AIRFOIL VIBRATION DAMPING APPARATUS

Airfoil vibration damping apparatus are disclosed. An example apparatus includes a metallic airfoil including a cavity, and a dilatant material disposed in the cavity to dampen vibrations of the metallic airfoil.

FIELD OF THE DISCLOSURE

This disclosure relates generally to aircraft engines and, more particularly, to metallic airfoil damping apparatus.

BACKGROUND

Gas turbine engines can operate in a variety of environmental conditions. As air passes through a gas turbine engine, blades in the gas turbine engine often encounter different aerodynamic loads. For example, engine blades may experience different aerodynamic loads as the gas turbine engine increases thrust, operates at higher altitudes, and/or encounters ice build-up. Such differing aerodynamic loads may cause stress on the fan blades or other engine parts.

DETAILED DESCRIPTION

Fan blades of a gas turbine engine can vibrate when the fan blades are in motion. In some instances, fan blade vibrations are caused by lubrication deterioration between the fan blade and a retaining pin that couples the fan blade to a disk. Specifically, the lubrication deterioration causes the fan blade to become stuck on the retaining pin, which prevents the fan blade from rotating about the retaining pin into a natural spinning position determined by centrifugal force as the disk rotates. That is, when the fan blade is stuck to the retaining pin, the centrifugal force may not act on a center of gravity of the fan blade, which can cause an imbalance in the load encountered by the fan blade resulting in a vibration. In other instances, the fan blade may resonate due to aerodynamic forces exciting natural frequency modes of the fan blade, which can cause high-amplitude vibrations that may cause blade damage.

In turn, the vibration of the fan blade can increase a noise output of the turbofan engine. Additionally, the vibration of the fan blade can reduce a consistency and/or an efficiency of airflow through the turbofan engine, which reduces a reliability of the turbofan engine. Moreover, when fan blades encounter high cycle fatigue as a result of vibrations, the fan blades can crack and/or fracture. Accordingly, maintenance is required for fan blades that encounter repetitive vibrations to reduce instances where the fan blades detach from an associated disk and cause further damage to the turbofan engine.

To increase the stability of the fan blades and counteract the vibrations, fan blades typically include platform dampers and/or shrouds. For instance, platform dampers can be positioned underneath blade platforms of adjacent fan blades and can press against the platforms in response to encountering a centrifugal force via a rotation of the disk. In turn, the platform damper can create friction when the blade platforms move relative to each other, which dampens vibrations at the platforms. However, platform dampers can be less effective in blades that have a reduced weight as the centrifugal force encountered by the associated platform is reduced, which reduces friction against the platform damper.

In some instances, shrouds can be at a tip of the blade (e.g., a tip-shroud) or at a partial span between a hub of the blade and the tip (e.g., a part-span shroud). Partial span and tip shrouds contact adjacent blades and provide damping when the shrouds rub against each other. However, shrouds obstruct a flow path between adjacent fan blades, which reduces a mass flow rate between the fan blades and, in turn, reduces a thrust produced by the turbofan engine. Tip-shrouds need a large tip fillet to reduce stress concentrations, which creates tip losses as geometries of the tip shrouds can reduce an efficiency of the airflow through the turbine engine.

Examples disclosed herein provide airfoil vibration damping apparatus. The airfoil vibration damping apparatus includes a dilatant material (e.g., a shear-thickening fluid) or a low modulus material disposed in a cavity of an airfoil to dampen vibrations of the airfoil. Specifically, the airfoil encounters shear stresses in response to vibrations, which causes the dilatant material to thicken and, in turn, increase a stiffness of the airfoil. Moreover, in response to thickening, the dilatant material exerts a force against an interior surface of the cavity that counteracts the vibrations and reduces a magnitude of the shear stresses encountered by the airfoil.

In some examples, the airfoil includes cells (e.g., sub-cavities) to contain the dilatant material. In some examples, the cells span throughout the cavity of the airfoil. In some examples, the cells span across a surface of the cavity. In some examples, the cells span across a portion of the surface of the cavity that encounters increased shear stresses when the airfoil encounters unsteady aerodynamic loads. In some examples, the dilatant material is disposed in one or more of the cells.

