Patent Description:
As is known in the art, gas turbines employ rows of buckets on the wheels / disks of a rotor assembly, which alternate with rows of stationary vanes on a stator or nozzle assembly. These alternating rows extend axially along the rotor and stator and allow combustion gasses to turn the rotor as the combustion gasses flow therethrough.

Axial / radial openings at the interface between rotating buckets and stationary nozzles can allow hot combustion gasses to exit the hot gas path and radially enter the intervening wheelspace between bucket rows. To limit such incursion of hot gasses, the bucket structures typically employ axially-projecting angel wings, which cooperate with discourager members extending axially from an adjacent stator or nozzle. These angel wings and discourager members overlap but do not touch, and serve to restrict incursion of hot gasses into the wheelspace.

In addition, cooling air or "purge air" is often introduced into the wheelspace between bucket rows. This purge air serves to cool components and spaces within the wheelspaces and other regions radially inward from the buckets as well as providing a counter flow of cooling air to further restrict incursion of hot gasses into the wheelspace. Angel wing seals therefore are further designed to restrict escape of purge air into the hot gas flowpath.

Nevertheless, most gas turbines exhibit a significant amount of purge air escape into the hot gas flowpath. For example, this purge air escape at the first and second stage wheelspaces may be between <NUM>% and <NUM>%. The consequent mixing of cooler purge air with the hot gas flowpath results in large mixing losses, due not only to the differences in temperature but also to the differences in flow direction or swirl of the purge air and hot gasses. <CIT> discloses a seal assembly between a disc cavity and a hot gas path in a gas turbine engine including a stationary vane assembly and a rotating blade assembly axially upstream from the vane assembly. A platform of the blade assembly has a radially outwardly facing first surface, an axially downstream facing second surface defining an aft plane, and a plurality of grooves extending into the second surface such that the grooves are recessed from the aft plane.

Other examples of turbine buckets are disclosed in <CIT>, <CIT> and <CIT>.

In the following, methods and/or apparatus referred to as embodiments that nevertheless do not fall within the scope of the appended claims are understood as examples helpful in understanding the invention.

It is noted that the drawings of the invention are not to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements among the drawings.

Turning now to the drawings, <FIG> shows a schematic cross-sectional view of a portion of a gas turbine <NUM> including a bucket <NUM> disposed between a first stage nozzle <NUM> and a second stage nozzle <NUM>. Bucket <NUM> extends radially outward from an axially extending rotor (not shown), as will be recognized by one skilled in the art. Bucket <NUM> comprises a substantially planar platform <NUM>, an airfoil extending radially outward from platform <NUM>, and a shank portion <NUM> extending radially inward from platform <NUM>.

Shank portion <NUM> includes a pair of angel wing seals <NUM>, <NUM> extending axially outward toward first stage nozzle <NUM> and an angel wing seal <NUM> extending axially outward toward second stage nozzle <NUM>. It should be understood that differing numbers and arrangements of angel wing seals are possible and within the scope of the invention. The number and arrangement of angel wing seals described herein are provided merely for purposes of illustration.

As can be seen in <FIG>, nozzle surface <NUM> and discourager member <NUM> extend axially from first stage nozzle <NUM> and are disposed radially outward from angel wing seals <NUM> and <NUM>, respectively. As such, nozzle surface <NUM> overlaps but does not contact angel wing seal <NUM> and discourager member <NUM> overlaps but does not contact angel wing seal <NUM>. A similar arrangement is shown with respect to discourager member <NUM> of second stage nozzle <NUM> and angel wing seal <NUM>. In the arrangement shown in <FIG>, during operation of the turbine, a quantity of purge air may be disposed between, for example, nozzle surface <NUM>, angel wing seal <NUM>, and platform lip <NUM>, thereby restricting both escape of purge air into hot gas flowpath <NUM> and incursion of hot gasses from hot gas flowpath <NUM> into wheelspace <NUM>.

While <FIG> shows bucket <NUM> disposed between first stage nozzle <NUM> and second stage nozzle <NUM>, such that bucket <NUM> represents a first stage bucket, this is merely for purposes of illustration and explanation. The principles and embodiments of the invention described herein may be applied to a bucket of any stage in the turbine with the expectation of achieving similar results.

<FIG> shows a perspective view of a portion of bucket <NUM>. As can be seen, airfoil <NUM> includes a leading edge <NUM> and a trailing edge <NUM>. Shank portion <NUM> includes a face <NUM> nearer leading edge <NUM> than trailing edge <NUM>, disposed between angel wing <NUM> and platform lip <NUM>.

