Claims:1. A fan assembly (16), comprising:
a fan casing (40); and
a fan (42) comprising a hub (44) and a plurality of fan blades (46) extending radially outward from the hub (44),
wherein at least one of the plurality of fan blades (46) comprises a blade tip extension (60) that is integrally coupled to tip (54) of the fan blade (46), and
wherein the blade tip extension (60) comprises a shape memory alloy.

2. The fan assembly (16) of claim 1, wherein the blade tip extension (60) has a first shape at a first temperature and has a second shape at a second temperature, wherein the second temperature is different from the first temperature.
3. The fan assembly (16) of claim 2, wherein length (l) of the blade tip extension (60) at the first shape is different from the length (l1, l2) of the blade tip extension (60) at the second shape.
4. The fan assembly (16) of claim 3, wherein a clearance (70) between the fan blade (46) and the fan casing (40) is less than 0.5 mm when the blade tip extension (60) is at the first shape or at the second shape.
5. The fan assembly (16) of claim 2, wherein linear strain of the blade tip extension (60) at the second shape is at least 2% of the blade tip extension (60) at the first shape.
6. The fan assembly (16) of claim 1, wherein the tip (54) of the fan blade (46) comprises a fiber-reinforced plastic material.
7. The fan assembly (16) of claim 1, wherein the blade tip extension (60) is mechanically joined to the tip (54) of the fan blade (46).
8. The fan assembly (16) of claim 1, wherein the blade tip extension (60) is partially embedded in the tip (54) of the fan blade (46).
9. The fan assembly (16) of claim 1, wherein the shape memory alloy comprises a NiTi alloy.
10. The fan assembly (16) of claim 1, wherein all fan blades (46) of the plurality of fan blades (46) comprise the blade tip extension (60).
11. A gas turbine engine (10) comprising a fan assembly (16), the fan assembly (16) comprising:
a fan casing (40); and
a fan (42) comprising a hub (44) and a plurality of fan blades (46) extending radially outward from the hub (44),
wherein at least one of the plurality of fan blades (46) comprises a blade tip extension (60) that is integrally coupled to the tip (54) of the fan blade (46), and
wherein the blade tip extension (60) comprises a shape memory alloy.
12. The gas turbine engine (10) of claim 11, wherein the blade tip extension (60) has a first shape at a first temperature and has a second shape at a second temperature, wherein the second temperature is different from the first temperature.
13. The gas turbine engine (10) of claim 12, wherein length (l) of the blade tip extension (60) at the first shape is different from the length (l1, l2) of the blade tip extension (60) at the second shape, and a clearance (70) of the fan blade (46) with the fan casing (40) is less than 0.3 mm when the blade tip extension (60) is at the first shape or at the second shape.
14. A method of controlling a clearance (70) of a fan assembly (16), the fan assembly (16) comprising a fan casing (40) and a fan (42) that comprises a hub (44) and a plurality of fan blades (46) extending radially outward from the hub (44), wherein at least one of the plurality of fan blades (46) comprises a blade tip extension (60) that is integrally coupled to tip (54) of the fan blade (46), and wherein the blade tip extension (60) comprises a shape memory alloy, the method comprising:
controlling a clearance (70) between the at least one of the plurality of fan blades (46) and the fan casing (40) by changing the shape of the blade tip extension (60), wherein changing the shape of the blade tip extension (60) comprises subjecting the blade tip extension (60) to a first temperature to adopt a first shape or subjecting the blade tip extension (60) to a second temperature to adopt a second shape, wherein the second temperature is different from the first temperature.
15. The method of claim 14, wherein subjecting the blade tip extension (60) to the first temperature or to the second temperature comprises induction heating.
16. The method of claim 15, wherein the induction heating is performed using an induction coil (102) that is embedded in the fan casing (40) of the fan assembly (16).
17. The method of claim 14, wherein subjecting the blade tip extension (60) to the first temperature or to the second temperature comprises exposing the blade tip extension to a flow gas.
18. The method of claim 14, wherein subjecting the blade tip extension (60) to the first temperature or to the second temperature is in response to a control algorithm of the fan assembly.
19. The method of claim 18, wherein the control algorithm is based on a prediction of a potential change in the clearance (70) between the at least one of the plurality of fan blades (46) and the fan casing (40).
20. The method of claim 14, further comprising:
predicting a potential change in the clearance (70) between the at least one of the plurality of fan blades (46) and the fan casing (40);
inputting the predicted potential change to a control algorithm; and
subjecting the blade tip extension (60) to the first temperature or to the second temperature by changing a supply of electricity to an induction coil (102) embedded in the fan casing (40), in response to an output of the control algorithm.
, Description:BACKGROUND
[0001] The present disclosure relates generally to a fan assembly having a blade tip extension and, more specifically, to a fan assembly having a blade tip extension including a shape memory alloy. It further relates to articles and systems including such fan assembly (e.g., a fan assembly in a gas turbine engine), and methods for controlling the clearance.
[0002] In a gas turbine engine, air is pressurized in a compressor, subsequently mixed with a fuel, and combusted in a combustor to generate combustion gases. One or more turbines disposed downstream relative to the combustor extract energy from the combustion gases and drive at least one of a compressor, a fan assembly, a propeller, and/or any other mechanical load via one or more shafts. The fan assembly is conventionally used in a gas turbine engine to force a primary air stream through the compressor and turbines of the engine and to force a secondary airflow through an annular radially outward bypass duct. It is desirable that clearance between the rotating fan blades and the internal surface of the fan casing of the fan assembly be kept as minimum as possible at all conditions to optimize the fan efficiency.
[0003] To maintain airflow performance of the fan assembly, generally, the clearance between fan blades and the fan casing is set to a short distance. The tight clearance prevents reverse flow leakage around the tip of the fan blades through the clearance. However, under some operating conditions, such tight clearance may result in rubbing of the tip of the fan blade with the fan casing that can lead to instability and failures of fan components. Such rubbing has been reduced in the past by increasing the clearance. However, increasing the clearance increases leakage flow around the blade tips and reduces the performance of the fan assembly. The negative impact on the performance of the fan assembly is two-fold; (1) reduced impeller working area lowering the efficiency of the fan assembly and (2) increased clearance that allows flow leakage in the opposite direction to the main flow. The loss in performance caused by the former can be regained to some extent, for example, by adjusting blade pitch angles. There exists a need for a more efficient fan assembly to minimize reverse flow leakage in the gas turbine engines.
BRIEF DESCRIPTION
[0004] In accordance with some embodiments, a fan assembly is disclosed. The fan assembly includes a fan casing and a fan. The fan includes a hub and a plurality of fan blades extending radially outward from the hub. At least one of the plurality of fan blades includes a blade tip extension that is integrally coupled to the tip of the fan blade. The blade tip extension includes a shape memory alloy.
[0005] In accordance with some embodiments, a gas turbine engine is disclosed. The gas turbine engine includes a fan assembly. The fan assembly includes a fan casing and a fan. The fan includes a hub and a plurality of fan blades extending radially outward from the hub. At least one of the plurality of fan blades includes a blade tip extension that is integrally coupled to the tip of the fan blade. The blade tip extension includes a shape memory alloy.
