Double wall tubes using additive manufacturing

A strut may include an outer tube including an outer tube first end, an outer tube second end, and a longitudinal axis extending from the outer tube first end to the outer tube second end. The outer tube may define an interior. The strut also may include an additively manufactured inner tube at least partially within the interior of the outer tube of the strut. The additively manufactured inner tube defines an additively manufactured inner tube first end and an additively manufactured inner tube second end. The additively manufactured inner tube first end is integrally joined to the outer tube proximate to the outer tube first end.

TECHNICAL FIELD

The disclosure relates to additive manufacturing techniques and to double-walled tubes.

BACKGROUND

Gas turbine engines include a core engine, which includes at least one compressor, a combustor, and at least one turbine. The core engine may be supported in an engine casing, which circumferentially surrounds the core engine. Fluids, such as air, oil, and fuel may be supplied to and/or removed from the core engine to support operation of the core engine. Additionally, the core engine may be supported within the engine casing by an annular support that includes a plurality of struts.

SUMMARY

In some examples, the disclosure describes a strut that includes an outer tube comprising an outer tube first end, an outer tube second end, and a longitudinal axis extending from the outer tube first end to the outer tube second end, wherein the outer tube defines an interior; and an additively manufactured inner tube at least partially within the interior of the outer tube of the strut, wherein the additively manufactured inner tube defines an additively manufactured inner tube first end and an additively manufactured inner tube second end, and wherein the additively manufactured inner tube first end is integrally joined to the outer tube proximate to the outer tube first end.

In some examples, the disclosure describes a gas turbine engine that includes an annular support including: an inner annular portion; an outer annular portion; and a plurality of struts joining the inner annular portion and the outer annular portion, wherein at least one strut of the plurality of struts comprises: an outer tube comprising an outer tube first end, an outer tube second end, and a longitudinal axis extending from the outer tube first end to the outer tube second end, wherein the outer tube defines an interior; and an additively manufactured inner tube at least partially within the interior of the outer tube of the strut, wherein the additively manufactured inner tube defines an additively manufactured inner tube first end and an additively manufactured inner tube second end, and wherein the additively manufactured inner tube first end is integrally joined to the outer tube proximate to the outer tube first end.

DETAILED DESCRIPTION

The disclosure generally describes struts and techniques for forming struts that include double-walled tubes. The struts may be used as mechanical supports for mechanical systems, such as gas turbine engines. For example, the support may include an annular support used to support a core engine or one or more components of a core engine within a casing of a gas turbine engine.

The support may include at least one strut that includes a double-walled tube as described herein. For example, the double-walled tube may join an inner annular portion and an outer annular portion of the annular support. The double-walled tube may provide mechanical support separating the inner and outer annular portions and also may provide a fluid path for one or more fluids to flow through. For instance, the at least one strut may include an outer tube that extends between a first end and a second end and defines an interior. The first end may be attached to the inner annular portion and the second end may be attached to the outer annular portion. The strut also may include an inner tube. At least a portion of the inner tube may be disposed within the interior of the outer tube. A first end of the inner tube may be joined to the outer tube near an end of the outer tube (e.g., the first end of the outer tube). The inner tube may provide a fluid path through which one or more fluids, such as air, oil, a coolant, fuel, or the like, flows.

The inner tube may be additively manufactured such that it is integrally formed with the outer tube. For example, the first end of the inner tube may formed using additive manufacturing with a surface of the outer tube as the build surface. This results in the inner tube being integrally formed with the outer tube, which may reduce a likelihood of failure at the location at which the inner and outer tubes are joined. In the absence of additive manufacturing, this location may be a joint between the inner tube and the outer tube, e.g., a welded joint or a brazed joint. Using additive manufacturing to form an inner tube integrally with an outer tube may reduce probability of damage to the mechanical systems (e.g., gas turbine engine) or components of the mechanical system due to fluid leaks. For instance, in implementations in which the fluid flowing through the inner tube is oil, leaking oil may contact high temperature surfaces or be exposed to high temperature gases. Either of these may result in fires due to combustion of the leaking oil. By reducing failure between the inner and outer tube and reducing probability of leaks, the strut described herein may reduce probability of fires within the mechanical system. Additionally, or alternatively, additive manufacturing of the inner tube may simplify manufacture of the strut, e.g., by eliminating brazing steps and potentially eliminating support structures, such as bosses, that facilitate brazing.

