US20180080450A1 - Flutter avoidance through control of texture and modulus of elasticity in adjacent fan blades - Google Patents
Flutter avoidance through control of texture and modulus of elasticity in adjacent fan blades Download PDFInfo
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- US20180080450A1 US20180080450A1 US15/269,540 US201615269540A US2018080450A1 US 20180080450 A1 US20180080450 A1 US 20180080450A1 US 201615269540 A US201615269540 A US 201615269540A US 2018080450 A1 US2018080450 A1 US 2018080450A1
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- fan
- blades
- natural frequency
- blade type
- disk
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/02—Selection of particular materials
- F04D29/023—Selection of particular materials especially adapted for elastic fluid pumps
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D19/00—Axial-flow pumps
- F04D19/002—Axial flow fans
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/26—Rotors specially for elastic fluids
- F04D29/32—Rotors specially for elastic fluids for axial flow pumps
- F04D29/321—Rotors specially for elastic fluids for axial flow pumps for axial flow compressors
- F04D29/324—Blades
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/26—Rotors specially for elastic fluids
- F04D29/32—Rotors specially for elastic fluids for axial flow pumps
- F04D29/325—Rotors specially for elastic fluids for axial flow pumps for axial flow fans
- F04D29/327—Rotors specially for elastic fluids for axial flow pumps for axial flow fans with non identical blades
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/26—Rotors specially for elastic fluids
- F04D29/32—Rotors specially for elastic fluids for axial flow pumps
- F04D29/38—Blades
- F04D29/388—Blades characterised by construction
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/66—Combating cavitation, whirls, noise, vibration or the like; Balancing
- F04D29/661—Combating cavitation, whirls, noise, vibration or the like; Balancing especially adapted for elastic fluid pumps
- F04D29/666—Combating cavitation, whirls, noise, vibration or the like; Balancing especially adapted for elastic fluid pumps by means of rotor construction or layout, e.g. unequal distribution of blades or vanes
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/66—Combating cavitation, whirls, noise, vibration or the like; Balancing
- F04D29/661—Combating cavitation, whirls, noise, vibration or the like; Balancing especially adapted for elastic fluid pumps
- F04D29/668—Combating cavitation, whirls, noise, vibration or the like; Balancing especially adapted for elastic fluid pumps damping or preventing mechanical vibrations
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
- F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
- F05D2300/00—Materials; Properties thereof
- F05D2300/60—Properties or characteristics given to material by treatment or manufacturing
- F05D2300/605—Crystalline
Definitions
- the present disclosure generally relates to fan blade systems for gas turbine engines. More particularly, but not exclusively, the present disclosure relates to configurations and orientations of fan blade texture relative to low pressure fans of turbofan engines.
- fan blade systems employ various geometries that redirect airflow or redistribute weight to reduce flutter.
- fan blade systems may include protruding portions that are directly bonded to the fan blade.
- protruding portions that are directly bonded to the fan blade.
- these options increase weight and decrease efficiency.
- the existing systems to mitigate the onset of fan blade flutter have various shortcomings relative to certain applications. Accordingly, there remains a need for further contributions in this area of technology.
- a fan for a turbofan engine having a plurality of blades constructed of an anisotropic material and a disk.
- the anisotropic material includes a rolled plate, sheet or forged product of some kind.
- a first blade type has a first crystallographic texture and a first natural frequency
- a second blade type has a second crystallographic texture and a second natural frequency.
- the first natural frequency is at least 4% greater than the second natural frequency
- the first blade type and the second blade type are attached to the disk in an alternating pattern to provide a flutter damping effect.
- a fan for a turbofan engine having a plurality of blades constructed of an anisotropic material attached to a disk.
- a first blade type is obtained from a round bar of an anisotropic material and has a first crystallographic texture and a first natural frequency.
- a second blade type has a second crystallographic texture and a second natural frequency. The first natural frequency is at least 4% greater than the second natural frequency, and the first blade type and the second blade type are attached to the disk in an alternating pattern to provide a flutter damping effect.
