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.

<CIT> discloses a prior art gas turbine engine having the features according to the preamble to claim <NUM>.

<CIT> discloses a prior art gas turbine engine component cooling circuit.

<CIT> discloses a prior art cooled airfoil.

<CIT> discloses a prior art hot gas path component with mesh and turbulated cooling.

<CIT> discloses a prior art turbine blade trailing edge with low flow framing channel.

<CIT> discloses a prior art article having a cooling passage with an undulating profile.

<CIT> discloses a prior art casting core for a blade outer air seal.

In accordance with a first aspect, the present invention provides a gas turbine engine article as claimed in claim <NUM>.

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

In accordance with a third aspect, the present invention provides a tool as claimed in claim <NUM>.

A further embodiment of any of the foregoing embodiments includes a third channel length of non-constant cross-section that is discontinuous with the second channel length. The second channel length is between the first channel length and the inlet mouth and the third channel length is between the first channel length and the outlet mouth.

In a further embodiment of any of the foregoing embodiments, the first channel length spans a length L1 and the constant cross-section defines a width W1 that is perpendicular to the length L1, and L1 is greater than W1 by a factor of at least <NUM>.

In a further embodiment of any of the foregoing embodiments, the length L1 is no greater than <NUM> times the width W1.

In a further embodiment of any of the foregoing embodiments, each of the pedestals has an aspect ratio of no greater than <NUM>.

A gas turbine engine according to a second aspect of the present disclosure includes a compressor section, a combustor in fluid communication with the compressor section, and a turbine section in fluid communication with the combustor. The turbine section has a turbine engine article according to any of the foregoing embodiments.

A tool according to a third aspect of the present disclosure includes a molding cavity operable for molding an investment core that is shaped to form a cooling passage network embedded in a wall of a gas turbine engine article. The investment core represents a negative of the cooling passage network in which solid structures of the investment core produce void structures in the cooling passage network and void structures of the investment core produce solid structures in the cooling passages network. The investment core has the negative of the following structures of the cooling passage network: an inlet orifice, a sub-passage region that has an array of pedestals, and at least one outlet orifice. The array of pedestals has first pedestals arranged in a first row and second pedestals arranged in a second, adjacent row. The first pedestals and the second pedestals define inter-row sub-passages there between. Each of the inter-row sub-passages have an inlet mouth, an outlet mouth, and a compound channel connecting the inlet mouth and the outlet mouth. The compound channel includes a first channel length over which the inter-row sub-passage has a constant cross-section and a second channel length over which the inter-row sub-passage has a non-constant cross-section.

"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 gas turbine engine article, namely a turbine airfoil <NUM> used in the turbine engine <NUM> (see also <FIG>). 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 airfoil, this disclosure is also applicable to turbine blades and blade outer air seals. The turbine airfoil <NUM> is also shown in a cross-sectioned view in <FIG>.

Referring to <FIG> and <FIG>, the turbine airfoil <NUM> includes an inner platform <NUM>, an outer platform <NUM>, and an airfoil section <NUM> that spans between the inner and outer platforms <NUM>/<NUM>. The airfoil section <NUM> includes an article wall or airfoil outer wall <NUM> that delimits the profile of the airfoil section <NUM>. The outer wall <NUM> defines a leading end (LE), a trailing end (TE), and first and second sides <NUM>/<NUM> that join the leading and trailing ends. In this example, the first side <NUM> is a pressure side and the second side <NUM> is a suction side. The outer wall <NUM> circumscribes an internal core cavity <NUM>, which in this example is partitioned by a rib <NUM> into a forward core cavity 74a and an aft core cavity 74b. As will be appreciated, there may alternatively be only a single core cavity or there may be additional ribs to partition additional core cavities.

There is at least one cooling passage network <NUM> embedded in the airfoil outer wall <NUM> between inner and outer portions 68a/68b of the airfoil wall <NUM>. For example, as shown (<FIG>) one or more of the cooling passage networks <NUM> is embedded in the second side <NUM> of the outer wall <NUM>, although one or more networks <NUM> could additionally or alternatively be embedded in the first side <NUM>. The cooling passage networks <NUM> may also be referred to as minicores or minicore passages. A "minicore" or "mini core passage" is a reference to the small investment casting core that is typically used to make such an embedded passage, as opposed to a main core that is used to form a main or central core cavity in an airfoil.

