Patent Application
20120324901
The present invention relates to a turbine engine. In particular, the invention relates to a fan-turbine rotor assembly for a tip turbine engine.
Conventional aircraft gas turbine engines include a forward bypass fan, a compressor, a combustor, and a turbine in sequential alignment along a single axis. The compressor provides pressurized air to the combustor, where the pressurized air is mixed with fuel and ignited to produce a high temperature, high velocity gas flow. The high temperature, high velocity gas flow impinges on turbine blades causing rotation of the turbine. Through its axial connection (either directly or through a gear box), the turbine drives the compressor and the forward fan. The rotating forward fan generates thrust through an axial bypass flow region to propel the aircraft. This conventional arrangement is very efficient in generating thrust, but the axial arrangement leads to an elongated engine shape that may not be suitable for some applications.
A more compact alternative to the conventional gas turbine engine is a tip turbine engine as disclosed in U.S. Pat. Nos. 7,845,157; 7,887,296, and 7,874,802. A tip turbine engine features fan blades located aft of a compressor, each fan blade having an internal passage that redirects pressurized air from the compressor from an axial direction to a radial direction. In doing so, the fan blades also function as a centrifugal compressor, radially accelerating and increasing the pressure of the pressurized air received from the axial compressor. The radially accelerated compressed air exits the fan blade in a forward direction and flows into a combustor positioned radially outward from the compressor. In the combustor, pressurized air is mixed with fuel and ignited to produce a high temperature, high velocity gas flow in an aft direction to impinge on turbine blades that are integrated into the tips of the fan blades, thus causing rotation of the fan blades to generate engine thrust. In addition to providing the thrust generated by the engine, the fan blades also drive the compressor, either directly or through a gear box. The result is a highly efficient gas turbine engine that is significantly shorter than a conventional gas turbine engine.
While tip turbine engines are efficient both dimensionally and in their thrust-to-weight ratio, their compact design exposes components to extreme physical loads and temperature gradients. This is particularly true of the unique hollow fan-turbine blades as they serve in their dual roles as fan blades and turbine blades.
An embodiment of the present invention is a tandem fan-turbine rotor assembly for a tip turbine engine. The rotor assembly includes a hollow fan blade rotor and a solid fan blade rotor. The hollow fan blade rotor includes a first fan blade rotor hub, hollow fan blades, and an inducer. The hollow fan blades are attached to the first fan blade rotor hub and extend radially outward from the first fan blade rotor hub. Each of the hollow fan blades includes an internal cavity extending the length of the hollow fan blade. The inducer is attached to the first fan blade rotor hub for directing air from an axial compressor to the internal cavities of the hollow fan blades. The solid fan blade rotor includes a second fan blade rotor hub, solid fan blades, an exo-ring, and tip turbine blades. The solid fan blades are attached to the second fan blade rotor hub and extend radially outward from the second fan blade rotor hub. The exo-ring connects the solid fan blades at their maximum outward radial extent. The tip turbine blades are connected to the exo-ring and extend radially outward from the exo-ring. The hollow fan blade rotor and the solid fan blade rotor rigidly attach to each other at the first and second fan blade rotor hubs.
The present invention is a tandem fan-turbine rotor assembly for use with a tip turbine engine. In contrast to a conventional hollow fan-turbine blade rotor, the tandem fan-turbine rotor assembly has two fan blade rotors configured in tandem: a hollow fan blade rotor and a solid fan blade rotor. As with a conventional hollow fan-turbine rotor, the hollow fan blade rotor acts as a centrifugal compressor, directing and further compressing a flow of compressed air from an axial compressor to a combustor located radially outward from the axial compressor. However, in contrast to the conventional design, the combustion gases generated by the combustor impinge on tip turbine blades attached not to a hollow fan blade rotor, but to a solid fan blade rotor. Forces generated on the tip turbine blades cause rotation of the solid fan blade rotor. The rotating solid fan blade rotor cause tandem rotation of the hollow fan blade rotor through a direct connection at the rotor hubs, thereby generating forward engine thrust. The solid fan blade rotor also causes rotation of the axial compressor through a gearbox connection. By splitting the functions of a conventional hollow fan-turbine blade rotor between two fan blade rotors configured as a tandem fan-turbine rotor assembly, the extreme physical loads and temperature gradients can be limited to the solid fan blade rotor. Without the need for an internal cavity, the solid fan blade rotor can be manufactured with techniques, such as forging, that produce superior strength and durability, rather than techniques necessary for complex, hollow shapes, such as casting, that do not produce the desired strength and durability. In addition, because the hollow fan blade rotor no longer carries the tip turbine blades, a hollow component (exducer) at the tip of the hollow fan blades can be isolated from the very hot combustion gas flow by an air gap. The air gap separation greatly reduces the temperature gradient across the exducer, simplifying its design and extending its lifespan. Finally, by carrying the bulk of the mechanical stress load in the durable solid fan blade, the lifespan of the hollow fan blades is also greatly extended.
