End wall configuration for gas turbine engine

A contoured turbine airfoil assembly including an end wall (30a) formed by platforms (30) located circumferentially adjacent to each other, and a row of airfoils (34a, 34b) integrally joined to the end wall (30a) and spaced laterally apart to define flow passages (46) therebetween for channeling gases in an axial direction. A trough (62) is defined between a pressure side ridge (48) and a suction side ridge (58) located forward of each pair of airfoils (34a, 34b). Each trough (62) has a direction of elongation aligned to direct flow into the flow passage (46) centrally between each pair of airfoils (34a, 34b).

TECHNICAL FIELD

The present invention relates generally to gas turbine engines and, more particularly, to end wall configurations for airfoil assemblies in gas turbine engines.

BACKGROUND ART

A gas turbine engine typically includes a compressor section, a combustor, and a turbine section. The compressor section compresses ambient air that enters an inlet. The combustor combines the compressed air with a fuel and ignites the mixture creating combustion products defining a working fluid. The working fluid travels to the turbine section where it is expanded to produce a work output. Within the turbine section are rows of stationary vanes directing the working fluid to rows of rotating blades coupled to a rotor. Each pair of a row of vanes and a row of blades forms a stage in the turbine section.

Advanced gas turbines with high performance requirements attempt to reduce the aerodynamic losses as much as possible in the turbine section. This in turn results in improvement of the overall thermal efficiency and power output of the engine. One possible way to reduce aerodynamic losses is to incorporate end wall contouring on the blade and vane shrouds in the turbine section. End wall contouring when optimized can result in a significant reduction in the effects of secondary flow vortices which can contribute to losses in the turbine stage.

SUMMARY OF INVENTION

In accordance with an aspect of the invention, a contoured turbine airfoil assembly is provided including an end wall formed by platforms located circumferentially adjacent to each other, and a row of airfoils integrally joined to the end wall and spaced laterally apart to define flow passages therebetween for channeling gases in an axial direction. Each of the airfoils include a concave pressure side and a laterally opposite convex suction side extending in a chordwise direction between opposite leading and trailing edges, the chordwise direction extending generally in the axial direction. A pressure side ridge is associated with each airfoil and is defined by an elongated crest extending from a location forward of the mid-chord on the pressure side of an associated airfoil and extending to a location axially forward of the leading edges of the airfoils.

The pressure side ridge can extend circumferentially into the flow passage between the pair of airfoils.

The elongated crest of the pressure side ridge can extend from about 15% upstream to about 10% downstream of the leading edge of each airfoil, measured relative to the chord length of the airfoils.

The pressure side ridge can extend to and define a raised area on a forward edge of the end wall.

A suction side ridge can be associated with each airfoil and can be defined by an elongated crest located forward of the leading edges of the airfoils, and a trough can be defined between the pressure side ridge and the suction side ridge for each pair of airfoils, the troughs having a direction of elongation aligned to direct flow into the flow passage centrally between each pair of airfoils.

An upstream edge of the end wall can define an undulating surface extending in the circumferential direction.

In accordance with another aspect of the invention, a contoured turbine airfoil assembly is provided including an end wall formed by platforms located circumferentially adjacent to each other, and a row of airfoils integrally joined to the end wall and spaced laterally apart to define flow passages therebetween for channeling gases in an axial direction. Each of the airfoils include a concave pressure side and a laterally opposite convex suction side extending in a chordwise direction between opposite leading and trailing edges, the chordwise direction extending generally in the axial direction. Troughs are defined in the end wall and are located forward of the leading edges of the airfoils and extend to an axial location at least even with the leading edges of the airfoils. The troughs have a direction of elongation aligned to direct flow into the flow passage centrally between each pair of airfoils.

Each trough can be defined between a pressure side ridge and a suction side ridge for each pair of airfoils, each pressure side ridge can extend from a pressure side of an associated airfoil forwardly of the leading edge of the associated airfoil and the suction side ridge can have an elongated crest extending adjacent to the suction side of an associated airfoil and located forward of the leading edges of the airfoils.

The trough can extend from an upstream edge of the end wall, and the upstream edge of the end wall can define an undulating surface extending in the circumferential direction.