In some examples, the airfoil includes one or more lattice structures, and/or baffles in the cavity to direct flow of the dilatant material. In some examples, the lattice structure(s) and/or the baffles increase the shear stresses encountered by the dilatant material and, thus, increase stabilizing forces provided by the dilatant material when the airfoil encounters vibrations. In some examples, the lattice structure(s) and/or the baffles increase shear stresses encountered by the dilatant material in certain areas of the cavity of the airfoil. As such, the lattice structures and/or the baffles can cause the dilatant material to have an increased thickness and, thus, provide increased vibration attenuation to a portion of the airfoil that encounters vibrations of greater magnitudes.

In certain examples, a wear-resistant coating surrounds the dilatant material to minimize or otherwise reduce wear encountered by the airfoil and structures positioned in the cavity of the airfoil, such as walls of the sub-cavities, the baffles, and/or lattice structure(s). In certain examples, the wear-resistant coating includes titanium, aluminum, and/or cobalt. For example, the wear-resistant coating can include at least one of titanium-aluminum-chromium, titanium-aluminum-chromium-yttrium-silicon, titanium-aluminum-niobium-tantalum, cobalt-molybdenum-chromium, and/or cobalt-chromium-tungsten-nickel. In certain examples, the wear-resistant coating includes one or more high-entropy alloys and/or a bulk metallic glass.

Referring now to the drawings,FIG.1is a schematic cross-sectional view of a prior art example of a turbofan engine100that may incorporate various examples disclosed herein. As shown inFIG.1, the turbofan engine100defines a longitudinal or axial centerline axis102extending therethrough for reference. In general, the turbofan engine100can include a core turbine or a core turbine engine104disposed downstream from a fan section106.

The core turbine engine104can generally include a substantially tubular outer casing108that defines an annular inlet110. The outer casing108can be formed from multiple solid segments. The outer casing108encloses, in serial flow relationship, a compressor section having a booster or low-pressure compressor112(“LP compressor112”) and a high-pressure compressor114(“HP compressor114”), a combustion section116, a turbine section having a high-pressure turbine118(“HP turbine118”) and a low-pressure turbine120(“LP turbine120”), and an exhaust section122. A high-pressure shaft or spool124(“HP shaft124”) drivingly couples the HP turbine118and the HP compressor114. A low-pressure shaft or spool126(“LP shaft126”) drivingly couples the LP turbine120and the LP compressor112. The LP shaft126can also couple to a fan shaft or spool128of the fan section106. In some examples, the LP shaft126can couple directly to the fan shaft128(i.e., a direct-drive configuration). In alternative configurations, the LP shaft126may couple to the fan shaft128via a reduction gearbox130(i.e., an indirect-drive or geared-drive configuration).

As shown inFIG.1, the fan section106includes a fan132coupled to and extending radially outwardly from the fan shaft128. An annular fan casing or nacelle134circumferentially encloses the fan section106and/or at least a portion of the core turbine engine104. The nacelle134can be supported relative to the core turbine engine104by a forward mount136. Furthermore, a downstream section138of the nacelle134can enclose an outer portion of the core turbine engine104to define a bypass airflow passage140therebetween.

As illustrated inFIG.1, air142enters an intake or inlet portion144of the turbofan engine100during operation thereof. A first portion146of the air142flows into the bypass airflow passage140, while a second portion148of the air142flows into the annular inlet110of the LP compressor112. One or more sequential stages of LP compressor stator vanes150and LP compressor rotor blades152(e.g., turbine blades) coupled to the LP shaft126progressively compress the second portion148of the air142flowing through the LP compressor112en route to the HP compressor114. Next, one or more sequential stages of HP compressor stator vanes154and HP compressor rotor blades156coupled to the HP shaft124further compress the second portion148of the air142flowing through the HP compressor114. This provides compressed air158to the combustion section116where it mixes with fuel and burns to provide combustion gases160.

The combustion gases160flow through the HP turbine118where one or more sequential stages of HP turbine stator vanes162and HP turbine rotor blades164coupled to the HP shaft124extract a first portion of kinetic and/or thermal energy therefrom. This energy extraction supports operation of the HP compressor114. The combustion gases160then flow through the LP turbine120where one or more sequential stages of LP turbine stator vanes166and LP turbine rotor blades168coupled to the LP shaft126extract a second portion of thermal and/or kinetic energy therefrom. This energy extraction causes the LP shaft126to rotate, thereby supporting operation of the LP compressor112and/or rotation of the fan shaft128. The combustion gases160then exit the core turbine engine104through the exhaust section122thereof.