[0006] In accordance with some embodiments, a method of controlling a clearance of a fan assembly is disclosed. The fan assembly includes a fan casing and a fan that includes a hub and a plurality of fan blades extending radially outward from the hub. At least one of the plurality of fan blades includes a blade tip extension that is integrally coupled to the tip of the fan blade. The blade tip extension includes a shape memory alloy. The method of controlling the clearance of the fan assembly includes controlling the clearance between the at least one of the plurality of fan blades and the fan casing by changing the shape of the blade tip extension. The shape of the blade tip extension is changed by subjecting the blade tip extension to a first temperature to adopt a first shape or subjecting the blade tip extension to a second temperature to adopt a second shape. The second temperature is different from the first temperature.
DRAWINGS
[0007] These and other features and aspects of embodiments of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings.
[0008] FIG. 1 is a schematic diagram of a gas turbine engine, in accordance with some embodiments of the present disclosure.
[0009] FIG. 2 is a schematic illustration of a fan assembly, in accordance with some embodiments of the present disclosure.
[0010] FIG. 3 is a schematic illustration of an integral coupling of a blade tip extension to the tip of a fan blade, in accordance with one exemplary embodiment of the present disclosure.
[0011] FIG. 4 is a schematic illustration of an integral coupling of a blade tip extension to the tip of a fan blade, in accordance with one exemplary embodiment of the present disclosure.
[0012] FIG. 5 is a schematic illustration of an integral coupling of a blade tip extension to the tip of the fan blade, in accordance with one exemplary embodiment of the present disclosure.
[0013] FIG. 6 is a schematic illustration of an integral coupling of a blade tip extension to the tip of a fan blade, in accordance with one exemplary embodiment of the present disclosure.
[0014] FIG. 7 is a schematic illustration of the construction of a blade tip extension, in accordance with one exemplary embodiment of the present disclosure.
[0015] FIG. 8 is a schematic illustration of a shape of a blade tip extension, in accordance with one exemplary embodiment of the present disclosure.
[0016] FIG. 9 is a schematic illustration of a shape of a blade tip extension, in accordance with one exemplary embodiment of the present disclosure.
[0017] FIG. 10 is a schematic illustration of a shape of a blade tip extension, in accordance with one exemplary embodiment of the present disclosure.
[0018] FIG. 11 is a schematic illustration of an induction coil embedded in a fan casing wherein the blade tip extension is at a first shape, in accordance with one exemplary embodiment of the present disclosure.
[0019] FIG. 12 is a schematic illustration of an induction coil embedded in the fan casing wherein the blade tip extension is at a second shape, in accordance with one exemplary embodiment of the present disclosure.
[0020] FIG. 13 is a schematic illustration of multiple induction coils embedded in a fan casing, in accordance with one exemplary embodiment of the present disclosure.
[0021] FIG. 14 is a schematic illustration of multiple nozzles embedded in a fan casing in accordance with one exemplary embodiment of the present disclosure.
[0022] FIG. 15 is an exemplary control algorithm that may be used for changing the shape of the blade tip extension, in accordance with one exemplary embodiment of the present disclosure.
DETAILED DESCRIPTION
[0023] The following detailed description illustrates embodiments of the invention by way of examples and not by way of limitation. It is contemplated that the invention has general application in providing enhanced sealing between rotating and stationary components in industrial, commercial, and residential applications.
[0024] As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.
[0025] To more clearly and concisely describe and point out the subject matter, the following definitions are provided for specific terms, which are used throughout the following description and the appended claims, unless specifically denoted otherwise with respect to particular embodiments. As used herein, “blade tip extension” refers to an extension to a fan blade at its distal end tip. A “blade tip extension that is integrally coupled to the tip of a fan blade” refers to an attachment of the blade tip extension to the tip of the fan blade such that the blade tip extension is an integral part of the fan blade at all operating conditions of the fan assembly. A “blade tip extension that is partially embedded in the tip of a fan blade” refers to the insertion of a portion of the blade tip extension within the tip of the fan blade. A shape-memory alloy is a material that is designed to change shape in response to certain range of temperatures. The change of shape of a shape-memory alloy in response to the temperature may manifest, for example, in a change in length, a change in volume, a change in geometry, or a combination thereof. The terms “first temperature” and “second temperature” are used to indicate two temperatures that are different from each other, without indicating any particular order of experiencing these temperatures by the blade tip extension. An “volumetric strain” refers to a change in volume (dV) with respect to the original volume (V), expressed in percentage. A “linear strain” refers to a change in length (dl) with respect to the original length (l), expressed in percentage. A “length of the blade tip extension” is the total length of the blade tip extension regardless of having any part of the blade tip extension engaged with or embedded within the tip of the fan blade. A “clearance between a fan blade and a fan casing” refers to the distance between the fan casing and the distal end point of the fan blade. When a fan blade includes a blade tip extension, the “clearance between the fan blade and the fan casing” refers to the distance between the fan casing and the distal end point of the blade tip extension. The clearance between the fan blade and the fan casing may vary during operation of the fan assembly.
[0026] FIG. 1 illustrates a schematic diagram of a gas turbine engine 10 in accordance with some embodiments of the disclosure. The gas turbine engine has, in serial flow communication, an inlet 12 for receiving ambient air 14, a fan assembly 16, a compressor 18, a combustor 20, a high-pressure turbine 22, and a low-pressure turbine 24 comprising turbine blades 25. The high-pressure turbine 22 is connected to compressor 18 by a high-pressure shaft 26, and the low-pressure turbine 24 is connected to fan assembly 16 by a low-pressure shaft, or a drive shaft 28. The compressor 18 may be a multistage compressor, and the high and low-pressure turbines 22 and 24 may be multistage turbines. Engine 10 has a centerline axis 32 extending from an upstream side 34 of engine 10 to a downstream side 36 of engine 10.
[0027] Fan assembly 16 includes a fan casing 40 about the centerline axis 32. Fan assembly 16 further includes a fan 42 that includes a hub 44 and a plurality of fan blades 46 extending radially outward from the hub 44. Each fan blade 46 includes a leading edge 48 and a trailing edge 50 in a direction 52 (indicated by an arrow). Each fan blade 46 includes a tip 54 at a radially distal end 56 of the fan blade 46. Blade tips 54 on each fan blade 46 define a rotor diameter 58. The fan casing 40 extends circumferentially about and substantially axially aligned with tips 54 to facilitate rotation of the fan blades 46. The fan casing 40 has an inner diameter 62 that is greater than the rotor diameter 58. Under normal operating conditions, clearance between a fan blade 46 and the fan casing is generally the difference between the rotor radius and the inner radius of the fan casing.
[0028] In operation, air flows through the fan assembly 16 and gets pressurized. A portion of the pressurized air may be fed to an inlet of the compressor 18 and a remaining portion of the pressurized air may bypass the compressor 18, the combustor 20, and the high-pressure turbine 22 to provide thrust to the engine 10. The compressor 18 compresses the pressurized air to generate a compressed air. The combustor 20 receives the compressed air from the compressor 18 and a fuel, such as natural gas, from a plurality of fuel injectors (not shown), and burns the fuel and the compressed air within a combustion zone (not shown) to generate combustion gases 38. The high-pressure turbine 22 receives the combustion gases 38 from the combustor 20 and expands the combustion gases 38 to convert energy of the combustion gases 38 to work. The high-pressure turbine 22 drives the compressor 18 through the high-pressure shaft 26. The low-pressure turbine 24 receives the expanded combustion gases from the high-pressure turbine 22 and converts remaining energy of the expanded combustion gases to work. The low-pressure turbine 24 drives the fan blades 46 through the low-pressure shaft 28.
