FILLING COMPONENTS

Abstract

A method of filling an internal cavity of a component for a machine with viscoelastic damping medium and/or insulating medium comprises pumping a plurality of capsules into the internal cavity using a peristaltic pump. Each capsule comprises a flexible skin encapsulating a viscoelastic damping medium, one or more viscoelastic damping medium precursors, an insulating medium, or one or more insulating medium precursors.

Claims

1. A method of filling an internal cavity of a component for a machine with viscoelastic damping medium and/or insulating medium, the method comprising: pumping a plurality of capsules into the internal cavity using a peristaltic pump; wherein each capsule comprises a flexible skin encapsulating a viscoelastic damping medium, one or more viscoelastic damping medium precursors, an insulating medium, or one or more insulating medium precursors.

2. The method according to claim 1, wherein the plurality of capsules comprises at least two different types of capsule having differing contents.

3. The method according to claim 1, wherein the plurality of capsules comprises capsules of at least two different sizes.

4. The method according to claim 1, further comprising: directing placement of the capsules inside the internal cavity using a positioning aid.

5. The method according to claim 1, wherein the plurality of capsules comprises low shear modulus capsules and high shear modulus capsules, the low shear modulus capsules having contents which (a) have a lower shear modulus than the contents of the high shear modulus capsules or (b) are curable to form a viscoelastic damping medium having a lower shear modulus than the viscoelastic damping medium formed on curing the contents of the high shear modulus capsules when subject to the same curing process, wherein the internal cavity comprises an inner region and an outer region, the outer region being adjacent an interior wall of the internal cavity and surrounding the inner region, and wherein the method comprises: arranging low shear modulus capsules in one of the inner region and the outer region; and arranging high shear modulus capsules in the other of the inner region and the outer region.

6. The method according to claim 1, wherein the plurality of capsules comprises capsules containing a plurality of stiffening elements dispersed in the viscoelastic damping medium, the one or more viscoelastic damping medium precursors, the insulating medium or the one or more insulating medium precursors.

7. The method according to claim 1, further comprising: curing the viscoelastic damping medium, the one or more viscoelastic damping medium precursors, the insulating medium or the one or more insulating medium precursors in the internal cavity, for example, by applying heat and/or pressure to the component.

8. The method according to claim 1, further comprising: heating the component, for example to about 60 C., during pumping of the plurality of capsules into the internal cavity.

9. The method according to claim 1, further comprising: evacuating the internal cavity prior to or during pumping of the plurality of capsules into the internal cavity; applying a gas back pressure on the plurality of capsules during pumping of the plurality of capsules into the internal cavity; and/or pumping the plurality of capsules into the internal cavity together with a foaming agent.

10. The method according to claim 1, wherein the component is a gas turbine engine component, for example, an aerofoil component such as a fan blade, compressor blade, turbine blade or guide vane for a gas turbine engine.

11. A capsule for use in a method according to claim 1, the capsule comprising a flexible skin encapsulating a viscoelastic damping medium, one or more viscoelastic damping medium precursors, an insulating medium or one or more insulating medium precursors.

12. The capsule according to claim 11 further containing a plurality of stiffening elements dispersed in the viscoelastic damping medium, the one or more viscoelastic damping medium precursors, the insulating medium or the one or more insulating medium precursors.

13. The capsule according to claim 11, wherein the viscoelastic damping medium or the one or more viscoelastic damping medium precursors comprise, or are curable to form, one or more thermosetting polymers, for example, one or more polyurethanes.

14. The capsule according to claim 11, wherein the insulating medium or the one or more insulating medium precursors comprise an insulating mineral filler, for example, mineral powder or mineral fibres.

15. The capsule according to any one of claims 11, wherein the flexible skin comprises a polymeric film, for example, comprising polyvinyl alcohol.

16. An aerofoil component for a gas turbine engine, the aerofoil component comprising an external body having an internal cavity at least partially filled with a viscoelastic damping medium having a non-uniform spatial distribution of shear modulus.

17. The aerofoil component according to claim 16, wherein the internal cavity comprises an inner region and an outer region, the outer region being adjacent an interior wall of the internal cavity and surrounding the inner region, and wherein the shear modulus of the viscoelastic damping medium is lower in the outer region than in the inner region.

18. The aerofoil component according to claim 17, wherein the viscoelastic damping medium in the inner region comprises a plurality of stiffening elements.

19. The aerofoil component according to claim 16, wherein the viscoelastic damping medium comprises one or more thermosetting polymers, for example, one or more polyurethanes.

20. The aerofoil component according to claim 16, wherein the internal cavity is partially filled with an insulating medium in addition to the viscoelastic damping medium.