- a method for producing a fan blade system for a turbofan engine includes providing a sheet of anisotropic metal having a crystallographic texture, the sheet characterized by a rolling direction and a transverse direction orthogonal to the rolling direction. The method further includes the steps of cutting a plurality of first fan blades from the sheet along the rolling direction, cutting a plurality of second fan blades from the sheet along the transverse direction, and mounting the first fan blades and second fan blades on a disk in an alternating arrangement in order to generate alternating blades with different natural frequencies that differ by more than 4%.
- FIG. 1 depicts a side sectional view of a turbofan engine including a plurality of fan blades attached to a disk.
- FIG. 2 depicts an isometric sectional view of fan blades attached to a disk.
- FIG. 2A depicts an isometric sectional view of fan blades attached to a disk.
- FIG. 3 depicts a schematic of compressor performance having operating regions known as flutter boundaries.
- FIG. 4 depicts a schematic showing angular variation of the Young's Modulus of various anisotropic metals.
- FIG. 5 depicts a perspective view of a rolled plate having hexagonal close packed crystal units subjected to unidirectional rolling.
- FIG. 6 depicts a plan view of a plate subjected to unidirectional rolling with specimens oriented relative to the rolling direction.
- FIG. 7 depicts the principal directions of a beam to illustrate the anisotropic mechanical properties of titanium.
- FIG. 8 depicts an isometric view of a simple cantilever beam to illustrate the concept of natural frequency.
- FIG. 8A depicts an isometric view of the simple cantilever beam of FIG. 8 in motion to illustrate the concept of natural frequency.
- FIG. 8B depicts a side sectional view of the simple cantilever beam of FIG. 8 along line 8 B- 8 B.
- FIG. 9 depicts a graphical representation of the effects of fan blade mistuning.
- Turbofan engine systems have numerous performance requirements to consider including: fuel efficiency, component strength, useful life, fan bade off (FBO) containment (which may entail debris of various size and energy), noise emission, and power output.
- Turbofan engine systems include a fan system comprising a plurality of fan blades, a disk, and a barrel.
- the fan blades may be made of a metal, such as titanium, or an alloy of various metals.
- Such alloys include Ti-6Al-4V (Ti-64) and Ti-6Al-2Sn-4Zr-2Mo-0.15Si (Ti-6242).
- the disk may be made from the same material as the blades, or a different metal altogether. The design constraints for disks and blades are somewhat different.
- the disk may be made of Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) or Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17).
- the barrel may be metallic, such as aluminum, or composite, and the containment blanket is typically made of dry fabric wrap comprising an aramid fiber such as KevlarTM.
- the fan blades must have sufficient capability to withstand the structural loads that exist.
- Hollow fan blades are optimized to be light and strong and may have significant cost and weight advantages over solid fan blade systems. Those benefits would be significantly reduced if the fan blade size was increased or if additional features were added to reduce the onset of flutter or to withstand flutter loads.
- Certain fan blade systems in service have metallic plates that are mechanically attached to one or more portions of the airfoil, to mistune fan blades. Those features increase cost and weight, and may reduce the overall efficiency of a fan blade system.
- a turbofan engine 50 having a fan blade 52 , a compressor section 54 , a combustor 56 , and a turbine section 58 , which together can be used to produce a useful power.
- Air enters the turbofan engine 50 is compressed through action of the compressor 54 , mixed with a fuel, and combusted in the combustor 56 .
- the turbine 58 is arranged to receive a flow from the combustor 56 and extract useful work from the flow.
- the turbofan engine 50 may have a disk 60 attached to the fan blades 52 that transfers power from the shaft to the blades which force air into the turbine section.
- the present disclosure contemplates use in other applications that may not be aircraft related such as industrial fan applications, power generation, pumping sets, naval propulsion, weapon systems, security systems, perimeter defense/security systems, and the like known to one of ordinary skill in the art.
- FIG. 2 and FIG. 2A side sectional views of two fan blade systems 60 a, 60 b show (1) a mechanical blade-disk attachment in which the fan blade 52 a has a dovetail 62 that is retained by the disk 60 a (analogous to a tongue and groove) and (2) a blisk arrangement in which the fan blade 52 b is attached to the disk 60 b (to form a blisk) by a weld 64 rather than a dovetail 62 or other root geometry that extends into a disk 60 a.
- a schematic of compressor performance shows flutter boundaries that result in flutter.
