Patent Description:
<CIT> discloses an interstage seal for a gas turbine. <CIT> discloses a seal for a turbine rotor. <CIT> discloses a seal for a turbine engine. <CIT> discloses an inter-stage cavity purge duct. <CIT> discloses a turbine inter-stage U-ring.

As is well known, a gas turbine is an energy conversion plant, which usually comprises, among other things, a compressor, to draw in and compress a gas, a combustor (or burner) to add fuel to heat the compressed air, a high pressure turbine, comprising a plurality of rotor assemblies, to extract power from the hot gas flow path and drive the compressor and a low pressure turbine, also comprising a plurality of rotor assemblies, mechanically connected to a load.

In low pressure turbines design in particular, precautions are usually taken to reduce the gas ingestion from the hot gas flow path, which may have detrimental impact on not hot gas components as wheels and spacers. The phenomenon of the gas ingestion from the hot gas flow path may occur when engine operates at partial load and/or when engine parts have been manufactured not fully conform to design requirements and/or when some parts (e.g. seals, purging pipes) have been damaged or worn during operation.

More specifically, a typical low pressure turbine comprises, as mentioned above, a plurality of rotor members, each having a rotor wheel with a rim, on which a plurality of blades is coupled.

Each blade comprises a male-shaped dovetail or root, designed to fit with one corresponding groove obtained on the rim of the rotor wheel. The wheels are usually made of a less noble material than the blades.

Between two adjacent, facing rotor wheels, a wheel space is individuated between two rotor wheels of two rotor members.

The phenomenon of the gas ingestion from the hot gas flow path usually occurs when part of the hot gas flows into the wheel space, thus causing wheel rims to operate above or close to their material temperature limits, which, being made of non-noble material, can get damaged, reducing the useful life of the wheels. It implies that this phenomenon might be the cause of wheel dovetail failure (e.g. large deformation) and subsequently release of blades.

In addition to the above, the wheel spaces are usually cooled. To this end, the gas turbines are equipped with a piping system to provide purging air coming from the compressor to low pressure turbine. In particular, the purging air is introduced into the wheel spaces of the low pressure turbines. In part this reduces the overall temperature of the wheel spaces.

The hot gas ingestion is normally prevented when the amount of purging air is equal or more than the amount of air pumped up by the wheels. If less, than pump effect will compensate what not provided by the purging system with hot gas air that will sucked in far from the wheel and pumped out near the wheel (recirculation). The recirculation may happen when engine is running at low power and subsequently the compressor provides less purging air to the low pressure turbine while the low pressure turbine may still run at its maximum speed.

In order to reduce the gas ingestion of the hot gas flow path passing through the low pressure gas turbine to the wheel spaces, some solutions are available in the state of the art.

In particular, spacers may be added between wheels, these spacers may have rims that axially cover the space not covered by the wheels, these spacer rims may also radially extend to the same outer diameter of the wheels so to minimize the portion of the wheel rim above the wheel space cavity. Although the spacers realize a physical barrier against the hot gas ingestion, they are normally not in contact with the rims of the adjacent wheels and therefore hot gas may flow inside the gaps and reach the wheel spaces. The spacer may protect adjacent wheels even when wheels have a different outer diameter by shaping conical the spacer rim.

Accordingly, an improved turbine and blade capable of reducing any possible gas ingestion from the hot gas flow path would be welcomed in the technology.

An improvement of the above mentioned spacers is the provision of a near seal flow path (NFPS), which are capable of pushing wheel space sealing near the hot gas path. The NFPSs have replaced the more traditional spacers, to better protect the wheel rims from hot gas ingestion that may take place not only inside the wheel cavities but also through the lab seal. Form a structural standpoint, the NFPS is a segment (i.e. arm members) and not a ring (as the spacers do), and therefore they introduce leak between adjacent rotor members. Besides they require a multi connection system, which necessarily increases the complexity of the solution, so as to have them engaged to internal supporting rotor wheels. The NFPS are indeed small components if compared to the traditional spacers and therefore may be made of more noble material.

However, recently, in order to increase the power and the efficiency of the gas turbines, the temperature of the hot gas flow path is increased. To this end, the purging air flow from the compressor is reduced, increasing the risk of gas ingestion from the hot gas flow path.

Also, when the low pressure turbine spins at a lower speed, the pressure undergoes proportionally to a reduced pressure variation, since the hot gas flow path has a lower expansion at lower velocity, passing from a stage to another or from a rotor assembly to another. At the same time, as said above, when the low pressure turbine spins at a lower speed the pumping effect is reduced.

