TURBINE ENGINE FRAME INCORPORATING SPLITTERS

A frame apparatus for a turbine engine includes: a turbomachinery stage discharging into a downstream flowpath, the stage including a rotor carrying an array of axial-flow rotor airfoils; and a frame disposed downstream of the turbomachinery stage, the frame including: a support structure comprising at least one of a hub and an annular casing; an annular array of stationary struts carried by the support structure, each strut having an airfoil shape with spaced-apart pressure and suction sides extending between a leading edge and a trailing edge thereof, the stationary struts defining spaces therebetween; and the stationary struts defining spaces therebetween; and a plurality of splitters carried by the support structure, the splitters positioned in the spaces between the stationary struts, wherein at least one of a chord dimension of the splitters and a span dimension of the splitters is less than the corresponding dimension of the stationary struts.

BACKGROUND OF THE INVENTION

This invention relates generally to gas turbine engines and more particularly to stationary frames in such engines.

A gas turbine engine includes, in serial flow communication, a compressor, a combustor, and turbine. The turbine is mechanically coupled to the compressor and the three components define a turbomachinery core. The core is operable to generate a flow of hot, pressurized combustion gases The core forms the basis for several aircraft engine types such as turbojets, turboprops, and turbofans.

Designers and engineers continually strive to produce gas turbine engines having greater output and lower fuel consumption. Newer gas turbine engine designs, including extensions of existing designs with uprated performance (i.e. “growth designs”), can have elevated turbine exit Mach numbers.

One problem with these designs it that they can lead to undesirable aeromechanical interaction between rotating airfoils and downstream frame structures.

BRIEF DESCRIPTION OF THE INVENTION

This problem is addressed by a stationary turbine engine frame which incorporates splitter airfoils. The splitters are effective to locally reduce a bow wave effect on upstream airfoils.

According to one aspect of the technology described herein, a frame apparatus for a turbine engine includes: an axial-flow turbomachinery stage that discharges into a downstream flowpath, the stage including a rotor carrying an array of axial-flow rotor airfoils; and a frame disposed downstream of the turbomachinery stage, the frame including: a support structure comprising at least one of a hub and an annular casing; an annular array of stationary struts carried by the support structure, each of the struts having an airfoil shape with spaced-apart pressure and suction sides extending between a leading edge and a trailing edge thereof, the stationary struts defining spaces therebetween; and the stationary struts defining spaces therebetween; and a plurality of splitters carried by the support structure, the splitters positioned in the spaces between the stationary struts, wherein at least one of a chord dimension of the splitters and a span dimension of the splitters is less than the corresponding dimension of the stationary struts.

According to another aspect of the technology described herein, a gas turbine engine includes: a compressor, a combustor, and a turbine, at least one of the compressor and the turbine being an axial-flow device; wherein at least one of the compressor and the turbine includes an axial-flow turbomachinery stage that discharges into a downstream flowpath, the turbomachinery stage including a rotor carrying an array of axial-flow rotor airfoils; and a frame disposed downstream of the turbomachinery stage, the frame including: a support structure comprising at least one of an annular hub and an annular casing; an annular array of stationary struts carried by the support structure, each of the struts having an airfoil shape with spaced-apart pressure and suction sides extending between a leading edge and a trailing edge thereof, the stationary struts defining spaces therebetween; and the stationary struts defining spaces therebetween; and a plurality of splitters carried by the support structure, the splitters positioned in the spaces between the stationary struts, wherein at least one of a chord dimension of the splitters and a span dimension of the splitters is less than the corresponding dimension of the stationary struts.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,FIG. 1depicts an exemplary gas turbine engine10. While the illustrated example is a high-bypass turbofan engine, the principles of the present invention are also applicable to other types of engines, such as low-bypass turbofans, turbojets, turboprops, etc. The engine10has a longitudinal center line or axis11and an outer stationary annular core casing12disposed concentrically about and coaxially along the axis11.