FIG. 1is a conceptual diagram illustrating an example gas turbine engine10that includes an annular support28that includes at least one strut including a dual walled tube, in accordance with one or more aspects of the present disclosure. Although annular support28is illustrated between HP turbine18and LP turbine20, annular support28may be positioned at any other location within gas turbine engine10, e.g., any other location along the axis of gas turbine engine10at which annular support28may support a rotating component, or at another location within gas turbine engine10where annular support28supports another (non-rotating) component. For instance, annular support28may be aft or LP turbine20, fore of compressor14, or the like, and/or gas turbine engine10may include multiple annular supports28.

Gas turbine engine10is a primary propulsion engine that provides shaft horsepower for operations of a vehicle, such as an aircraft, marine vehicle, or the like. In some examples, gas turbine engine10is a two-spool engine having a low pressure (LP) spool that includes a low pressure (LP) turbine20, a lower pressure (LP) shaft24, and a propulsor12, and a high pressure (HP) spool that includes a compressor14, a high pressure shaft22, and a high pressure (HP) turbine18. In other examples, gas turbine engine10may include a single spool or three or more spools, e.g., may include an intermediate pressure (IP) spool and/or other spools. In some examples, gas turbine engine10may include any suitable turbine or electrically powered-engine propulsion system, including but not limited to, a turboprop engine, a turbo fan engine, or a turboshaft engine (including rotary wing aircraft).

Gas turbine engine10includes compressor14, a combustor16, HP turbine18, and LP turbine20, each of which is fluidically disposed in series with respect to one another as shown in the example ofFIG. 1. That is, air enters compressor14, which produces first stage compressed air that is directed into combustor16.

Combustor16is fluidically disposed between compressor14and HP turbine18, and as such is in series flow downstream from compressor14. In some examples, combustor16includes a combustion liner (not shown) that encloses a continuous combustion process using the compressed air and fuel. In other examples, combustor16may take other forms, and may be, for example, a wave rotor combustion system, a rotary valve combustion system, a pulse detonation combustion system, or a slinger combustion system, and may employ deflagration and/or detonation combustion processes. Combustor16outputs the result of burning the fuel as hot expanding gases.

HP turbine18is fluidically disposed between combustor16and LP turbine20, and as such is in series flow downstream of combustor18. HP turbine18utilizes the hot expanding gases to drive the HP spool, which in turn drives compressor14. The hot expanding gases pass through HP turbine18to LP turbine20, thereby driving LP shaft24. LP shaft24may be coupled to a gearbox or device, which provides mechanical energy to drive propulsor12. Propulsor12provides thrust, lift, and/or rotational control for the vehicle.

Compressor14includes one or more compressor stages. Each compressor stage may include a compressor stator vane row along the axial circumference of gas turbine engine10and a compressor rotor (which may refer to compressor blades attached along an axial circumference of a rotor disc), both of which are not shown for ease of illustration purposes in the example ofFIG. 1. The compressor rotors for compressor14are spun between the compressor stator vane rows of compressor14via HP shaft22to produce the compressed air.

Each of HP turbine18and LP turbine20include one or more turbine stages. Each turbine stage may include a stator vane row along the axial circumference of gas turbine engine10and a turbine rotor (which may refer to turbine blades attached along an axial circumference of a rotor disc), both of which again are not shown in the example ofFIG. 1for ease of illustration purposes. The gas emitted by combustor16drives the turbine rotors of HP turbine18and LP turbine20, which spin between the respective stator vane rows of HP turbine18and LP turbine20. The rotation or spinning drives respective HP shaft22and LP shaft24, which as noted above drive compressor14and propulsor12.