Along with the turbofan engine100, the core turbine engine104serves a similar purpose and sees a similar environment in land-based turbines, turbojet engines in which the ratio of the first portion146of the air142to the second portion148of the air142is less than that of a turbofan, and unducted fan engines in which the fan section106is devoid of the nacelle134. In each of the turbofan, turbojet, and unducted engines, a speed reduction device (e.g., the reduction gearbox130) can be included between any shafts and spools. For example, the reduction gearbox130can be disposed between the LP shaft126and the fan shaft128of the fan section106.

As depicted therein, the turbofan engine100defines an axial direction A, a radial direction R, and a circumferential direction C. In general, the axial direction A extends generally parallel to the axial centerline axis102, the radial direction R extends orthogonally outward from the axial centerline axis102, and the circumferential direction C extends concentrically around the axial centerline axis102.

FIG.2illustrates an airfoil200of the fan132ofFIG.1. In the illustrated example ofFIG.2, the airfoil200extends from a root portion202to a tip portion204, and from a leading axial edge206to a trailing axial edge208. The root portion202can be coupled to the fan shaft128ofFIG.1to enable the airfoil200to rotate. InFIG.2, the airfoil200includes a tip shroud210extending from the tip portion204. InFIG.2, the airfoil200includes a partial span shroud212extending from a sidewall214of the airfoil200. Additionally, the airfoil200can include another partial span shroud (not shown) extending from a sidewall of the airfoil opposite the sidewall214ofFIG.2.

Accordingly, the tip shroud210and the partial span shroud212can cause the airfoil200to encounter friction in response to vibrating, which dampens the vibrations. However, the tip shroud210and the partial span shroud212occupy space between the airfoil200and an adjacent airfoil in the fan132, which reduces a mass flow rate of air that passes between the airfoil200and the adjacent airfoil as the fan132rotates. As such, although the tip shroud210and the partial span shroud212may dampen vibrations of the airfoil200, a thrust produced by the turbofan engine100is reduced.

FIG.3Aillustrates a side view of a first example airfoil damping apparatus300in accordance with the teachings of this disclosure.FIG.3Billustrates an example radially-inward view of the first example airfoil damping apparatus300. InFIGS.3A-B, the first example airfoil damping apparatus300includes an airfoil302(e.g., a hollow fan blade). For example, the airfoil302can be implemented in the fan132of the turbofan engine100ofFIG.1. The airfoil damping apparatus300increases vibration damping of the airfoil302over the prior art airfoil200ofFIG.2. Additionally, the airfoil damping apparatus300enables a mass flow rate of air that passes between the airfoil302and an adjacent airfoil (e.g., in the fan132) to be increased during rotation compared to the airfoil200ofFIG.2as a protrusion(s) (e.g., the tip shroud210, the partial span shroud212) is not required to dampen vibrations of the airfoil302.

The airfoil302includes an internal cavity304between a leading edge306and a trailing edge308of the airfoil302. InFIGS.3A-B, the airfoil302includes a dilatant material310(e.g., a shear-thickening fluid, a low modulus material, etc.) disposed in the internal cavity304. The dilatant material310can include solid particles dispersed in a fluid (e.g., silica nano-particles dispersed in polyethylene glycol, Armourgel®, etc.). When the airfoil302is stable, the solid particles in the dilatant material310encounter electrostatic or steric forces that overcome interparticle forces (e.g., Hamaker attraction forces, Van der Waals forces) between the solid particles, which prevents the solid particles from approaching each other.

InFIGS.3A-B, when the airfoil302encounters vibrations, the airfoil302encounters shear stresses, which cause the dilatant material310to encounter shear strain in the internal cavity304. When the shear stress or strain encountered by the dilatant material310surpasses a threshold (e.g., a critical shear rate) associated with the dilatant material310, the solid particles approach each other and, in turn, the interparticle forces overcome the electrostatic or steric forces. That is, the solid particles in the dilatant material310encounter flocculation, which causes the solid particles to clump together. In turn, a thickness and viscosity of the dilatant material310increases as the dilatant material310behaves more like a solid. As a result, the dilatant material310provides a resisting force on a surface312of the internal cavity304that acts against the vibratory movements of the airfoil302and, thus, stabilizes the airfoil302.