The end wall adjacent to a suction side mid-chord location of each airfoil can include a mid-chord bulge, the mid-chord bulge defining a higher elevation than a circumferentially opposite, pressure side mid-chord location of an adjacent airfoil.

A continuous low elevation channel can be defined extending in the circumferential direction between the mid-chord bulge and the pressure side mid-chord location at the adjacent airfoil.

The continuous low elevation channel can be defined by a region having an axial extent without ridges and troughs, and extending circumferentially between the mid-chord bulge and the pressure side mid-chord location at the adjacent airfoil.

In accordance with a further aspect of the invention, a contoured turbine airfoil assembly is provided including an end wall formed by platforms located circumferentially adjacent to each other, and a row of airfoils integrally joined to the end wall and spaced laterally apart to define flow passages therebetween for channeling gases in an axial direction. Each of the airfoils include a concave pressure side and a laterally opposite convex suction side extending in a chordwise direction between opposite leading and trailing edges, the chordwise direction extending generally in the axial direction. A mid-chord bulge is located on the end wall adjacent to a suction side mid-chord location of each airfoil, the mid-chord bulge defining a higher elevation than a circumferentially opposite, pressure side mid-chord location of an adjacent airfoil.

The mid-chord bulge can extend from the suction side of each airfoil laterally to an outer edge, and the elevation of the bulge can decrease in axially forward and aft directions at locations where the mid-chord bulge intersects the suction side of the airfoil.

A continuous low elevation channel can be defined extending in the circumferential direction between the mid-chord bulge and the pressure side mid-chord location at the adjacent airfoil.

The continuous low elevation channel can be defined by a region having an axial extent without ridges and troughs, and extending circumferentially between the mid-chord bulge and the pressure side mid-chord location at the adjacent airfoil.

The mid-chord ridge can be generally semi-spherical at the suction side of each airfoil.

A pressure side ridge can be associated with each airfoil and defined by an elongated crest extending from a location forward of the pressure side mid-chord location at the adjacent airfoil and extending to a location axially forward of the leading edges of the airfoils.

A suction side ridge can be associated with each airfoil and defined by an elongated crest located forward of the leading edges of the airfoils, and each pressure side ridge can be positioned at a circumferential location between the circumferential locations of the leading edges of adjacent airfoils.

A trough can be defined between the pressure side ridge and the suction side ridge for each pair of airfoils, the trough having a direction of elongation aligned to direct flow into the flow passage centrally between each pair of airfoils.

DESCRIPTION OF EMBODIMENTS

One possible way to reduce aerodynamic losses in the turbine section of a gas turbine engine is to incorporate end wall contouring on the vane and/or blade shrouds in the turbine section. End wall contouring when optimized can result in a significant reduction in secondary flow vortices which can contribute to high losses in the stage. In addition, end wall contouring can also help reduce heat load into the part, which may permit a reduction in the cooling requirements of the part as well as improving part life. However, it has been observed that, even with end wall contouring, the actual turbine efficiency may be lower than an efficiency predicted for an end wall contour design. Such losses may be due to a negative impact associated with an interaction between purge flow and secondary flows produced in flow passages between adjacent airfoils.

In accordance with an aspect of the invention, a configuration for end wall contouring is provided to prevent or limit mixing of the purge flow and the secondary flows. The end wall contour mitigates horseshoe and end wall vortices, and in accordance with a particular aspect of the invention, directs the purge flow as a substantially separate flow close to the end wall, spaced from and generally following the suction side of the airfoil.

For purposes of the following description, it should be understood that “axial direction” refers to a direction parallel to the rotational axis ARof the rotor28(FIG. 1), and the “chordwise direction” or “chordwise dimension” is defined by a chord line having a length extending from the leading edge42to the trailing edge44of an airfoil34a,34b(FIG. 2). The terms “circumferential direction”, “circumferentially” and “laterally” refer to a direction extending along an end wall30athat is perpendicular to the axial direction. The terms “upstream” and “downstream” are described with reference to the direction of flow of hot gases through the flow path20and can correspond to the directions of “forward” and “aft”, respectively. The terms “radially” and “elevation” refer to a direction that is perpendicular to both the axial and the circumferential directions. The term “mid-chord” refers to a location that is about 50% along the length of a chord line extending between the leading and trailing edges of an airfoil, measured in a circumferential direction from the chord line to the airfoil surface, and can include an axial span adjacent to a maximum of curvature of either the pressure or suction side of an airfoil.