Gas turbine engine10also includes a casing26surrounding or otherwise forming portions of compressor14, combustor16, HP turbine18, LP turbine20and possibly other components of gas turbine engine10that are not shown for ease of illustration in the example ofFIG. 1. For example, the above noted compressor stator vane rows may be affixed to casing26. Likewise, the turbine stator vane rows may be affixed to casing26.

To support operation of the core of gas turbine engine10(e.g., including compressor14, combustor16, and/or turbines18and20), fluids may be transferred between locations near casing26and locations near HP shaft22and LP shaft24(e.g., radially inward and/or outward with respect to HP shaft22and LP shaft24). The fluids may include, for example, air, oil, coolant, fuel, or the like. Additionally, components of the core are supported in casing26and separated from casing26. In accordance with aspects of the disclosure, gas turbine engine10includes an annular support28that supports components of the core within casing26and enables flow of fluids through annular support28.

Annular support28may include, for example, a first support portion, a second support portion, and at least one strut that joins the first support portion and the second support portion. For instance, in the example ofFIG. 1, in which annular support28supports one or more components of a core engine within casing26, the first support portion may include an inner annular structure and the second support portion may include an outer annular structure. The least one strut includes an outer tube and an inner tube. The outer tube may include an outer tube first end, an outer tube second end, and may define a longitudinal axis extending from the outer tube first end to the outer tube second end. The outer tube defines an interior in which an additively manufactured inner tube is at least partially disposed. The additively manufactured inner tube defines an additively manufactured inner tube first end and an additively manufactured inner tube second end. At least the additively manufactured inner tube first end is integrally joined to the outer tube proximate to the outer tube first end.

Using additive manufacturing to form an inner tube integrally with an outer tube may reduce probability of damage to the mechanical systems (e.g., gas turbine engine10) or components of the mechanical system due to fluid leaks. For instance, in implementations in which the fluid flowing through the inner tube is oil, leaking oil may contact high temperature surfaces of gas turbine engine10or be exposed to high temperature working gases within gas turbine engine10. Either of these may result in fires due to combustion of the leaking oil. By reducing failure between the inner and outer tube and reducing probability of leaks, the strut described herein may reduce probability of fires within the mechanical system. Additionally, or alternatively, additive manufacturing of the inner tube may simplify manufacture of the strut, e.g., by eliminating brazing steps and potentially eliminating support structures, such as bosses, that facilitate brazing.

FIG. 2shows an example of annular support28ofFIG. 1. In particular,FIG. 2is a conceptual diagram illustrating an example annular support32that includes a plurality of struts34. Plurality of struts34join an inner annular portion36and an outer annular portion38of annular support32. At least one strut of plurality of struts34may enable flow of fluid through the strut from outer annular portion38to inner annular portion36and/or vice versa. In the example, ofFIG. 2, each strut of the plurality of struts34enables flow of fluid through the strut from outer annular portion38to inner annular portion36and/or vice versa, as illustrated by the plurality of fittings40connected to outer annular portion38. In other examples, fewer than all of the plurality of struts34enable flow of fluid through the strut from outer annular portion38to inner annular portion36and/or vice versa. AlthoughFIG. 2illustrates an annular support32, in other examples, the support joined by a double tube strut described herein may have another form, such as a support with two portions of any shape joined by one or more double tube struts. The two portions may be selected from linear, curved, segmented, or curvilinear shapes.