<FIG> shows a cross-sectional side view of a portion of a turbine bucket <NUM>. As can be seen in <FIG>, a distal end <NUM> of platform lip <NUM> is angled radially outward toward airfoil <NUM>.

<FIG> shows a perspective view of the bucket <NUM> of <FIG>. A plurality of voids <NUM> are provided along distal end <NUM> of platform lip <NUM>. As shown in <FIG>, voids <NUM> are substantially trapezoidal in shape, although this is neither necessary nor essential. Voids having other shapes may also be employed, including, for example, rectangular, rhomboid, or arcuate shapes.

For example, <FIG> shows a perspective view of a bucket <NUM>. Here, platform lip <NUM> extends axially from platform <NUM> (i.e., a distal end is not angled toward airfoil <NUM>, as in <FIG>). Voids <NUM> extend through platform lip <NUM> in an arcuate path such that remaining portions of platform lip <NUM> adjacent voids <NUM> include an arcuate face <NUM>.

The embodiment of the invention shown in <FIG> shows a perspective view of bucket <NUM>. Here, platform lip <NUM> includes an angled distal end <NUM>, as in <FIG>. However, voids <NUM> are formed in a body <NUM> of platform lip <NUM> rather than at its distal end <NUM>. As noted above, voids <NUM> may take any number of shapes, including, for example, rectangular, trapezoidal, rhomboid, arcuate, etc..

<FIG> show perspective views of other embodiments of the invention. In <FIG>, voids <NUM> are elliptical in shape and angled with respect to a radial axis of bucket <NUM>.

In <FIG>, elliptical voids <NUM> of differing sizes are employed with void size increasing along platform lip <NUM> from an end nearer the concave trailing face toward the convex leading face of airfoil <NUM>. In such an embodiment, the effect of voids <NUM> on purge air between platform lip <NUM> and angel wing <NUM> will generally be more pronounced adjacent the larger voids. This may be desirable, for example, where a loss of purge air or an incursion of hot gas is greater in the area of the larger voids.

In <FIG>, elliptical voids <NUM> of differing size are employed with void size decreasing along platform lip <NUM> from an end nearer the concave trailing face toward the convex leading face of airfoil <NUM>. As should be recognized from the discussion above, such an embodiment may be desirable, for example, where a loss of purge air or an incursion of hot gas is greater in the area of the larger voids.

<FIG> show perspective views of turbine buckets <NUM> in accordance with various embodiments of the invention. In each of the embodiments in <FIG>, voids are disposed unevenly along platform lip <NUM>.

In <FIG>, a plurality of substantially rectangular voids <NUM> are disposed along platform lip <NUM> nearer the convex leading face than the concave trailing face of airfoil <NUM>.

In <FIG>, the area of void concentration is opposite that in <FIG>, with the plurality of substantially rectangular voids <NUM> disposed along platform lip <NUM> nearer the concave trailing face than the convex leading face of airfoil <NUM>.

<FIG> show embodiments similar to those in <FIG>, respectively, in which voids <NUM> are rhomboid in shape rather than substantially rectangular. The use of rhomboid voids <NUM> may be employed, for example, to direct purge air toward either convex leading face or concave trailing face of airfoil <NUM>.

<FIG> shows a schematic view of purge air flow in a typical turbine bucket. Purge air <NUM> is shown concentrated and having a higher swirl velocity in area <NUM>, with a significant amount of escaping purge air <NUM> entering hot gas flowpath <NUM>. The concentration of purge air <NUM> having a higher swirl velocity in area <NUM>, closer to face <NUM>, allows for incursion of hot gas <NUM> into wheelspace <NUM>.

In contrast, <FIG> shows the effect of voids <NUM> on purge air <NUM> according to various embodiments of the invention. As can be seen in <FIG>, the area <NUM> in which purge air <NUM> is concentrated and exhibits a higher swirl velocity is distanced further from face <NUM> and toward a distal end of platform lip <NUM>, as compared to <FIG>. This, in effect, produces a curtaining effect, restricting incursion of hot gas <NUM> from hot gas flowpath <NUM> while at the same time reducing the quantity of escaping purge air from wheelspace <NUM> into hot gas flowpath <NUM>.

