CAST STEEL FRAME FOR GAS TURBINE ENGINE
A gas turbine engine comprises a first turbine module, a second turbine module, and a frame interconnecting the first turbine module with the second turbine module. The frame includes a plurality of circumferentially distributed struts extending radially between an inner hub and an outer case, and is formed from a single steel sand casting.
This application claims the benefit of U.S. Provisional Application No. 61/747,271 filed Dec. 29, 2012 for “CAST STEEL FRAME FOR GAS TURBINE ENGINE” by Jonathan Ariel Scott and PCT Application No. PCT/US 13/77124 filed Dec. 20, 2013 for “CAST STEEL FRAME FOR GAS TURBINE ENGINE” by Jonathan Ariel Scott.
BACKGROUNDThe described subject matter relates generally to gas turbine engines, and more specifically to cases and frames for gas turbine engines.
Gas turbine engines operate according to a continuous-flow, Brayton cycle. A compressor section pressurizes an ambient air stream, fuel is added and the mixture is burned in a combustor section. The combustion products expand through a turbine section where bladed rotors convert thermal energy from the combustion products into mechanical energy for rotating one or more centrally mounted shafts. The shafts, in turn, drive the forward compressor section, thus continuing the cycle. Gas turbine engines are compact and powerful power plants, making them suitable for powering aircraft, heavy equipment, ships and electrical power generators. In power generating applications, the combustion products can also drive a separate power turbine attached to an electrical generator.
Gas turbine engines are supported by frames which typically include one or more struts. The struts connect outer and inner cases and cross a flow passage carrying working gases such as combustion products. Due to the need for the struts to retain their strength at high temperatures, frames used on the turbine side of the engine have been produced using investment cast superalloys. However, casting of superalloys becomes more difficult and expensive as the radial dimension of the frame increases. Increased frame size thus has required the struts to be individually cast along with separate inner and outer cases, which are then individually welded or otherwise bonded. This results in a tradeoff between engine size and manufacturing effort.
SUMMARYA gas turbine engine comprises a first turbine module, a second turbine module, and a frame interconnecting the first turbine module with the second turbine module. The frame comprises a single, unified steel casting which includes a plurality of circumferentially distributed struts extending radially between an inner hub and an outer case.
A turbine exhaust case (TEC) assembly for a gas turbine engine comprises a frame and a fairing assembly. The frame comprises a single, unified steel casting which includes a plurality of circumferentially distributed struts extending radially between an inner hub and an outer case. The fairing assembly includes at least one fairing segment secured over a plurality of annular frame surfaces between the inner case and the outer hub, and defines a main gas flow passage through the frame.
A gas turbine engine frame comprises an outer case, an inner hub, and a plurality of struts distributed circumferentially around the frame and extending radially between the inner hub and the outer case. The outer case, the inner hub, and the plurality of struts are formed from a single unified steel casting.
The diameter of some gas turbine frames, including the inner and outer frame cases, can in some cases exceed 2 meters. The case can comprise a single cast steel frame to simplify manufacturing. Sand casting can be used to make the steel frame as a single, unitary, and monolithic piece. In certain embodiments, struts are cast solid, and passages for cooling and service tubes are machined radially through the struts after casting. Machining may be performed with high-speed milling equipment due to the resulting radial length of the passages. Fairings pass through the cast frame to define a main gas flow passage. Operating temperature of the frame can be reduced or maintained using a combination of sealing, internal cooling, external cooling, film cooling, and/or heat shields.
As is well known in the art of gas turbines, incoming ambient air 30 becomes pressurized air 32 in compressors 16, 18. Fuel mixes with pressurized air 32 in combustor section 20, where it is burned. Once burned, combustion gases 34 expand through turbine sections 22, 24 and power turbine 26. High and low pressure turbine sections 22, 24 can drive respective high and low pressure rotor shafts 36, 38. Shafts 36, 38 can be rotated in response to the combustion products and in turn can rotate the attached compressor sections 18, 16. Free turbine section 26 may, for example, drive an electrical generator, pump, or gearbox (not shown) via power turbine shaft 39.