- Flutter is an aero-structural self-excited vibration that leads to undesired instability and is common with fan blades.
- Some important forms of flutter include stall flutter, unstalled flutter, supersonic unstalled flutter, supersonic stalled flutter, trans-sonic stalled flutter, and choke flutter.
- the crystallographic texture of a material is a statistical measure of what proportion of the macroscopic material is aligned to specific crystallographic directions.
- the elastic modulus varies as a function of direction within the hexagonal closed packed directions ( FIG. 4 ).
- the formation of a crystallographic texture as a result of the thermo-mechanical processing of the titanium alloy can change the effective elastic modulus that a macroscopic component will exhibit depending upon the thermos-mechanical processing path followed.
- texture can be controlled by controlling the direction of processing such as by rolling a sheet of titanium, or forging the anisotropic material in a way that causes the material to undergo strain that results in a desired crystallographic texture.
- the angular modulus behavior of E for 0° ⁇ 90° for the group of hexagonal close-packed metals comprising: hafnium (Hf), titanium (Ti), zirconium (Zr), and scandium (Sc).
- E-behavior in FIG. 4 tends to exhibit a maximum on the (0001) basal plane (i.e. when ⁇ is zero and N coincides with the [0001] direction) and a maximum (in some cases) on the prismatic planes where ⁇ is 90°. In most cases, E tends to exhibit a minimum value between 0° ⁇ 90°. In the case of Ti, the behavior of E exhibits a maximum when ⁇ is zero and a minimum when ⁇ is 90°. This illustrates the anisotropic nature of various HCP materials with regard to modulus of elasticity.
- Extruded rods of hexagonal metals such as pure Ti often exhibit a cylindrical symmetry fiber texture where the basal plane poles (i.e. [0001]) of the grains are perpendicular to the extrusion axis. Consequently the tensile modulus along the extrusion axis should approach that of the modulus normal to the prismatic planes of the monocrystal ( ⁇ 104 GPa).
- FIG. 5 an example orientation of the HCP crystal units 68 in a Ti-6Al-4V plate 66 subjected to unidirectional rolling in a rolling (processing) direction 70 is shown.
- rolling a plate of titanium alloy will impart a texture, as the basal planes align with the transverse direction 72 , and increase the anisotropic nature of the material as illustrated further below.
- the mechanical properties of a plate of rolled titanium alloy 74 may be tested using a series of specimens 78 that are cut from the plate 74 at various angles with respect to the processing direction which is the rolling direction 76 .
- a beam 77 is shown to illustrate the hexagonal close packed 79 crystal arrangement having a texture.
- a simple cantilever beam 80 a is shown having a fixed end 82 a, attached to a support 81 a, and a free end 84 a.
- FIG. 8A illustrates a beam 80 b having a fixed end 82 b, attached to a support 81 b.
- the beam 80 b is shown oscillating at the free end 84 b to illustrate the concept of natural frequency.
- FIG. 8B shows a side sectional view of the simple cantilever beam 80 a and support 81 a of FIG. 8 along line 8 B- 8 B.
- a closed form equation for natural frequencies of a cantilever beam are:
- nf LD E ⁇ ( LD )
- nf LD 0.8935 ⁇ ⁇ ⁇ nf TD ( 3 )
- the natural frequency in the transverse direction is 11.9% larger than the natural frequency in the longitudinal direction.
- Control of the modulus of elasticity of the material used to make the fan blade allows for control the natural frequency of the individual fan blades.
- the rolled or super-plastically formed sheet material is processed by cutting out fan blade shaped layers of titanium that are sandwiched together to form a fan blade type structure.
- the layers of titanium may be heated and inflated to form a hollow fan blade using a gas.
- the fan blades 52 b are arranged in a way that alternating blades (odd) have a natural frequency of the first magnitude, and even blades have a natural frequency of the second magnitude (11.9% greater than the first magnitude).
- odd fan blades are cut along the processing or rolling direction (corresponding to 0° in FIG. 6 ) and even blades are cut along the transverse direction (90° in FIG. 6 ).
- FIG. 9 a graphical representation of the effects of fan blade mistuning (represented by application factor) according to a simulation is shown.
- Amplification factor is shown as a value between 0 and 700.