[0029] In some embodiments illustrated herein, at least one of the plurality of fan blades 46 includes a blade tip extension 60 that is integrally coupled to the tip 54 of the fan blade 46. In some embodiments, all fan blades 46 of the plurality of fan blades have the blade tip extension. In some embodiments, certain fan blades 46 of the plurality of fan blades have the blade tip extensions, while some other fan blades of the plurality of fan blades may not have the blade tip extensions. However, in cases wherein only certain fan blades have the blade tip extensions and certain other fan blades do not have the blade tip extension, precautions are taken (e.g., by appropriate arrangement of fan blades on the hub) to control any imbalance in the fan assembly that may otherwise result.
[0030] In some embodiments, the blade tip extension 60 is integrally coupled with the tip 54 at all operating conditions of the fan assembly 16. In the embodiments, wherein the blade tip extension 60 is integrally coupled to the tip 54 of the fan blade 46, the distal end point of the blade tip extension 60 defines the rotor diameter 58, and hence the length of the fan blade 46.
[0031] The fan blade 46 may be constructed of materials such as, but not limited to, metals, alloys, plastics or composite materials. In some embodiments, the fan blade 46 is formed of titanium metal. In some other embodiments, the fan blade 46 is formed of a reinforced plastic material. The reinforced plastic material may provide desirable characteristics, such as, but not limited to, low weight, high strength and easy conformation to complicated shapes. The reinforcements in the plastic may include, but not limited to, fillers, beams, fibers, and foams. In some embodiments, the fan blade 46 is formed of a fiber-reinforced plastic material that can be reliably operated at relatively lower temperatures than the low pressure and high-pressure turbine sections downstream of the combustion section. Fiber may include filaments in a variety of configurations and lay-up directions, sometimes about a core and/or with local metal reinforcement or surface shielding. A variety of materials may be used as fibers, including, but not limited to, carbon, graphite, glass, and metals. Some non-limiting examples of the fibers that may be used to reinforce the plastic material include S glass and organic fibers such as KEVLARTM. In some embodiments, the fan blade 46 is made of resin matrix composites including stacked, laminated layers. In some embodiments, the fan blade 46 is formed by a S glass fiber-reinforced plastic material.
[0032] Fan casing 40 of the fan assembly 16 prevents engine stresses and also increases the radial and axial stiffness of the engine 10. The fan casing may be fabricated from a metallic material, an alloy, or a composite material. In some embodiments, the fan casing is formed by titanium metal. In some embodiments, the fan casing 40 includes a composite material. The composite material may be a fiber-reinforced plastic, wherein a core having a plurality of core layers of reinforcing fiber may be bonded together with a thermosetting polymeric resin. In some embodiments, each core layer may include a plurality of braided reinforcing fibers with the braids of reinforcing fibers aligned in a circumferential direction.
[0033] In some embodiments, at least one of the fan blades 46 has a blade tip extension 60 that has a shape memory alloy. The shape-memory alloy changes its shape, in a pre-determined manner, in response to certain range of temperatures. The change in shape of the shape memory alloy is due to a temperature related, solid state micro-structural phase change that enables the alloy to change from one physical shape to another physical shape. In some embodiments, the shape change of the blade tip extension 60 may manifest as a change in the external contour of the blade tip extension 60. In some embodiments, a shape change may manifest as a further change in length, in addition to the change in the external contour.
[0034] In some other embodiments, the shape change of the blade tip extension 60 may manifest as a change in volume, i.e. expanded or contracted but similarly shaped blade tip extension 60. However, this change in volume is clearly distinguished from a change in volume due to mere thermal expansion of materials by its magnitude. For example, the volumetric strain of a shape-memory alloy employed herein in some of the embodiments is at least 2% of the original volume of the blade tip extension 60, which is far beyond the volumetric strain imparted by the thermal expansion of materials. In some embodiments, the linear strain of the blade tip extension at the second shape is at least 2% of the blade tip extension at the first shape. In some embodiments, the linear strain of the blade tip extension at the second shape is at least 5% of the blade tip extension at the first shape. In some other embodiments, the linear strain of the blade tip extension at the second shape is in a range of 2% to 10% of the blade tip extension at the first shape.
[0035] The change in shape with respect to temperature due to the shape memory effect is advantageously used for controlling a clearance between the fan blade 46 and the fan casing 40. The changes in shape and /or volume of the shape memory alloys may be developed by working and annealing a preform of the alloy at or above a temperature at which the solid state micro-structural phase change of the shape memory alloy occurs. The temperature at which such phase change occurs is generally referred to as the critical temperature or transition temperature of the alloy. In the manufacture of the blade tip extension 60 intended to change shape during operation of the fan assembly 16, the blade tip extension 60 is formed to have one operative shape (e.g., a first shape) below a transition temperature and have another shape (e.g.,. a second shape) at or above the transition temperature.
[0036] Some shape memory alloys used herein are characterized by a temperature -dependent phase change. These phases include a martensite phase and an austenite phase. The martensite phase generally refers to a lower temperature phase whereas the austenite phase generally refers to a higher temperature phase. The martensite phase is generally more deformable, while the austenite phase is generally less deformable. When the shape memory alloy is in the martensite phase and is heated to above a certain temperature, the shape memory alloy begins to change into the austenite phase. The temperature at which this phenomenon starts is referred to as the austenite start temperature (As). The temperature at which this phenomenon is complete is called the austenite finish temperature (Af). When the shape memory alloy is in the austenite phase and is cooled, it begins to transform into the martensite phase. The temperature at which this phenomenon starts is referred to as the martensite start temperature (Ms). The temperature at which the transformation to martensite phase is completed is called the martensite finish temperature (Mf). As used herein, the term “transition temperature” without any further qualifiers may refer to any of the martensite transition temperature and austenite transition temperature. Further, “below transition temperature” without the qualifier of “start temperature” or “finish temperature” generally refers to the temperature that is lower than the martensite finish temperature, and the “above transition temperature” without the qualifier of “start temperature” or “finish temperature” generally refers to the temperature that is greater than the austenite finish temperature.
[0037] In some embodiments, the blade tip extension 60 has a first shape at a first temperature and has a second shape at a second temperature, wherein the second temperature is different from the first temperature. Further, in some embodiments, one of the first temperature and the second temperature is below the transition temperature and the other one may be at or above the transition temperature. Thus, in some embodiments, the first temperature may be below the transition temperature and the second temperature may be at or above the transition temperature, while in some other embodiments, the first temperature may be at or above the transition temperature and the second temperature may be below the transition temperature.
[0038] In some embodiments, the material of the blade tip extension is different from the material of the fan blade. Suitable shape memory alloy materials that can be used as a blade tip extension 60 for controlling clearance between the fan blade 46 and the fan casing 40 include, but are not intended to be limited to, nickel-aluminum based alloys, nickel-titanium based alloys, and copper-aluminum-nickel based alloys. The alloy composition is selected so as to provide the desired shape memory effect for the application such as, but not limited to, transformation temperature and strain, the strain hysteresis, yield strength (of martensite and austenite phases), damping ability, resistance to oxidation and hot corrosion, ability to change shape through repeated cycles, capability to exhibit one-way or two-way shape memory effect, and a number of other engineering design criteria. Suitable shape memory alloy compositions may include, but are not limited to NiTi, NiTiHf, NiTiPt, NiTiPd, NiTiCu, NiTiNb, NiTiVd, TiNb, CuAlBe, CuZnAl and some ferrous based alloys. The compositions disclosed hereinabove may include the constituent elements in any proportions that facilitate the shape memory effect in the desired temperature ranges, and does not necessarily indicate an equi-atomic ratio of the constituent elements.