As shown in
As seen in
In the illustrated embodiment, frame 46 includes outer case 54, inner hub 56, and a circumferentially distributed plurality of struts 58 (only one shown in
In the embodiment shown, fairing assembly 48, which includes outer fairing platform 60, inner fairing platform 62, and strut liners 64. Outer fairing platform 60, inner fairing platform 62, and fairing strut liners 64 define a portion of main gas flow passage 51. Outer fairing platform 60 and inner fairing platform 62 each have a generally conical shape secured over annular surfaces of outer case 54 and inner hub 56. Inner fairing platform 62 is spaced from outer platform 60 by strut liners 64, which are secured over surfaces of each strut 58 extending through main gas flow passage 51. In this example, outer fairing platform 60 is disposed radially inward of outer case 54, while inner fairing platform 62 can be disposed radially outward of inner frame hub 56.
Upstream (first) turbine module 44 includes outer case 70 connected to a forward side of outer case 54 via fasteners 72, while downstream (second) turbine module 45 includes outer case 74 connected to an aft side of outer case 54 via fasteners 76. Outer case 54 similarly includes forward flange 79A and aft flange 79B. TEC assembly 42 includes aft casing flange 79A and forward casing flange 79B for interconnecting TEC assembly 42 with other modules in engine 10 (shown in
In addition, main gas flow passage 51 can be sealed around these and other interconnections to prevent fluid leakage and unwanted heating of frame 42. In one example, seals (not shown) are located around the edges 80 of fairing assembly 48. One or more of these seals may be part of a larger seal assembly (not shown) adapted to perform multiple sealing and support functions while helping to direct secondary air flow in and around frame 46.
TEC assembly 42 also can include heat shield assembly 82 comprising one or more heat shield segments 84. Heat shield assembly 82 reduces radiative heating of frame 46 by reflecting thermal radiation back toward fairing assembly 48 and away from annular surfaces of frame 46. Certain embodiments of heat shield assembly 82 also reduce convective heating to varying degrees, depending on whether one of more heat shield segments 84 are free to thermally grow.
Heat shield segments 84 are generally arranged in lines of sight between fairing assembly 48 and frame 46, but are not secured directly to the hottest portions of fairing assembly 48 designed to be exposed to working gas flow 34. Rather, heat shield segments 84 can be secured to cooler portions of TEC assembly 42 such as frame 46 or external fairing flanges 86 as shown in
In the illustrated example, two heat shield segments 84 include a case portion parallel to respective outer and inner fairing platforms 60, 62. These two segments also can include radial extensions. Other segments 84 can include both axial and radial portions. One or more segments 84 can overlap. Overlapping segments can be fastened or welded together. Alternatively, overlapping segments can rest against one another and be free to thermally grow as needed.
Frame 46 can also include passages 90 (shown in phantom) formed radially through struts 58. To further reduce temperature of frame 46, at least one passage 90 can carry cooling air between outer cavity 92 and inner cavity 94. This cooling air can be used for convective cooling, film cooling, and/or impingement cooling of frame 46, fairing assembly 48, and/or heat shield assembly 82. Inner cavity 94 is disposed radially inward of inner hub 56, and is defined by inner hub 56, bearing support 96, and outer flow divider wall 98. As such, additional passages 90 may carry oil or buffer air service lines (not shown in
These and other features of frame 46 allow for substitution of lower temperature materials and processes in place of more expensive temperature-resistant materials such as investment cast nickel-based superalloys. Here, frame 46 can be formed from a single-piece steel sand casting as described below.
Frame 46 (shown in
Casting 114 can comprise a corrosion-resistant chromium steel with high thermal resistance and mechanical strength. In certain embodiments, the steel alloy comprises between about 11 wt % and about 14 wt % chromium, as well as about 3 wt % to about 5 wt % nickel. In certain of these embodiments, the steel further comprises up to about 1 wt % molybdenum. ASTM A743 class steel is one suitable non-limiting example in this range of compositions. More specifically, ASTM A743, Grade CA-6NM has been found to offer a suitable balance of castability, corrosion resistance, and thermal resistance among other factors.