In some examples, the thickness and viscosity of the dilatant material310and, thus, the resistance to vibrations provided by the dilatant material310is based on a size and/or a quantity of the solid particles in the dilatant material310. As such, in turbofan engines that have multistage fans, a first dilatant material (e.g., the dilatant material310) having more solid particles and/or larger solid particles can be utilized in a first row of fan blades that encounters more vibrations, and a second dilatant material having fewer solid particles and/or smaller solid particles can be utilized in a second row of fan blades that encounters less vibrations than the first row of fan blades. Additionally or alternatively, when a first portion of the airfoil302tends to encounter more vibrations than a second portion of the airfoil302, a first portion of the internal cavity304can include the first dilatant material and a second portion of the internal cavity304can include the second dilatant material.

InFIGS.3A-B, the surface312of the internal cavity includes a wear-resistant coating314. As such, the wear-resistant coating314minimizes or otherwise reduces wear that results from friction between the surface312and the dilatant material310when the dilatant material310behaves more like a solid in response to vibrations. In some examples, the wear-resistant coating314includes titanium, cobalt, and/or aluminum. For example, the wear-resistant coating314can include titanium-aluminum-chromium, titanium-aluminum-chromium-yttrium-silicon, titanium-aluminum-niobium-tantalum, cobalt-molybdenum-chromium, and/or cobalt-chromium-tungsten-nickel. In some examples, the wear-resistant coating314includes one or more high entropy alloys and/or a bulk metallic glass. In some examples, the wear-resistant coating314includes a thickness between 0.01 centimeters (cm) and 0.10 cm. In some examples, the airfoil damping apparatus300is formed via additive manufacturing and/or diffusion bonding. In some examples, the airfoil damping apparatus300is formed via machined pockets with an attached cover plate. However, other conventional manufacturing techniques may additionally or alternatively be used to form the airfoil damping apparatus300.

FIG.4Aillustrates a side view of a second example airfoil damping apparatus400in accordance with the teachings of this disclosure.FIG.4Billustrates an example radially-inward view of the second example airfoil damping apparatus400. InFIGS.4A-B, the second example airfoil damping apparatus400includes a nested lattice structure402coupled to the surface312of the internal cavity304of the airfoil302.

FIGS.4C-Dillustrate magnified views of the nested lattice structure402. InFIGS.4A-D, the nested lattice structure402includes a first lattice structure404and a second lattice structure406. The first lattice structure404is coupled to the leading edge306and a root portion408of the airfoil302. The second lattice structure406is coupled to the trailing edge308and a tip portion410of the airfoil302. The first lattice structure404is positioned around the second lattice structure406to define a passageway412.

InFIGS.4A-D, the dilatant material310is disposed in the passageway412. InFIGS.4A-D, an interior surface414of the first lattice structure404and a surface416of the second lattice structure406are coated with the wear-resistant coating314to prevent or otherwise reduce wear encountered by the first lattice structure404and the second lattice structure406as a result of the dilatant material310moving in the passageway412. In some examples, a portion of the surface312of the internal cavity304that is coupled to the first lattice structure404or the second lattice structure406and/or defines an end of the passageway412also includes the wear-resistant coating314.

When the airfoil302encounters vibrations, the first lattice structure404and the second lattice structure406move relative to each other. As a result, the dilatant material310encounters shear strain, which causes the dilatant material310to thicken and, in turn, exert a force against the interior surface414of the first lattice structure404and the surface416of the second lattice structure406. Specifically, the force produced by the dilatant material310counteracts the movement of the first lattice structure404relative to the second lattice structure406. As such, the dilatant material310stabilizes the first lattice structure404and the second lattice structure406. Moreover, because the first lattice structure404is coupled to the leading edge306and the root portion408while the second lattice structure406is coupled to the trailing edge308and the tip portion410, the force provided by the dilatant material310counteracts movement between the leading edge306and the trailing edge308of the airfoil302and/or the root portion408and the tip portion410to attenuate vibrations and stabilize the airfoil302.

FIG.5Aillustrates a side view of a third example airfoil damping apparatus500in accordance with the teachings of this disclosure.FIG.5Billustrates a side view of a fourth example airfoil damping apparatus550in accordance with the teachings of this disclosure. InFIGS.5A-B, the internal cavity304of the airfoil302includes baffles502that guide movement of the dilatant material310within the internal cavity304. In some examples, the baffles502are solid, as shown inFIG.5A. In some examples, the baffles502include perforations504, as shown inFIG.5B. InFIGS.5A-B, the baffles502span along a chordwise direction defined by the airfoil302. InFIGS.5A-B, adjacent ones of the baffles502alternate between being coupled to the tip portion410of the airfoil302and the root portion408of the airfoil302.