[0039] In some embodiments, shape memory alloy includes a NiTi alloy. In some embodiments, NiTi alloys having transition temperatures between 5° C and 150° C are used. NiTi alloys change from austenite to martensite upon cooling. The NiTi alloy is an alloy comprising nickel and titanium, and does not imply anything about the relative amounts of the constituent elements. In certain embodiments, the first temperature of the blade tip extension is in a range from about 10° C to about 50° C and the second temperature of the blade tip extension is in a range from about 60° C to about 90° C.
[0040] Depending on specific applications, the shape-memory alloys used herein may have one-way or two-way shape characteristics. A one-way shape-memory alloy blade tip extension 60 is in a first shape at a first temperature and transitions to a second shape upon reaching a second temperature above its transition temperature and remains in that operative shape even after the blade tip extension cools below the transition temperature to attain the first temperature. A two-way shape memory alloy blade tip extension 60 transitions from a first shape to a second shape when the temperatures changes from the first temperature to the second temperature above the transition temperature. The two-way shape memory alloy reverts to the first shape, or to another intermediate shape, when the temperature drops from the second temperature to the first temperature that is below the transition temperature.
[0041] In some embodiments, the blade tip extension 60 may have a change in length along with the change in shape, when the blade tip extension experiences a change in the temperatures to above or below its transition temperature. Thus, in some embodiments, length of the blade tip extension 60 at the first shape is different from the length of the blade tip extension 60 at the second shape.
[0042] FIG. 2 illustrates an enlarged side view of a part of the fan assembly 16 including the fan blade 46 and fan casing 40 (shown in FIG. 1), in accordance with some embodiments. In these embodiments, the blade tip extension 60 is integrally coupled to the tip 54 of the fan blade 46 at a flow path 68 of air to the fan assembly 16. In some embodiments, the blade tip extension 60 is integrally coupled to only a portion (not shown in figures) of the tip 54. In some other embodiments, the blade tip extension 60 covers the entire width of the tip 54. Blade tip extension 60 extends from the tip 54 of the fan blade 46 towards fan casing 40 to facilitate reducing a clearance 70 between fan casing 40 and the fan blade 46.
[0043] The blade tip extension 60 having a length “l” may be flexible or rigid when existing in any of its shapes. In some embodiments, the blade tip extension 60 is flexible, enabling the blade tip extension 60 to flex while riding against a fan casing 40 in the event of rubbing against the fan casing 40.
[0044] The volume of the blade tip extension 60 may be selected such that it accommodates extreme loading and/or pre-determined clearances in different running conditions of the fan blade 46. The shape (first shape and/or the second shape) and length (length at the first shape and/or length at the second shape) may be pre-determined to achieve the desired clearance 70 between the fan blade 46 and fan casing 40 at all operating conditions of the gas turbine engine 10. For example, if the clearance between the fan blade and the fan casing increases due to a change in operating conditions, the length of the blade tip extension may be made to increase and close the increased clearance (e.g., by subjecting the shape-memory alloy of the blade tip extension to a particular temperature so as to increase the length of the blade tip extension), thereby controlling the clearance. In other words, the clearance during that particular operating condition can be actively set to a lesser value than the normal expected clearance in the absence of the shape change in the blade tip extension 60. The blade tip extension 60 may be formed in any starting geometry that permits adequate change in shape with respect to temperature and effectively prevents the air passing through the blade tip extension 60. Non-limiting examples for the starting geometries of the blade tip extension include, but not limited to, solid or hollow blocks, plates, strips, foils, and a plurality of filaments. In some embodiments, the blade tip extension 60 is in the form of a plurality of filaments that facilitate easy transition from one shape to another shape.
[0045] In general, the clearance between a fan blade and a fan casing of the gas turbine engine in cold stationary conditions (e.g., while on the ground) may be generally about 2.5 mm. However, the clearance between the fan blade and the fan casing during operation is generally designed to be in a range from about 0.3 mm to about 0.5 mm. In some embodiments, a clearance between the fan blade and the fan casing of the gas turbine is designed to be less than 0.5 mm when the blade tip extension is at the first shape or at the second shape. In some embodiments, a clearance between the fan blade and the fan casing is less than 0.3 mm when the blade tip extension is at the first shape or at the second shape. In some embodiments, the clearance between the fan blade and the fan casing is less than 0.3 mm when the blade tip extension is at the first shape and at the second shape. In some embodiments, the clearance between the fan blade and the fan casing is in a range from about 0.001 mm to about 0.3 mm when the blade tip extension is at the first shape and at the second shape. In some embodiments, the clearance between the fan blade and the fan casing is substantially zero when the blade tip extension is at the first shape and at the second shape, such that the fan blades do not rub on the fan casing. Different methods may be used to integrally couple the blade tip extension 60 to the tip 54 of the fan blade 46 including physical joining, chemical joining and mechanical joining. In some embodiments, the blade tip extension 60 is mechanically joined to the tip 54 of the fan blade 46, non-limiting exemplary embodiments of which are illustrated in FIGs 3-6. The mechanical joining may include, without limitation, embedding, adhesive joining, capping, and attaching by using nut and bolts or rivets.
[0046] FIG. 3 illustrates an embodiment in which the blade tip extension 60 is partially embedded in the tip 54 of the fan blade 46. As used herein “the blade tip extension is partially embedded” refers to the partial insertion of the blade tip extension in the tip 54. The partial insertion of a first part 82 of the blade tip extension having a length “l” into the tip 54 enables the blade tip extension 60 to be integrally coupled to the tip 54 and releases a second part 84 of the blade tip extension 60 to change the shape as per the requirement during operation of the gas turbine engine. In one embodiment, the blade tip extension 60 is partially embedded in between the fibers of the fiber-reinforced plastic tip 54 of the fan blade 46. The plastic material that holds the fibers of the fiber-reinforced structure of the tip 54 may also hold the blade tip extension 60. While other forms and geometries of the blade tip extension 60 are conceivable to one skilled in the art, the blade tip extension 60 illustrated here is in the form of plurality of filaments, or foils in the flow path of air. In some embodiments, the blade tip extension 60 in the form of plurality of filaments is capable of substantially preventing leakage of air in between the fan blades 46.
[0047] FIG. 4 illustrates an embodiment in which the blade tip extension 60 is in the form of a cap that is joined to the tip 54, for example, by using an adhesive 86. Non-limiting examples for the adhesive that can be used include araldite. The shape of the blade tip 54 may be altered to firmly secure the blade tip extension 60 on to the tip 54. In this embodiment, first part 82 of the blade tip extension 60 is secured to the tip 54 using the adhesive material 86, and hence may not participate in the shape change during operation. Second part 84 of the blade tip extension is free to change the shape as required during the operation. While FIG. 4 illustrates only one of the exemplary embodiments, different shapes and designs of the tip 54, blade tip extension 60, and the adhesive material 86 may be used to secure the blade tip extension 60 to the tip 54 of the fan blade 46. The blade tip extension 60 having a length “l” illustrated herein is in the form of a solid or hollow dome shaped cap, partially embedding the tip 54, and placed in the flow path of air. In some embodiments, the blade tip extension 60 in the form of dome shaped cap is capable of substantially preventing leakage of air in between the fan blades 46 and the fan casing 40.