- the graph 100 shows the effects of mistuning using blades having a change in natural frequency represented by %.
- the graph 100 shows areas of low amplification factor ( 102 , 104 , 106 , 108 ), areas of medium amplification factor ( 110 , 112 , 114 , 116 , 118 ), and areas of high amplification factor ( 120 , 122 , 124 , 126 ).
- two types of blades may be installed in a number of different arrangements such as an alternating pattern (ex: 1, 2, 1, 2, etc.), a grouped pattern (ex: 1, 1, 2, 2, 1, 1, 2, 2, etc.), or a random pattern (ex: 1, 1, 2, 1, 2, 2, 2, 1, 1, 2, etc.).
- the preferred amplification factor of the fan blade should preferably be less than 200.
- Forging is another way to achieve fan blades with dissimilar texture.
- the forging process used to forge, solution heat treat, and cool adjacent blades of the same alloy in a finished component may be used to provide the mistuning needed in a fan blade design. To demonstrate this, consider two blade types forged in the following ways.
- the dies used in the forging process of the first blade type are designed so that the radial direction in the blade sees a strain that is effectively the same as the longitudinal direction (rolling direction) of a rolled plate.
- the radial direction of the first blade type will have an elastic modulus of 107 GPa in this case.
- the dies used in the forging process for the second blade type are designed so that the radial direction of the blade sees a strain that is effectively the same as the transverse direction in the rolled plate. Hence the radial direction of the second blade type will have an elastic modulus of 134 GPa in this case.
- the blade is superplastic formed (SPF) in which material flow is a result of grain boundary sliding and not plastic deformation
- the crystallographic texture of the input stock material only needs to be controlled or processed in a manner to get the desired crystallographic texture.
- SPF superplastic formed
- the intensity of the crystallographic texture in the sheet will reduce in intensity but remains essentially the same texture.
- the anisotropy in the crystallographic texture or elastic modulus following SPF will diminish but persists following the SPF process.
- all one would do is control the crystallographic of the sheet stock material and directions of the input sheet material used during the superplastic forming process (i.e. the sheet will have a pronounced crystallographic texture due to rolling along a processing direction—such as shown in FIG. 5 having a Young's modulus of 107 GPa in one direction and 134 in another orthogonal direction.
- the sheet stock is oriented with the rolling direction at 12 o'clock. These blades will have an elastic modulus of 107 GPa.
- Alloys that recrystallize which may be treated to control crystallographic texture, modulus and natural frequency include titanium alloys, nickel alloys, aluminum alloys, zinc alloys, iron alloys, cadmium alloys, beryllium alloys, zirconium alloys, and cobalt alloys.
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Abstract
Description
- The present disclosure generally relates to fan blade systems for gas turbine engines. More particularly, but not exclusively, the present disclosure relates to configurations and orientations of fan blade texture relative to low pressure fans of turbofan engines.
- Providing engine equipment to contend with potentially disruptive phenomena, such as flutter, remains an area of interest. Some fan blade systems employ various geometries that redirect airflow or redistribute weight to reduce flutter. Specifically, fan blade systems may include protruding portions that are directly bonded to the fan blade. However, these options increase weight and decrease efficiency. Overall, the existing systems to mitigate the onset of fan blade flutter have various shortcomings relative to certain applications. Accordingly, there remains a need for further contributions in this area of technology.
- According to one aspect, a fan for a turbofan engine having a plurality of blades constructed of an anisotropic material and a disk is provided. The anisotropic material includes a rolled plate, sheet or forged product of some kind. A first blade type has a first crystallographic texture and a first natural frequency, and a second blade type has a second crystallographic texture and a second natural frequency. The first natural frequency is at least 4% greater than the second natural frequency, and the first blade type and the second blade type are attached to the disk in an alternating pattern to provide a flutter damping effect.
- According to another aspect, a fan for a turbofan engine having a plurality of blades constructed of an anisotropic material attached to a disk is provided. A first blade type is obtained from a round bar of an anisotropic material and has a first crystallographic texture and a first natural frequency. A second blade type has a second crystallographic texture and a second natural frequency. The first natural frequency is at least 4% greater than the second natural frequency, and the first blade type and the second blade type are attached to the disk in an alternating pattern to provide a flutter damping effect.