21. The aerofoil component according to claim 16, wherein the aerofoil component is a fan blade, compressor blade, turbine blade or guide vane.

22. A gas turbine engine comprising a plurality of aerofoil components according to claim 16.

Description

DESCRIPTION OF THE DRAWINGS

[0101] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0102] FIG. 1 is a sectional side view of a gas turbine engine;

[0103] FIG. 2 is a sectional side view of an outlet guide vane filled with viscoelastic damping medium;

[0104] FIG. 3 is a sectional side view of an outlet guide vane prior to filling with viscoelastic damping medium;

[0105] FIG. 4 is a sectional view of a capsule for use in filling an outlet guide vane with viscoelastic damping medium;

[0106] FIG. 5 is a schematic illustration of an arrangement of viscoelastic damping medium capsules inside a portion of an outlet guide vane;

[0107] FIG. 6 is a flowchart illustrating a method of filling a component with viscoelastic damping medium;

[0108] FIG. 7 is a sectional side view of an outlet guide vane filled with viscoelastic damping medium and thermally insulating medium; and

[0109] FIG. 8 is a sectional view of a capsule for use in filling an outlet guide vane with thermally insulating medium.

DETAILED DESCRIPTION

[0110] FIG. 1 illustrates a gas turbine engine 10 having a principal rotational axis 9. The engine 10 comprises an air intake 12 and a propulsive fan 23 that generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 comprises a core 11 that receives the core airflow A. The engine core 11 comprises, in axial flow series, a low pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, a low pressure turbine 19 and a core exhaust nozzle 20. A nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass exhaust nozzle 18. The bypass airflow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low pressure turbine 19 via a shaft 26 and an epicyclic gearbox 30.

[0111] The nacelle 21 is secured to the engine core 11 in part by a plurality of circumferentially spaced radially extending bypass outlet guide vanes (OGVs) 31. The OGVs 31 provide a stiff structure for efficiently transferring structural loads between the nacelle 21 and the core 11 without significant weight, noise or bypass losses. The OGVs 31 also straighten the air flow B from the fan.

[0112] In use, the core airflow A is accelerated and compressed by the low pressure compressor 14 and directed into the high pressure compressor 15 where further compression takes place. The compressed air exhausted from the high pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel and the mixture is combusted. The resultant hot combustion products then expand through, and thereby drive, the high pressure and low pressure turbines 17, 19 before being exhausted through the nozzle 20 to provide some propulsive thrust. The high pressure turbine 17 drives the high pressure compressor 15 by a suitable interconnecting shaft 27. The fan 23 generally provides the majority of the propulsive thrust. The epicyclic gearbox 30 is a reduction gearbox.

[0113] Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in FIG. 1 has a split flow nozzle 20, 22 meaning that the flow through the bypass duct 22 has its own nozzle that is separate to and radially outside the core engine nozzle 20. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct 22 and the flow through the core 11 are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example. In some arrangements, the gas turbine engine 10 may not comprise a gearbox 30.

[0114] The geometry of the gas turbine engine 10, and components thereof, is defined by a conventional axis system, comprising an axial direction (which is aligned with the rotational axis 9), a radial direction (in the bottom-to-top direction in FIG. 1), and a circumferential direction (perpendicular to the page in the FIG. 1 view). The axial, radial and circumferential directions are mutually perpendicular.

[0115] An OGV 31 is shown in more detail in cross-section in FIG. 2. The OGV 31 comprises an aerofoil body 32 formed from metal, such as titanium, which incorporates a three-dimensional twist. The body 32 defines an internal cavity 33 which is filled with two regions of viscoelastic damping medium 34 and 35. Outer region 34 is formed from a polyurethane-based viscoelastic damping compound and inner region 35 is formed from the same polyurethane-based viscoelastic damping compound in which stiffening elements are dispersed. Together the regions 34 and 35 of viscoelastic damping compound fill the entire cavity 33.

[0116] In use, turbulent air exiting the fan impacts and passes through the bypass OGVs. In existing gas turbine engines, this turbulence may be a source of significant vibration of the OGVs and multiple modes of resonance. Other sources of vibration in or external to the gas turbine engine may also cause vibration of the OGVs. Such vibrations can, over time, lead to the formation and growth of fatigue cracks in the OGV metal body and eventual component failure. However, the presence of the viscoelastic damping compound in OGV 31 enables a substantial proportion of the vibrations to be damped and fatigue crack initiation and growth to be retarded.

