Patent Description:
Airfoils in the turbine section are typically formed of a superalloy and may include thermal barrier coatings to extend temperature capability and lifetime. Ceramic matrix composite ("CMC") materials are also being considered for airfoils. Among other attractive properties, CMCs have high temperature resistance. Despite this attribute, however, there are unique challenges to implementing CMCs in airfoils.

<CIT> discloses a turbine vane assembly having ceramic matrix composite components with an expandable spar support.

According to an aspect of the present invention, a spar, for a vane arc segment of a gas turbine engine, is provided in accordance with claim <NUM>.

Optionally, and in accordance with any of the above, the pin fairing includes a bearing surface.

Optionally, and in accordance with any of the above, the bearing surface includes a wear-resistant coating such as a hardcoat.

Optionally, and in accordance with any of the above, the pin fairing has an apex that defines the throat of the internal passage. The internal passage changing at the apex from converging to diverging.

A vane arc segment according to an example of the present invention is provided in accordance with claim <NUM>.

Optionally, and in accordance with the above, the pin fairing seals the pin from the internal passage.

Optionally, and in accordance with any of the above, the pin fairing includes a bearing surface in contact with the pin.

A gas turbine engine according to an example of the present invention is provided in accordance with claim <NUM>.

<FIG> illustrates a line representation of an example of a vane arc segment <NUM> from the turbine section <NUM> of the engine <NUM> (see also <FIG>). It is to be understood that although the examples herein are discussed in context of a vane from the turbine section, the examples can be applied to other vanes that have support spars.

The vane arc segment <NUM> includes an airfoil fairing <NUM> that is formed by an airfoil wall <NUM>. The airfoil fairing <NUM> is comprised of an airfoil section <NUM> and first and second platforms <NUM>/<NUM> between which the airfoil section <NUM> extends. The airfoil section <NUM> generally extends in a radial direction relative to the central engine axis A. Terms such as "inner" and "outer" used herein refer to location with respect to the central engine axis A, i.e., radially inner or radially outer. Moreover, the terminology "first" and "second" used herein is to differentiate that there are two architecturally distinct components or features. It is to be further understood that the terms "first" and "second" are interchangeable in that a first component or feature could alternatively be termed as the second component or feature, and vice versa.

The airfoil wall <NUM> is continuous in that the platforms <NUM>/<NUM> and airfoil section <NUM> constitute a unitary body. As an example, the airfoil wall <NUM> is formed of a ceramic matrix composite, an organic matrix composite (OMC), or a metal matrix composite (MMC). For instance, the ceramic matrix composite (CMC) is formed of ceramic fiber tows that are disposed in a ceramic matrix. The ceramic matrix composite may be, but is not limited to, a SiC/SiC ceramic matrix composite in which SiC fiber tows are disposed within a SiC matrix. Example organic matrix composites include, but are not limited to, glass fiber tows, carbon fiber tows, and/or aramid fiber tows disposed in a polymer matrix, such as epoxy. Example metal matrix composites include, but are not limited to, boron carbide fiber tows and/or alumina fiber tows disposed in a metal matrix, such as aluminum. A fiber tow is a bundle of filaments. As an example, a single tow may have several thousand filaments. The tows may be arranged in a fiber architecture, which refers to an ordered arrangement of the tows relative to one another, such as, but not limited to, a 2D woven ply or a 3D structure.

The airfoil section <NUM> circumscribes an interior through-cavity <NUM>. The airfoil section <NUM> may have a single through-cavity <NUM>, or the cavity <NUM> may be divided by one or more ribs. The vane arc segment <NUM> further includes a spar <NUM> that extends through the through-cavity <NUM> and mechanically supports the airfoil fairing <NUM>. The spar <NUM> includes a spar platform 72a and a spar leg 72b that extends from the spar platform 72a into the through-cavity <NUM>. Although not shown, the spar platform 72a includes attachment features that secure it to a fixed support structure, such as an engine case. The spar leg 72b defines an interior through-passage 72c.

The spar leg 72b has a distal end portion <NUM> that has a clevis mount <NUM>. The end portion <NUM> of the spar leg 72b extends past the platform <NUM> of the airfoil fairing <NUM> so as to protrude from the fairing <NUM>. There is a support platform <NUM> adjacent the platform <NUM> of the airfoil fairing. Although not shown, the support platform <NUM>, the platform <NUM> of the airfoil fairing <NUM>, or both may have flanges or other mounting features through which the support platform <NUM> interfaces with the platform <NUM>.

The support platform <NUM> includes a through-hole <NUM> through which the end portion <NUM> of the spar leg 72b extends such that at least a portion of the clevis mount <NUM> protrudes from the support platform <NUM>. The clevis mount <NUM> includes aligned holes <NUM> through which a pin <NUM> extends. The pin <NUM> is wider than the through-hole <NUM>. The ends of the pin <NUM> thus abut the face of the support platform <NUM> and thereby prevent the spar leg 72b from being retracted in the through-hole <NUM>. The pin <NUM> thus locks the support platform <NUM> to the spar leg 72b such that the airfoil fairing <NUM> is mechanically trapped between the spar platform 72a and the support platform <NUM>. It is to be appreciated that the example configuration could be used at the outer end of the airfoil fairing <NUM>, with the spar <NUM> being inverted such that the spar platform 72a is adjacent the platform <NUM> and the support platform <NUM> is adjacent the platform <NUM>. The spar <NUM> may be formed of a relatively high temperature resistance, high strength material, such as a single crystal metal alloy (e.g., a single crystal nickel- or cobalt-alloy).