The increases in turbine efficiencies achieved using embodiments of the invention can be attributed to a number of factors. First, as noted above, increases in swirl velocity reduces the escape of purge air into hot gas flowpath <NUM>, changes in swirl angle reduce the mixing losses attributable to any purge air that does so escape, and the curtaining effect induced by voids according to the invention reduce or prevent the incursion of hot gas <NUM> into wheelspace <NUM>. Each of these contributes to the increased efficiencies observed.

In addition, the overall quantity of purge air needed is reduced for at least two reasons. First, a reduction in escaping purge air necessarily reduces the purge air that must be replaced. Second, a reduction in the incursion of hot gas <NUM> into wheelspace <NUM> reduces the temperature rise within wheelspace <NUM> and the attendant need to reduce the temperature through the introduction of additional purge air. Each of these reductions to the total purge air required reduces the demand on the other system components, such as the compressor from which the purge air is provided.

While reference above is made to the ability of platform lip voids to change the swirl velocity of purge air within a wheelspace, and particularly within a wheelspace adjacent early stage turbine buckets, it should be noted that platform lip voids may be employed on turbine buckets of any stage with similar changes to purge air swirl velocity and angle. In fact, Applicants have noted a very favorable result when platform lip voids are employed in the last stage bucket (LSB).

Spikes in total pressure (PT) and swirl profiles at the inner radius region of the diffuser inlet are a consequence of a mismatch between the hot gas flow and the swirl of purge air exiting the wheelspace adjacent the LSB. Applicants have found that platform lip voids according to various embodiments of the invention are capable of both increasing PT spikes at a diffuser inlet close to the inner radius while at the same time decreasing swirl spikes at or near the same location. Each of these improves diffuser performance. Platform lip voids, for example, have been found to change the swirl angle of purge air exiting the LSB wheelspace by <NUM>-<NUM> degrees while also increasing PT spikes by <NUM>-<NUM>%.

<FIG> shows a schematic view of a LSB <NUM> adjacent diffuser <NUM>. Hot gas <NUM> enters diffuser <NUM> at diffuser inlet plane <NUM> and passes toward struts <NUM>. Platform lip voids according to embodiments of the invention reduce the swirl mismatch of purge air as it combines with hot gas <NUM>, preventing separation of hot gas <NUM> as it enters struts <NUM>. At the same time, such platform lip voids increase the PT spike.

<FIG> shows a graph of swirl spike as a function of diffuser inlet plane height. Profile A represents a swirl spike profile for a turbine having platform lip voids according to embodiments of the invention. Profile B represents a swirl spike profile for a turbine having a platform lip known in the art. Profile A exhibits a marked decrease in swirl spike at a radially inward position of the diffuser inlet plane.

<FIG> shows a graph of PT spike as a function of diffuser inlet plane height. Profile A represents a PT spike profile for a turbine having platform lip voids according to embodiments of the invention. Profile B represents a PT spike profile for a turbine having a platform lip known in the art. Profile A exhibits an increase in PT spike at a radially inward position of the diffuser inlet plane.

The principle of operation of the voids described above may also be applied to the operation of steam turbines. For example, <FIG> shows a schematic cross-sectional view of a steam turbine bucket <NUM> having an airfoil <NUM> and a shank <NUM> affixed to a disk <NUM>. A magnified view is provided of platform lip <NUM>, along which voids <NUM> (shown in phantom) may be deployed similarly to the voids shown in <FIG>, <FIG> above.

Steam turbines employing embodiments of the invention such as those described herein will typically realize improvements in efficiency of between <NUM>% and <NUM>%, depending, for example, on the leakage flow and the stage at which the features are employed.

Claim 1:
A turbine bucket (<NUM>) of a gas turbine or a steam turbine comprising:
a platform (<NUM>) portion;
an airfoil (<NUM>) extending radially outward from the platform (<NUM>) portion;
a shank portion (<NUM>) extending radially inward from the platform (<NUM>) portion;
at least one angel wing (<NUM>) extending axially from a face (<NUM>) of the shank portion (<NUM>);
a platform lip (<NUM>) extending axially from the platform (<NUM>) portion, the platform lip (<NUM>) being disposed radially outward of, and spaced from, the at least one angel wing (<NUM>), and including a continuous distal end (<NUM>) that is angled in a radially outward direction; and
a plurality of voids (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) disposed along the platform lip (<NUM>), the voids (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) extending through a body of the platform lip (<NUM>) and being configured to increase swirl velocity of purge air (<NUM>) concentrated in an area (<NUM>) between the platform lip (<NUM>) and the angel wing (<NUM>), and to distance the area (<NUM>) further from the face (<NUM>).