[0048] FIG. 5 illustrates an embodiment in which the blade tip extension 60 is in the form of a cap and is joined to the tip 54 using a rivet 88. In some embodiments, a nut and bolt arrangement or any other form of physical attachment of the blade tip extension 60 to the tip 54 may be used for joining. In some other embodiments, an adhesive material 86 may be used in conjunction with the rivet 88 to further firm up the coupling of the blade tip extension 60 to the tip 54, as shown in FIG. 5. The shape of the blade tip 54 may further be altered to firmly secure the blade tip extension 60 on to the tip 54. In the exemplary embodiment illustrated herein, first part 82 of the blade tip extension 60 is secured to the tip 54 using the rivet 88 and the adhesive material 86, and hence may not participate in the shape change during operation. However, the second part 84 of the blade tip extension is free to change the shape as required during the operation. While FIG. 5 illustrates only one of the exemplary embodiments, different shapes and designs of the tip 54, blade tip extension 60, rivet 88, and the adhesive material 86 may be used to secure the blade tip extension 60 to the tip 54 of the fan blade 46. The blade tip extension 60 having a length “l” illustrated here is in the form of a solid or hollow dome shaped cap partially embedding the tip 54, placed in the flow path of air, and is capable of substantially preventing leakage of air in between the fan blades 46 and the fan casing 40.
[0049] FIG. 6 illustrates an embodiment in which the blade tip extension 60 is integrally coupled to the tip 54 of the fan blade 46 using a holder 89. A holder may be any component, different from the tip 54 and the blade tip extension 60, which aids in securing the blade tip extension 60 to the tip 54. A rivet 88, an adhesive material 86, or a combination of the rivet 88 and the adhesive material 86 may be used along with the holder 89 to enable further firm securement of the blade tip extension 60 to the tip 54. In this embodiment, any part of the blade tip extension 60 is not embedded in the tip 54 and any part of the tip 54 is not embedded in the blade tip extension. However, both the tip 54 and the blade tip extension 60 are partially embedded in the holder 89. The optional adhesive material 86 may be used at the distal end of the tip 54 to attach the blade tip extension 60 to the tip 54 or may further be used in the side surfaces (not shown) of tip to attach the holder 89 to the tip 54. The optional rivet 88 may be used to secure the holder 89 to the tip 54, the blade tip extension 60 (not shown in FIG. 6), or a combination thereof. In this exemplary embodiment, the partial insertion by embedding first part 82 of the blade tip extension 60 into the holder 89 enables the blade tip extension 60 to be integrally coupled to the tip 54, and make second part 84 of the blade tip extension 60 available to change the shape as per the requirement during operation of the gas turbine engine. While other forms and shapes of the blade tip extension 60 are conceivable to one skilled in the art, the blade tip extension 60 having a length “l” illustrated herein is in the form of plurality of filaments or foils in the flow path of air and is capable of substantially preventing leakage of air in between the fan blades 46 and the fan casing 40.
[0050] In some embodiments, such as those illustrated in FIG.s 4, 5, and 6, the blade tip extension may be added to the existing tip 54 of the fan blade 46, without damaging and/or modifying the fan blade 46. Further, the blade tip extension 60 may be removed and/or replaced with another one without damaging the tip 54.
[0051] In some embodiments, a gas turbine engine is provided that includes a fan assembly. The fan assembly includes a fan casing and a fan having the plurality of fan blades extending radially outward from a hub. At least one of the plurality of the fan blades include a blade tip extension that is integrally coupled to the tip of the fan blade. The blade tip extension includes a shape memory alloy. The blade tip extension of the fan assembly of the gas turbine engine has a first shape at a first temperature, and has a second shape at a second temperature that is different from the first temperature. In some embodiments, the length of the blade tip extension at the first shape is different from the length of the blade tip extension at the second shape. In some embodiments, a clearance between the fan blade and the fan casing of the gas turbine is less than 0.4 mm when the blade tip extension is at the first shape or at the second shape. In some embodiments, a clearance between the fan blade and the fan casing of the gas turbine is less than 0.5 mm when the blade tip extension is at the first shape or at the second shape. In some embodiments, the clearance between the fan blade and the fan casing of the gas turbine is less than 0.5 mm when the blade tip extension is at the first shape and at the second shape. In some embodiments, the clearance between the fan blade and the fan casing of the gas turbine is in a range from about 0.001 mm to about 0.3 mm when the blade tip extension is at the first shape and at the second shape. In some embodiments, the clearance between the fan blade and the fan casing is substantially zero when the blade tip extension is at the first shape and at the second shape.
[0052] Some embodiments include a method for forming the blade tip extension from a shape memory alloy. Shape memory alloys may be utilized in controlling the clearance between the fan blades and fan casing in response to temperature ranges. The blade tip extension including the shape memory alloy may be imparted with a desired geometry and/or configuration for shape change before or during joining of the blade tip extension to the fan blade and made to change the shape as required, during the operation of the fan assembly.
[0053] In some embodiments, a method of controlling a clearance of a fan assembly is disclosed. The fan assembly includes a fan casing and a fan. The fan includes a hub and a plurality of fan blades extending radially outward from the hub. At least one of the plurality of fan blades includes a blade tip extension that is integrally coupled to tip of the fan blade and the blade tip extension includes a shape memory alloy. In some embodiments, the blade tip extension is made up of a shape memory alloy. In an exemplary embodiment, the blade tip extension is constructed of NiTi shape memory alloy and is operated in the temperature range from about 5ºC to about 150ºC. In some embodiments, the NiTi shape memory alloy has about 50 atomic % of nickel. In one embodiment, the method of controlling the clearance of the fan assembly includes controlling a clearance of the at least one of the plurality of fan blades with the fan casing by changing the shape of the blade tip extension.
[0054] The blade tip extension that includes the shape-memory alloy may be designed to change shape in response to the temperatures experienced by the fan assembly while in use. For example, the blade tip extension may be manufactured and thermo-mechanically trained to facilitate the change in shape of the blade tip extension during operation of the fan assembly.
[0055] Shape memory alloys can exhibit a one-way shape memory effect or a two-way shape memory effect. The two-way shape memory effect may be an intrinsic two-way shape memory effect or an extrinsic two-way shape memory effect, depending on the particular alloy composition, processing history, and - in the case of extrinsic - the constructions of the blade tip extension. Annealed shape memory alloys typically exhibit the one-way shape memory effect. In the shape memory alloys exhibiting the one-way shape memory effect, heating above the austenite finish temperature subsequent to low-temperature deformation (below Mf) of the shape memory material recovers the original, high-temperature austenite (above Af) shape. Hence, one-way shape memory effects are observed upon heating.
