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.
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.
The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:
Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,
It is noted that, as used herein, the terms “axial” and “longitudinal” both refer to a direction parallel to the centerline axis 11, 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” in
The engine 10 has a fan 14, booster 16, compressor 18, combustor 20, high pressure turbine 22, and low pressure turbine 24 arranged in serial flow relationship. In operation, pressurized air from the compressor 18 is mixed with fuel in the combustor 20 and ignited, thereby generating combustion gases. Some work is extracted from these gases by the high pressure turbine 22 which drives the compressor 18 via an outer shaft 26. The combustion gases then flow into the low pressure turbine 24, which drives the fan 14 and booster 16 via an inner shaft 28. The inner and outer shafts 28 and 26 are rotatably mounted in bearings 30 which are themselves mounted in a fan frame 32 and a turbine rear frame 34.
The fan frame 32 includes a central hub 36 connected to an annular fan casing 38 by an annular array of radially extending struts 40. An annular array of fan outlet guide vanes (“OGVs”) 42 extend across the fan flowpath just downstream of the fan 14. In this example, the OGVs 42 are aero-turning elements and the struts 40 serve as structural supports for the fan casing 38. In other configurations, a single row of airfoil-shaped elements perform both the aerodynamic and structural functions. The fan 14 and the OGVs 42 are 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 frame 34 has a central hub 44 connected to the core casing 12 by an annular array of radially-extending struts 46. The low-pressure turbine 24 and the turbine rear frame 34 are 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 frame 34 as an example, it will be understood that those concepts are applicable to any stationary structure within the engine 10 including 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”.
Each strut 46 has a span (or span dimension) “S1” (
During engine operation, a bow wave 72 (see
As the turbine blades 50 rotate, they cut through the bow waves 72. The interaction of the bow waves 72 and the turbine blades 50 create a forcing function, resulting in aeroelastic effects in the turbine blades 50. Because the turbine blades 50 are cantilevered from the rotor 48, their effective stiffness at the outer portions near the tips 54 is less than at their roots 52; accordingly the aeroelastic effects are strongest near the tips 54. These effects can lead to excessive deflection, stresses, and potential cracking or component failure.
To reduce the strength of the bow waves 72, the turbine frame 34 may be provided with an array of splitters, as shown in
The splitters 74 function to locally increase the solidity and thereby reduce the strength of the above-mentioned bow waves 72. A similar effect could be obtained by simply increasing the number of struts 46, and therefore reducing the strut-to-strut spacing. An undesirable side effect of increased solidity is greater flow blockage. Therefore, the dimensions of the splitters 74 and 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 splitters 74 may be set to provide best performance and efficiency to suit a specific application. As an example, the splitters 74 may be positioned so that their leading edges 84 are located within a range from approximately 15% of the chord C1 axially forward of the strut leading edges 68, to approximately 30% of the chord C1 axially rearward of the strut leading edges 68.
The span S2 and/or the chord C2 of the splitters 74 may be some fraction less than unity of the corresponding span S1 and chord C1 of the struts 46. These may be referred to as “part-span” and/or “part-chord” splitters. For example, the span S2 may be equal to or less than the span S1. Preferably for reducing blockage and frictional losses, the span S2 is 50% or less of the span S1. As another example, the chord C2 may be equal to or less than the chord C1. Preferably for reducing blockage and frictional losses, the chord C2 is 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 splitters 74 may be streamlined to reduce aerodynamic drag and losses associated therewith.
The number, location, and configuration of the splitters 74 may be altered to suit a particular application. In the example shown in
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.
Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.