FIG. 1illustrates an exemplary a gas turbine engine10that can incorporate aspects of the present invention. The engine10includes a compressor section12, a combustor14, and a turbine section16. The compressor section12compresses ambient air18that enters an inlet22. The combustor14combines the compressed air with a fuel and ignites the mixture creating combustion products defining a working fluid. The working fluid travels to the turbine section16. Within the turbine section16are rows of stationary vanes24and rows of rotating blades26coupled to a rotor28, and each pair of rows of vanes24and blades26form a stage in the turbine section16. The vanes24and blades26extend radially into an axial flow path20extending through the turbine section16. The vanes24include a plurality of radially inner and outer shrouds or platforms30,32integral with the vanes24and forming respective inner and outer end walls30a,32a. The working fluid expands through the turbine section16and causes the blades26, and therefore the rotor28, to rotate. The rotor28extends into and through the compressor12and may provide power to the compressor12and output power to a generator (not shown).

Referring toFIG. 2, a portion of a turbine stage is depicted with two adjacent airfoil structures including a first airfoil34aand a second airfoil34b, which for the present description may be understood to be airfoils associated with a row of vanes24. However, it should be understood that the description and concepts presented herein could also be implemented in relation to a row of blades26comprising laterally spaced airfoils.

The airfoils34a,34bare each integrally attached to a platform30,32of respective radially inner and outer end walls30a,32a, only end wall30abeing shown inFIG. 2. It may be understood that one or more airfoils may be attached to a pair of inner and outer platforms30,32, and that the end walls30a,32aare continuous circumferential structures formed by the plurality of circumferentially adjacent platforms30,32. Plural inner platforms30located adjacent to each other at a junction (depicted by dotted line33) formed between mating faces of the platforms30, as seen inFIG. 3. Further, it should be understood that the airfoils34a,34bare referenced as representative of all of the airfoils forming the vane row24, and that row of vanes24is formed by a plurality of identical airfoils34a,34bspaced laterally around the circumferential extent of the flow path20.

The airfoils34a,34beach include a generally concave pressure side38and a generally convex suction side40, each of the pressure and suction sides38,40being defined by a radially extending spanwise dimension and an axially extending chordwise dimension, the chordwise dimension extending between a leading edge42and a trailing edge44. The adjacent airfoils34a,34bform a flow passage46therebetween bounded by the radially inner and outer end walls30a,32a. During operation, the working fluid flows axially downstream through the flow passage46defined between the airfoils34a,34b. The airfoils34a,34bare shaped for extracting energy from the working fluid as the working fluid passes through the flow path20.

In a prior or baseline configuration of a flow path between adjacent airfoils, such as one without end wall contouring, horseshoe vortices can be formed, extending downstream from a junction of the inner platform and the leading edge of the airfoil. The baseline configuration may be understood to be formed by platforms30,32that have elevations which are nominally axisymmetric. The horseshoe vortices produced in the baseline configuration progress through the flow passage which can result in the creation of turbulence and can decrease the aerodynamic efficiency of the stage.

In accordance with an aspect of the invention, the end wall30aillustrated inFIG. 2has been configured with a specific 3D contour that, in accordance with one aspect of the invention, avoids or weakens the formation of horseshoe vortices and thereby improves the efficiency of the turbine16. The 3D contour is depicted by contour lines of common elevation displaced from a nominally axisymmetric end wall, as described by a baseline configuration, and where the contour line depicted with a “0” value is a reference value that can correspond to the baseline end wall. It may be understood that the 3D contour is formed by continuous smooth surface elevation transitions between the depicted contour lines.