[0056] Depending on specific applications, the shape-memory alloys used in the blade tip extension may have one-way or two-way shape characteristics. For example, a blade tip extension having a one-way shape memory alloy may be in a first shape at a first temperature and transitions to a second shape upon reaching a second temperature above the transition temperature of the shape memory alloy. The blade tip extension may remain in that second shape even after cooling below the transition temperature to attain the first temperature. A blade tip extension having a two-way shape memory alloy may transition from a first shape to a second shape when the temperatures changes from a first temperature to a second temperature above the transition temperature of the shape memory alloy. The blade tip extension having the two-way shape memory alloy may revert to the original first shape, or another intermediate shape, when the temperature drops from the second temperature to the first temperature that is below the transition temperature of the shape memory alloy.
[0057] In some embodiments, the blade tip extension includes a one-way shape memory alloy. In some embodiments, the blade tip extension may include some incidental materials other than the one-way shape memory alloy, wherein such incidental materials do not affect the shape memory effect-related performance of the blade tip extension by more than 5%. In certain embodiments, the blade tip extension is formed of a one-way shape memory alloy. In some embodiments, a second shape is imparted to the blade tip extension before integrally coupling the blade tip extension to the fan blade. The second shape may be the shape of the blade tip extension during the operation of the fan assembly at the second temperature. In some embodiments, the second temperature is above the transition temperature of the shape memory alloy used in the construction of the blade tip extension. The second shape may be developed by working and annealing a preform of the alloy of the blade tip extension at or above the transition temperature. Upon cooling to the martensite phase, the blade tip extension having the one-way shape memory alloy retains the second shape of the austenite phase. During operation, depending on the condition of the fan assembly, the blade tip extension may be subjected to a deformation in the martensite phase. The second shape of the blade tip extension may be recovered upon reheating the blade tip extension to above the transition temperature.
[0058] In some embodiments, the blade tip extension includes an intrinsic two-way shape memory alloy. In some embodiments, the blade tip extension may include some incidental materials other than the intrinsic two-way shape memory alloy, wherein the such incidental materials do not affect the shape memory effect- related performance of the blade tip extension by more than 5%. In certain embodiments, the blade tip extension is formed of an intrinsic two-way shape memory alloy. The intrinsic two-way shape memory behavior may be induced in the shape memory material of the blade tip extension through thermo-mechanical training. The thermo-mechanical training imparted to the blade tip extension herein may include deformation of the material while in the martensite phase, followed by repeated heating and cooling through the transformation temperature under constraint. An example of deforming may include imparting a plastic strain of at least 2%. Once the blade tip extension material has been trained to exhibit the two-way shape memory effect, the shape change between the low- and high-temperature states is generally reversible and persists through a high number of thermal cycles. This trained blade tip extension material may be integrally coupled to the tip of the fan blade to be used during operation to control the clearance between the fan blade and the fan casing.
[0059] In some embodiments, the blade tip extension includes an extrinsic two-way shape memory alloy. In some embodiments, the blade tip extension may include some incidental materials other than the extrinsic two-way shape memory alloy, wherein the such incidental materials do not affect the shape memory effect- related performance of the blade tip extension by more than 5%. In certain embodiments, the blade tip extension is formed of an extrinsic two-way shape memory alloy. The blade tip extension having an extrinsic two-way shape memory effect may be formed by combining a first shape memory alloy that exhibits a one-way effect with a second shape memory alloy that provides a restoring force to recover the low-temperature shape. Examples of imparting an extrinsic two-way shape memory effect includes affixing the shape memory alloy to a dissimilar material, modifying the surface of the shape memory alloy by techniques, such as laser annealing and shot peening. In such cases, a portion of the blade tip extension is used to induce the one-way shape memory actuation on heating, while another portion of the blade tip extension is used to provide the shape-restoring force on cooling through the transformation temperature.
[0060] The blade tip extension including the shape memory alloy may be made using vacuum melting, such as vacuum induction melting, or vacuum arc melting, to form an ingot of the shape memory alloy composition, optionally followed by deformation processing, such as rolling, extrusion, forging, drawing, and/or swaging. Alternatively, the blade tip extension may be manufactured by deposition (e.g., thermal spray, physical vapor deposition, vacuum arc deposition) or through powder consolidation. Once made, the blade tip extension may be heated to a temperature sufficient to impart the desired high temperature shape, for example to a temperature above the austenite finish temperature. The blade tip extensions may be integrally coupled to the tip of the fan blade as illustrated in FIGs 3-6.
[0061] Although reference has been made to affixing the blade tip extension having a shape memory alloy onto the tip of the fan blade, a blade tip extension having the shape memory alloy of the present disclosure may also be manufactured integrally along with the fan blade and the desired low temperature and high temperature shapes may be imparted to the blade tip extension as desired.
[0062] In some embodiments, the blade tip extension may further have a change in length along with the change in volume, when the blade tip extension experiences a change in the temperatures above or below its transition temperature. Thus, in some embodiments, length of the blade tip extension at the first shape is different from the length of the blade tip extension at the second shape. As used herein, a “length of the blade tip extension” is the total length of the blade tip extension regardless of having first part 82 of the blade tip extension engaged with the tip 54 and having second part 84 free to change the shape in response to a change in temperature as shown in FIGs. 3-6. Thus, in some embodiments, the length of the blade tip extension is additive of the length of the two parts 82, 84 illustrated in FIGs. 3-6. In some embodiments, a change in length of the blade tip extension at the first shape as compared to the length at the second shape is manifested as change in length of the second part 84 of the blade tip extension 60. Thus, in some embodiments, length of the second, free to move, part 84 of the blade tip extension at the first shape is different from the length of the second part 84 of the blade tip extension at the second shape.
[0063] In operation, changing the shape of the blade tip extension includes subjecting the blade tip extension to a first temperature to adopt a first shape or subjecting the blade tip extension to a second temperature to adopt a second shape, wherein the second temperature is different from the first temperature. The change in shape may be manifested by a change in the length of the blade tip extension, thereby a change in length of the fan blade. The blade tip extension may be subjected to the first temperature or to the second temperature to preserve the clearance between the fan blade and the fan casing at a value that is less than 0.3 mm. In some embodiments, the clearance between the fan blade and the fan casing is at a value that is less than 0.3 mm at all operating conditions, regardless of the blade tip extension being present at the first shape or at the second shape.
[0064] In some embodiments, the clearance between the fan blade and the fan casing may be preserved at a value that is less than 0.3 mm at all operating conditions of the embodiments, by predicting a potential change in the clearance between the at least one of the plurality of fan blades and the fan casing and varying the shape and/or length of the blade tip extension to compensate for the change in the clearance.
[0065] Under normal conditions, the clearance between the at least one of the plurality of fan blade and the fan casing may change depending on the operating conditions of the fan assembly. For example, if the fan assembly is a part of a gas turbine engine used in an aviation system, the clearance between the at least one of the plurality of fan blade and the fan casing may vary, for example, at the time of take-off, cruise, maneuver, landing, and aborted landing instances. Non-limiting, exemplary embodiments that may be used for controlling the clearance of the at least one of the plurality of fan blades for operating the fan assembly 16 of a gas turbine engine used in an aviation system during a maneuver are illustrated below using FIGs. 7-10.
[0066] In some embodiments, the blade tip extension may be constructed in its first shape 90 using a shape memory alloy and may use the first shape 90 having a length “l” in a normal cruise condition, as illustrated in FIG. 7. The clearance 70 between the at least one of the plurality of fan blades 46 with the fan casing 40 may be maintained below 0.3mm at the first shape 90 of the blade tip extension 60. During a maneuver, depending on the direction of rotation, the clearance 70 of the at least one of the plurality of fan blades 46 with the fan casing 40 may increase or decrease. These increase or decrease of the clearance may be predicted by the engine using one or more sensors that may be built-in in the gas turbine engine. The sensors may be located at a place that is internal to the fan assembly or external to the fan assembly.