Finally, the temperatures of wheel spaces are normally monitored by appropriate thermocouples. However, owing to the always more compact layout of the turbines, the installation of the thermocouples has become way more complicated, with subsequent lower reliability of the thermocouples. All the more reasons, the thermocouple installation is complicated when spacers or any other mechanical barrier is arranged between two rotor assemblies. Then, the number of installed thermocouples tends to be reduced, this causing a reduced control of the risk of temperature increase of wheel rims and their possible deterioration.

Improvements to gas turbines have been discovered. Gas turbines have many parts, among them low pressure turbines. Such low pressure turbines are formed of many blades radiating from a central hub, and angled to move air through the engine. Some areas of the gas turbine are very hot. Others are cooler. A known problem is that part of the hot gas moved by the blades flows toward the central hub, thus causing damages and reducing the useful life of the turbines.

The inventors discovered that this problem may be alleviated and/or addressed by arranging a new deflector element in correspondence of the shank of each blade and interposed between the blade itself and a spacer, arranged between each blade. The deflector is shaped to deflect any possible gas ingestion from the hot gas flow path, toward the upper surface of the spacer. In this way, the deflector protects the turbine internal parts, preventing an average increase of the temperature therein.

<FIG> illustrates schematically, a gas turbine, wholly indicated with the reference number <NUM>. The gas turbine <NUM> includes, among other things: a compressor <NUM>, to draw in compress a gas to be supplied to a combustor or burner (not shown in the figure) to add fuel to heat the compressed air, a high pressure turbine <NUM>, comprising a plurality of rotor assemblies, to extract power from the hot gas flow path and drive the compressor <NUM>, a shaft <NUM>, connecting the compressor <NUM> and the high pressure turbine <NUM>, and a low pressure turbine <NUM>, also comprising a plurality of rotor assemblies, for driving, by a further shaft <NUM>, for example, a gear box and a centrifugal compressor, or any other load.

In addition, the gas turbine <NUM> includes a purging system <NUM>, to provide purging air to low the pressure turbine <NUM>. The purging system generally comprises a bleed extraction <NUM>, connected by a connection pipe <NUM> to a cooler <NUM>, which, in its turn, is connected by a purging pipe <NUM> to the low pressure turbine <NUM>, to cool the wheel spaces (see below) between the rotor assemblies. This has the effect and the function to reduce in part the overall temperature of the wheel spaces.

Referring also now to <FIG> and <FIG>, the low pressure turbine <NUM> usually comprises a plurality of rotor members, herein indicated with reference number <NUM>, rotate around an axis of rotation R and are coupled with the shaft <NUM>.

More specifically, each rotor member <NUM> comprises a rotor wheel <NUM>, coupled to the shaft <NUM> and having a rim <NUM> and a plurality of circumferentially spaced female dovetail-shaped slots or grooves <NUM> about the rim <NUM>. In the embodiment each groove <NUM> has a fit-three shape. However, in some embodiment the grooves can have a different shape.

Each rotor member <NUM> also comprises a plurality of blades <NUM>, each one comprising, in its turn, a male-shaped dovetail or root <NUM>, designed to fit with one corresponding groove <NUM> of the rotor wheel <NUM>, along an insertion direction. Therefore, each roots <NUM> has almost the same shape of a corresponding groove <NUM>.

The roots <NUM> of the blade <NUM> have only the mechanical function to firmly couple the blade <NUM> to the rotary wheel <NUM>, and, in particular, to the grooves <NUM> of the rotor wheel <NUM>.

Each blade <NUM> also comprise a platform or shank <NUM>, which the root <NUM> is connected to, and an airfoil <NUM>, coupled to the shank <NUM>. The airfoil <NUM> is made of a noble material, since the airfoil <NUM> is subject to a remarkable thermal and mechanical stress. At the top of the airfoil <NUM> there is an airfoil shroud <NUM>, for connecting each blade <NUM> to the neighboring ones, to prevent the blades <NUM> to bend while the turbine rotates because of the variable pressure field the airfoils <NUM> are subject to.

As said, between two adjacent and facing rotor wheels, a wheel space <NUM> is individuated and between two rotor wheels <NUM> of two rotor members <NUM>.

<FIG> also illustrates a stator spacer <NUM> of the turbine <NUM> stator (not shown in the figures), interposed between two rotor member <NUM>, and a nozzle <NUM>'.

The hot gas flow path flows on a hot gas flow path channel, which is indicated with the arrow F, which of course passes through the airfoils <NUM> of the blades <NUM>.

Between two adjacent blades <NUM> a spacer <NUM> is arranged, which has the function of realizing a barrier to prevent gas ingestion from the hot gas flow path channel F to the wheel space <NUM>, which may cause an increase of temperature in the upper side of the wheel spaces <NUM>, and consequently of the temperature of the roots <NUM> of the blades <NUM>. As a said, in excess of thermal stress to the roots <NUM> is detrimental for their operation. In this embodiment, the spacer <NUM> is conical. However, in some embodiments the spacer <NUM> can be cylindrical or with others shapes, always with the function of defining and creating a protection for the wheel spaces <NUM>. Also, on the upper surface <NUM> of each spacer <NUM>, which faces the stator spacer <NUM>, there is a labyrinth seal <NUM>, for sowing the speed of the gas flowing between the spacer <NUM> and the stator spacer <NUM>.