<FIG> shows an "inverse" or negative view of a representative one of the cooling passage networks <NUM>. The inverse view is also representative of an investment core that may be used in an investment casting process to form the network <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 cooling passage network <NUM>. In the inverse view, solid structures of the investment core produce void structures in the cooling passage network <NUM> and void structures of the investment core produce solid structures in the cooling passage network <NUM>. Thus, the investment core has the negative of the structural features of the cooling passage network <NUM>. It is to be understood that although the inverse views presented herein may be used to describe features of the network <NUM>, each negative view also represents an investment core and a corresponding cavity in a molding tool that is operable to molding the investment core.

The cooling passage network <NUM> includes at least one inlet orifice <NUM> through the inner portion 68a of the airfoil outer wall <NUM> (<FIG>) to receive cooling air from the internal core cavity <NUM>. Most typically, the network <NUM> will include two inlet orifices <NUM>. A single, exclusive inlet orifice <NUM> is also contemplated, as well as more than two inlet orifices <NUM>, although fabrication may be challenging.

The inlet orifices <NUM> open into a radially-elongated manifold region <NUM> (see <FIG>, radial direction RD), which serves to distribute the cooling air to a downstream sub-passage region <NUM>, which then leads into an exit region <NUM> that feeds into one or more outlet orifices 81a (<FIG>) through the outer portion 68b of the airfoil wall <NUM>. In this example, the exit region <NUM> includes a plurality of flow guides 81b. For instance, the flow guides 81b have a teardrop shape and facilitate straightening and guiding flow into the one or more outlet orifices 81a. In general, the inlet orifices <NUM> of the network <NUM> are located forward of the one or more outlet orifices 81a.

One of the inlet orifices <NUM> is located in the radially upper half of the manifold region <NUM> and the other of the inlet orifices <NUM> is in the radially lower half of the manifold region <NUM>. Most typically, the radially upper and lower halves of the network <NUM> are mirror images, i.e., symmetric relative to the midline of the network <NUM> between the two inlet orifices <NUM>.

In this example, the region <NUM> includes an array of pedestals <NUM>. The array of pedestals <NUM> includes first pedestals <NUM> and second pedestals <NUM>. The first pedestals <NUM> are arranged in a first row <NUM> and the second pedestals <NUM> are arranged in a second row <NUM>. The rows <NUM>/<NUM> extend in the radial direction RD in the airfoil <NUM>, which is perpendicular to the engine axis A. The second pedestals <NUM> are also radially offset from the first pedestals <NUM> and interleaved with the first pedestals <NUM> so as to define inter-row sub-passages <NUM> there between, as opposed to intra-row sub-passages within the rows <NUM>/<NUM> defined between either adjacent first pedestals <NUM> or defined between adjacent second pedestals <NUM>.

The first and second pedestals <NUM>/<NUM> as shown have a triangular shape and are all of unequal size in cross-section, although in modified examples the pedestals <NUM>/<NUM> can be of equal size in cross-section. For example, the triangular shape of the cross-section of the pedestals <NUM>/<NUM> defines three points, or apexes, and three sides that connect the three apexes. In general, the sides may be curved, linear, or combinations of curved and linear.

<FIG> shows a magnified view of a representative one of the inter-row sub-passages <NUM> (hereafter "sub-passage <NUM>"), in which various sections of the sub-passage <NUM> are identified by dashed lines. The sections are arranged along a central sub-passage axis A1, which is the midline between the sides of the adjacent first and second pedestals <NUM>/<NUM> that define the sub-passage <NUM>.

The sub-passage <NUM> has an inlet mouth <NUM>, an outlet mouth <NUM>, and a compound channel <NUM> connecting the inlet mouth <NUM> and the outlet mouth <NUM>. The inlet mouth <NUM> converges and the outlet mouth <NUM> diverges with regard to the direction of flow through the sub-passage <NUM>. The limits of these sections are demarcated by inflections on one or both of the sides of the pedestals <NUM>/<NUM> at which the geometry of the sides distinctly changes, such as but not limited to, locations where a curved portion changes to a linear portion, locations where two linear portions of different slope meet, or locations where two curved portions of different radii of curvature meet. In the examples herein (e.g., see <FIG> and <FIG>), the sides of the pedestals are designated with break lines B1 that represent locations B2 on the sides at which the geometry of the pedestals distinctly changes.