- According to another aspect, a method for producing a fan blade system for a turbofan engine includes providing a sheet of anisotropic metal having a crystallographic texture, the sheet characterized by a rolling direction and a transverse direction orthogonal to the rolling direction. The method further includes the steps of cutting a plurality of first fan blades from the sheet along the rolling direction, cutting a plurality of second fan blades from the sheet along the transverse direction, and mounting the first fan blades and second fan blades on a disk in an alternating arrangement in order to generate alternating blades with different natural frequencies that differ by more than 4%.
- Other aspects and advantages will become apparent upon consideration of the following detailed description and the attached drawings wherein like numerals designate like structures throughout the specification.
-
FIG. 1 depicts a side sectional view of a turbofan engine including a plurality of fan blades attached to a disk. -
FIG. 2 depicts an isometric sectional view of fan blades attached to a disk. -
FIG. 2A depicts an isometric sectional view of fan blades attached to a disk. -
FIG. 3 depicts a schematic of compressor performance having operating regions known as flutter boundaries. -
FIG. 4 depicts a schematic showing angular variation of the Young's Modulus of various anisotropic metals. -
FIG. 5 depicts a perspective view of a rolled plate having hexagonal close packed crystal units subjected to unidirectional rolling. -
FIG. 6 depicts a plan view of a plate subjected to unidirectional rolling with specimens oriented relative to the rolling direction. -
FIG. 7 depicts the principal directions of a beam to illustrate the anisotropic mechanical properties of titanium. -
FIG. 8 depicts an isometric view of a simple cantilever beam to illustrate the concept of natural frequency. -
FIG. 8A depicts an isometric view of the simple cantilever beam ofFIG. 8 in motion to illustrate the concept of natural frequency. -
FIG. 8B depicts a side sectional view of the simple cantilever beam ofFIG. 8 alongline 8B-8B. -
FIG. 9 depicts a graphical representation of the effects of fan blade mistuning. - For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the disclosure as described herein are contemplated as would normally occur to one skilled in the art to which the disclosure relates.
- Turbofan engine systems have numerous performance requirements to consider including: fuel efficiency, component strength, useful life, fan bade off (FBO) containment (which may entail debris of various size and energy), noise emission, and power output. Turbofan engine systems include a fan system comprising a plurality of fan blades, a disk, and a barrel. The fan blades may be made of a metal, such as titanium, or an alloy of various metals. Such alloys include Ti-6Al-4V (Ti-64) and Ti-6Al-2Sn-4Zr-2Mo-0.15Si (Ti-6242). The disk may be made from the same material as the blades, or a different metal altogether. The design constraints for disks and blades are somewhat different. For example, high tensile strength and low cycle fatigue resistance are most relevant for disk materials, and high cycle fatigue and creep resistance are the main desired characteristics for blades. For example the disk may be made of Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) or Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17). The barrel may be metallic, such as aluminum, or composite, and the containment blanket is typically made of dry fabric wrap comprising an aramid fiber such as Kevlar™.
- During a flutter event, the fan blades must have sufficient capability to withstand the structural loads that exist. Hollow fan blades are optimized to be light and strong and may have significant cost and weight advantages over solid fan blade systems. Those benefits would be significantly reduced if the fan blade size was increased or if additional features were added to reduce the onset of flutter or to withstand flutter loads. Certain fan blade systems in service have metallic plates that are mechanically attached to one or more portions of the airfoil, to mistune fan blades. Those features increase cost and weight, and may reduce the overall efficiency of a fan blade system.
