Patent Description:
The high pressure turbine drives the high pressure compressor through an outer shaft to form a high spool, and the low pressure turbine drives the low pressure compressor through an inner shaft to form a low spool. The fan section may also be driven by the low inner shaft. A direct drive gas turbine engine includes a fan section driven by the low spool such that the low pressure compressor, low pressure turbine and fan section rotate at a common speed in a common direction.

A prior art airfoil having the features of the preamble to claim <NUM> is disclosed in <CIT>.

From a first aspect, the present invention provides an airfoil as claimed in claim <NUM>.

From a second aspect, the present invention provides a gas turbine engine as claimed in claim <NUM>.

Embodiments of each above aspect of the invention are as claimed in the dependent claims thereof.

From a third aspect, the present invention provides a gas turbine engine as claimed in claim <NUM>.

"Low corrected fan tip speed" is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R) / (<NUM> °R)]^<NUM> (where °R = K x <NUM>/<NUM>).

<FIG> illustrates a representative example of a turbine airfoil <NUM> used in the turbine engine <NUM> (see also <FIG>); <FIG> illustrates a sectioned view of the airfoil <NUM>; and <FIG> shows a partial cutaway view of the airfoil <NUM>. As shown, the turbine airfoil <NUM> is a turbine vane; however, it is to be understood that, although the examples herein may be described with reference to the turbine vane, this disclosure is also applicable to turbine blades.

The turbine airfoil <NUM> includes an inner or first platform <NUM>, an outer or second platform <NUM>, and an airfoil section <NUM> that spans in a longitudinal direction A1 (which is also a radial direction relative to the engine central axis A) between the first and second platforms <NUM>/<NUM>. Terms such as "radially," "axially," or variations thereof are used herein to designate directionality with respect to the engine central axis A.

The airfoil section <NUM> includes an airfoil outer wall <NUM> that delimits the profile of the airfoil section <NUM>. The outer wall <NUM> defines a leading end 68a, a trailing end 68b, and first and second sides 68c/68d that join the leading and trailing ends 68a/68b. The first and second sides 68c/68d span in the longitudinal direction between first and second ends 68e/68f. The first and second ends 68e/68f are attached, respectively, to the first and second platforms <NUM>/<NUM>. In this example, the first side 68c is a suction side and the second side 68d is a pressure side. As shown in a sectioned view through the airfoil section <NUM> in <FIG>, the outer wall <NUM> circumscribes an internal core cavity <NUM>. Cooling air may be bled from the compressor section <NUM> and fed into the internal core cavity <NUM> to cool the airfoil section <NUM>.

The first platform <NUM> defines a shelf <NUM>. The shelf <NUM> generally extends outwards from the base of the airfoil section <NUM> at the first end 68e. The shelf <NUM> extends forward from the first end 68e at the leading end 68a of the airfoil section <NUM> to a platform leading edge 72a, aft from the first end 68e at the trailing end 68b of the airfoil section <NUM> to a platform trailing edge 72b, laterally from the first end 68e at the first side 68c of the airfoil section <NUM> to a first platform side edge 72c, and laterally from the first end 68e at the second side 68d of the airfoil section <NUM> to a second platform side edge 72d. It is to be understood that the second platform <NUM> may have different aerodynamic contours than the first platform <NUM> but has substantially the same type of features as the first platform <NUM>. Moreover, although the examples herein may be described with reference to the first platform <NUM>, it is to be appreciated that the examples are also applicable to the second platform <NUM>.

As depicted in <FIG>, the shelf <NUM> includes a plenum <NUM>. The plenum <NUM> is also represented in <FIG>, which shows an "inverse" or negative view of the plenum <NUM>. The inverse view is also representative of an investment core that may be used in an investment casting process to form the plenum <NUM> in the airfoil <NUM>. Most typically, the investment casting core is injection molded from a material that contains ceramic or metal alloy. The investment core is shaped to form the plenum <NUM>. In the inverse view, solid structures of the investment core produce void structures in the plenum <NUM> and void structures of the investment core produce solid structures in the plenum <NUM>. Thus, the investment core has the negative of the structural features of the platform <NUM>. It is to be understood that although the inverse views presented herein may be used to describe features of the plenum <NUM> and/or platform <NUM>, each negative view may also represents an investment core and a corresponding cavity in a molding tool that is operable to molding the investment core.

The shelf <NUM> includes a plurality of cooling orifices <NUM> that extend from the plenum <NUM> toward the platform edge. In this example, the platform edge is the first platform side edge 72c. The shelf <NUM> only contains the cooling orifices <NUM> on one side such that there are no such orifices on the second platform side edge 72d.

<FIG> illustrates a sectioned view through the platform <NUM> and a representative one of the cooling orifices <NUM>. The cooling orifice <NUM> has a first orifice end 76a that opens to the plenum <NUM> and a second, closed orifice end 76b that is adjacent the first platform side edge 72c. In the example shown, the first orifice end is flared, to facilitate smooth inflow of cooling air into the cooling orifice <NUM>. There is a relatively thin wall segment <NUM> between the second, closed orifice end 76b and the first platform side edge 72c. As depicted, the cooling orifice <NUM> is of uniform cross-section along its length. However, as shown in <FIG>, the cooling orifice <NUM> may alternatively be tapered from the first orifice end 76a to the second orifice end 76b.