The compound channel <NUM> includes a first channel length <NUM> over which the sub-passage <NUM> has a constant cross-section, which is represented at 91a, and a second channel length <NUM> over which the sub-passage <NUM> has a non-constant cross-section, which is represented at 92a. In a further example, the first channel length <NUM> is also linear. Although "first" and "second" are used to designate the sections of the channel lengths <NUM>/<NUM>, it is to be understood that such designations do not necessarily represent the serial flow order of the sections. The cross-sections 91a/92a are sections taken perpendicular to the central sub-passage axis A1.

The second channel length <NUM> is situated between the inlet mouth <NUM> and the first channel length <NUM>. For instance, the second channel length <NUM> starts at the terminal end of the inlet mouth <NUM> and spans continuously to its own terminal end, at which the first channel length <NUM> then starts. The first channel length <NUM> is situated between the second channel length <NUM> and the outlet mouth <NUM>. For instance, the first channel length <NUM> starts at the terminal end of the second channel length <NUM> and spans continuously to its own terminal end, at which the outlet mouth <NUM> then starts.

The first channel length <NUM> extends over a length L1 and the second channel length <NUM> extends over a length L2. For example, the lengths L1 and L2 are the distances along the central sub-passage axis A1. In the example shown, the length L1 of the first channel length <NUM> is equal to the length L2 of the second channel length L2 within +/- <NUM>%.

During operation of the engine <NUM>, cooling air, such as bleed air from the compressor section <NUM>, is provided to the internal core cavity <NUM> and flows into the network <NUM> via the inlet orifices <NUM>. The manifold region <NUM> serves to distribute the flow of cooling air to the sub-passage region <NUM>, where the cooling air flows through the sub-passages <NUM> and then into the exit region <NUM> before being discharged through the one or more outlet orifices 81a to the exterior of the airfoil <NUM>.

With regard to the sub-passages <NUM>, the cooling air first enters the inlet mouth <NUM>, which feeds the cooling air into the second channel length <NUM>. In this example, the non-constant cross-section 92a converges toward the constant cross-section 91a and thereby compresses and accelerates the flow of cooling air. For instance, the non-constant cross-section 92a converges starting from the inlet mouth <NUM> and up to the first channel length <NUM>. The second channel length <NUM> feeds the accelerated flow of cooling air into the first channel length <NUM>, which then feeds the flow of cooling air to the outlet mouth <NUM> where the cooling air is discharged from the sub-passage <NUM>. In one example, the second channel length <NUM> converges at an angle of <NUM>° to <NUM>°, and especially <NUM>° to <NUM>°. As an alternative, to tailor the cooling effects, the non-constant cross-section 92a may instead diverge toward the constant cross-section 91a and thereby expand and decelerate the flow of cooling air.

The constant cross-section 91a of the first channel length <NUM> is the narrowest stretch of the sub-passage <NUM> and thus serves to meter the flow of cooling air through the sub-passage <NUM> to facilitate controlled cooling of the airfoil wall <NUM>, and in particular to facilitate controlled cooling of the outer portion 68b of the airfoil wall <NUM>.

In addition to the metering function, the constant cross-section 91a of the first channel length <NUM> also enables enhanced durability in the fabrication process of the investment core used to form the network <NUM>. More specifically, the material that is injected into the tool cavity to form the investment core contains ceramic or metal that erodes the wall of the tool cavity over molding cycles, changing original design dimensions that are important for flow metering. For instance, in locations where the tool cavity converges, the material impinges more directly against the cavity wall during injection and thereby accelerates erosion at that location in comparison to non-converging locations. In a sub-passage that has a singular point location of convergence to meter flow, that singular point location corresponds to such a location of greater erosion in the tool cavity during the molding process. As a result, the tool cavity at that singular point location, which is designed to have a particular dimension for proper flow metering, enlarges over multiple molding cycles due to erosion. In turn, over many molding cycles in the tool cavity, the resulting singular point location in the sub-passage enlarges and departs from design tolerances, thereby potentially changing the flow of cooling air through the sub-passage. And in instances where the design dimension departs significantly, the tool may need to be repaired or replaced.