- Referring to
FIG. 1 , aturbofan engine 50 is illustrated having afan blade 52, acompressor section 54, acombustor 56, and aturbine section 58, which together can be used to produce a useful power. Air enters theturbofan engine 50, is compressed through action of thecompressor 54, mixed with a fuel, and combusted in thecombustor 56. Theturbine 58 is arranged to receive a flow from thecombustor 56 and extract useful work from the flow. Theturbofan engine 50 may have adisk 60 attached to thefan blades 52 that transfers power from the shaft to the blades which force air into the turbine section. Further, the present disclosure contemplates use in other applications that may not be aircraft related such as industrial fan applications, power generation, pumping sets, naval propulsion, weapon systems, security systems, perimeter defense/security systems, and the like known to one of ordinary skill in the art. - Referring to
FIG. 2 andFIG. 2A , side sectional views of twofan blade systems fan blade 52 a has adovetail 62 that is retained by thedisk 60 a (analogous to a tongue and groove) and (2) a blisk arrangement in which thefan blade 52 b is attached to thedisk 60 b (to form a blisk) by aweld 64 rather than adovetail 62 or other root geometry that extends into adisk 60 a. - Referring to
FIG. 3 , a schematic of compressor performance shows flutter boundaries that result in flutter. Flutter is an aero-structural self-excited vibration that leads to undesired instability and is common with fan blades. Some important forms of flutter include stall flutter, unstalled flutter, supersonic unstalled flutter, supersonic stalled flutter, trans-sonic stalled flutter, and choke flutter. - The crystallographic texture of a material is a statistical measure of what proportion of the macroscopic material is aligned to specific crystallographic directions. In Ti alloys the elastic modulus varies as a function of direction within the hexagonal closed packed directions (
FIG. 4 ). The formation of a crystallographic texture as a result of the thermo-mechanical processing of the titanium alloy can change the effective elastic modulus that a macroscopic component will exhibit depending upon the thermos-mechanical processing path followed. For example, texture can be controlled by controlling the direction of processing such as by rolling a sheet of titanium, or forging the anisotropic material in a way that causes the material to undergo strain that results in a desired crystallographic texture. - Many physical, chemical and mechanical properties of crystals depend on their crystalline orientations and it follows that directionality or anisotropy of these properties will result wherever a texture exists in polycrystalline materials. Some of the important examples are elastic modulus (E), Poison's ratio, strength, ductility, toughness, magnetic permeability and the energy of magnetization. These types of anisotropy apply to materials of cubic as well as lower crystal symmetry. In hexagonal metals, other properties such as thermal expansion and electrical conductivity may also show directionality.
- Referring to
FIG. 4 , the angular modulus behavior of E for 0°<θ<90° for the group of hexagonal close-packed metals comprising: hafnium (Hf), titanium (Ti), zirconium (Zr), and scandium (Sc). - As a general observation, with the exception of titanium, E-behavior in
FIG. 4 tends to exhibit a maximum on the (0001) basal plane (i.e. when θ is zero and N coincides with the [0001] direction) and a maximum (in some cases) on the prismatic planes where θ is 90°. In most cases, E tends to exhibit a minimum value between 0°<θ<90°. In the case of Ti, the behavior of E exhibits a maximum when θ is zero and a minimum when θ is 90°. This illustrates the anisotropic nature of various HCP materials with regard to modulus of elasticity. - It is possible to make some general comments on the effects of crystallographic texture on elastic anisotropy of HCP polycrystals. First, the metals with polar diagrams which most approach circularity with an anisotropy factor close to unity should experience smaller directional variations in the resulting elastic moduli, E and G, as result of metal processing. These include Mg and Y. In contrast, metals with significant departures from circularity, and anisotropy factors much less or greater than unity, are likely to experience considerable directional variations in their elastic moduli as a result of processing. In particular, these include Zn and Cd. Important metals such as Be, Ti Zr and Co are likely to experience some variations in their polycrystal moduli, but not to the same extent as Zn and Cd.
- If a strong texture is present it is possible to anticipate some elastic anisotropy effects. Extruded rods of hexagonal metals such as pure Ti often exhibit a cylindrical symmetry fiber texture where the basal plane poles (i.e. [0001]) of the grains are perpendicular to the extrusion axis. Consequently the tensile modulus along the extrusion axis should approach that of the modulus normal to the prismatic planes of the monocrystal (˜104 GPa).