InFIGS.5A-B, the baffles502increase the shear stress and strain encountered by the dilatant material310when the airfoil302encounters chordwise bending and vibrations. In turn, the baffles502cause the dilatant material310to have an increased viscosity and/or thickness when the airfoil302encounters chordwise vibrations. Additionally, the baffles502cause the viscosity and/or the thickness of the dilatant material310to increase at a faster rate in response to the airfoil302encountering chordwise vibrations. InFIG.5B, when the airfoil302vibrates, the dilatant material310is forced through the perforations504in the baffles502, which further increases the shear stress and strain encountered by the dilatant material310and, thus, further increases the viscosity of the dilatant material310as well as the rate at which the viscosity of the dilatant material310increases.

As such, the third example airfoil damping apparatus500and the fourth example airfoil damping apparatus550provide increased vibration damping in response to chordwise vibrations. Accordingly, the third example airfoil damping apparatus500and/or the fourth example airfoil damping apparatus550may be utilized with certain airfoils that include a structure that encounters more chordwise bending. Additionally or alternatively, the third example airfoil damping apparatus500and/or the fourth example airfoil damping apparatus550may be utilized in certain locations in turbofan engines (e.g., the turbofan engine100ofFIG.1) that encounter greater imbalanced forces in the chordwise direction.

InFIGS.5A-B, the baffles502and the surface312of the internal cavity304are coated with the wear-resistant coating314. As such, the wear-resistant coating314prevents the baffles502and the surface312from encountering wear as a result of friction from movement of the dilatant material310.

FIG.6illustrates an example radially-inward view of a fifth example airfoil damping apparatus600in accordance with the teachings of this disclosure. InFIG.6, the internal cavity304of the airfoil302includes baffles602that direct movement of the dilatant material310within the internal cavity304. InFIG.6, the baffles602span along a chordwise direction defined by the airfoil302similar to the baffles502ofFIGS.5A and/or5B. InFIG.6, adjacent ones of the baffles602alternate between being coupled to the leading edge306of the airfoil302and the trailing edge308of the airfoil302.

InFIG.6, the baffles602increase the shear stress and strain encountered by the dilatant material310when the airfoil302encounters chordwise bending and vibrations. As a result, the fifth example airfoil damping apparatus600provides increased vibration damping in response to chordwise vibrations, similar to the baffles502ofFIGS.5A and/or5B. InFIG.6, the baffles602and the surface312of the internal cavity304include the wear-resistant coating314, which prevents the baffles602and/or the airfoil302from encountering wear as a result of friction from movement of the dilatant material310.

FIG.7Aillustrates a radially-inward view of a sixth example airfoil damping apparatus700in accordance with the teachings of this disclosure.FIG.7Billustrates a radially-inward view of a seventh example airfoil damping apparatus710in accordance with the teachings of this disclosure.FIG.7Cillustrates a radially inward view of an eighth example airfoil damping apparatus720in accordance with the teachings of this disclosure. InFIGS.7A-C, the airfoil302includes chordwise walls702that define chambers704(e.g., chordwise cavities, sub-cavities, etc.) filled with the dilatant material310. InFIGS.7A-C, the chordwise walls702are solid and, thus, the chambers704are secluded.

InFIGS.7B-7C, the airfoil302includes the baffles602positioned in the chambers704to increase shear stresses and strains encountered by the dilatant material310in the chambers704and, thus, increase vibration damping provided by the dilatant material310. The dilatant material310can be disposed in one or more of the chambers704to provide vibration damping. In some examples, all of the chambers704include the dilatant material310, as shown inFIG.7B. In some examples, a first portion of the airfoil302includes the dilatant material310and a second portion of the airfoil302includes air, as shown inFIG.7C. In the illustrated example ofFIG.7C, the dilatant material310is disposed in one of the chambers704and a remainder of the chambers704include air. In some examples, a leading one of the chambers704and a trailing one of the chambers704can be filled with the dilatant material310while a middle one of the chambers704is filled with air.

FIG.7Dillustrates a radially-inward view of a ninth example airfoil damping apparatus720. InFIG.7D, the airfoil302includes the chordwise walls702that define the chambers704filled with the dilatant material310. InFIG.7D, the chordwise walls702include perforations706and, thus, the dilatant material310can move between the chambers704. Additionally, the perforations706cause the dilatant material310to encounter an increased shear stress and strain in response to moving between the chambers704.

