Patent Description:
As is known, a gas turbine for power plants comprises a compressor, a combustor and a turbine.

In particular, the compressor comprises an inlet supplied with air and a plurality of rotating blades compressing the passing air. The compressed air leaving the compressor flows into a plenum, i.e. a closed volume delimited by an outer casing, and from there into the combustor. Inside the combustor, the compressed air is mixed with at least one fuel and combusted. The resulting hot gas leaves the combustor and expands in the turbine. In the turbine the hot gas expansion moves rotating blades connected to a rotor, performing work.

Both the compressor and the turbine comprise a plurality of stator assemblies axially interposed between rotor assemblies.

Each rotor assembly comprises a rotor disk rotating about a main axis and a plurality of blades supported by the rotor disk.

Each stator assembly comprises a plurality of stator vanes supported by a respective vane carrier and a stator ring arranged about the rotor.

A plurality of inter-assembly cavities is defined between the stator assemblies and the rotor assemblies.

In the turbine, sealing air is normally bled from the compressor and introduced in said inter-assembly cavities in order to avoid or limit the hot gas ingestion from the hot gas path in the inter-assemblies cavities.

Some examples are disclosed in documents <CIT> <CIT><CIT>, <CIT>, <CIT>, <CIT>.

The minimization of the amount of air spent to seal and cool the inter-assembly cavities is beneficial to the power plant performance. However, said minimization implies the use of expensive advanced materials and/or the adoption of arrangements having a very complex geometry.

The object of the present invention is therefore to provide a stator assembly for a gas turbine, which enables avoiding or at least mitigating the described drawbacks.

In particular, it is an object of the present invention to provide a stator assembly having an improved structure able to minimize the amount of sealing air and preserving, at the same time, the thermal conditions of the stator and rotor parts.

According to said objects the present invention relates to a stator assembly for a gas turbine comprising:.

the stator ring being provided with at least one trailing cooling hole having an inlet facing the annular cooling channel and an outlet arranged on the annular trailing radial face; wherein the trailing cooling hole extends along an extension axis; on a tangential plane defined by the longitudinal axis and a circumferential direction, which is orthogonal to the longitudinal axis and orthogonal to a radial direction in turn orthogonal to the longitudinal axis, a first angle is defined by the projection of the extension axis on the tangential plane and the axial direction and is comprised between <NUM>° and <NUM>°.

Advantageously, the presence of trailing cooling holes creates a sealing flow in the trailing inter-assembly cavity interacting with the hot gas flow deriving from the ingestion.

Thanks to the radial position and inclination of the trailing cooling holes, the sealing cooling air coming from the trailing cooling holes is directed towards the entrance of the trailing inter-assembly cavity.

In this way, the sealing cooling air coming from the trailing cooling holes penetrates the hot flow ingested favoring a more adequate sealing/cooling of the trailing inter-assembly cavity.

According to a variant of the present invention, each stator vane comprises an airfoil, an outer shroud and an inner shroud coupled to the stator ring; the inner shroud comprising a platform.

Preferably, the radial distance between the center of the outlet of the trailing cooling hole and the inner edge of the stator ring being comprised in the range between <NUM>,<NUM>·DP and <NUM>,<NUM>-DP, wherein DP is the radial distance between the outer face of the platform and the inner edge of the stator ring.

According to a variant of the present invention, the trailing cooling hole extends along an extension axis; on a longitudinal axial plane defined by the longitudinal axis and a radial direction orthogonal to the longitudinal axis and intersecting the extension axis, a second angle defined by the projection of the extension axis on the longitudinal axial plane (A-R) and the radial direction is comprised between <NUM>° and <NUM>°.

According to a variant of the present invention, the inlet of the trailing cooling hole has a diameter comprised between <NUM> and <NUM>.

According to a variant of the present invention, the trailing cooling hole has a constant cross section.

According to a variant of the present invention, the stator ring is provided with a plurality of trailing cooling holes.

According to a variant of the present invention, the outlets of the plurality of trailing cooling holes are evenly distributed along the annular trailing radial face.

