Patent Description:
As is known, a gas turbine assembly 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.

A plurality of inter-assembly cavities is defined between the stator assemblies and the 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 without touching it.

However, as the compressor provides positive pressure gradients along the main air flow direction, part of the compressed air flow enters the downstream inter-assembly cavity of the stator assembly, pass through the axial gap between the stator ring and the rotor and come back to the upstream inter-assembly cavity of the stator assembly (being at a pressure lower than the pressure of the downstream inter-assembly cavity) and finally is injected again in the main air flow upstream of the vane (see the arrows in <FIG> showing schematically a prior art solution).

The above backward recirculation negatively affects the compressor efficiency, generates pressure losses, and also deflects the main flow towards the leading edge of the vanes creating additional dangerous vorticity.

Sometimes, the discharge of said recirculated air flow upstream of the vane leading edge may induce flow separation at the vane leading edge, affecting also the compressor stability and operability.

A solution to reduce said backward recirculation is to arrange a labyrinth seal between the rotor and the stator ring to avoid communication between the inter-assembly cavities (see <FIG> showing a prior art solution). However, the efficiency of this device is strongly affected by the clearance gap variation between the labyrinth seal teeth. In general, in order to satisfy all transient condition during the engine operation preventing teeth rubbing, such clearance is quite high, and the labyrinth seal cannot avoid the backward flow recirculation.

<CIT> discloses a prior art stator assembly for a compressor of a gas turbine assembly.

The object of the present invention is therefore to provide a stator assembly for a compressor of a gas turbine assembly, 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 air recirculating about the stator ring through the inter-assembly cavities.

According to said objects the present invention relates to a stator assembly for a compressor of a gas turbine assembly wherein air flows along a direction D; the stator assembly comprising a stator ring, which extends about a longitudinal axis and comprises a leading wall and a trailing wall; the leading wall being arranged upstream of the trailing wall along the air flow direction; the trailing wall being is shaped so as to define an open cavity.

Advantageously, the open cavity in the trailing wall prevents the backward recirculation around the stator ring of the compressor.

The cavity promote local vorticity inside blocking the air flowing towards the axial gap. The generated vorticity acts also as an aero-dynamical barrier to limit itself the quantity of air entering the trailing inter-assembly cavity.

It is also an object of the present invention to provide an efficient compressor for a gas turbine assembly, wherein the amount of air recirculating about the stator ring through the inter-assembly cavities is minimized. According to said objects the present invention relates to a compressor of a gas turbine assembly 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 assembly (schematically shown in <FIG>).

The gas turbine assembly <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 compressor <NUM> is shown.

Arrow D indicates the direction of the air flow flowing in a compression channel <NUM> of the compressor <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 of the trailing inter-assembly cavity 27b along the hot gas flow direction D.

With reference to <FIG> and <FIG>, the stator ring <NUM> extends about the respective rotor disk <NUM> without touching it.

In particular, the stator ring <NUM> comprises a leading wall <NUM>, a trailing wall <NUM> and an axial wall <NUM> extending between the leading wall <NUM> and the trailing wall <NUM>. The leading wall <NUM> is upstream of the trailing wall <NUM> along the air flow direction D.

Preferably, leading wall <NUM> and trailing wall <NUM> are radially arranged with respect to axis A. The leading wall <NUM> is provided with an annular leading face 33a and the trailing wall <NUM> is provided with an annular trailing face 33b.

Between the axial wall <NUM> of the stator ring <NUM> and the respective rotor disk <NUM> an axial gap <NUM> is present.

In said axial gap <NUM> a labyrinth seal <NUM> is arranged.

As schematically shown in <FIG>, the labyrinth seal <NUM> is defined by a plurality of teeth <NUM> protruding from the axial wall <NUM> and a plurality of opposite and staggered teeth <NUM> protruding from the respective rotor disk <NUM>.

The plurality of stator vanes <NUM> are coupled alongside one another to the stator ring <NUM>.

According to the invention, the trailing wall <NUM> is shaped so as to define a cavity <NUM> which has at least one opening <NUM> facing a rotating part of the rotor assembly <NUM>. The rotating part of the rotor assembly can be a rotor disk <NUM> or a portion of a root of a rotor blade <NUM>.