Annular support28, including struts34, inner annular portion36, and outer annular portion38may be formed from any suitable material. For instance, struts34, inner annular portion36, and outer annular portion38may be formed from any suitable metal or alloy, including those suitable for forming an additively manufactured component. In some examples, the metal or alloy includes a high-performance metal or alloy for forming component used in mechanical systems, such as a steel (e.g., stainless steel), a nickel-based alloy, a cobalt-based alloy, a titanium-based alloy, or the like. In some examples, the metal or alloy powder may include a nickel-based, iron-based, or titanium-based alloy that includes one or more alloying additions such as one or more of Mn, Mg, Cr, Si, Co, W, Ta, Al, Ti, Hf, Re, Mo, Ni, Fe, B, Nb, V, C, and Y. In some examples, the metal or alloy may include a polycrystalline nickel-based superalloy or a polycrystalline cobalt-based superalloy, such as an alloy including NiCrAlY or CoNiCrAlY. For example, the metal or alloy may include an alloy that includes 9 to 10.0 wt. % W, 9 to 10.0 wt. % Co, 8 to 8.5 wt. % Cr, 5.4 to 5.7 wt. % Al, about 3.0 wt. % Ta, about 1.0 wt. % Ti, about 0.7 wt. % Mo, about 0.5 wt. % Fe, about 0.015 wt. % B, and balance Ni, available under the trade designation MAR-M-247, from MetalTek International, Waukesha, Wis. In some examples, the metal or alloy may include an alloy that includes 22.5 to 24.35 wt. % Cr, 9 to 11 wt. % Ni, 6.5 to 7.5 wt. % W, less than about 0.55 to 0.65 wt. % of C, 3 to 4 wt. % Ta, and balance Co, available under the trade designation MAR-M-509, from MetalTek International. In some examples, the metal or alloy may include an alloy that includes 19 to 21 wt. % Cr, 9 to 11 wt. % Ni, 14 to 16 wt. % W, about 3 wt. % Fe, 1 to 2 wt. % Mn, and balance Co, available under the trade designation L605, from Rolled Alloys, Inc., Temperance, Mich. In some examples, t metal or alloy may include a chemically modified version of MAR-M-247 that includes less than 0.3 wt. % C, between 0.05 and 4 wt. % Hf, less than 8 wt. % Re, less than 8 wt. % Ru, between 0.5 and 25 wt. % Co, between 0.0001 and 0.3 wt. % B, between 1 and 20 wt. % Al, between 0.5 and 30 wt. % Cr, less than 1 wt. % Mn, between 0.01 and 10 wt. % Mo, between 0.1 and 20. % Ta, and between 0.01 and 10 wt. % Ti. In some examples, the metal or alloy may include a nickel based alloy available under the trade designation IN-738 or Inconel 738, or a version of that alloy, IN-738 LC, available from All Metals & Forge Group, Fairfield, N.J., or a chemically modified version of IN-738 that includes less than 0.3 wt. % C, between 0.05 and 7 wt. % Nb, less than 8 wt. % Re, less than 8 wt. % Ru, between 0.5 and 25 wt. % Co, between 0.0001 and 0.3 wt. % B, between 1 and 20 wt. % Al, between 0.5 and 30 wt. % Cr, less than 1 wt. % Mn, between 0.01 and 10 wt. % Mo, between 0.1 and 20 wt. % Ta, between 0.01 and 10 wt. % Ti, and a balance Ni. In some examples, the metal or alloy may include may include an alloy that includes 5.5 to 6.5 wt. % Al, 13 to 15 wt. % Cr, less than 0.2 wt. % C, 2.5 to 5.5 wt. % Mo, Ti, Nb, Zr, Ta, B, and balance Ni, available under the trade designation IN-713 from MetalTek International, Waukesha, Wis. In some examples, the metal or alloy may include may include an alloy that includes 50 to 55 wt. % Ni plus Co, 17 to 21 wt. % Cr, 4.75 to 5.5 wt. % Nb plus Ta, 2.8 to 3.3 wt. % Mo, 0.65 to 1.15 wt. % Ti, 0.2 to 0.8 wt. % Al, less than 1 wt. % Co, less than 0.08 wt. % C, less than 0.35 wt. % Mn, less than 0.35 wt. % Si, less than 0.015 wt. % P, less than 0.015 wt. % S, less than 0.006 wt. % B, less than 0.3 wt. % Cu, and a balance Fe, available under the trade designation IN-718 from MetalTek International, Waukesha, Wis. In some examples, the metal or alloy may include may include a titanium alloy referred to as Ti-6Al-4V. In some examples, the metal or alloy may include a refractory metal or a refractory metal alloy, such as molybdenum or a molybdenum alloy (such as a titanium-zirconium-molybdenum or a molybdenum-tungsten alloy), tungsten or a tungsten alloy (such as a tungsten-rhenium alloy or an alloy of tungsten and nickel and iron or nickel and copper), niobium or a niobium alloy (such as a niobium-hafnium-titanium alloy), tantalum or a tantalum alloy, rhenium or a rhenium alloy, or combinations thereof.