According to a variant of the present invention, the number of trailing cooling holes is comprised in the range between <NUM>,<NUM>·NV and <NUM>·NV, wherein NV is the number of stator vanes of the stator assembly.

According to a variant of the present invention, the inner shroud comprises a leading flange and a trailing flange, both extending radially inward from the platform; the leading flange being coupled to the leading wall and the trailing flange being coupled to the trailing wall; the trailing flange being coupled to the trailing wall so as to leave a trailing radial gap between the trailing wall and the platform and to define a trailing surface of the trailing flange facing said trailing radial gap.

According to a variant of the present invention, the trailing flange is provided on the trailing surface with at least one secondary cooling hole in fluid communication with the annular cooling channel.

According to a variant of the present invention, the trailing flange is provided on the trailing surface with a plurality of secondary cooling holes circumferentially aligned.

According to a variant of the present invention, the secondary cooling holes are evenly distributed.

It is also an object of the present invention to provide a gas turbine which is reliable and wherein the consumption of sealing air is reduced. According to said objects the present invention relates to a gas turbine as claimed in claim <NUM>.

The present invention will now be described with reference to the accompanying drawings, which illustrate some non-limitative embodiment, in which:.

In <FIG> reference numeral <NUM> indicates a gas turbine electric power plant (schematically shown in <FIG>).

The plant <NUM> comprises a compressor <NUM>, a combustion chamber <NUM>, a gas turbine <NUM> and a generator (for simplicity, not shown in the attached figures).

The compressor <NUM>, turbine <NUM> and generator (not shown) are mounted on the same shaft to form a rotor <NUM>, which is housed in stator casings <NUM> and extends along an axis A.

In greater detail, the rotor <NUM> comprises a front shaft <NUM>, a plurality of rotor assemblies <NUM> and a rear shaft <NUM>.

Each rotor assembly <NUM> comprises a rotor disk <NUM> and a plurality of rotor blades <NUM> coupled to the rotor disk <NUM> and radially arranged.

The plurality of rotor disks <NUM> are arranged in succession between the front shaft <NUM> and the rear shaft <NUM> and preferably clamped as a pack by a central tie rod <NUM>. As an alternative, the rotor disks may be welded together.

A central shaft <NUM> separates the rotor disks <NUM> of the compressor <NUM> from the rotor disks <NUM> of the turbine <NUM> and extends through the combustion chamber <NUM>.

Further, stator assemblies <NUM> are alternated with the compressor rotor assemblies <NUM>.

Each stator assembly <NUM> comprises a stator ring <NUM> and a plurality of stator vanes <NUM>, which are radially arranged and coupled to the stator ring <NUM> and to the respective stator casing <NUM>.

In <FIG> an enlarged view of a stator assembly <NUM> between two rotor assemblies <NUM> in the turbine <NUM> is shown.

Arrow D indicates the direction of the hot gas flow flowing in a hot gas channel <NUM> of the turbine <NUM>.

Between the rotor assemblies <NUM> and the stator assembly <NUM> inter-assembly cavities <NUM> are arranged.

In particular, each stator assembly <NUM> defines a leading inter-assembly cavity 27a and a trailing inter-assembly cavity 27b, wherein the leading inter-assembly cavity 27a is upstream the trailing inter-assembly cavity 27b along the hot gas flow direction D.

With reference to <FIG> and <FIG>, the stator ring <NUM> (only a part of which is visible in <FIG> and <FIG>) extends about the longitudinal axis A and comprises an inner edge <NUM> and an outer edge <NUM>, which is provided with an annular groove <NUM>.

The plurality of stator vanes <NUM> are coupled alongside one another to the outer edge <NUM> of the stator ring <NUM> so as to close the annular groove <NUM> and define an annular cooling channel <NUM>.

The annular cooling channel <NUM> is fed with air preferably coming from the compressor <NUM>.

The annular groove <NUM> defines a leading wall <NUM> and a trailing wall <NUM>. The leading wall <NUM> is upstream the trailing wall <NUM> along the hot gas flow direction D.

The trailing wall <NUM> is also provided with an annular trailing radial face 36a and with an annular trailing axial face 36b.