Still referring to <FIG>, arrow P shows the purging air path, which comes from the purging system <NUM>. The purging air has the function to reduce the temperature of the wheel spaces <NUM> as well as to create, with its pressure, a pressure barrier against the gas injection from the hot gas flow path channel F. The shank <NUM> of each blade <NUM> has a deflector <NUM>, obtained on the shank <NUM> of each blade <NUM> and arranged in correspondence with the spacer <NUM>, and particularly of its edge, so as to be arranged to cover a gap <NUM> between each spacer <NUM> and the rotor member <NUM>, and in particular, with reference to the embodiment of <FIG>, between the spacer <NUM> and the rim <NUM> of the rotor wheel <NUM>.

In other words, in some embodiments, the deflector <NUM>, which actually is ring-shaped, has the protruding edge faced in front of the edge of the spacer <NUM>, so as to be in correspondence of the same, to close the gap between the spacer <NUM> and the rotor wheel <NUM>. In fact, the spacer <NUM> is also ring-shaped, with an edge facing the rotary wheel <NUM>. The surface of the deflector <NUM> is such that it can deflect hot gases as better explained below.

In the embodiment shown in <FIG>, and in particular referring to the zoomed window shown in the same figure, the deflector <NUM> is shaped having a upper surface <NUM>, intended to deflect the possible gas ingestion from the hot gas flow path channel F, toward the upper surface <NUM> and over the labyrinth seal <NUM> of the spacer <NUM>, and a lower surface <NUM>, this intended to allow the purging air coming from the wheel space <NUM> passing through the gap <NUM> between the between each spacer <NUM> and the rotor member <NUM>.

In some embodiments the deflector <NUM> can be arranged in different positions and, more specifically, it may be obtained on the rotor wheel <NUM>, almost in correspondence with the rim <NUM>.

In general, it is required that the deflector <NUM> is able to deflect any possible gas ingestion from the hot gas flow path channel F that can overcome the mechanical barrier of the spacer <NUM> and whenever, for instance, the purging air pressure P from the wheel spacer <NUM> is not enough for preventing that in general the hot gas to enter the wheel spaces <NUM>.

The low pressure turbine <NUM> and the deflector <NUM> operate as follows.

When the low pressure turbine <NUM> operates and the rotor members <NUM> rotates, the purging air P coming from the compressor <NUM> and conveyed by the purging pipe <NUM>, cools the wheel spaces <NUM>. At the same time, the combined effect of the pumping effect, due to the spinning velocity of the low pressure turbine <NUM>, namely of the rotor members <NUM>, along with the barrier realized by the spacer <NUM>, prevents the gas ingestion from the hot gas flow path channel F into the wheel spaces <NUM>. Also, any possible gas ingestion, even local, is further prevented by the action of the deflector <NUM>, which, on the one hand, being it arranged in correspondence with the spacer <NUM>, it does deflect possible local gas ingestions from the hot gas flow path channel F by the first surface <NUM>, and on the other hand, it also allows the purging air P to pass through the gap <NUM>. Local gas ingestion can take place owing also to the fact that the pressure field caused by the hot gas flow in the hot gas flow path channel F is not always constant. With reference to the deflector <NUM>, being arranged in correspondence with the spacer <NUM> means in some embodiments that it is capable of deflecting the hot gases toward the upper surface of the spacer <NUM>.

The operation of the deflector has a particular impact in case the spinning velocity of the low pressure gas turbine <NUM> is reduced, for instance, when a low pressure gas turbine <NUM> operates at <NUM>% of its nominal operational speed. In this case the protective action of the pumping effect is reduced proportionally to the velocity reduction.

In particular, in order to better describe the operation of the deflector <NUM>, <FIG> illustrate some operating conditions of the low pressure turbine <NUM>. In <FIG> a typical flow path of the purging air P is seen, where no gas ingestion is foreseen. In this case, the purging air P coming from the compressor <NUM> passes through the wheel spaces <NUM> and reaches the hot gas flow path channel F, protecting the wheel spaces <NUM> from the high temperature of the hot gases.