As illustrated in
Hollow fan blade rotor 44 and solid fan blade rotor 46 connect at their tandem connection flanges 56, 68 to form tandem fan-turbine rotor assembly 24. Tandem connection flange 56 is connected to hollow fan blade rotor hub 48. Hollow fan blade rotor hub 48 connects inducer 50 to hollow fan blades 54, which extend radially from hollow fan blade rotor hub 48. Hollow fan blades 54 are connected to exducer 52 at their maximum outward radial extent. Tandem connection flange 68 is connected to solid fan blade rotor hub 62. Solid fan blades 72 extend radially from solid fan blade rotor hub 62. Solid fan blades 72 are connected to exo-ring 64 at their maximum outward radial extent. Tip turbine blades 66 are attached to exo-ring 64 and extend radially outward from exo-ring 64 to interact with tip turbine stators 42 of turbine section 20. Tip turbine stators 42 are attached to a non-rotating support portion of tip turbine engine 10. Tandem fan-turbine rotor assembly 24 connects to gearbox 22 at gearbox connection flange 70.
Combustor housing 38 largely surrounds combustion chamber 40. Combustor 18 connects to turbine section 20 such that combustion gases generated in combustion chamber 40 are directed into turbine section 20.
In operation, splitter 32 divides incoming air between fan section 16 and axial compressor 12. Air entering axial compressor 12 is compressed by the rotation of compressor rotor 26 of axial compressor 12 and the interaction of compressor blades 28 with compressor vanes 30. As compressed air exits axial compressor 12 it is drawn into inducer 50 of hollow fan blade rotor 44 of adjacent rotating tandem fan-turbine rotor assembly 24. Inducer 50 directs the compressed air from an axial direction to a radial direction and into internal cavity 58 within each of hollow fan blades 54. Internal cavity 58 within each of hollow fan blades 54 extends the length of each of hollow fan blades 54. As tandem fan-turbine rotor assembly 24 rotates, the compressed air within internal cavity 58 accelerates radially, further compressing the air. The further compressed air exits hollow fan blades 54 through exducer 52. Exducer 52 directs the further compressed air from the radial direction from hollow fan blades 54 to an axial direction opposite the axial direction of the compressed air entering inducer 50, and into combustor housing 38. In addition, exducer 52 acts as a shroud for hollow fan blades 54, providing structural stability to reduce vibration and twisting of hollow fan blades 54. The further compressed air flows into combustion chamber 40 through multiple openings between combustor housing 38 and combustion chamber 40, where it is mixed with fuel and ignited by a flame to produce combustion gases with a high temperature and a high gas flow velocity. Optionally, exducer 52 may include diffuser elements to slow the further compressed air, additionally increasing its pressure, thereby preventing the compressed air from blowing out the flame in combustion chamber 40. The combustion gases exit combustion chamber 40 into turbine section 20 and impinge tip turbine blades 66 in a series of stages, each stage including at least one tip turbine blade 66 and at least one tip turbine stator 42 (two stages illustrated in
As noted above, hollow fan blade rotor 44 and solid fan blade rotor 46 connect at hollow fan blade rotor hub 48 and solid fan blade rotor hub 62 by way of their respective tandem connection flanges 56, 68 to form tandem fan-turbine rotor assembly 24. This connection also positions solid fan blades 72 with respect to hollow fan blades 54.