The constant cross-section 91a of the first channel length <NUM> mitigates the effect of such erosion. Specifically, the location in the tool cavity corresponding to the leading end of the first channel length <NUM> may experience erosion. However, the location in the tool cavity corresponding to the first channel length <NUM> is eroded from the leading end thereof (adjacent the second channel length <NUM>) toward the trailing end thereof (adjacent the outlet mouth <NUM>). As an example, over a first number of injection molding cycles, the location in the tool cavity corresponding to the first channel length <NUM> may erode over <NUM>% of the length L1 starting from the leading end thereof. The cross-section 91a of the <NUM>% of the initial portion of the first channel length <NUM> would thus enlarge beyond the initial cross-section 91a. The remaining <NUM>% of the length L1 of the first channel length <NUM> would experience no erosion, or at least less erosion, and the initial cross-section 91a would thus be preserved.

Similarly, over a second, greater number of injection molding cycles, the location in the tool cavity corresponding to the first channel length <NUM> may erode over <NUM>% of the length L1 from the leading end thereof. The cross-section 91a of the <NUM>% of the initial portion of the first channel length <NUM> would thus enlarge beyond the initial cross-section 91a. The remaining <NUM>% of the length L1 of the first channel length <NUM> would experience no erosion, or at least less erosion, and the initial cross-section 91a would thus be preserved.

The preservation of the initial cross-section 91a over at least a portion of the length L1 in such a manner thereby ensures that the investment cores that are produced after many molding cycles are not unduly oversized and that the sub-passages <NUM> that are eventually produced from the investment cores have a narrowest portion that is dimensioned to properly meter the flow of cooling air. As will be further appreciated, the molding tool can also be used for a longer period of time before repair or replacement is necessary.

The first channel length <NUM> is configured to mitigate the above-described erosion concerns. As will be appreciated from the description above, designing the first channel length <NUM> with a greater length L1 would enhance mitigation of the erosion concern, as more molding cycles would be required to erode the full length of the first channel length <NUM>. Inversely, a shorter length L1 would somewhat diminish mitigation of the erosion concern, as fewer molding cycles would be necessary to erode the full length of the first channel length <NUM>. In this regard, it is contemplated that the first channel length <NUM> should have a minimum relative size in order achieve enhanced mitigation of erosion. As an example, the first channel length <NUM>, spans over the length L1 and the constant cross-section 91a defines a width W1 along the direction perpendicular to the central sub-passage axis A1 between the sides of the adjacent pedestals <NUM>/<NUM>. The length L1 is at least equal to the width W1, and in further example the length L1 is greater than width W1. In an additional example, the length L1 is greater than the width W1 by a factor of at least <NUM> or by a factor of at least <NUM>. As will be appreciated, there may be constraints on the size and number of the pedestals <NUM>/<NUM> and overall "footprint" size of the network <NUM> in the airfoil <NUM>. Given these constraints, it is thus contemplated that the first channel length <NUM> will also have a maximum size in which the length L1 is no greater than <NUM> times the width W1.

As will also be appreciated, the geometry of the pedestals <NUM>/<NUM> and the number of rows <NUM>/<NUM> can also be varied to tailor flow of the cooling air and the resulting cooling effects while also retaining the above-described sub-passages <NUM>. <FIG>, <FIG> illustrate such modified examples, although it is to be understood that this disclosure is not limited. In the example shown in <FIG>, the network <NUM> contains two first rows, represented at <NUM> and <NUM>, and two second rows, represented at <NUM> and <NUM>. Where appropriate in this disclosure, identical whole numbers designate corresponding elements among the examples and the addition of a trailing decimal number is used as indication of a modification in the particular example being described. Also where appropriate, identical whole numbers may be used with the addition of one-hundred or multiples of one-hundred to designate corresponding elements among different embodiments.

The array of pedestals <NUM> includes first pedestals <NUM> that are arranged in the first row <NUM>, and second pedestals <NUM> that are arranged in the second row <NUM>. The array of pedestals <NUM> further includes an additional set of first pedestals <NUM> that are arranged in the other first row <NUM>, and an additional set of second pedestals <NUM> that are arranged in the other second row <NUM>. The second pedestals <NUM> are radially offset from the first pedestals <NUM> and interleaved with the first pedestals <NUM> so as to define the sub-passages <NUM> there between. Likewise, the second pedestals <NUM> are radially offset from the first pedestals <NUM> and interleaved with the first pedestals <NUM> so as to define the sub-passages <NUM> there between.