InFIGS.7A-D, when the airfoil302vibrates, a viscosity and thickness of the dilatant material310increases and, in turn, the dilatant material310provides a force against the surface312of the internal cavity304that resists the movement of the airfoil302and dampens the vibrations. InFIGS.7A-D, the chordwise walls702along with the surface312of the internal cavity304are coated with the wear-resistant coating314.

FIG.8Aillustrates a side view of a tenth example airfoil damping apparatus800.FIG.8Billustrates a side view of an eleventh example airfoil damping apparatus820.FIG.8Cillustrates a side view of a twelfth example airfoil damping apparatus840. InFIGS.8A-C, the airfoil302includes baffles802that span in the axial direction of an associated turbofan engine (e.g., the axial direction A of the turbofan engine100ofFIG.1) and guide a flow of the dilatant material310within the internal cavity304. InFIGS.8A-C, adjacent ones of the baffles802alternate between being coupled to the leading edge306of the airfoil302and the trailing edge308of the airfoil302. InFIGS.8A-C, the baffles802and the surface312of the internal cavity304are coated with the wear-resistant coating314.

InFIG.8A, a separation distance between adjacent ones of the baffles802is approximately equivalent throughout the internal cavity304. Accordingly, uniform spacing between the baffles802causes the dilatant material310to provide uniform vibration attenuation between the root portion408of the airfoil302and the tip portion410of the airfoil302.

InFIG.8B, a separation distance between adjacent ones of the baffles802is reduced towards the tip portion410of the airfoil302to enable the dilatant material310to provide increased vibration damping towards the tip portion410. For example, the baffles802can include a first baffle804adjacent a second baffle806and a third baffle808adjacent a fourth baffle810. InFIG.8B, the first and second baffles804,806are positioned closer to the tip portion410than the third baffle808and the fourth baffle810. InFIG.8B, the first baffle804and the second baffle806are separated by a first distance, and the third baffle808and the fourth baffle810are separated by a second distance greater than the first distance. As such, the first baffle804and the second baffle806cause the dilatant material310to encounter greater shear stress and strain than the third baffle808and the fourth baffle810. Thus, in the eleventh example airfoil damping apparatus820, the dilatant material310can include a greater thickness increase towards the tip portion410of the airfoil302, which enables the dilatant material310to provide greater vibration damping towards the tip portion410.

Conversely, inFIG.8C, the third baffle808and the fourth baffle810are separated by a third distance, and the first baffle804and the second baffle806are separated by a fourth distance greater than the third distance. As such, inFIG.8C, the third baffle808and the fourth baffle810can cause the dilatant material310to encounter greater shear stress and strain than the first baffle804and the second baffle806. Accordingly, in the twelfth example airfoil damping apparatus840, the dilatant material can include a greater thickness increase towards the root portion408of the airfoil302, which enables the dilatant material to provide greater vibration damping towards the root portion408.

FIG.8Dillustrates a thirteenth example airfoil damping apparatus860. InFIG.8D, the airfoil302includes walls862that are coupled to the leading edge306and the trailing edge308of the airfoil302. In turn, the walls862define radially oriented cavities864within the airfoil302. In some examples, the dilatant material310is disposed in one or more of the radially oriented cavities864. In some examples, the dilatant material310includes solid particles of a first quantity or a first size in one of the radially oriented cavities864and solid particles of a second quantity or a second size in another one of the radially oriented cavities864. Accordingly, the radially oriented cavities864enable the dilatant material310to provide localized vibration damping to certain portions of the airfoil302. InFIG.8D, the walls862along with the surface312of the internal cavity304are coated with the wear-resistant coating314.

FIG.8Eillustrates a side view of a fourteenth example airfoil damping apparatus880.FIG.8Fillustrates a side view of a fifteenth example airfoil damping apparatus890. InFIGS.8E-8F, the radially oriented baffles802are positioned in the radially oriented cavities864. Accordingly, the radially oriented baffles802increase shear stresses and strains encountered by the dilatant material310in the radially oriented cavities864and, thus, increase vibration damping provided by the dilatant material310. The dilatant material310can be disposed in one or more of the radially oriented cavities864to provide vibration damping. In some examples, all of the radially oriented cavities864include the dilatant material310, as shown inFIG.8E. In some examples, a first portion of the airfoil302includes the dilatant material310and a second portion of the airfoil302includes air, as shown inFIG.8F. In the illustrated example ofFIG.8F, the dilatant material310is disposed in one of the radially oriented cavities864and a remainder of the radially oriented cavities864include air.