As shown in
The present invention splits the functions of a conventional hollow fan-turbine blade rotor between hollow fan blade rotor 44 and solid fan blade rotor 46 of tandem fan-turbine rotor assembly 24. In doing so, the extreme physical loads associated with turbine section 20 of tip turbine engine 10 are removed from hollow fan blade rotor 44. The large torque required to drive axial compressor 12 is limited to solid fan blade rotor 46 and gearbox 22 so hollow fan blade rotor 44 and its hollow fan blades 54 need not be over-built to handle this stress. The tremendous centrifugal stress generated by tip turbine blades 66 is also limited to exo-ring 64, solid fan blades 72, and solid fan blade rotor hub 62. Without the need for an internal cavity, exo-ring 64, solid fan blades 72, and solid fan blade rotor hub 62 can be manufactured with techniques, such as forging, that produce superior strength and durability, rather than techniques necessary for complex, hollow shapes, such as casting, that do not produce the desired strength and durability.
Thermal gradient stress is also greatly reduced with the present invention. Conventional tip turbine engine designs integrate turbine blades into exducers at the tips of the fan blades. Thus, the exducer, which must be manufactured with great precision to handle the tight tolerances associated with maintaining turbine tip clearances, is exposed to a very large temperature gradient caused by the passage of moderately hot compressed air through the interior of the exducer while the exterior of the exducer, where the tip turbine blades are attached, experiences extreme combustion temperatures. This extreme thermal stress combined with the extreme physical loads described above result in a relatively short exducer lifetime. In contrast, in the present invention, because hollow fan blade rotor 44 no longer carries tip turbine blades 66, exducer 52 at the tip of hollow fan blades 54 is able to be isolated from the very hot combustion gas flow by air gap 74 between exducer 52 and combustion chamber 40. The separation create by air gap 74 greatly reduces the temperature gradient across exducer 52, greatly simplifying its design, and extending its lifespan. Exo-ring 64 attached to solid fan blades 72 is exposed to the extreme combustion temperatures in turbine section 20, but exo-ring 64 is a simpler component than an exducer and thus, can more easily be designed and manufactured to handle extreme temperature gradients and mechanical stresses.
In the embodiments described above, exducer 52 is part of tandem fan-turbine rotor assembly 24 and physically attached to hollow fan blades 54. However, it is understood that in an alternative embodiment, exducer 52 is not physically attached to hollow fan blades 54 and is not part of tandem fan-turbine rotor assembly 24, but is attached to combustor 18. In this embodiment, because exducer 52 is separate from hollow fan blades 54, the centrifugal forces on hollow fan blades 54 are reduced. In addition, exducer 52 may be less costly to produce as a non-rotating component. It is also understood that in this embodiment, because exducer 52 is not available to act as a shroud, hollow fan blades 54 should be shrouded to provide structural stability to reduce vibration and twisting.
The present invention is a tandem fan-turbine rotor assembly for use with a tip turbine engine. In contrast to a conventional hollow fan-turbine blade rotor, the tandem fan-turbine rotor assembly has two fan blade rotors configured in tandem: a hollow fan blade rotor and a solid fan blade rotor. By splitting the functions of a conventional hollow fan-turbine blade rotor between two fan blade rotors configured as a tandem fan-turbine rotor assembly, the extreme physical loads and temperature gradients can be limited to the solid fan blade rotor. Without the need for an internal cavity, the solid fan blade rotor can be manufactured with techniques, such as forging, that produce superior strength and durability, rather than techniques necessary for complex, hollow shapes, such as casting, that do not produce the desired strength and durability. In addition, because the hollow fan blade rotor no longer carries the tip turbine blades, an exducer at the tip of the hollow fan blades can be isolated from the very hot combustion gas flow by an air gap. The air gap separation greatly reduces the temperature gradient across the exducer, greatly simplifying its design and extending its lifespan. Finally, by carrying the bulk of the mechanical stress load in the solid fan blade, the lifespan of the hollow fan blades is also greatly extended.
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.