The cavity <NUM> is shaped so as to obtain a recirculation of the air entering the trailing inter-assembly cavity 27b.

In particular, the cavity <NUM> is an open cavity extending along an annular path on the annular trailing radial face 33b of the trailing wall <NUM>.

With reference to the enlarged view of <FIG>, the annular trailing face 33b is provided with an outer planar portion <NUM> at the outer edge facing the inlet of the trailing inter-assembly cavity 27b and an inner planar portion <NUM> at the inner edge in contact with the axial wall <NUM>. The outer planar portion <NUM> and the inner planar portion <NUM> are radially arranged.

The radial length of the outer planar portion <NUM> is preferably lower than the radial length of the inner planar portion <NUM>.

According to a variant not shown, the radial length of the outer planar portion <NUM> can be substantially equal to the radial length of the inner planar portion <NUM>.

The cavity <NUM> is arranged between the outer planar portion <NUM> and the inner planar portion <NUM>.

In particular, the cavity <NUM> is defined by a concave portion <NUM> having at least one radius of curvature R1 and a convex portion <NUM> having at least one radius of curvature R2.

The concave portion <NUM> preferably extends so as to subtend an angle α comprised between <NUM>°- <NUM>°.

The convex portion <NUM> preferably extends so as to subtend an angle β comprised between <NUM>° - <NUM>°.

The convex portion <NUM> extends so to define a rounded section <NUM> of the cavity <NUM> for allowing air recirculating.

At the meeting between the inner planar portion <NUM> and the convex portion <NUM> a kick-out edge <NUM> is defined.

The kick-out edge <NUM> has a radial height (intended as the measure from the axis A along a radial direction) greater than the radial height of the innest point P of the convex portion <NUM>.

The concave portion <NUM> defines an inlet edge <NUM>.

According to a variant not shown, between the concave portion <NUM> and the convex portion <NUM> a further planar portion can be arranged, preferably radially arranged.

In use, the air coming from the compression channel <NUM> enters the trailing inter-assembly cavity 27b and is guided in the cavity <NUM> where circulates and is swirled towards the compression channel <NUM> as shown by the arrows in <FIG> and <FIG>.

In particular, the air coming from the compression channel <NUM> enters the trailing inter-assembly cavity 27b and is firstly deflected inward by the concave portion <NUM>, then it is recirculated by the convex portion <NUM> to generate a vortex inside the rounded section <NUM> and finally it is ejected again in the trailing inter-assembly cavity 27b with a direction mostly opposite to the entering direction.

Eventually, it may happen that a small amount of air ejected from the cavity <NUM> impacts the rotating part of the rotor assembly <NUM> facing it and it is directed at lower radius towards the air gap <NUM>. In this case, however, the strong pressure losses provided by the vortexes inside the cavity <NUM> and by the labyrinth seal <NUM> prevents the airflow to reach the leading inter-assembly cavity 27a and so to be ejected upstream of the vane <NUM>.

In this way, an aerodynamic sealing barrier against back-flow recirculation around the compressor stator ring <NUM> is obtained. The sealing effect is stronger than the one obtained by traditional devices currently used as labyrinth seals (see <FIG>).

Moreover, the cavity <NUM> is not involved in any variation of the clearance in the axial gap <NUM>. Therefore, it provides a constant and reliable sealing effectiveness during all operating conditions of the gas turbine assembly.

Finally, the shape and the dimensions of the cavity <NUM> do not affect the mechanical reliability of the stator ring <NUM> and, if needed, it can be also used to improve the static and modal response of the ring stator by modifying its mass.

Claim 1:
Stator assembly (<NUM>) for a compressor of a gas turbine assembly wherein air flows along a direction (D); the stator assembly comprising a stator ring (<NUM>), which extends about a longitudinal axis (A) and comprises a leading wall (<NUM>) and a trailing wall (<NUM>); the leading wall (<NUM>) being arranged upstream of the trailing wall (<NUM>) along the air flow direction (D); characterized in that the trailing wall (<NUM>) is shaped so as to define an open cavity (<NUM>).