FIG.9illustrates a radially-inward view of a sixteenth example airfoil damping apparatus900. InFIG.9, the airfoil302includes baffles902that span in the axial direction of an associated turbofan engine (e.g., the axial direction A of the turbofan engine100ofFIG.1) and guide a flow of the dilatant material310within the internal cavity304. InFIG.9, adjacent ones of the baffles902alternate between being coupled to the root portion408(not shown) and the tip portion410(not shown) of the airfoil302, as opposed to being coupled to the leading edge306and the trailing edge308of the airfoil302, as shown inFIGS.8A-Cand8E-F. InFIG.9, the baffles902and the surface312of the internal cavity304are coated with the wear-resistant coating314to prevent or otherwise reduce wear encountered by the baffles902and the surface312as a result of friction produced by the dilatant material310moving in the internal cavity304.

FIG.10Aillustrates a side view of a seventeenth example airfoil damping apparatus1000. InFIG.10A, the airfoil302includes first walls1002coupled to the leading edge306and the trailing edge308of the airfoil302. InFIG.10B, the airfoil302includes second walls1004coupled to the root portion408and the tip portion410of the airfoil302. Accordingly, the first walls1002and the second walls1004intersect to define cells1006to contain the dilatant material310. The first walls1002and the second walls1004are coated with the wear-resistant coating314

InFIG.10A, the dilatant material310is positioned in each of the cells1006. In some examples, the dilatant material310is not positioned in one or more of the cells1006. For example,FIG.10Billustrates an eighteenth example airfoil damping apparatus1020in which the dilatant material310only fills the cells1006that border the leading edge306and the trailing edge308of the airfoil302. Accordingly, the cells1006that do not include the dilatant material310may not be coated with the wear-resistant coating314.

InFIG.10A, the cells1006are positioned throughout the internal cavity304. In some examples, only a portion of the internal cavity304includes the cells1006. For example,FIG.10Cillustrates a nineteenth example airfoil damping apparatus1040. InFIG.10C, the cells1006are only located against the leading edge306and the trailing edge308of the airfoil302. InFIG.10C, the dilatant material310provides localized vibration damping at the leading edge306and the trailing edge308of the airfoil.

The foregoing examples of airfoil damping apparatus can be used in turbofan engines. Although each example airfoil damping apparatus disclosed above has certain features, it should be understood that it is not necessary for a particular feature of one example airfoil damping apparatus to be used exclusively with that example. Instead, any of the features described above and/or depicted in the drawings can be combined with any of the examples, in addition to or in substitution for any of the other features of those examples. One example's features are not mutually exclusive to another example's features. Instead, the scope of this disclosure encompasses any combination of any of the features.

In some examples, an apparatus includes means for producing aerodynamic forces. For example, the means for producing may be implemented by airfoils, such as the airfoil302.

In some examples, an apparatus includes means for thickening in response to encountering shear forces, the means for thickening to dampen vibrations encountered by the means for producing aerodynamic forces. For example, the means for thickening may be implemented by dilatant materials, such as the dilatant material310.

In some examples, an apparatus includes means for resisting wear between the means for thickening and the means for producing aerodynamic forces. For example, the means for resisting may be implemented by the wear-resistant coating314. In some examples, the means for resisting wear includes titanium, aluminum, and/or cobalt. In some examples, the means for resisting wear includes titanium-aluminum-chromium, titanium-aluminum-chromium-yttrium-silicon, titanium-aluminum-niobium-tantalum, cobalt-molybdenum-chromium, and/or cobalt-chromium-tungsten-nickel. In some examples, the means for resisting wear includes one or more high entropy alloys and/or a bulk metallic glass.

In some examples, an apparatus includes means for directing flow of the means for thickening positioned within the means for producing. For example, the means for directing flow may be implemented by the nested lattice structure402, the baffles502, the perforations504, the baffles602, the chordwise walls702, the perforations706, the baffles802, the walls862, the baffles902, the first walls1002, and/or the second walls1004.

The terms “upstream” and “downstream” refer to the relative direction with respect to a flow in a pathway. For example, with respect to a fluid flow, “upstream” refers to the direction from which the fluid flows, and “downstream” refers to the direction to which the fluid flows.