During operation of the engine <NUM> cooling air is provided to the airfoil <NUM>. For example, bleed air form the compressor section <NUM> is provided through the platform <NUM> into the core cavity <NUM>. The cooling air flows in the plenum <NUM> prior to flowing into the core cavity <NUM>. However, the thin wall segment <NUM> blocks the cooling air from flowing through the cooling orifices <NUM> (although the cooling air may enter and circulate in the cooling orifices <NUM>). Over time, the first platform side edge 72c, which may be formed of metal such as a nickel alloy, may corrode, erode, or both, thereby causing the wall segment <NUM> to be lost and eventually opening the end 76b of the cooling orifice <NUM>, as depicted in <FIG>. Once the end 76b is open, the cooling air can then flow through the cooling orifice <NUM> and is then discharged at the first platform side edge 72c. In the case of the tapered orifice <NUM> of <FIG>, as more of the platform <NUM> corrodes and is lost, the tapered orifice <NUM> opens wider to provide a greater amount of cooling air flow until there is enough flow to substantially stop local oxidation.

The configuration of the cooling orifices <NUM> may be adapted to provide different types of cooling once opened. As an example, <FIG> illustrates two of the airfoils, designated at 60a and 60a, arranged next to each other in the engine <NUM>. That is, the first platform side edge 72c of the first airfoil 60a is arranged next to the second platform side edge 72d of the second airfoil 60b such that there is a gap <NUM> between the edges 72c/72d. Additionally, the first platform side edge 72c includes a first slot portion 82a and the second platform side edge 72d includes a second slot portion 82b. The first seal slot portion 82a is overlapping with the cooling orifice <NUM> in the longitudinal direction A1. That is, a line parallel to the longitudinal direction A1 intersects both the first seal slot portion 82a and the cooling orifice <NUM>.

The slot portions 82a/82b together form a seal slot <NUM>. A feather seal <NUM> is disposed in the seal slot <NUM> and spans across the gap <NUM>. Although not directly in the core gas path, the temperatures in the gap <NUM> can cause oxidation of the platforms <NUM>, and particularly the edges 72c/72d. However, upon corrosion and loss of the wall segment <NUM>, the cooling orifices <NUM> open to provide cooling air into the gap <NUM>. The cooling air facilitates the reduction of further oxidation and loss at the edges 72c/72d. For instance, a portion of the cooling air may bleed from the cooling orifice <NUM> along the edge 72c to provide cooling and/or may jet across the gap <NUM> to impinge on the edge 72d to provide cooling. In this regard, the cooling orifice <NUM> is straight in order to jet the cooling air into the gap <NUM>. As an example, the cooling orifice <NUM> (central orifice axis A2) is perpendicularly oriented to the longitudinal direction A1, and the end 76b is flat (non-tapered). The end 76b may thus substantially completely open once the wall segment <NUM> is lost.

<FIG> illustrates another example of a cooling orifice <NUM>. In this example, the cooling orifice <NUM> (central orifice axis A2) is obliquely angled to the longitudinal direction A1 and the end 176b is tapered. As an example, the cooling orifice <NUM> forms an angle between <NUM>° and <NUM>° with a line parallel to the longitudinal direction A1. The cooling orifice <NUM> (central orifice axis A2) may also be obliquely angled to the engine central axis A. As an example, the cooling orifice <NUM> forms an angle between <NUM>° and <NUM>° with a line parallel to the engine central axis A. Thus, the cooling orifice <NUM> may be angled both longitudinally (radially) and axially. However, as shown in <FIG>, the cooling orifice <NUM> may alternatively be tapered from the first orifice end 76a to the second orifice end 176b.

As depicted in the <FIG>, once wall segment <NUM> corrodes and is lost, the end 176b opens. In this example, the bottom surface of the platform <NUM> in the figure borders the core gas path. The angling of the cooling orifice <NUM> provides a film of cooling air along the oxidized surface around the end 176b, to facilitate reduction in further oxidation and loss. In the case of the tapered orifice <NUM> of <FIG>, as more of the platform <NUM> corrodes and is lost, the tapered orifice <NUM> opens wider to provide a greater amount of cooling air flow until there is enough flow to substantially stop local oxidation.

Claim 1:
An airfoil (<NUM>) for a gas turbine engine (<NUM>), the airfoil (<NUM>) comprising:
an airfoil section (<NUM>) having an airfoil wall (<NUM>) defining leading and trailing ends (68a, 68b) and first and second sides (68c, 68d) joining the leading and trailing ends (68a, 68b), the first and second sides (68c, 68d) spanning in a longitudinal direction (A1) between first and second ends (68e, 68f), the airfoil wall (<NUM>) circumscribing an internal core cavity (<NUM>); and
a platform (<NUM>) from which the airfoil section (<NUM>) extends, the platform (<NUM>) defining a shelf (<NUM>) that extends from the airfoil section (<NUM>) to a platform edge (72c), the shelf (<NUM>) including a plenum (<NUM>, <NUM>) and a plurality of cooling orifices (<NUM>) extending from the plenum (<NUM>, <NUM>) toward the platform edge (72c), each of the cooling orifices (<NUM>) having a first orifice end (276a) opening to the plenum (<NUM>, <NUM>) and a second orifice end (276b) adjacent the platform edge (72c), but separated therefrom by a wall segment (<NUM>) which blocks the cooling air from flowing from the cooling orifices (<NUM>) to the platform edge (72c),
characterised in that:
the platform (<NUM>) defines a bridge passage (<NUM>) interconnecting the cooling orifices (<NUM>);
the platform has a first platform side edge (72c) and a second platform side edge (72d), respectively configured to be positioned adjacent to a second platform side edge (72d) and a first platform side edge (72c) of platforms (<NUM>) of circumferentially adjacent airfoils (<NUM>).