Patent Description:
Gas turbine engines, such as those utilized in commercial and military aircraft, include a compressor section that compresses air, a combustor section in which the compressed air is mixed with a fuel and ignited, and a turbine section across which the resultant combustion products are expanded. The expansion of the combustion products drives the turbine section to rotate. The turbine section is connected to the compressor section via a shaft, and rotation of the turbine section further drives the compressor section to rotate. In some examples, a fan is also connected to the shaft and is driven to rotate via rotation of the turbine as well.

Each of the compressor and the turbine sections include multiple stages, with each stage being constructed of a ring of rotating rotor blades paired with a ring of static vanes. In some examples, the static vanes are constructed of clusters, where multiple circumferentially adjacent vanes in a given stage are a single integral component. Each integral component is referred to as a cluster.

During operation, the compressor and turbine sections are exposed to high operating temperatures. In some cases the high operating temperatures are mitigated via the use of active cooling systems that pass cooling air through the static vanes. The cluster construction can, in some examples, result in inbound regions between the vanes in a single cluster that are difficult to cool using conventional cooling systems.

<CIT> discloses a vane cluster for a gas turbine engine according to the preamble of claim <NUM>.

<CIT> discloses a cooled vane cluster, <CIT> discloses a multi-lobed cooling hole, and <CIT> discloses a turbine airfoil segment having a film cooling hole arrangement.

The present invention relates to a vane cluster, according to claim <NUM>.

The present invention also provides a gas turbine engine as set forth in claim <NUM>.

In another example of any of the above the plurality of vanes consists of the first vane and the second vane.

In an example of any of the above each EDM hole in the plurality of EDM holes is disposed in a visually obstructed region of the first vane.

The geared architecture <NUM> may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM>:<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>).

In some examples, each of the compressor stages and/or turbine stages includes multiple vanes configured as vane clusters. The vane clusters are single integral components including an outer diameter platform, an inner diameter platform, and two or more vanes spanning from the inner diameter platform to the outer diameter platform. The vane clusters are arranged in a ring with each vane cluster being adjacent to two other vane clusters in order to form the completed stage. Defined between the vanes in each vane cluster is an inbound region. When the vane cluster includes more than two vanes, an inbound region is defined between each adjacent vane in the vane cluster. In some example engines, it can be necessary to provide cooling air to the leading edge of one or more vanes in the vane cluster, and the configuration of the vanes can obstruct existing manufacturing techniques for incorporating this cooling.

<FIG> schematically illustrate an exemplary cooling scheme for providing cooling to the leading edge of a vane <NUM> in a vane cluster <NUM>, where the vane <NUM> has a suction side surface facing the inbound region <NUM>, according to one embodiment. It should be appreciated that the cooling scheme can be applied to vane clusters including three, four, or any other number of additional vanes, with the illustrated features being disposed on any vanes with a suction side surface facing the inbound region.

With regards to <FIG>, an exemplary vane cluster <NUM> is illustrated. The vane cluster <NUM> includes an outer diameter platform <NUM>, an inner diameter platform <NUM>, and multiple vanes <NUM> spanning from the outer diameter platform <NUM> to the inner diameter platform <NUM>. Each of the vanes <NUM> includes a leading edge <NUM> and a trailing edge <NUM>. The leading edge <NUM> is connected to the trailing edge <NUM> via a suction side surface and a pressure side surface. An inbound region <NUM> is defined between the vanes <NUM>. Within the inbound region <NUM>, is a visually obstructed region <NUM> on the suction side surface. The visually obstructed region <NUM> is a portion of the vane <NUM> where direct line of sight is obscured by another feature of the vane cluster <NUM>, such as the other vane <NUM>.

Included within each of the vanes <NUM> are multiple core cooling passages <NUM>, <NUM> (see <FIG>) including a leading edge core <NUM> and a trailing edge core <NUM>. The leading edge core <NUM> is positioned proximate to the leading edge <NUM> of the vane <NUM>, and provides a cooling flow that cools the leading edge <NUM>. Similarly, the trailing edge core <NUM> is provided proximate to the trailing edge <NUM> and provides a cooling flow that cools the trailing edge <NUM> of the vane <NUM>. In alternate examples, additional cores can be included beyond the leading edge core <NUM> and the trailing edge core <NUM>.

To cool the leading edge <NUM> of the vane <NUM>, multiple cooling holes <NUM> are included at or near the leading edge <NUM>. Existing systems utilize cooling holes connecting the trailing edge core <NUM> to a forward portion of the suction side surface, and position the cooling holes correspondingly offset from the leading edge <NUM>. In some examples, the positioning of the holes required to allow coolant to be drawn from a trailing edge core <NUM> is too far downstream of the leading edge <NUM> of the vane, and insufficient cooling is provided to the leading edge <NUM> of the vane <NUM>.

Further, in some existing systems, due to the integral structure of the vane cluster <NUM>, it can be difficult to create desirable cooling holes <NUM> in the vane <NUM> using existing techniques such as laser machining, when the vane <NUM> has a suction side surface facing the inbound region <NUM>. In alternative embodiments including more than two vanes per cluster <NUM>, each vane <NUM> that has a suction side surface facing an inbound region <NUM> can similarly require the cooling holes <NUM> and faces similar constructions difficulties using the existing techniques. The cooling hole configuration described herein can be extended to each of these vanes as well.