Preferably, the leading wall <NUM> is provided with a plurality of leading cooling holes <NUM> in fluidic communication with the annular cooling channel <NUM>.

Preferably, the cooling openings <NUM> are arranged in the proximity of the inner edge <NUM>.

In the non-limiting example here disclosed and illustrated, the cooling openings <NUM> are circumferentially aligned and evenly distributed.

The trailing wall <NUM> is provided with at least one trailing cooling hole <NUM> in fluidic communication with the annular cooling channel <NUM>.

In more detail, each trailing cooling hole <NUM> passes through the trailing wall <NUM> and has an inlet <NUM> facing the annular cooling channel <NUM> and an outlet <NUM> arranged on the annular trailing radial face 36a facing, in use, the trailing inter-assembly cavity 27b.

Each stator vane <NUM> comprises an airfoil <NUM>, an outer shroud <NUM> and an inner shroud <NUM> coupled to the stator ring <NUM>.

The airfoil <NUM> is provided with a cooling air duct 45a fed by a dedicated opening 45b on the outer shroud <NUM>.

The outer shroud <NUM> is coupled to the respective stator casing <NUM>.

The inner shroud <NUM> comprises a platform <NUM>, a leading flange <NUM> and a trailing flange <NUM> extending radially inward from the platform <NUM>. The leading flange <NUM> is upstream the trailing flange <NUM> along the hot gas flow direction D.

The leading flange <NUM> is coupled to the leading wall <NUM>, while the trailing flange <NUM> is coupled to the trailing wall <NUM>.

In the non-limiting example here disclosed and illustrated, the leading flange <NUM> engages a respective annular seat <NUM> of the leading wall <NUM>, while the trailing flange <NUM> engages a respective annular seat <NUM> of the trailing wall <NUM>.

With reference to <FIG>, the leading flange <NUM> is coupled to the leading wall <NUM> so as to leave a leading radial gap <NUM> between the leading wall <NUM> and the platform <NUM> and to define a leading surface <NUM> of the leading flange <NUM> facing said leading radial gap <NUM>.

The trailing flange <NUM> is coupled to the trailing wall <NUM> so as to leave a trailing radial gap <NUM> between the trailing wall <NUM> and the platform <NUM> and to define a trailing surface <NUM> of the trailing flange <NUM> facing said trailing radial gap <NUM>.

The leading flange <NUM> is provided, on the leading surface <NUM>, with at least one primary cooling hole <NUM> in fluid communication with the annular cooling channel <NUM>.

Preferably, the leading flange <NUM> is provided, on the leading surface <NUM>, with a plurality of primary cooling holes <NUM> circumferentially aligned.

The trailing flange <NUM> is provided, on the trailing surface <NUM>, with at least one secondary cooling hole <NUM> in fluid communication with the annular cooling channel <NUM>.

Preferably, the trailing flange <NUM> is provided, on the trailing surface <NUM>, with a plurality of secondary cooling holes <NUM> circumferentially aligned.

In the non-limiting example here disclosed and illustrated, the secondary cooling holes <NUM> are evenly distributed.

According to the non-limitative embodiment here disclosed and illustrated, the secondary cooling holes <NUM> have a passage section smaller than the passage section of the primary cooling holes <NUM>.

With reference to <FIG> and <FIG>, the stator assembly <NUM> preferably comprises a plurality of trailing cooling holes <NUM>, which are evenly distributed and preferably circumferentially aligned on the annular trailing radial face 36a.

Preferably, the number of trailing cooling holes <NUM> is comprised in the range between <NUM>,<NUM>·NV and <NUM>·NV, wherein NV is the number of stator vanes <NUM> of the stator assembly <NUM>.

In particular, the distance DH between the centre of the outlet <NUM> of the cooling hole <NUM> and the inner edge <NUM> of the stator ring <NUM> is comprised in the range between <NUM>,<NUM>-DP and <NUM>,<NUM>·DP, wherein DP is the radial distance between the outer face 46a of the platform <NUM> and the inner edge <NUM> of the stator ring <NUM>.