[0117] In particular, the stiffening elements have been found to effectively increase the shear modulus or stiffness of the inner region 35 relative to the outer region 34. It has also been found that having stiffer material in the centre of the OGV and less stiff material adjacent internal walls of the inner cavity leads to more effective vibrational damping in comparison to OGVs filled with a single viscoelastic damping medium having a uniform shear modulus distribution. It is believed that use of stiffening elements in the inner region 35 also leads to more effective damping because many internal shear interfaces are formed between the stiffening elements and the surrounding viscoelastic damping compound at which vibrational energy can be dissipated.

[0118] The OGV 31 is manufactured by pumping viscoelastic damping medium precursors in an encapsulated liquid form into the internal cavity 33 of the metal body 32. The body 32 itself is formed using standard metal working and shaping processes known to the person skilled in the art. For example, the body 32 may be formed from metal sheet or cast metal.

[0119] In order to pump the viscoelastic damping medium precursors into the cavity 33, a series of apertures 36 are formed through the body 32 into the cavity 33, as shown in FIG. 3. The size of the apertures 36 varies depending on location along the length of the OGV body. For example, smaller apertures may be located adjacent narrower regions of the internal cavity 33. Capsules containing viscoelastic damping medium precursors are then pumped, using peristaltic pumps, into the cavity 33 through tubes which are inserted through the apertures 36 into the cavity 33.

[0120] An example capsule structure 37 is shown in FIG. 4. Capsule 37 includes an external skin 38 made of a polyvinyl alcohol film which encapsulates viscoelastic damping medium precursors 39 and dispersed stiffening elements 40. The skin 38 can be between about 10 m and about 150 m thick.

[0121] The stiffening elements 40 are generally formed from solid polymeric material. The stiffening elements 40 may have regular or irregular shapes; for example, the stiffening elements may include substantially spherical beads, irregularly shaped particles, or dendritic structures resembling brushes, Christmas trees or snowflakes. The stiffening elements 40 may include polymer webs or nets. The stiffening elements can be between about 1 m and about 2 mm in diameter.

[0122] Peristaltically pumping capsules containing viscoelastic damping medium precursors has been found to be significantly easier than directly pumping viscoelastic damping medium precursors, which are generally highly viscous. By easier, it is meant that the process is more reliable with less equipment and/or process (i.e. filling) failure, with less stress on equipment. In addition, the combination of encapsulation within a polymeric skin and peristaltic pumping reduces damage to the stiffening elements which can occur during direct pumping. Peristaltic pumping also results in reduced capsule rupture in comparison to direct pumping of the capsules.

[0123] The placement of capsules within the cavity 33 is controlled by directing the tubes connected to the peristaltic pumps through the apertures 36 and controlling the pumping rates. Positioning aids or imaging devices such as borescopes may be used to direct placement of the tubes and consequently the arrangement of capsules within the cavity. Different apertures are used for placing different types or sizes of capsules within the cavity. For example, smaller capsules can be pumped into narrower regions of the cavity, or into outer regions of the cavity adjacent internal walls in order to provide a closer fit with the cavity walls, while larger capsules may be used to fill inner regions of the cavity. Capsules lacking stiffening elements can also be pumped around the outer regions, while capsules including stiffening elements can be used to fill the inner region. By using multiple apertures, many different arrangements of capsule size and type are possible, allowing precise control of the spatial distribution of the viscoelastic damping medium within the cavity. For example, FIG. 5 shows how capsules of two different sizes (smaller capsule types A and larger capsule types B) and two different fill types (capsules including stiffening elements being indicated by cross-hatching and capsules lacking stiffening elements being unfilled) can be used to create a complex spatial distribution of shear modulus within a cavity.

[0124] Pumping of the capsules into the cavity 33 can be assisted by reducing friction between the capsules and the interior walls of the cavity through lubrication or by heating the OGV, for example, to about 60 C. Pumping can also be assisted by increasing a pressure gradient acting on the capsules, for example, by evacuating the internal cavity of air, applying a gas back pressure on the capsules in the pump, or pumping the capsules through the tubes together with a foaming agent. The OGV may be vibrated or centrifugal motion may be used to assist in filling and reducing gaps between capsules in the cavity. Because the polymer skin of the capsules is flexible, pressure on the capsules due to backfilling of the cavity can deform the capsules to the shape of the cavity, further improving filing and reducing air gaps.

[0125] Once the cavity 33 is filled with capsules, the apertures may be sealed, for example with titanium plugs. The viscoelastic damping medium precursors in the capsules is then cured by heating the OGV to the appropriate curing temperature, for example, in an autoclave. The capsule skins 37 may break or dissolve during the curing process but movement of the stiffening elements within the curing medium is low.