[0067] If an increase in the clearance is predicted or experienced between the fan casing and one of the plurality of fan blades during a maneuver, sensor may indicate the possible increase in the clearance and, the length “l” of the blade tip extension 60 integrally coupled to the tip of that fan blade may be increased by changing the shape of the blade tip extension 60 to the second shape 92 with an increased length “l1”, as shown in FIG. 8. This increase in the length of the blade tip extension decreases the opened-up clearance and thereby controls the clearance 70 to be within the prescribed limit, such as for example, 0.3mm. In this instance, the length of the blade tip extension 60 is longer at the second shape 92 than the length of the blade tip extension 60 at the first shape 90. In some embodiments, the length of the blade tip extension 60 is at least 2 % longer at the second shape 92 than the length of the blade tip extension at the first shape 90. When the engine is back to the cruise condition from the maneuver condition, the blade tip extension 60 may be returned to the first shape with the decreased length at the first shape 90. A two-way shape memory alloy may be used in the blade tip extension to alternately change in between the first shape and the second shape.
[0068] If a decrease in the clearance is predicted or experienced between the fan casing and one of the plurality of fan blades during a maneuver, sensor may indicate the possible decrease in the clearance and, the length “l” of the blade tip extension 60 that is integrally coupled to the tip of that fan blade may be decreased by changing the shape of the blade tip extension 60 to the second shape 94 with a decreased length l2, as shown in FIG. 9. The second shape 94 is shorter than the first shape 90 to avoid rubbing of the blade tip extension 60 with the fan casing 40. In some embodiments, the length of the blade tip extension is at least 2 % shorter at the second shape 94 than the length of the blade tip extension 60 at the first shape 90. When the engine is back to the cruise condition from the maneuver condition, the blade tip extension may be returned to the first shape with the increased length at the first shape 90. A two-way shape memory alloy may be used in the blade tip extension to alternately change in between the first shape and the second shape.
[0069] Alternatively, when a one-way memory shape memory alloys is used, and if a decrease in the clearance is predicted during a maneuver, the length “l” of the blade tip extension 60 may not be changed to avoid rubbing against the fan casing 40. Instead, the shape of the blade tip extension 60 and length “l” of the blade tip extension 60 may be changed to the second shape 96 and to the decreased length l2 by rubbing against the fan casing 40, as shown in FIG. 10. When the engine is back to the cruise condition from the maneuver condition, the blade tip extension 60 may be returned to the first shape with the increased length at the first shape 90. Further, when a one-way memory shape memory alloys is used, the shape memory alloy may be constructed to have a longer length below the transition temperature and the shape memory effect may be used to shorten the length of the blade tip extension. In this embodiment, the shape memory effect may be used to increase the clearance and the shape may be reverted using the centrifugal force of the one of the plurality of fan blades 46. Thus, a one-way shape memory alloy may also be used in the blade tip extensions where an increase or decrease in the clearance during maneuver occurs as compared to the first shape 90 of the blade tip extension in a normal cruise mode.
[0070] In some embodiments, subjecting the blade tip extension to the first temperature or to the second temperature includes induction heating of the blade tip extension. An induction coil may be embedded in the blade tip extension or in the proximity to the blade tip extension so as to heat the blade tip extension as per the requirement during operation of the fan assembly. In some embodiments, the proximity may be the distance between the induction coil and the blade tip extension, through which the induction heating of the blade tip extension by the induction coil is effective to change the shape of the blade tip extension. In some embodiments, the induction coil is embedded in the fan casing as shown in FIGs. 11 and 12.
[0071] FIG. 11 illustrates an induction coil 102 embedded in the fan casing 40 wherein the blade tip extension 60 having a length “l” is at the first shape at the first temperature that is below the transition temperature of the shape memory alloy of the blade tip extension. The first shape of the blade tip extension, in this embodiment, is in a shape at which the blade tip extension does not have a strain. FIG. 12 illustrates an induction coil 102 embedded in the fan casing 40 wherein the blade tip extension 60 is at the second shape having a decreased length “l2” at the second temperature that is above the transition temperature. In this embodiment, the second shape of the blade tip extension is a constrained shape of the blade tip extension, having a linear strain associated with it. In some embodiments, the linear strain of the blade tip extension 60 due to a shape change is at least 2% or more of the blade tip extension. The linear strain may be positive, i.e. increase in length, or negative, i.e, decrease in length when changed from the first shape to the second shape. In some embodiments, the second shape of the blade tip extension has a volumetric strain associated with it. In some embodiments, the volumetric strain of the blade tip extension 60 due to a shape change is at least 2% or more of the blade tip extension.
[0072] During operation, for example in a cruise mode, the clearance 70 between the blade tip extension 60 of the at least one of the plurality of blades and the fan casing at the first shape of blade tip extension 60 may be maintained at a value that is advantageous for the efficient running of the gas turbine engine by blocking most of the air flow through the fan assembly. At this mode, the induction coil is generally kept in its “Off” state such that it does not heat the blade tip extension to keep the blade tip extension below the transition temperature of the shape memory alloy of the blade tip extension. During a maneuver, the fan blades may drift towards the fan casing in at least one side of the fan assembly, thereby creating a possibility of a rub of the blade tip extension of the at least one of the plurality of fan blades against the fan casing. This possibility may be sensed using different parameters such as, for example, an input from the operator intending a change in the operating condition or a torque experienced by any part of the fan assembly. The induction coil may be turned “On” by sensing the possibility of rubbing, to heat the blade tip extension 60 to increase its temperature above the transition temperature to change the shape to the second shape as shown in FIG. 12. When the shape is changed to the second shape, and the drifting of the fan blades towards the fan casing occurs, the clearance 70 between the at least one of the plurality of blades and the fan casing is still maintained at a value that is advantageous for the efficient running of the gas turbine engine.
[0073] A plurality of induction coils 102 may be strategically positioned within the fan casing 40 such that during an idle condition or at any point during operation, each of the fan blade 46 having a blade tip extension 60 is proximate to at least one induction coil 102, as illustrated in FIG. 13. Having a fan blade 46 proximate to at least one induction coil 102 aids subjecting the blade tip extension to a rapid change in temperature as per a requirement at that moment. For example, considering that a maneuver happens during a flight condition that increases the clearance 70 at one side A of the fan assembly, there is a possibility that the clearance at another side, such as for example side B may not get affected at all or may actually decrease from its original value, at the time of cruise. In such cases, it is desirable that the length of the blade tip extensions 60 at the side A need to increase while keeping the length of the blade tip extensions at the side B intact or subjecting them to decrease. This finer control of the change in length of different blade tip extensions at different part of the fan assembly, at a time, is feasible by having individual control of the heat dissipated to the individual blade tip extensions at any given time.