- Referring to
FIG. 5 , an example orientation of theHCP crystal units 68 in a Ti-6Al-4V plate 66 subjected to unidirectional rolling in a rolling (processing)direction 70 is shown. As stated above, rolling a plate of titanium alloy will impart a texture, as the basal planes align with thetransverse direction 72, and increase the anisotropic nature of the material as illustrated further below. - Referring to
FIG. 6 , the mechanical properties of a plate of rolledtitanium alloy 74 may be tested using a series ofspecimens 78 that are cut from theplate 74 at various angles with respect to the processing direction which is the rollingdirection 76. - Referring to
FIG. 7 , abeam 77 is shown to illustrate the hexagonal close packed 79 crystal arrangement having a texture. - The orientation dependence of mechanical properties (anisotropy) is clear from the experimental data below. The mechanical properties were measured for a titanium plate illustrated in
FIG. 7 . In the longitudinal direction, tensile strength is 1027 MPa, yield strength is 952 MPa, and the elastic modulus is 107 GPa. In the transverse direction tensile strength is 1358 MPa, yield strength is 1200 MPa, and the elastic modulus is 134 GPa. In the short transverse direction tensile strength is 938 MPa, yield strength is 924 MPa, and the elastic modulus is 104 GPa. - The natural frequencies of objects are related to the elastic modulus of the material the object is constructed of and the physical geometry of the object. Referring to
FIG. 8 , asimple cantilever beam 80 a is shown having afixed end 82 a, attached to asupport 81 a, and afree end 84 a.FIG. 8A illustrates abeam 80 b having afixed end 82 b, attached to asupport 81 b. Thebeam 80 b is shown oscillating at thefree end 84 b to illustrate the concept of natural frequency.FIG. 8B shows a side sectional view of thesimple cantilever beam 80 a andsupport 81 a ofFIG. 8 alongline 8B-8B. A closed form equation for natural frequencies of a cantilever beam are: -
- The natural frequencies of two cantilever beams, one extracted from a rolled titanium plate in the longitudinal direction, the other extracted in the transverse directions can be compared as follows:
-
- Hence the natural frequency in the transverse direction is 11.9% larger than the natural frequency in the longitudinal direction. Control of the modulus of elasticity of the material used to make the fan blade allows for control the natural frequency of the individual fan blades.
- The rolled or super-plastically formed sheet material is processed by cutting out fan blade shaped layers of titanium that are sandwiched together to form a fan blade type structure. The layers of titanium may be heated and inflated to form a hollow fan blade using a gas.
- In order to mistune the
fan blisk 60 b, thefan blades 52 b are arranged in a way that alternating blades (odd) have a natural frequency of the first magnitude, and even blades have a natural frequency of the second magnitude (11.9% greater than the first magnitude). - For example, odd fan blades are cut along the processing or rolling direction (corresponding to 0° in
FIG. 6 ) and even blades are cut along the transverse direction (90° inFIG. 6 ). - Referring to
FIG. 9 , a graphical representation of the effects of fan blade mistuning (represented by application factor) according to a simulation is shown. - Amplification factor is shown as a value between 0 and 700. The
graph 100 shows the effects of mistuning using blades having a change in natural frequency represented by %. Thegraph 100 shows areas of low amplification factor (102, 104, 106, 108), areas of medium amplification factor (110, 112, 114, 116, 118), and areas of high amplification factor (120, 122, 124, 126). - If blades are arranged in an alternating fashion, only a 4% change in the natural frequency of each blade would be required to achieve acceptable level of mistuning.
- To provide a flutter dampening effect two types of blades may be installed in a number of different arrangements such as an alternating pattern (ex: 1, 2, 1, 2, etc.), a grouped pattern (ex: 1, 1, 2, 2, 1, 1, 2, 2, etc.), or a random pattern (ex: 1, 1, 2, 1, 2, 2, 2, 1, 1, 2, etc.). To provide a mistuning effect, the preferred amplification factor of the fan blade should preferably be less than 200.
- Forging is another way to achieve fan blades with dissimilar texture. The forging process used to forge, solution heat treat, and cool adjacent blades of the same alloy in a finished component may be used to provide the mistuning needed in a fan blade design. To demonstrate this, consider two blade types forged in the following ways.
- The dies used in the forging process of the first blade type are designed so that the radial direction in the blade sees a strain that is effectively the same as the longitudinal direction (rolling direction) of a rolled plate. Hence the radial direction of the first blade type will have an elastic modulus of 107 GPa in this case.
- The dies used in the forging process for the second blade type are designed so that the radial direction of the blade sees a strain that is effectively the same as the transverse direction in the rolled plate. Hence the radial direction of the second blade type will have an elastic modulus of 134 GPa in this case.