A pressure side ridge48is associated with each airfoil34a,34band is described herein with particular reference to the airfoil34b. The pressure side ridge48extends circumferentially into the flow passage46between the pair of airfoils34a,34b, and includes an elongated crest50defining a maximum elevation of the ridge48extending between an upstream location51that is axially forward of the leading edge of the airfoil34band a downstream location531that is downstream from the leading edge42and is forward of a mid-chord location52on the pressure side38of the airfoil34b. The upstream location51is about 15% upstream of the leading edge42of each airfoil34b, measured relative to the chord length of the airfoil34b, and the downstream location531is about 10% downstream of the leading edge42of each airfoil34b, measured relative to the chord length of the airfoil34b. Further, the crest50has an axial extent along the pressure side38, extending from the location531, defining a forward location, to an aft location532. The pressure side ridge48is angled to direct a purge flow54of gases passing axially through the flow passage46. The purge flow54comprises purge or cooling air that passes into the flow path20from a purge cavity55(FIG. 1) located radially inward from the end wall30a. In particular, the purge air can pass radially into the flow path20from the purge cavity55through a gap57(FIG. 3) between the inner end wall30aand blade platforms59associated with the rotating blades26.

An axis of elongation AE1of the crest50is oriented at an angle that is close to the leading edge metal angle, α, which is described as an angle between the axial direction and a line49tangent to the mean camber line at the leading edge42. In particular, the axis of elongation AE1of the crest50is oriented at an angle that is about 10° relative the leading edge metal angle, as indicated by an angle, σ, between the axis of elongation AE1and a line49′ that is parallel to the line49. The pressure side ridge48extends to and defines a raised area at the forward edge56of the end wall30a, and is configured to redirect flow upstream of the airfoil34bto guide the purge flow54and to substantially reduce or eliminate formation of horseshoe vortices at the leading edge42of the airfoil34a,34band extending into the flow passage46along the pressure side38.

Referring toFIG. 2, a suction side ridge58is associated with each airfoil34a,34band is described herein with particular reference to the airfoil34a. The suction side ridge58is located adjacent to the suction side40of the airfoil34aand includes an elongated crest60having an axial extent that is entirely located forward of the axial location of the leading edge42. The elongated crest60is spaced from the leading edge42and has an axis of elongation AE2that extends generally parallel to a portion of the suction side40that is directly adjacent to the elongated crest60, i.e., a portion of the suction side40that can be intersected by a line extending from the crest60and perpendicular to the axis of elongation AE2. The axis of elongation AE2of the crest60is preferably oriented at an angle, β, that is greater than an angle of the crest50relative to the axial direction. The suction side ridge58extends to the forward edge56of the end wall30aand is configured to redirect flow upstream of the airfoil34ato guide the purge flow54and to substantially reduce or eliminate formation of horseshoe vortices at the leading edge42and extending into the flow passage46along the suction side40.

The pressure side ridge48and suction side ridge58define a trough62therebetween. The trough62is formed as a low elevation channel beginning upstream of the leading edges42of the airfoils34a,34b, extending from the forward edge56of the inner end wall30ainto the flow passage46, and directs the purge flow adjacent to the inner platform30ainto the flow passage46laterally centrally between the airfoils34a,34b. As can be seen inFIG. 4, the forward edge56is formed with an uneven or undulating surface, extending in the circumferential direction, to locate the inlet of the trough62at the gap57where the purge air exits the purge cavity55

With reference to the airfoil34ainFIG. 2, a mid-chord bulge64is located at the suction side40, and is axially centered at about a mid-chord location66. The mid-chord bulge64extends from a maximum elevation, depicted by an exemplary magnitude of “2”, laterally to an outer edge68. The elevation of the mid-chord bulge64, extending along an intersection with the suction side40, decreases in the axial forward and aft directions. Hence, the mid-chord bulge64can be described as a generally semi-spherical ridge or bulge that extends laterally from the suction side40toward the opposing pressure side38of the airfoil34b.