It is noted that, as used herein, the terms “axial” and “longitudinal” both refer to a direction parallel to the centerline axis11, while “radial” refers to a direction perpendicular to the axial direction, and “tangential” or “circumferential” refers to a direction mutually perpendicular to the axial and tangential directions. As used herein, the terms “forward” or “front” refer to a location relatively upstream in an air flow passing through or around a component, and the terms “aft” or “rear” refer to a location relatively downstream in an air flow passing through or around a component. The direction of this flow is shown by the arrow “F” inFIG. 1. These directional terms are used merely for convenience in description and do not require a particular orientation of the structures described thereby.

The engine10has a fan14, booster16, compressor18, combustor20, high pressure turbine22, and low pressure turbine24arranged in serial flow relationship. In operation, pressurized air from the compressor18is mixed with fuel in the combustor20and ignited, thereby generating combustion gases. Some work is extracted from these gases by the high pressure turbine22which drives the compressor18via an outer shaft26. The combustion gases then flow into the low pressure turbine24, which drives the fan14and booster16via an inner shaft28. The inner and outer shafts28and26are rotatably mounted in bearings30which are themselves mounted in a fan frame32and a turbine rear frame34.

The fan frame32includes a central hub36connected to an annular fan casing38by an annular array of radially extending struts40. An annular array of fan outlet guide vanes (“OGVs”)42extend across the fan flowpath just downstream of the fan14. In this example, the OGVs42are aero-turning elements and the struts40serve as structural supports for the fan casing38. In other configurations, a single row of airfoil-shaped elements perform both the aerodynamic and structural functions. The fan14and the OGVs42are one example of an apparatus within a gas turbine engine having a rotating airfoil row immediately upstream of a row of stationary struts.

The turbine rear frame34has a central hub44connected to the core casing12by an annular array of radially-extending struts46. The low-pressure turbine24and the turbine rear frame34are another example of an apparatus in a gas turbine engine having a rotating airfoil row immediately upstream of a row of stationary struts.

While the concepts of the present invention will be described using the turbine rear frame34as an example, it will be understood that those concepts are applicable to any stationary structure within the engine10including a rotating airfoil row immediately upstream of a row of stationary struts. It will also be understood that the concepts described herein may be applied to other types of turbines other than gas turbine engines, referred to generically as “turbine engines”.

FIGS. 2-4illustrate a portion of the low pressure turbine24and the turbine rear frame34. The aft turbine stage includes a rotor48carrying a plurality of airfoil-shaped turbine blades50each extending from a root52to a tip54. The airfoil-shaped struts46of the turbine rear frame34are bounded by the hub44and the casing12, respectively. The hub44defines an annular inner flowpath surface56, and the casing12defines an annular outer flowpath surface58. Each strut46extends from a root60at the inner flowpath surface56to a tip62at the outer flowpath surface58, and includes a concave pressure side64joined to a convex suction side66at a leading edge68and a trailing edge70.

Each strut46has a span (or span dimension) “S1” (FIG. 4) defined as the radial distance from the root60to the tip62. Depending on the specific design of the struts46, its span S1may be different at different axial locations. For reference purposes, the relevant measurement would be the span S1at the leading edge68. Each strut46has a chord (or chord dimension) “C1” (FIG. 3) defined as the length of an imaginary straight line connecting the leading edge68and the trailing edge70. Depending on the specific design of the struts46, its chord C1may be different at different locations along the span S1. For purposes of the present invention, the relevant measurement would be the chord C1at the root60or tip62. The struts46are uniformly spaced apart around the periphery of the inner flowpath surface56. A mean circumferential spacing “s” (seeFIG. 4) between adjacent struts46is defined as s=2πr/Z, where “r” is a designated radius of the struts46(for example at the root60) and “Z” is the number of struts46. A nondimensional parameter called “solidity” is defined as c/s, where “c” is equal to the strut chord as described above.

During engine operation, a bow wave72(seeFIG. 3) is generated immediately ahead of the leading edge68of each of the struts46. The physical size of the bow wave72is known to be proportional to the spacing s between the struts46. As the size of the bow wave72increases, its dimensions increase in both axial and tangential directions. The magnitude of the impact on the last stage rotor48from the downstream frame is related to the size of the bow wave72.