In this example, the pedestals <NUM>, <NUM>, and <NUM> have a triangular shape and may be of equal or unequal size in cross-section. In comparison to the pedestals <NUM> and <NUM>, the pedestals <NUM>, <NUM>, and <NUM> are somewhat larger, especially in the radial direction RD. The pedestals <NUM> have a non-triangular shape. In the example shown, the pedestals <NUM> have an irregular diamond cross-section which is defined by four points, or apexes, and four sides that connect the four apexes. In general, the sides may be curved, linear, or combinations of curved and linear.

The modified examples of the network <NUM> shown in <FIG> are similar to the example of <FIG>. However, the network <NUM> as shown in <FIG> is somewhat smaller, with fewer pedestals in the rows, while the network <NUM> in <FIG> is somewhat larger, with additional pedestals in the rows. Additionally, a portion of the pedestals in <FIG> have a similar shape as the pedestals of <FIG> but additionally include diamond-shaped pedestals in the last row.

<FIG> illustrates another example of a cooling passage network <NUM>. In this example, the network <NUM> contains two first rows, represented at <NUM> and <NUM>, and two second rows, represented at <NUM> and <NUM>. The array of pedestals <NUM> includes first pedestals <NUM> that are arranged in the first row <NUM>, and second pedestals <NUM> that are arranged in the second row <NUM>. The array of pedestals <NUM> further includes an additional set of first pedestals <NUM> that are arranged in the other first row <NUM>, and an additional set of second pedestals <NUM> that are arranged in the other second row <NUM>. The second pedestals <NUM> are radially offset from the first pedestals <NUM> and interleaved with the first pedestals <NUM> so as to define the inter-row sub-passages <NUM> there between. Likewise, the second pedestals <NUM> are radially offset from the first pedestals <NUM> and interleaved with the first pedestals <NUM> so as to define the sub-passages <NUM> there between.

In this example, the pedestals <NUM>, <NUM>, <NUM>, and <NUM> have a lobed-diamond shape in which each of the faces of the diamond has concavities such that the tips of the diamond form rounded projections, i.e., a lobes. As a result, the geometry of the sub-passage <NUM> differs somewhat from that of the sub-passage <NUM>.

<FIG> shows a magnified view of a representative one of the sub-passages <NUM>, in which various sections of the sub-passage <NUM> are identified by dashed lines. The sections are arranged along the central sub-passage axis A1, which is the midline between the sides of the adjacent first and second pedestals <NUM>/<NUM> (or alternatively <NUM>/<NUM>) that define the sub-passage <NUM>.

The sub-passage <NUM> has an inlet mouth <NUM>, an outlet mouth <NUM>, and a compound channel <NUM> connecting the inlet mouth <NUM> and the outlet mouth <NUM>. For instance, the inlet mouth <NUM> converges and the outlet mouth <NUM> diverges with regard to the direction of flow through the sub-passage <NUM>. Again, the limits of these sections may be demarcated by inflections or other locations on the sides of the pedestals at which the geometry of the sides distinctly changes.

The compound channel <NUM> includes a first channel length <NUM> over which the sub-passage <NUM> has a constant cross-section, which is represented at 191a, and a second channel length <NUM> over which the sub-passage <NUM> has a non-constant cross-section, which is represented at 192a. In a further example, the first channel length <NUM> is also linear.

In this example, the second channel length <NUM> is situated between the inlet mouth <NUM> and the first channel length <NUM>. For instance, the second channel length <NUM> starts at the terminal end of the inlet mouth <NUM> and spans continuously to its own terminal end, at which the first channel length <NUM> then starts. The first channel length <NUM> is situated between the second channel length <NUM> and the outlet mouth <NUM>. However, in this example, rather spanning continuously to the outlet mouth <NUM>, there is a third channel length <NUM> interposed between the terminal end of the first channel length <NUM> and the start of the outlet mouth <NUM>. For instance, the second and third channel lengths <NUM>/<NUM> are formed, at least in part, by concavities in the sides of the pedestals. Similar to the second channel length <NUM>, the third channel length <NUM> has a non-constant cross-section, represented at 193a. The second and third channel lengths <NUM>/<NUM>, which are interrupted by the first channel length <NUM>, thus form a discontinuous passage of non-constant cross-section.