Cooling air, such as bleed air from the compressor section <NUM>, is conveyed into and through the through-passage 72c of the spar <NUM>. This cooling air is destined for a downstream cooling location, such as a tangential onboard injector (TOBI). Cooling air may also be provided into cavity <NUM> in the gap between the airfoil wall <NUM> and the spar leg 72b. The through-passage 72c is fully or substantially fully isolated from the gap. Thus, the cooling air in the through-passage 72c does not intermix with cooling air in the gap.

<FIG> illustrates the end portion <NUM> of the spar leg 72b and clevis mount <NUM>. The clevis mount <NUM> includes first and second prongs 84a/84b. The prongs 84a/84b are connected along the trailing end side of the spar leg 72b in the illustrated example, although they could alternatively be separated. There is a pin fairing <NUM> that extends over the region between the prongs 84a/84b where the pin <NUM> extends. Once the pin <NUM> is inserted through the holes <NUM>, the pin fairing <NUM> extends over the pin <NUM> and thereby provides an aerodynamic surface over the pin <NUM> for guiding the cooling air flowing through the through passage 72c. Moreover, the pin fairing <NUM> in this example is integral with the walls of the spar leg 72b such that the pin fairing <NUM> seals the pin <NUM> from the through-passage 72c. Thus, cooling air cannot leak from the through-passage 72c at the location of the pin <NUM>.

The pin fairing <NUM> has a geometry that facilitates flow of the cooling air over the surface of the pin fairing <NUM>. For instance, in the illustrated example, the pin fairing <NUM> is a cylindrical segment. The rounded shape of the cylindrical segment avoids abrupt changes in flow direction and thus serves to help reduce pressure loss. As an example, as shown in <FIG>, cooling air CA flow through the through-passage 72c in the spar leg 72b. As the cooling air encounters the pin fairing <NUM>, the cooling air gradually turns and flows over the pin fairing <NUM> before being discharged from the through-passage 72c.

The rounded shape of the pin fairing <NUM> defines a throat <NUM> in the through passage 72c. The throat <NUM> represents the minimum cross-sectional flow area of the through-passage 72c in the end portion <NUM>. The throat <NUM> is defined by the apex <NUM> of the curvature of the pin fairing <NUM>. The through-passage 72c changes from converging to diverging at the apex <NUM>. The flow area at the throat <NUM>, the convergence, and the divergence may be selected to modulate the flow of the cooling air through the through-passage 72c.

The pin fairing <NUM> may also serve as a bushing for the pin <NUM>. In this regard, the interior surface of the pin fairing <NUM> includes a bearing surface <NUM> in contact with the pin <NUM>. Although the pin <NUM> may not be designed to substantially translate or rotate, some movement may be expected due to engine vibration. The bearing surface <NUM> may include a wear-resistance hardcoat 92a to reduce wear on the pin fairing <NUM> and/or pin <NUM>. As an example, the hardcoat 92a is a cobalt alloy that is harder than the alloy from which the spar leg 72b is made.

The pin fairing <NUM> may be formed integrally with the other portions of the spar leg 72b. For example, the spar leg 72b is formed in a process such as, but not limited to, casting or additive manufacturing, and the pin fairing <NUM> is formed in situ along with the prongs 84a/84b of the spar leg 72b during the process.

Alternatively, a pin fairing can be pre-fabricated and then attached to the prongs 84a/84b after formation of the spar leg 72b. For example, a pin fairing may be formed from sheet metal or cast separately and then attached over the pin <NUM>. One such example falling outside the wording of the claims is illustrated in <FIG> in which pin fairing <NUM> is welded to the first and second prongs 84a/84b. In this example, the pin fairing <NUM> is formed of sheet metal and is substantially planar. The pin fairing <NUM> provides a "ramp" to deflect the cooling air in the through-passage 72c such that the cooling air flows around the pin <NUM>.

As best shown in <FIG>, the pin <NUM> in the illustrated examples is offset toward one side of the spar leg 72b. In this case, the pin <NUM> is offset toward the trailing end side of the spar leg 72b and there is an inset <NUM> at the leading end side such that the leading edges of the prongs 84a/84b are offset from the leading edge side of the spar leg 72b. The inset <NUM> is open and thus also serves as a portion of the outlet of the through-passage 72c. The inset <NUM> increases the overall area of the outlet of the through-passage 72c, in comparison to a straight outlet. It is to be appreciated that the inset <NUM> and the prongs 84a/84b may alternatively be flipped such that the prongs 84a/84b are offset toward the leading edge side of the spar leg 72b and the inset is at the trailing edge side of the spar leg 72b. <FIG> illustrates a modified example in which the pin <NUM> is centrally located between leading and trailing sides of the spar leg 72b. In this case, there is no inset and the pin fairing <NUM> diverts the cooling air CA forward and aft of the pin <NUM>.

Claim 1:
A spar (<NUM>) for a vane arc segment (<NUM>) of a gas turbine engine, the spar (<NUM>) comprising:
a spar platform (72a) and a hollow spar leg (72b) that extends from the spar platform (72a), the hollow spar leg (72b) having
an internal passage (72c) for receiving cool air therethrough,
a clevis mount (<NUM>) that is distal from the spar platform (72a), the clevis mount (<NUM>) including first and second prongs (84a, 84b) with aligned holes (<NUM>) for receiving a pin (<NUM>) therethrough, and
a pin fairing (<NUM>; <NUM>) extending over the aligned holes (<NUM>) between the first and second prongs (84a, 84b) for guiding the cooling air, wherein the pin fairing (<NUM>; <NUM>) is a cylindrical segment,
characterised in that:
the pin fairing (<NUM>; <NUM>) extends across the internal passage (72c) of the hollow spar leg (72b) so as to define a throat (<NUM>) in the internal passage (72c), wherein the throat (<NUM>) comprises a minimum cross-sectional flow area of the internal passage (72c).