- If these two blades are the inertial welded next to one another on a blisk the two blades will have an 11% change in their natural frequencies. Based upon
FIG. 9 , the alternating arrangement of these blades will provide an aerodynamic damping effect (mistuning) that is appreciable and does not require any changes in the inertial welding process used in the fabrication of the blisk. - If the blade is superplastic formed (SPF) in which material flow is a result of grain boundary sliding and not plastic deformation, the crystallographic texture of the input stock material only needs to be controlled or processed in a manner to get the desired crystallographic texture. During superplastic forging the intensity of the crystallographic texture in the sheet will reduce in intensity but remains essentially the same texture.
- The anisotropy in the crystallographic texture or elastic modulus following SPF will diminish but persists following the SPF process. In order to utilize this anisotropy in tuning a pair of blades, all one would do is control the crystallographic of the sheet stock material and directions of the input sheet material used during the superplastic forming process (i.e. the sheet will have a pronounced crystallographic texture due to rolling along a processing direction—such as shown in
FIG. 5 having a Young's modulus of 107 GPa in one direction and 134 in another orthogonal direction. On even number blades the sheet stock is oriented with the rolling direction at 12 o'clock. These blades will have an elastic modulus of 107 GPa. On odd numbered blades the rolling direction is aligned at 3 o'clock (orthogonal to the even blades). These blades will have an elastic modulus of 134 GPa. Hence one would then expect a ˜11% difference in the fundamental frequencies of the blades. It is important to note that the texture intensity diminishes during the SPF process, as this anisotropy is what provides the anisotropy that drives the change in elastic modulus and hence fundamental frequencies of the blades. - Alloys that recrystallize which may be treated to control crystallographic texture, modulus and natural frequency include titanium alloys, nickel alloys, aluminum alloys, zinc alloys, iron alloys, cadmium alloys, beryllium alloys, zirconium alloys, and cobalt alloys.
- The embodiment(s) detailed above may be combined, in full or in part, with any alternative embodiment(s) described.
- Important advantages of a fan blade system comprising a plurality of blades comprising an anisotropic material that includes at least two blade types having different natural frequencies includes improved resistance to flutter (mistuning), reduction in the weight of the blade (when compared to other anti-flutter solutions), and increased life of the fan blade system.
- The use of the terms “a” and “an” and “the” and similar references in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the disclosure and does not pose a limitation on the scope of the disclosure unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the disclosure.
- Numerous modifications to the present disclosure will be apparent to those skilled in the art in view of the foregoing description. Various embodiments of this disclosure are described herein, including the best mode known to the inventors for carrying out the disclosure. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the disclosure.
Claims (20)
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US15/269,540 US20180080450A1 (en) | 2016-09-19 | 2016-09-19 | Flutter avoidance through control of texture and modulus of elasticity in adjacent fan blades |
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US20190107123A1 (en) * | 2017-10-06 | 2019-04-11 | Pratt & Whitney Canada Corp. | Mistuned fan for gas turbine engine |
WO2020029716A1 (en) * | 2018-08-06 | 2020-02-13 | 中国航发商用航空发动机有限责任公司 | Load reduction apparatus for fan blade-out event of aero-engine |
US10670041B2 (en) | 2016-02-19 | 2020-06-02 | Pratt & Whitney Canada Corp. | Compressor rotor for supersonic flutter and/or resonant stress mitigation |
US10689987B2 (en) | 2017-09-18 | 2020-06-23 | Pratt & Whitney Canada Corp. | Compressor rotor with coated blades |
US10865806B2 (en) | 2017-09-15 | 2020-12-15 | Pratt & Whitney Canada Corp. | Mistuned rotor for gas turbine engine |
US11002293B2 (en) | 2017-09-15 | 2021-05-11 | Pratt & Whitney Canada Corp. | Mistuned compressor rotor with hub scoops |
US12012865B2 (en) | 2021-12-29 | 2024-06-18 | Rolls-Royce North American Technologies Inc. | Tailored material property tuning for turbine engine fan blades |
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US12012865B2 (en) | 2021-12-29 | 2024-06-18 | Rolls-Royce North American Technologies Inc. | Tailored material property tuning for turbine engine fan blades |
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