FIG. 3is a conceptual diagram illustrating an example strut42that includes a double-walled tube. Strut42may be an example of struts34ofFIG. 2and/or the struts described with reference to annular support28ofFIG. 1. Strut42includes an outer tube44and an inner tube46. Outer tube44extends from a first end48to a second end50and defines a longitudinal axis52extending from first end48to second end50. In the example ofFIG. 3, outer tube44extends substantially linearly in the direction of longitudinal axis52, while in other examples, outer tube44may define any linear, curved, curvilinear, or segmented shape. Each segment of a segmented shape may be linear, curved, or curvilinear.

Outer tube44defines an outer surface54and an inner surface56. Each of outer surface54and inner surface56may define any cross-sectional shape in a plane orthogonal to longitudinal axis52, and the cross-sectional shapes of outer surface54and inner surface56may be the same or different. Additionally, the cross-sectional shapes of outer surface54and inner surface56may be consistent along the length of longitudinal axis52or may change along the length of longitudinal axis52. Suitable cross-sectional shapes include circular, elliptical, polygonal (e.g., quadrilateral), rounded polygonal (e.g., polygonal with rounded rather than sharp vertices), or more complex shapes, such as that shown inFIG. 7below. Inner surface56of outer tube44defines an interior58of outer tube44.

Outer tube44also defines a first opening78near or at first end48and a second opening80at or near second end50. First and second openings78and80fluidly communicate with interior58of outer tube44to define an optional flow path through inner tube44from first end48to second end50or vice/versa.

Inner tube46is positioned at least partially within interior58of outer tube44. Inner tube46extends from a first end60to a second end62. One or both of first end60or second end62is integrally formed with outer tube44, e.g., using additive manufacturing. In some examples, one of first end60or second end62is integrally formed with outer tube44and the other of first end60or second end62is not directly attached to outer tube44. In some examples, as shown inFIG. 3, a portion of inner tube46extends out of the interior58of outer tube44, e.g., first end60may be integrally formed with outer tube44and second end62may extend out of the interior58of outer tube44.

In some examples, inner tube46extends substantially parallel to longitudinal axis52, as shown inFIG. 3. In other examples, inner tube46may extend non-parallel to longitudinal axis52, e.g., non-parallel to outer tube44. Inner tube46may extend substantially linearly in the direction of longitudinal axis52, or may define any linear, curved, curvilinear, or segmented shape. Each segment of a segmented shape may be linear, curved, or curvilinear.

Inner tube46defines an outer surface64and an inner surface66. Each of outer surface64and inner surface66may define any cross-sectional shape in a plane orthogonal to longitudinal axis52, and the cross-sectional shapes of outer surface64and inner surface66may be the same or different. Additionally, the cross-sectional shapes of outer surface64and inner surface66may be consistent along the length of inner tube46or may change along the length of inner tube46. The cross-sectional shape of inner tube46at a position along longitudinal axis52may be the same or different from the cross-sectional shape of outer tube44at the same position along longitudinal axis52. Suitable cross-sectional shapes include circular, elliptical, polygonal (e.g., quadrilateral), rounded polygonal (e.g., polygonal with rounded rather than sharp vertices), or more complex shapes, such as that shown inFIG. 7below. Inner surface66of inner tube46defines an interior68of inner tube46through which fluid may flow.