With reference to <FIG>, the inlet <NUM> of the trailing cooling hole <NUM> has preferably a diameter d comprised between <NUM> and <NUM>.

Preferably, the trailing cooling hole <NUM> has a constant cross section.

The trailing cooling hole <NUM> extends along an extension axis O; on a longitudinal axial plane A-R defined by the longitudinal axis A and a radial direction R orthogonal to the longitudinal axis A and intersecting the extension axis O, an angle α defined by the projection of the extension axis O on the longitudinal axial plane A-R and the axial direction is comprised between <NUM>° and <NUM>°. The angle α is measured from the axial direction A to the projection of the extension axis O in a counter-clockwise direction looking in a tangential direction having on the left the compressor side.

While, on a tangential plane defined by the longitudinal axis A and a circumferential direction C, which is orthogonal to the longitudinal axis A and orthogonal to a radial direction R in turn orthogonal to the longitudinal axis A, an angle β is defined by the projection of the extension axis on the tangential plane and the axial direction A.

Preferably, the trailing cooling hole <NUM> has a tangential inclination (defined by angle β), which is concordant with the direction of rotation of the machine W (counter-clockwise around axis A looking from the compressor side).

Said angle β is comprised between <NUM>° and <NUM>°.

The angle β is measured from the axial direction A to the projection of the extension axis O in a counter-clockwise direction looking in a tangential direction having on the left the compressor side.

In use, the hot gas flowing in the hot gas channel <NUM> is ingested in the trailing inter-assembly cavity 27b. however, thanks to the radial position and inclination of the trailing cooling holes <NUM>, the sealing cooling air coming from the trailing cooling holes <NUM> is directed towards the entrance of the trailing inter-assembly cavity 27b.

In this way, the sealing cooling air coming from the trailing cooling holes <NUM> penetrates the hot flow ingested favoring a more adequate sealing/cooling of the trailing inter-assembly cavity 27b.

In particular, when the sealing cooling air coming from the trailing cooling holes <NUM> swirls in the direction of rotation, the difference of tangential velocity between the ingested hot gas and the sealing cooling air flow is reduced; this leads to a decrease of the shear-stress between the two interacting flows and facilitates the penetration of the sealing cooling air in the hot gas.

In this way, in the trailing inter-assembly cavity 27b the flow resulting from the interaction between the hot gas ingested flow and the sealing cooling air flow exhibits a more uniform swirl number distribution that ensures a significantly improved sealing / cooling capability.

In this way, the claimed solution allows to enhance the sealing effectiveness and the thermal state of the trailing inter-assembly cavity 27b and therefore to significantly reduce the total sealing air amount spent to seal the trailing inter-assembly cavity 27b, with a consequent improvement in engine performance.

Claim 1:
Stator assembly (<NUM>) for a gas turbine comprising:
• a stator ring (<NUM>), which extends about a longitudinal axis (A) and comprises an inner edge and an outer edge (<NUM>); the outer edge being provided with an annular groove (<NUM>); the annular groove (<NUM>) defining a leading wall (<NUM>) and a trailing wall (<NUM>); the trailing wall (<NUM>) being provided with an annular trailing radial face (36a) and with an annular trailing axial face (36b);
• a plurality of stator vanes (<NUM>) radially arranged and coupled alongside one another to the outer edge (<NUM>) of the stator ring (<NUM>) so as to close the annular grove (<NUM>) and define an annular cooling channel (<NUM>);
• the stator ring (<NUM>) being provided with at least one trailing cooling hole (<NUM>) having an inlet (<NUM>) facing the annular cooling channel (<NUM>) and an outlet (<NUM>) arranged on the annular trailing radial face (36b); wherein the trailing cooling hole (<NUM>) extends along an extension axis (O); on a tangential plane defined by the longitudinal axis (A) and a circumferential direction (C), which is orthogonal to the longitudinal axis (A) and orthogonal to a radial direction (R) in turn orthogonal to the longitudinal axis (A), a first angle (β) is defined by the projection of the extension axis (O) on the tangential plane and the axial direction (A) characterized in that the first angle is comprised between <NUM>° and <NUM>°.