The first channel length <NUM> extends over a length L1, the second channel length <NUM> extends over a length L2, and the third channel length <NUM> extends over a length L3. The lengths L1, L2, and L3 are the distances along the central sub-passage axis A1. In the example shown, the length L1 of the first channel length <NUM> is greater than the length L2 of the second channel length L2 by at least <NUM>%, and the length L1 is also greater than the length L3 of the third channel length <NUM> by at least <NUM>%. Similar to the sub-passage <NUM>, the length L1 of the sub-passage <NUM> is at least equal to the width W1 and may be greater than the width W1, such as by a factor of at least <NUM> or by a factor of at least <NUM>. Moreover, the length L1 may also be no greater than <NUM> times the width W1 for the reasons discussed above.

In this example, the pedestals <NUM>, <NUM>, <NUM>, and <NUM> have a regular diamond shape in which each of the faces of the diamond are substantially flat. As a result, the geometry of the sub-passage <NUM> differs from that of the sub-passage <NUM>/<NUM>.

<FIG> shows a magnified view of a representative one of the sub-passages <NUM>, in which various sections of the sub-passage <NUM> arranged along the central sub-passage axis A1. The sub-passage <NUM> has an inlet mouth <NUM>, an outlet mouth <NUM>, and a compound channel <NUM> connecting the inlet mouth <NUM> and the outlet mouth <NUM>. For instance, the inlet mouth <NUM> converges and the outlet mouth <NUM> diverges with regard to the direction of flow through the sub-passage <NUM>. Again, the limits of these sections may be demarcated by inflections or other locations on the sides of the pedestals at which the geometry of the sides distinctly changes.

The compound channel <NUM> includes a first channel length <NUM> over which the sub-passage <NUM> has a constant cross-section, which is represented at 291a, and a second channel length <NUM> over which the sub-passage <NUM> has a non-constant cross-section, which is represented at 292a. In a further example, the first channel length <NUM> is also linear.

In this example, the second channel length <NUM> is situated between the inlet mouth <NUM> and the first channel length <NUM>. For instance, the second channel length <NUM> starts at the terminal end of the inlet mouth <NUM> and spans continuously to its own terminal end, at which the first channel length <NUM> then starts. The first channel length <NUM> is situated between the second channel length <NUM> and the outlet mouth <NUM>. Rather than spanning continuously to the outlet mouth <NUM>, the channel length <NUM> is interposed between the terminal end of the first channel length <NUM> and the start of the outlet mouth <NUM>. While the second and third channel lengths <NUM>/<NUM> or the prior example are formed at least in part by concavities in the pedestal sides, the second and third channel lengths <NUM>/<NUM> in this example are formed by an offset between the flat side portions of the pedestals. For instance, the leading end of the flat side portion of one of the pedestals is located farther upstream in the sub-passage <NUM> than the leading end of the flat side portion of the opposite pedestal. Inversely, the trailing end of the flat side portion of one of the pedestals is located farther downstream in the sub-passage <NUM> than the trailing end of the flat side portion of the opposite pedestal. That is, the flat side portions are staggered axially but radially overlap (relative to axis A1). It is the overlap portion that defines the first channel length <NUM>.

Similar to the second channel length <NUM>, the third channel length <NUM> has a non-constant cross-section, represented at 293a. The second and third channel lengths <NUM>/<NUM>, which are interrupted by the first channel length <NUM>, thus form a discontinuous passage of non-constant cross-section.

The first channel length <NUM> extends over a length L1, the second channel length <NUM> extends over a length L2, and the third channel length <NUM> extends over a length L3. In the example shown, the length L1 of the first channel length <NUM> is greater than each of the lengths L2 and L3 by at least <NUM>%. Similar to the sub-passage <NUM>, the length L1 of the sub-passage <NUM> is at least equal to the width W1 and may be greater than its width W1, such as by a factor of at least <NUM> or by a factor of at least <NUM>. Moreover, the length L1 may also be no greater than <NUM> times the width W1 for the reasons discussed herein.

<FIG> schematically illustrates an investment casting tool <NUM> that may be used in a molding process to form any of the investment cores disclosed herein. For example, the casting tool <NUM> is formed of a metal alloy and may contain a hard-facing or other protective surface to reduce wear and erosion. The tool <NUM> includes a molding cavity <NUM>. In this example, the molding cavity <NUM> is shown as an inverse view, e.g., the investment core as represented and described in <FIG>. The molding cavity <NUM> thus has the attributes of the core and/or cooling passage network as described herein. It is to be understood that the tooling cavity <NUM> may alternatively have the shape and attributes of any of the cooling passage networks herein, all of which are incorporated by reference into the disclosure of <FIG> and the casting tool <NUM>.