As shown inFIG. 3, inner tube46includes a first opening70at first end60and a second opening72at second end62. First and second openings70and72fluidly communicate with interior68of inner tube46to define a flow path through inner tube46from first end60to second end62. As shown inFIG. 3, in some examples in which first end60is integrally formed with outer tube44, first opening70is fluidly connected to an opening74defined in outer tube44to allow fluid flow into and/or out of strut42.

Inner tube46is integrally formed with outer tube44. For example, inner tube46may be additively manufactured within outer tube44, with surface76of outer tube44defining the build surface on which inner tube46is additively manufactured. As another example, outer tube44and inner tube46may be additively manufactured as a single piece.

In some examples, inner tube46may be coupled to outer tube44only at or near first end60of outer tube44. For example, second end62of outer tube44may not be directly attached to outer tube44. This may allow relative movement between a majority (e.g., greater than half) or substantially all (e.g., all except for first end60) of inner tube46relative to outer tube44. Relative movement may be due to thermal expansion and contraction (e.g., due to temperature differences and/or material differences between inner tube46and outer tube44), mechanical forces (e.g., vibration), or the like. Allowing relative movement may reduce a likelihood of cracking of inner tube46and/or cracking where inner tube46and outer tube44are integrally formed.

Using additive manufacturing to form inner tube46integrally with outer tube44may reduce probability of damage to the mechanical systems (e.g., gas turbine engine10) or components of the mechanical system due to fluid leaks. For instance, in implementations in which the fluid flowing through interior68of inner tube46is oil, leaking oil may contact high temperature surfaces of gas turbine engine10or be exposed to high temperature working gases within gas turbine engine10. Either of these may result in fires due to combustion of the leaking oil. By reducing failure between the inner tube46and outer tube44and reducing probability of leaks, strut42may reduce probability of fires within the mechanical system. Additionally, or alternatively, additive manufacturing of inner tube46and, optionally, outer tube44, may simplify manufacture of strut42, e.g., by eliminating brazing steps and potentially eliminating support structures, such as bosses, that facilitate brazing.

In some examples, an inner tube may include additional structural features that accommodate thermal expansion and contraction differences between different components. For example,FIG. 4is a conceptual diagram illustrating another example strut92that includes a double-walled tube, and includes an inner tube94including at least one portion96configured to preferentially deform in the direction of the longitudinal axis of the inner tube94. Strut92may be similar to or substantially the same as strut42shown inFIG. 3, aside from the differences described herein.

Unlike strut42, strut92includes an inner tube94including at least one deformable portion96configured to preferentially deform in the direction of the longitudinal axis of the inner tube94. At least one deformable portion96may be formed integrally with (e.g., additively manufactured as part of) inner tube94. For instance, at least one deformable portion96may include a bellows-like structure of alternating ridges and valleys, may include a portion of inner tube94having a thinner wall, a curved wall portion (like a surface of a sphere or a portion of a sphere), or another structure that deforms more easily in the direction of longitudinal axis52than surrounding portions of inner tube94. In any case, at least one deformable portion96may facilitate longitudinal expansion or contraction of inner tube94. This may be beneficial when second end72of inner tube94is coupled to another component, e.g., to enable fluid flow through strut92to and/or from the other component. Second end72of inner tube94may be retained relative to the other component, and the other component may move relative to strut92, e.g., due to vibration, thermal expansion or contraction, or the like. By facilitating dimensional changes of inner tube94along longitudinal axis52, at least one deformable portion96may help reduce likelihood of damage, such as cracks, to inner tube94and/or at the location at which inner tube94attaches to outer tube44.

In some examples, a strut may include a dual-walled tube that includes a lateral support between an inner tube and an outer tube. Such a lateral support may reduce lateral or transverse motion between the inner tube and the outer tube, which may reduce stress at points where the inner tube and outer tube are integrally formed. For example,FIG. 5is a conceptual diagram illustrating another example strut102that includes a double-walled tube. Strut102may be similar to or substantially the same at strut42shown inFIG. 3and strut92shown inFIG. 4, aside from the differences described herein.