As the turbine blades50rotate, they cut through the bow waves72. The interaction of the bow waves72and the turbine blades50create a forcing function, resulting in aeroelastic effects in the turbine blades50. Because the turbine blades50are cantilevered from the rotor48, their effective stiffness at the outer portions near the tips54is less than at their roots52; accordingly the aeroelastic effects are strongest near the tips54. These effects can lead to excessive deflection, stresses, and potential cracking or component failure.

To reduce the strength of the bow waves72, the turbine frame34may be provided with an array of splitters, as shown inFIGS. 5-7. In this example, an array of splitters74extend radially inward from the outer flowpath surface58. Two splitters74are disposed between each adjacent pair of struts46. In the circumferential direction, the splitters74may be evenly spaced or circumferentially biased between two adjacent struts46. Each splitter74extends from a root76to a tip78, and includes a concave pressure side80joined to a convex suction side82at a leading edge84and a trailing edge86. As best seen inFIG. 6, each splitter74has a span (or span dimension) “S2” defined as the radial distance from the root76to the tip78. Depending on the specific design of the splitter74, its span S2may be different at different axial locations. For reference purposes, the relevant measurement would be the span S2at the leading edge84. Each splitter74has a chord (or chord dimension) “C2” defined as the length of an imaginary straight line connecting the leading edge84and the trailing edge86. Depending on the specific design of the splitter74, its chord C2may be different at different locations along the span S2. For purposes of the present invention, the relevant measurement is the chord C2at the tip78.

The splitters74function to locally increase the solidity and thereby reduce the strength of the above-mentioned bow waves72. A similar effect could be obtained by simply increasing the number of struts46, and therefore reducing the strut-to-strut spacing. An undesirable side effect of increased solidity is greater flow blockage. Therefore, the dimensions of the splitters74and their position may be selected to reduce bow wave strength while minimizing their surface area and resulting flow blockage and frictional losses. The axial position of the splitters74may be set to provide best performance and efficiency to suit a specific application. As an example, the splitters74may be positioned so that their leading edges84are located within a range from approximately 15% of the chord C1axially forward of the strut leading edges68, to approximately 30% of the chord C1axially rearward of the strut leading edges68.

The span S2and/or the chord C2of the splitters74may be some fraction less than unity of the corresponding span S1and chord C1of the struts46. These may be referred to as “part-span” and/or “part-chord” splitters. For example, the span S2may be equal to or less than the span S1. Preferably for reducing blockage and frictional losses, the span S2is 50% or less of the span S1. As another example, the chord C2may be equal to or less than the chord C1. Preferably for reducing blockage and frictional losses, the chord C2is 50% or less of the chord C1.

For the purpose of reducing bow wave strength, the cross-sectional shape of the splitters is not critical. In a practical application, the splitters74may be streamlined to reduce aerodynamic drag and losses associated therewith.

The number, location, and configuration of the splitters74may be altered to suit a particular application. In the example shown inFIGS. 5-7, two splitters74are positioned between each pair of adjacent struts46, equally spaced in the circumferential direction, and the splitters74have equal chord dimensions.

FIG. 8illustrates an alternative embodiment. In this example, four splitters174are positioned between each pair of adjacent struts46. the splitters174are equally spaced in the circumferential direction, and the splitters174have equal chord dimensions.

FIG. 9illustrates another alternative embodiment. In this example four splitters274,276,278,280are positioned between each pair of adjacent struts46. the splitters274,276,278,280are equally spaced in the circumferential direction. The splitters have a variable chord, with the chord of the splitter274closest to the suction side66of the strut46being the largest, tapering down to the chord of the splitter280being the smallest. This arrangement is useful because aerodynamic loading is strongest on the suction side66of the strut46and weaker adjacent the pressure side64of the adjacent strut; accordingly the splitters274,276,278,280can be preferentially sized to mitigate bow wave strength while minimizing flow blockage and friction losses.

The turbine engine frame structure having the splitters described herein has advantages over the prior art. In particular, by applying part span splitters, the bow wave effect can be locally reduced allowing for improved durability and/or reduced spacing.

The foregoing has described a gas turbine engine with a splittered frame. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.