From the foregoing, it will be appreciated that example airfoils have been disclosed that dampen encountered vibrations. The example airfoils include a cavity and a dilatant material (e.g., a shear-thickening fluid) disposed in the cavity to reduce a magnitude of vibrations encountered by the airfoil. Specifically, the dilatant material thickens when the airfoil encounters shear stresses as a result of vibrations. In turn, the dilatant material stiffens and exerts forces that oppose the vibrating motion of the airfoil to stabilize the airfoil. In some examples, the example airfoils include internal structures, such as baffles and/or lattice structures, to direct a flow of the dilatant material and, in turn, control stabilizing forces provided by the dilatant material. In some examples, the example airfoils include cells or sub-cavities to contain the dilatant material within a portion of the airfoil that is less stable and/or encounters increased magnitudes of shear stress when the airfoil encounters unsteady aerodynamic forces.

Example airfoil damping apparatus are disclosed herein. Further examples and combinations thereof include the following:

An apparatus comprising a metallic airfoil including a cavity, and a dilatant material disposed in the cavity to dampen vibrations of the metallic airfoil.

The apparatus of any preceding clause, further including a wear-resistant coating surrounding the dilatant material.

The apparatus of any preceding clause, wherein the wear-resistant coating includes at least one of titanium, aluminum, or cobalt.

The apparatus of any preceding clause, wherein the wear-resistant coating includes at least one of titanium-aluminum-chromium, titanium-aluminum-chromium-yttrium-silicon, titanium-aluminum-niobium-tantalum, cobalt-molybdenum-chromium, or cobalt-chromium-tungsten-nickel.

The apparatus of any preceding clause, further including baffles positioned in the cavity to direct flow of the dilatant material.

The apparatus of any preceding clause, further including a first lattice structure in the cavity, a second lattice structure positioned around the first lattice structure to define a passageway, the dilatant material disposed in the passageway, a first wear-resistant coating on a surface of the first lattice structure to separate the dilatant material from the first lattice structure, and a second wear-resistant coating on an interior surface of the second lattice structure to separate the dilatant material from the second lattice structure.

The apparatus of any preceding clause, wherein the dilatant material includes solid particles suspended in a fluid.

A turbofan engine comprising a hollow fan blade, a shear-thickening fluid disposed in the hollow fan blade, and a wear-resistant coating between the shear-thickening fluid and an interior surface of the hollow fan blade.

The turbofan engine of any preceding clause, further including baffles disposed in the hollow fan blade, the wear-resistant coating to cover the baffles.

The turbofan engine of any preceding clause, wherein the baffles are perforated.

The turbofan engine of any preceding clause, further including chordwise cavities disposed in the hollow fan blade, the shear-thickening fluid disposed in at least one of the chordwise cavities.

The turbofan engine of any preceding clause, further including baffles positioned in the chordwise cavities.

The turbofan engine of any preceding clause, further including radially oriented cavities disposed in the hollow fan blade, the shear-thickening fluid disposed in at least one of the radially oriented cavities.

The turbofan engine of any preceding clause, further including baffles positioned in the radially oriented cavities.

The turbofan engine of any preceding clause, further including first baffles positioned in a first portion of the hollow fan blade, the first portion of the hollow fan blade including the shear-thickening fluid, and second baffles positioned in a second portion of the hollow fan blade, the second portion of the hollow fan blade including air.

The turbofan engine of any preceding clause, wherein the wear-resistant coating is between the first baffles and the shear-thickening fluid in the first portion of the hollow fan blade.

The turbofan engine of any preceding clause, wherein the wear-resistant coating includes at least one of titanium, aluminum, or cobalt.

The turbofan engine of any preceding clause, wherein the wear-resistant coating includes at least one of titanium-aluminum-chromium, titanium-aluminum-chromium-yttrium-silicon, titanium-aluminum-niobium-tantalum, cobalt-molybdenum-chromium, or cobalt-chromium-tungsten-nickel.

The turbofan engine of any preceding clause, further including cells in the hollow fan blade, the shear-thickening fluid disposed in at least one of the cells.

An apparatus comprising means for producing aerodynamic forces, means for thickening in response to encountering shear forces, the means for thickening to dampen vibrations encountered by the means for producing aerodynamic forces, and means for resisting wear between the means for thickening and the means for producing aerodynamic forces.