In certain embodiments, sand casting 114 has a minimum radial dimension d measuring at least about 1.5 meters (about 59 inches). In certain of these embodiments, sand casting 114 has a minimum radial dimension d measuring at least about 2.1 meters (about 80 inches). These dimensions allow for a larger engine power core, and more efficient energy recovery from the downstream turbine module, such as power turbine 26 (shown in
In this view, heat shield segments 84 are disposed around strut 58 between fairing strut liners 64 and outer strut surface 129. Cooling air can flow radially through one or both sides of heat shield segments 84
Passage 90 is defined by inner strut wall surface 130. In certain embodiments, portions of inner strut wall surface 130 can be shaped to accommodate one or more service lines 132. For example, inner strut wall surface 130 includes grooves 133 for larger service lines 132.
Thus in certain embodiments, passages 90 are formed radially through solid strut bars 120 (shown in
While the machining equipment is more expensive and tooling life is relatively short, the combination of high-speed machining with a single sand cast frame provides a repeatable, cost effective alternative for large turbine frames as compared to investment cast or welded superalloys.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
Claims
1. A gas turbine engine comprising:
- a first turbine module;
- a second turbine module;
- a frame interconnecting the first turbine module with the second turbine module, the frame comprising a single, unified steel casting which includes a plurality of circumferentially distributed struts extending radially between an inner hub and an outer case.
2. The engine of claim 1, wherein the single unified steel casting has a minimum radial dimension measuring at least about 60 inches (about 1.5 meters).
3. The engine of claim 1, wherein the single unified steel casting has a minimum radial dimension measuring at least about 80 inches (about 2.1 meters).
4. The engine of claim 1, wherein the frame includes a radially extending cooling passage formed through each of the plurality of struts.
5. The engine of claim 4, wherein the radially extending cooling passages are machined through solid cast struts.
6. The engine of claim 1, further comprising:
- a fairing assembly including at least one fairing segment secured over a plurality of annular frame surfaces between the inner case and the outer hub, the fairing assembly defining a main gas flow passage through the frame.
7. The engine of claim 6, further comprising:
- a heat shield assembly including at least one heat shield segment disposed between the at least one fairing segment and an annular frame surface.
8. The engine of claim 1, wherein the first module comprises a low pressure turbine module and the second module comprises a power turbine module.
9. A turbine exhaust case (TEC) assembly for a gas turbine engine, the TEC assembly comprising:
- a frame comprising a single unified steel casting, the frame including a plurality of circumferentially distributed struts extending radially between an inner hub and an outer case; and
- a fairing assembly including at least one fairing segment secured over a plurality of annular frame surfaces between the inner case and the outer hub, the fairing assembly defining a main gas flow passage through the frame.
10. The assembly of claim 9, wherein the single unified steel casting has a minimum radial dimension measuring at least about 60 inches (about 1.5 meters).
11. The assembly of claim 9, wherein the single unified steel casting has a minimum radial dimension measuring at least about 80 inches (about 2.1 meters).
12. The assembly of claim 9, wherein the frame includes a ballistically machined cooling passage formed through each of the plurality of struts.
13. The assembly of claim 9, wherein the single unified steel casting comprises at least about 11 wt % chromium and at least about 3 wt % nickel.
14. A gas turbine engine frame comprising:
- an outer case;
- an inner hub; and
- a plurality of struts distributed circumferentially around the frame and extending radially between the inner hub and the outer case, the outer case, the inner hub, and the plurality of struts formed as a single unified steel casting.
15. The frame of claim 14, wherein a radial dimension of the frame measures at least about 60 inches (about 1.5 meters).
16. The frame of claim 14, wherein a radial dimension of the frame measures at least about 80 inches (about 2.1 meters).
17. The frame of claim 14, wherein the single steel sand casting includes a plurality of solid cast strut bars.
18. The frame of claim 17, further comprising:
- a radial cooling passage ballistically machined through each of the struts, each passage extending between the outer case and the inner hub.
19. The frame of claim 18, further comprising:
- a cooling hole providing fluid communication between the passage and an outer surface of the strut.
20. The frame of claim 14, wherein the single steel sand casting comprises at least about 11 wt % chromium and at least about 3 wt % nickel.
Type: Application
Filed: Dec 20, 2013
Publication Date: Nov 12, 2015
Inventor: Jonathan Ariel Scott (Southington, CT)
Application Number: 14/650,683