Unlike strut42and strut92, strut102includes a lateral support106joining an outer tube44and inner tube104at a location between first end60of inner tube104and second end62of inner tube104. Lateral support106joins outer surface64of inner tube104to inner surface56of outer tube44. Lateral support106reduces or substantially eliminates lateral motion (e.g., motion in a direction substantially orthogonal to longitudinal axis52at the position along the longitudinal axis at which lateral support106is located.

Lateral support106may be integrally formed with inner tube104and/or outer tube44. For instance, lateral support106may be additively manufactured with inner tube104and/or outer tube44.

Lateral support106may be located at any position along inner tube104(e.g., along longitudinal axis52). In some examples, lateral support106may be located at about a mid-point of the length of inner tube104as measured along longitudinal axis52(e.g., within 10% of the length of inner tube104from a mid-point of the length of inner tube104). In some instances, lateral support106may not be substantially rigid, e.g., may include one or more features or properties that allow lateral support106to flex parallel to axis52and/or transverse to axis52. For example, lateral support106may be oriented at a non-orthogonal angle to axis52, such that lateral support106is oriented at a non-orthogonal angle to inner tube104and outer tube44. As another example, lateral support106may include a bellows or spring structure to provide flexibility to lateral support106, or may be formed from a material and/or thickness that allows inherent flexibility of lateral support106.

FIG. 5illustrates an example strut that includes a single lateral support106. In other examples, lateral support106may include a plurality of lateral supports106(e.g., at least two lateral supports106).

Lateral support106may be formed from any suitable material. In some examples, lateral support106may be formed form the same material as inner tube104to reduce or substantially eliminate differences in thermal expansion or contraction between inner tube104and lateral support106.

Lateral support106may constrain dimensional changes of inner tube104in the direction of longitudinal axis52. As such, in some implementations, inner tube104may include at least one deformable portion108,110configured to preferentially deform in the direction of longitudinal axis52of inner tube104. For instance, inner tube104may include a deformable portion for each segment of inner tube104. In the example ofFIG. 5, inner tube104includes two deformable portions108,110. First deformable portion108is part of a first segment of inner tube104between first end60and lateral support106. Second deformable portion110is part of a second segment of inner tube104between lateral support106and second end62. Each of deformable portions108,110may be formed integrally with (e.g., additively manufactured as part of) inner tube104.

Each of deformable portions108,110may have the same configuration (e.g., bellows-like structure, a thinner wall, a curved wall portion) or they may have different configurations. In any case, each deformable portion108,110may facilitate longitudinal expansion or contraction of the segment of inner tube104of which the deformable portion108,110is part. As such, first deformable portion108may allow dimensional changes of inner tube104along longitudinal axis52while inner tube104is constrained at first end60and lateral support106. Similarly, second deformable portion110may allow dimensional changes of inner tube104along longitudinal axis52while inner tube104is constrained at lateral support106and second end62. The example strut102ofFIG. 5may reduce stress at first end60of inner tube104by reducing transverse movement of inner tube104relative to outer tube44due to lateral support106while allowing longitudinal dimensional changes of inner tube104due to deformable portions108and110. As such, lateral support106and deformable portions108and110may help reduce cracking at first end60and leaks of fluid out of inner tube104.

The inner tube and outer tube of the strut may have any suitable cross-sectional shape in a plane orthogonal (e.g., perpendicular) to longitudinal axis52, including circular, elliptical, oval, polygonal, rounded polygonal (e.g., polygonal with rounded vertices rather than pointed vertices), or other, more complex shapes such as airfoils. For instance,FIG. 6is a conceptual diagram illustrating another example strut112that includes a double-walled tube with a more complex cross-sectional shape.FIG. 7is a perspective diagram illustrating the example strut112ofFIG. 6. Strut112may be similar to or substantially the same at strut42shown inFIG. 3, strut92shown inFIG. 4, or strut102shown inFIG. 5, aside from the differences described herein.