[0126] It will be appreciated that many different types of viscoelastic damping medium could be used to fill the internal cavity of the OGV using this method. Example viscoelastic damping media include viscoelastic polymers, such as viscoelastic thermosetting polymers or elastomers, including viscoelastic polyurethanes (e.g. branched polyurethanes), liquid crystal elastomers (e.g. liquid crystal silicone), polyesters, polyamides, polyacrylates, or epoxy resins. Depending on the choice of viscoelastic damping medium, the capsules could contain the viscoelastic damping medium per se (for example, where the viscoelastic damping medium is a viscoelastic liquid, such as a non-Newtonian fluid) or one or more precursors which react to form the viscoelastic damping medium (for example, epoxy resin precursors). In some examples, the capsules contain bisphenol A-epichlorohydrin resin, a branched polyurethane and an amine hardener. In some examples, the capsules contain one or more linear or branched polyols and a polyisocyanate which react with one another to form a polyurethane. In some examples, the capsules contain the polyurethane-based viscoelastic damping medium Sorbothane, available from Sorbothane, Inc. A suitable viscoelastic damping medium does not decompose at OGV operating temperatures, for example up to about 200 C.

[0127] The polyvinyl alcohol skin of the capsules could be replaced by any suitable polymer skin having a lower shear modulus than the material (e.g. titanium) used to form the body of the OGV. The material used to form the polymer skin should, however, not generate vapour decomposition products at OGV operating temperatures, for example up to about 200 C.

[0128] The capsules may be formed using standard methods and apparatus known in the field of packaging, such as those used to form polymer-encapsulated pharmaceuticals, food products or detergents. For example, the polymer skin of the capsules may be formed by heat-sealing a polymer film. The polymer film may be heat-sealed to form a tube, the tube may be filled with the viscoelastic damping medium or precursors and/or the stiffening elements, and the tube may be then be heat-sealed to encapsulate the material. Alternatively, the capsules may be formed using additive manufacturing techniques (e.g. 3D-printing).

[0129] Similar methods may be used to fill other types of vane with viscoelastic damping media, such as outlet guide vanes located downstream of the combustion chamber or turbines or inlet guide vanes located upstream of the fan or upstream of the combustion chamber. Such methods may also be used to fill other machine components with viscoelastic damping media. For example, the method could be used to fill other gas turbine engine components such as internal cavities of fan blades or flow splitters, cavities housing sensors, or cavities formed in shields around pipes.

[0130] The method of filling a machine component cavity is illustrated as a flowchart in FIG. 5. Block 100 comprises pumping capsules containing viscoelastic damping medium or viscoelastic damping medium precursors through one or more apertures into the cavity using one or more peristaltic pumps. Block 101 comprises sealing the apertures once the cavity is filled. Block 102 comprises optionally curing the capsules (where the capsules contain viscoelastic damping medium precursors) within the cavity to form a cured viscoelastic damping medium.

[0131] Similar methods may also be used to fill machine components with materials other than viscoelastic damping media. For example, such methods may be used to fill machine components with insulating media, such as thermally insulating media.

[0132] As an example, an OGV 201 is shown in cross-section in FIG. 7. The OGV 201 comprises an aerofoil body 202 formed from metal, such as titanium, which incorporates a three-dimensional twist. The body 202 defines an internal cavity 203 which is filled with one region of viscoelastic damping medium 204 and one region of thermally insulating medium 205. The region of viscoelastic damping medium 204 is formed from a polyurethane-based viscoelastic damping compound. The region of thermally insulating medium 205 is formed primarily from a thermally insulating mineral filler, such as alumina or chalk. Together the regions 204 and 205 fill the entire cavity 203.

[0133] The region 205 may be filled with thermally insulating medium by peristaltically pumping capsules containing thermally insulating medium or thermally insulating medium precursors into the cavity. An example capsule structure 206 is shown in FIG. 8. Capsule 206 includes an external skin 207 made of a polyvinyl alcohol film which encapsulates insulating damping medium precursors 208. The insulating damping medium precursors 208 consist of the thermally insulating mineral filler suspended in a carrier liquid. The region 204 is filled with viscoelastic damping medium by peristaltically pumping capsules containing viscoelastic damping medium or viscoelastic damping medium precursors, such as those shown in FIG. 4, into the cavity.

[0134] The method may be used to direct placement of insulating media to regions of the cavity subjected to higher temperatures during use of the component. For example, insulating media may be selectively located adjacent interior cavity walls to protect viscoelastic damping media from elevated temperatures which might lead to polymer decomposition, for example.

[0135] Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. By way of example such engines may have an alternative number of interconnecting shafts (e.g. two) and/or an alternative number of compressors and/or turbines. Further the engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan.

[0136] It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.