Further, the mid-chord bulge64defines a higher elevation than the end wall adjacent to the mid-chord location52on the opposing pressure side38of the airfoil32b. In particular, the area forward and aft of the pressure side mid-chord location52is formed without ridge or trough features, as depicted by the area of the pressure side38associated with exemplary magnitudes in the range of about “4” to “−4”, forming a continuous declining slope in the aft direction. Additionally, these low level elevations extend laterally from the pressure side38toward the suction side40of the opposing airfoil34a. That is, in accordance with an aspect of the invention, it can be seen inFIG. 2that the contour line depicting the magnitude “0”, and constant elevation contours to either side of the “0” magnitude contour line, extend from a location on the pressure side38to a laterally opposite location on the suction side40adjacent to the mid-chord bulge64. The described low level elevations form a continuous low elevation channel70that extends in the circumferential direction between the mid-chord bulge64and the pressure side mid-chord location52, e.g., within at least the axial span of contour lines in the range of about “4” to “−4”, and can include an axial area extending within the range of about “6” to “−6”.

The mid-chord bulge64defines a curved surface that requires the flow velocity to accelerate as it passes over the bulge64, with an associated decrease in pressure at the mid-chord location66of the suction side40. In accordance with an aspect of the invention, the low pressure region created by the bulge64accelerates secondary vortices away from the purge flow54, reducing losses that could otherwise result from mixing of the purge flow54and secondary vortices.

It may be noted that the end wall contour includes additional troughs to facilitate control of vortex flows. Specifically, an upstream suction side trough74is located adjacent to the suction side40between the mid-chord bulge64and the suction side ridge58, a downstream suction side trough76is located adjacent to the suction side40between the mid-chord bulge64and the trailing edge44, and a downstream pressure side trough78is located adjacent to the pressure side38between the low elevation channel70and the trailing edge44. It may be understood that the additional described troughs74,76,78function together with the ridges48,60, the mid-chord bulge64and the low elevation channel70to substantially reduced formation of vortices and to avoid or reduce mixing of the purge flow54and flows including secondary vortices.

As noted above, the contour line magnitude “0” can correspond to a baseline elevation, i.e., an elevation corresponding to an end wall without contouring (flat end wall), and the numerical designations for the contour line magnitudes generically denotes relative elevations forming the 3D contour on the end wall30a. Each integer value of magnitude depicted by the contour lines and specified magnitudes inFIG. 2may correspond to a predetermined change of elevation, specified as a percent of the airfoil span. For example, a change in elevation depicted by a change in magnitude of “1” may correspond to an elevation change equal to between 0.5% and 1.5% of the airfoil span.

As can be seen inFIG. 3, the incoming purge flow54flowing adjacent to the end wall passes through the trough62, between the pressure side ridge48and the suction side ridge58(see alsoFIG. 4). From the above description, it may be understood that the pressure side ridge48is positioned at a circumferential location between the circumferential locations of the leading edge42of the airfoil34aand the leading edge42of the adjacent airfoil34bto direct flow centrally into the flow passage46. The purge flow exits the trough62, as designated by purge flow54a, and passes into the low elevation channel70that is formed without ridges or troughs. In the area of the low elevation channel70, the purge flow (designated54b) flows laterally (circumferentially) and axially across the passage46along the low elevation channel70. Hence, mixing of the purge flow54with the secondary vortices is substantially avoided or reduced, and losses associated with mixing are substantially reduced to improve the efficiency of the turbine16.

FIGS. 5A and 5Bfurther illustrate aspects of the invention.FIG. 5Adepicts flows, based on CFD modeling, as they are believed to exist in a prior art flow passage46Phaving a flat end wall. The flows depicted inFIG. 5Ainclude a purge flow54Pthat interacts with a secondary flow72Pincluding vortices, in which it can be seen that an interface region74Pbetween the purge flow54Pand the secondary flow72Pdefines an area of substantial mixing between the flows. In contrast,FIG. 5Bdepicts flows, based on CFD modeling, that are believed to be formed in the flow passage46by the present 3D end wall contour, in which the purge flow54is substantially separated from the secondary flow72as depicted by an interface region74of reduced or minimal interaction. Hence, the present configuration for an end wall contour of the present invention can operate to form a separation between the purge flow54and the secondary flows, such as are formed by secondary vortices, to reduce losses normally associated with mixing of these two flows.