Strut112includes outer tube44and inner tube114. Each of inner tube114and outer tube44includes a non-circular cross-sectional shape in the direction orthogonal to longitudinal axis52. The cross-sectional shape is shown inFIG. 7. In some instances, outer surface54of strut112may define a cross-sectional shape defined by function and configuration of strut112and the support of which strut112is a part. In some implementations, the cross-sectional shape of inner surface56may correspond to (e.g., be substantially the same shape as) the cross-sectional of outer surface54. Similarly, in some implementations, the cross-sectional shape of outer surface64of inner tube114may correspond to (e.g., be substantially the same shape as) the cross-sectional shape of inner surface56of outer tube44, and the cross-sectional shape of inner surface66of inner tube114may correspond to (e.g., be substantially the same shape as) the cross-sectional shape of outer surface64. This may maximize the volume of interior68of inner tube114to allow flow of fluid through inner tube114from first opening120adjacent first end60to second opening122adjacent second end62or vice versa.

Additionally, as shown inFIG. 6, outer tube44may also define a flow path from first opening116adjacent to first end48to second opening118adjacent second end50. This may allow flow of a second fluid through strut112, increasing functionality of strut112.

Although not shown inFIGS. 6 and 7, strut112may include at least one deformable portion as shown inFIGS. 4 and 5and/or at least one lateral support as shown inFIG. 5.

In some instances, it may be desirable to have additional fluid flows through a strut. In some such examples, a strut may include multiple inner tubes within a single outer tube.FIG. 8is a conceptual diagram illustrating an example strut132that includes a double-walled tube including an outer tube44and two parallel inner tubes46and134. First and second inner tubes46and134are disposed in parallel (e.g., next to each other) within interior58of outer tube44. First and second inner tubes46and134may be similar or different, e.g., in material, diameter, wall thickness, positioning, or the like. The characteristics of first and second inner tubes46and134may be selected based on the purpose for first and second inner tubes46and134, e.g., the type and pressure of fluid flowing through the inner tube. As shown inFIG. 8, second inner tube134extends from a first end136integrally formed with outer tube44to a second end138. Further, second inner tube134defines a flow path that extends from a first opening140to a second opening142. Although first and second openings140and142are positioned at opposite ends of outer tube44in the example ofFIG. 8, in other examples, each of first and second openings140and142may be independently positioned at any desired location along second tube134. Similarly, first and second openings70and72of first tube46may be independently positioned at any desired location along first tube46. By including two inner tubes46and134, additional fluids may flow through strut132, increasing functionality of strut132.

As another example, a strut may include concentric inner tubes.FIG. 9is a conceptual diagram illustrating an example strut152that includes a double-walled tube including an outer tube44and two concentric inner tubes154and156. First and second inner tubes154and156may be similar or different, e.g., in material, diameter, wall thickness, positioning, or the like. The characteristics of first and second inner tubes154and156may be selected based on the purpose for first and second inner tubes154and156, e.g., the type and pressure of fluid flowing through the inner tube. As shown inFIG. 9, first inner tube154extends from a first end60integrally formed with outer tube44to a second end62. Further, first inner tube154defines a flow path that extends from a first opening162to a second opening164. First opening162is positioned at in a wall of outer tube44. In other examples, each of first opening162may be positioned at any desired location along outer44. Similarly, first and second openings166and168of second tube156may be independently positioned at any desired location along second tube156. By including two inner tubes154and156, additional fluids may flow through strut152, increasing functionality of strut152.

The inner tube and, optionally, the outer tube may be formed using additive manufacturing. Any suitable additive manufacturing system and technique may be used to form the inner tube and, optionally, the outer tube. For example, fused filament fabrication, stereolithography, powder bed deposition, blown powder deposition, directed energy deposition, or the like may be used to form the inner tube and, optionally, the outer tube.