 and a high-pressure compressor 26. The compressor may also be an intermediate compressor of a three-spool engine. Any or all of the compressors, including the low-pressure compressor 24, the high-pressure compressor 26 and/or the intermediate compressor (not shown), may include a plurality of spaced apart stator assemblies 28 and rotor assemblies 30. The stator assemblies 28 may include a plurality of segments, each having one or more stator vanes disposed between an inner platform and an optional outer platform. The segments of each stator assembly 28 collectively form an annular structure that is disposed adjacent a rotor assembly 30. If desired, each stator assembly 28 may be asymmetrical wherein the number of blades on one half of the stator assembly is different in number from the number of blades on a second half of the stator assembly 28. Also, if desired, the vanes of the stator assembly 28 may be cantilevered structures (in which case the outer platform is not present).
Each rotor assembly 30 includes a rotor array formed by a plurality of blades 32 and a disk 34 rotatable around the axially extending centerline 22 of the engine 10. The disk 34 includes a hub 36, a rim 38 defining a circumference 50 for the rotor assembly 30, and a web 40 extending there between. The blades 32 are attached to and extend radially out from the rim 38. Each blade 32 includes a tip 42 that is disposed at a tip angle relative to the axial centerline 22 that is greater than zero. The blade tip angle for each blade 32 in a particular rotor assembly 30 is the same for each blade 32 within that rotor assembly 30. Different rotor assemblies 30 however may have different blade tip angles. The rotor assemblies 30, for example within the low-pressure compressor 24, may be mechanically attached to one another and therefore rotate together. The rotor assemblies 30 within the high-pressure compressor 26 may also be mechanically attached to one another and therefore rotate together.
A shaft connects the compressor 14 to the turbine 18. In those embodiments that include a low-pressure compressor 24 and a high-pressure compressor 26, the high-pressure compressor 26 is connected by a first shaft 44 (“HP shaft”) to a high-pressure turbine section 46 and the low-pressure compressor 24 is connected by a second shaft (“LP shaft”) to a low-pressure turbine section 49.
Referring now to
The asymmetric rotor assemblies 30′ described herein may be located along the length of the compressor section 26. If desired, a plurality of asymmetric rotor assemblies 30′ may be located within the compressor section 26. Each asymmetric rotor assembly 30′ may be located between two spaced apart stator assemblies 28. As discussed above, the stator assemblies 28 may each be asymmetrical stator assemblies if desired.
The use of asymmetrical rotor assemblies such as that described above, particularly in combination with asymmetrical stator assemblies, change the airfoil blade-to-blade spacing around the stage to break up the relatively strong forcing associated with symmetric rotor assemblies. An advantage of a reduced level of forcing is that it may allow the rotor assembly to be positioned closer to the vanes of the stator assemblies. As a result, overall engine length, cost and weight may be reduced.
Further, the asymmetrical rotor assemblies reduce the rotor driven stresses on adjacent stator vanes. Stress reduction is accomplished by not allowing vibrational energy in the stator assembly to build up and sustain itself over one complete revolution of the rotor assembly. This is due to the asymmetric spacing splitting excitation frequencies. Separating the frequencies distributes the energy in multiple response peaks, with a lower overall stress than in the single frequency symmetric spacing configuration. Further, by reducing the stress on the stator vanes, it is possible to reduce the weight of the stator vanes.
While the asymmetric rotor assemblies set forth herein have been described as being used in a compressor section of a jet engine, it should be recognized that they also could be used in a turbine section of the gas turbine engine or could be used in turbine machinery in general.
There has been described herein a rotor asymmetry. While the rotor asymmetry has been described in the context of specific embodiments thereof, other unforeseen alternatives, modifications, and variations may become apparent to those skilled in the art having read the foregoing description. Accordingly, it is intended to embrace those alternatives, modifications, and variations as fall within the broad scope of the appended claims.