In order to mitigate stresses at the inbound region <NUM> resulting from insufficient cooling, the example vane cluster <NUM> shifts the forward most cooling holes <NUM> closer to the leading edge <NUM> of the vane <NUM>, into the visually obstructed region <NUM> and connects the forward most cooling holes <NUM> to the leading edge core <NUM>.

The illustrated example of <FIG> omits the conventional laser machined holes on the suction side of the vane <NUM>, and replaces them with a set of electrical discharge machined (EDM) cooling holes <NUM> in the visually obstructed region <NUM> of the vane <NUM>. With continued reference to <FIG> schematically illustrates a cross sectional view along view line A-A, of the example of <FIG>. In one example the set of EDM cooling holes <NUM> at the leading edge <NUM> includes eight EDM cooling holes <NUM>. The visually obstructed region <NUM> includes from six to ten EDM cooling holes <NUM>.

The exemplary system of <FIG> includes a greater flow of coolant through the leading edge core <NUM> than previous systems, and the removal of coolant from the leading edge core <NUM> due to the added EDM cooling holes <NUM> is offset by the increased cooling flow. In order to facilitate the increased cooling flow, the metering feature feeding the leading edge core was enlarged relative to previous systems. Further, the trailing edge core <NUM> is connected to fewer film cooling holes than existing systems, as shaped EDM cooling holes <NUM> provide better film cooling with fewer EDM cooling holes <NUM> than laser machined holes. The improved film effectiveness of the shaped EDM cooling holes arises primarily due to the shape of the diffuser <NUM> shown in <FIG>. The EDM process enables the production of diffuser shapes that are more efficient than can be produced by the laser machine process.

EDM manufacturing allows shaped EDM cooling holes <NUM> to be created instead of the simple holes created via laser machining, further facilitating the distribution of cooling air in a film cooling layer along the suction side surface. With continued reference to <FIG> schematically illustrates a cross section of an exemplary shaped hole <NUM>. <FIG> illustrates an alternative construction of the shaped film cooling hole <NUM> according to one example. The shaped EDM cooling holes <NUM> include a primary passage portion <NUM>, and a diffuser portion <NUM> connecting the primary passage portion <NUM> to the visually obstructed region <NUM>. The primary passage portion <NUM> directs the cooling flow from the source (the leading edge core <NUM>) to the visually obstructed region <NUM>, while the diffuser section <NUM> diffuses the flow through the film cooling hole <NUM>. The diffusion increases the adhesion of the cooling flow to the exterior surface of the vane <NUM>, increasing the film cooling effect.

In some examples, such as the illustrated shaped hole <NUM>, the primary passage portion <NUM> extends a majority of the wall's thickness and is joined to the diffuser portion <NUM> via an opening <NUM>. The diffuser portion <NUM> expands the air, causing the air to remain closer to the surface. In order to facilitate diffusion, the diffuser portion <NUM> has a diameter <NUM> that increases from the opening <NUM> to an exit <NUM> at the visually obstructed region <NUM>. In some examples, the diameter of the primary passage portion <NUM> is approximately <NUM> inches (<NUM>).

In some examples, such as the illustrated examples, the transition along the diffuser portion <NUM> can be gradual. In yet more specific examples the diffuser portion <NUM> can be configured such that each diffuser surface is angled <NUM> degrees from a cooling hole centerline defined by the primary passage <NUM>. Such a configuration is referred to as a <NUM>/<NUM>/<NUM> hole. In alternative examples, the diffuser portion <NUM> increases in diameter as a single step, or as multiple steps, instead of the gradual transition.

While illustrated in the instant example as being a doublet (including two vanes), it should be understood that the vane cluster <NUM> could include any number of additional vanes <NUM>. In such an example the features related to, and facilitating, the leading edge EDM cooling holes <NUM>, described above, are incorporated into each vane <NUM> whose suction side faces an inbound region <NUM>.

Claim 1:
A vane cluster (<NUM>) for a gas turbine engine (<NUM>) comprising:
an outer diameter platform (<NUM>);
an inner diameter platform (<NUM>);
a plurality of vanes (<NUM>) spanning from the outer diameter platform (<NUM>) to the inner diameter platform (<NUM>);
at least one inbound region (<NUM>) defined between a first vane (<NUM>) of said plurality of vanes (<NUM>) and a second vane (<NUM>) of said plurality of vanes (<NUM>), the first vane (<NUM>) including a suction side facing the inbound region (<NUM>) and a leading edge (<NUM>), and each of said vanes (<NUM>) including a leading edge core passage (<NUM>) and a trailing edge core passage (<NUM>); and
a plurality of electrical discharge machined (EDM) holes (<NUM>) each connecting the leading edge core passage (<NUM>) of the first vane (<NUM>) to an exterior surface of the first vane (<NUM>),
characterised in that:
the EDM holes (<NUM>) are disposed within <NUM> (<NUM> inches) of the leading edge (<NUM>) of the first vane (<NUM>), and the plurality of EDM holes (<NUM>) consists of six to ten holes, wherein each EDM hole (<NUM>) in the plurality of EDM holes (<NUM>) includes a primary passage portion (<NUM>) and a diffuser portion (<NUM>).