<FIG> illustrates another example gas turbine engine article <NUM>, namely a blade outer air seal <NUM>. The blade outer air seal <NUM> is an arc segment that is mounted in the engine <NUM> with like seals <NUM> to form an annular seal around the tips of the turbine blades. In this example, the cooling passage network <NUM> is employed in the blade outer air seal <NUM>. It is to be understood that although the blade outer air seal <NUM> is shown with network <NUM>, that the blade outer air seal <NUM> may alternatively employ any of the example networks <NUM>/<NUM> and features described or shown herein. In this example, the blade outer air seal <NUM> includes an article wall <NUM>. The wall <NUM> defines a leading end 103a, a trailing end 103b, a gaspath side 103c, and a non-gaspath side 103d. The gaspath side 103c faces toward the core gaspath of the engine <NUM> and may, at times, contact tips of the turbine blades. The wall <NUM> defines or includes attachment members 169a/169b, which serve to secure and mount the seal <NUM> to a case structure in the engine <NUM>.

The non-gaspath side 103d, and in this example also the attachment members 169a/169b, define a cavity <NUM>. The network <NUM> is embedded in the wall <NUM> between inner and outer portions 168a/168b of the wall <NUM>. The inlet orifice <NUM> of the network <NUM> opens through the inner portion 168a to the cavity <NUM>. Similar to the airfoil <NUM>, bleed air from the compressor section <NUM> can be provided to the cavity <NUM> to provide cooling air through the inlet orifice <NUM> into the network <NUM>.

Claim 1:
A gas turbine engine article (<NUM>, <NUM>) comprising:
an article wall (<NUM>, <NUM>) defining a cavity (<NUM>, <NUM>); and
a cooling passage network (<NUM>, <NUM>, <NUM>) embedded in the article wall (<NUM>, <NUM>) between inner and outer portions (68a, 168a, 68b, 168b) of the article wall (<NUM>, <NUM>), the cooling passage network (<NUM>, <NUM>, <NUM>) having an inlet orifice (<NUM>) through the inner portion (68a, 168a) of the article wall (<NUM>, <NUM>) to receive cooling air from the cavity (<NUM>, <NUM>), a sub-passage region (<NUM>) including an array of pedestals (<NUM>, <NUM>, <NUM>), and at least one outlet orifice (81a) through the outer portion (68b, 168b),
the array of pedestals (<NUM>, <NUM>, <NUM>) including first pedestals (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) arranged in a first row (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and second pedestals (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) arranged in a second, adjacent row (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>),
characterised in that:
the first pedestals (<NUM>... <NUM>) and the second pedestals (<NUM>...<NUM>) defining inter-row sub-passages (<NUM>, <NUM>, <NUM>) there between, each inter-row sub-passage (<NUM>, <NUM>, <NUM>) being defined between, respectively, one of the first pedestals (<NUM>... <NUM>) and one of the second pedestals (<NUM>...<NUM>);
each of the inter-row sub-passages (<NUM>, <NUM>, <NUM>) has an inlet mouth (<NUM>, <NUM>, <NUM>), an outlet mouth (<NUM>, <NUM>, <NUM>), and a compound channel (<NUM>, <NUM>, <NUM>) connecting the inlet mouth (<NUM>, <NUM>, <NUM>) and the outlet mouth (<NUM>, <NUM>, <NUM>), the compound channel (<NUM>, <NUM>, <NUM>) including a first channel length (<NUM>, <NUM>, <NUM>) over which the inter-row sub-passage (<NUM>, <NUM>, <NUM>) has a constant cross-section (91a, 191a, 291a) and from which the outlet mouth (<NUM>, <NUM>, <NUM>) diverges, and a second channel length (<NUM>, <NUM>, <NUM>) over which the inter-row sub-passage (<NUM>, <NUM>, <NUM>) has a non-constant cross-section (92a, 192a, 292a) and into which the inlet mouth (<NUM>, <NUM>, <NUM>) converges; and
the limits of the inlet mouth (<NUM>, <NUM>, <NUM>), the first channel length (<NUM>, <NUM>, <NUM>), the second channel length (<NUM>, <NUM>, <NUM>), and the outlet mouth (<NUM>, <NUM>, <NUM>) are each demarcated by inflections on one or both of the sides of the respective first and second pedestals.