Referring now to <FIG>, it is illustrated a low gas ingestion phenomenon, where part (see arrow F') of the hot gas of the hot gas flow path channel F reaches the spacer <NUM>, and in particular the upper surface <NUM> and the labyrinth seal <NUM> also thank to the deflector <NUM>. In this case, the gas ingestion in the wheel spaces <NUM> is at least in part prevented either by the deflector <NUM> as well as by the purging air P coming from the compressor <NUM>, which is allowed to contrast the ingested gas F' from the hot hair flow path F by the shape of the lower surface <NUM> of the deflector <NUM>. The hot gas reaches the shank <NUM>, raising its temperature, thus causing a potential risk for the roots <NUM> of the blades <NUM>. The deflector <NUM> aids to prevent that possibly the hot ingested gas F' coming from the hot gas flow of the hot gas flow path channel F can leak in the wheel spacers <NUM>, so warming the shank <NUM>.

In <FIG> is shown the case of high gas ingestion phenomenon in case for instance of low speed of the low pressure turbine. In particular, there are shown a first arrow F", which represents the hot gas of the hot gas flow path channel F ingested in case of the blade <NUM> is not equipped with the deflector <NUM>, where it's clear that the hot gas reaches the wheel spaces <NUM> and heats up the shank <NUM>, and consequently the root <NUM> of the blade <NUM>, causing its damage; and a second arrow F‴, which represents the hot gas of the hot gas flow path channel F ingested in case of the blade <NUM> is equipped with the deflector <NUM>. It's easily appreciated that in this latter case, the hot gas is deflected and prevented to reach the wheel spaces <NUM>.

In the operating condition mentioned above, where, as said, the low pressure turbine <NUM> is operating at low speed, the purging air P coming from the wheel spaces <NUM> is not enough for contrasting the ingested gas F"', and so the deflector <NUM> deflects the ingested gas flow F‴ toward the upper surface <NUM> of the spacer <NUM> and the labyrinth seal <NUM>. The upper surface <NUM> of the deflector <NUM> from one side obstructs the ingested gas F‴ to reach the wheel spaces <NUM>, and, from the other side, deflects, as said above, the hot gas over the spacer <NUM> away from the shank <NUM>, thus allowing a reduction of the temperature of the shank <NUM> itself, and, consequently, of the root <NUM> of the blade <NUM>.

Referring to <FIG> a second embodiment of an improved low pressure turbine <NUM> is shown. In the mentioned figure the same reference numbers designate the same or corresponding parts, elements or components already illustrated in <FIG> and described above, and which will not be described again. In this case, however, the spacer <NUM> is not conical but cylindrical. Also in this case, the deflector <NUM> is placed on the shank <NUM> or on the rim <NUM> of the rotor wheel <NUM>, in correspondence of the spacer <NUM>.

<FIG> illustrates also several paths of the purging air P coming from the compressor <NUM> through the purging pipe <NUM>.

The operation of the low power turbine <NUM> in this case is the same of that disclosed in the previous figure.

While the invention has been described in terms of various specific embodiments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without departing form the scope of the claims. In addition, unless specified otherwise herein, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments.

Reference has been made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope of the disclosure. Reference throughout the specification to "one embodiment" or "an embodiment" or "some embodiments" means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase "in one embodiment" or "in an embodiment" or "in some embodiments" in various places throughout the specification is not necessarily referring to the same embodiment(s). Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

Claim 1:
A turbine (<NUM>), comprising:
a downstream rotor member (<NUM>) and an upstream rotor member (<NUM>), both rotor members (<NUM>) being configured to rotate due to the expansion of hot burned gas flowing into a hot gas flow path channel (F),
wherein each rotor member (<NUM>) comprises a rotor wheel (<NUM>), a plurality of blades (<NUM>) and a spacer (<NUM>) arranged between two adjacent blades (<NUM>) of the downstream rotor member and the facing upstream rotor member (<NUM>), the spacer (<NUM>) having an upper surface (<NUM>) facing a hot gas ingestion flow (F), and being configured to avoid the ingested gas flow (F', F‴) from the hot gas flow path channel (F) to reach a wheel space (<NUM>) between the facing downstream and upstream rotor members (<NUM>); and
a purging system (<NUM>) to introduce purging air (P) in the turbine (<NUM>), wherein the purging air (<NUM>) passes through the wheel space (<NUM>), to reach the hot gas flow path channel (F),
characterized in that the upstream rotor member (<NUM>) comprises a deflector (<NUM>), configured to deflect the ingested gas flow, wherein the deflector (<NUM>) has a lower surface (<NUM>) spaced apart from the spacer (<NUM>) and an upper surface (<NUM>), configured to deflect the possible gas ingestion from the hot gas flow path (F), toward the upper surface (<NUM>) of the spacer (<NUM>);
a gap (<NUM>) between the lower surface (<NUM>) of the deflector and the spacer (<NUM>) being configured to allow purging air to flow out of the wheel space (<NUM>); and
wherein the spacer (<NUM>) is arranged at a downward angle towards a rotation axis from the upstream rotor member (<NUM>) to the downstream rotor member (<NUM>).