[0074] Embedding the induction coil in the fan casing is advantageous in the embodiments wherein the fan casing and/or the fan blades are constructed of materials that do not get heated up by induction heating. For example, when the fan casing and the fan blades are constructed of some of the fiber reinforced plastic that do not include the inductionally heatable material in large quantity, the induction coil heats only the blade tip extension without wasting the induction power. Further, in some embodiments, it may be advantageous to embed in or place upon the induction coil with the fan casing, as compared with that of the fan blade, so that an electrical power supply to the induction coil is not disturbed by the rotating movements of the fan blades.
[0075] In some embodiments, subjecting the blade tip extension to the first temperature or to the second temperature includes exposing the blade tip extension to a flow gas. The flow gas may be from the gas turbine engine that includes the fan assembly or an external flow gas source. In some embodiments, the flow gas is used in its “hot” condition, to heat up the blade tip extension to a second shape from a first shape. The flow gas may be cut off from flowing through the at least one of the plurality of fan blades 46 to reduce the temperature and convert the blade tip extension from the second shape to the first shape or an intermediate shape. Further, in some embodiments, the flow gas may be used in its “cold” condition to cool the blade tip extension to convert it to the second shape from the first shape.
[0076] In some embodiments, wherein subjecting the blade tip extension to the first temperature or to the second temperature includes exposing the blade tip extension to a flow gas, a plurality of nozzles 104 may be strategically positioned within the fan casing 40 such that during an idle condition or at any point during operation, each of the fan blade 46 having a blade tip extension 60 is proximate to at least one nozzle 104 that can pass the flow gas, as illustrated in FIG. 14. Having a fan blade 46 proximate to at least one nozzle 104 aids subjecting the blade tip extension to a rapid change in temperature as per a requirement at that moment. For example, change in length of different blade tip extensions 60 at different parts such as, for example A1 and B1, of the fan assembly can be differentially controlled, at a time, by having individual control of the heat dissipated to the individual blade tip extensions by the flow gases passing from the individual nozzles 104 at any given time.
[0077] In some embodiments, subjecting the blade tip extension to the first temperature or to the second temperature is in response to a control algorithm of the fan assembly. The control algorithm may have the inputs from the sensors that predict the increase or decrease in clearance. The sensors may use inputs such as, but not limited to, a low pressure turbine speed, angle of change, thrust load on the fan blade to give an output about the increase or decrease of clearance. The output may also provide the value of expected clearance between the at least one of the plurality of fan blades and the fan casing. A non-limiting, exemplary embodiment of the working of the control algorithm 110, wherein a decrease in the clearance is predicted by the sensor is illustrated in FIG. 15.
[0078] Considering a normal, cruise condition as the start point 112, the control algorithm may use a pinch point 114 decision about changing the clearance of the fan assembly. The pinch point 114 refers a decision point about a change in condition of the fan assembly. In some embodiments, wherein a clearance between the at least one of the plurality of fan blades and the fan casing decreases and a possibility of rubbing the blade tip extension with the fan casing is predicted or sensed by the sensor input 116, an affirmative “Yes” output from the pinch point 114 initiates heating of the blade tip extension at step 118.
[0079] The heating of the blade tip extension started at step 118 deforms the shape memory alloy at step 120 to open up the clearance between the at least one of the plurality of fan blades and the fan casing at step 122 to keep the clearance under control during the maneuver. The pinch point 114 may be in the “Yes” state and the clearance in the open state until the maneuver is over and if the sensor input 116 indicates a normal state for the fan assembly, and thereby a “No” from the pinch point 114 decision, the heating of the blade tip extension may be stopped at step 124 and the blade tip extension may be reverted to the original shape at step 126 to close the clearance at step 128 there by reducing the clearance at that condition between the at least one of the plurality of fan blades and the fan casing. The state of closed clearance may continue until the sensor input 116 indicates a “Yes” state for the pinch point 114 again, which will initiate the heating.
[0080] In some embodiments, a method of controlling a clearance of a fan assembly includes controlling a clearance between the at least one of the plurality of fan blades with the fan casing by changing the shape of the blade tip extension. The steps of changing the shape of the blade tip extension may include predicting a potential change in the clearance between the at least one of the plurality of fan blades and the fan casing, inputting the predicted potential change to a control algorithm, and subjecting the blade tip extension to the first temperature or to the second temperature by changing a supply of electricity to an induction coil embedded in the fan casing, in response to an output of the control algorithm.
[0081] While FIG. 15 illustrates an exemplary algorithm wherein a decrease in the clearance may be catered to, it may be appreciated that, in another algorithm, the pinch point 114 may also refer to a decision point about a change in the condition, wherein a clearance between the at least one of the plurality of fan blades and the fan casing increases and this clearance is decreased using the shape change of the blade tip extension. Further, in some embodiments, a comprehensive control algorithm may be used to control the clearance between the at least one of the plurality of fan blades and the fan casing that will cater to many differentvariances in the operation of the fan assembly, including, but not limited to, take-off, cruise, maneuver, decel, and re-accel. Further, while the embodiments disclosed herein are with respect to the at least one of the plurality of fan blades having the blade tip extension, the blade tip extension may be integrally coupled to the multiple fan blades of the plurality of fan blades. In some embodiments, the blade tip extensions integrally coupled to all the fan blades of the fan assembly.
[0082] Integrally coupling of the blade tip extension to the fan blades may further facilitate reducing rotor whirl during rub events. Moreover, blade tip extension facilitates reducing and/or eliminating abrading damage and erosion/wear field issues of the fan blades and fan casing. During manufacture/assembly of the gas turbine engine, the blade tip extension may facilitate increasing fan assembly clearance tolerances, thereby reducing the need for a tighter control of the clearance during the manufacture.
[0083] While the illustrated gas turbine engine 10 is a representation of a high-bypass turbofan engine, the principles described herein may be equally applicable to turboprop, turbojet, and turbo shaft engines, as well as other types of engines used for other vehicles or stationary applications. Furthermore, while the fan assembly 16 of the gas turbine engine 10 is used as an example, it will be understood that the embodiments of the present invention may be applied to any fan assembly that may be operated at the operating temperatures capable of facilitating working principle of the blade tip extension 60 described herein.
[0084] The blade tip extensions disclosed herein are generally suited to the tip of the fan blades as compared to the tip of the turbine blades of a gas turbine engine. The working principle of the blade tip extension disclosed herein may better benefit the fan blades that experience a low temperature that is less than about 50 ºC during operation. Further, shape memory alloys used in the present disclosure may be able to retain their intended shape at a particular temperature while the fan blades may be rotating at a low speed that is less than about 6000 rpm. Furthermore, a shape memory alloys disclosed herein are particularly suited for use in the tip part of the fan blades, as the shape memory alloys need not bear any further loads.
EXAMPLE
[0085] The following example is merely illustrative, and should not be construed to be any sort of limitation on the scope of the claimed invention. The wires used hereinbelow were procured from Dynalloy Inc.
[0086] In one set of experiments, a test on wettability of epoxy resin on shape memory alloy wires was performed. NiTi alloy wire samples of about 0.3 mm diameter were used for the test. A first wire was used in its pristine condition. A second wire was imparted a roughened surface by rubbing with a 1200 grit sandpaper. Both these wires were tested with epoxy resin droplets for wettability. Contact angles were measured using microscope. It was found that roughened, second sample had better wettability than the first, pristine sample. Similar two samples were embedded in epoxy resin material and wire pull out tests were performed using instron machine to evaluate the bonding strength. Results showed that surface roughness can be detrimental for having a good bonding strength.
[0087] In another set of experiments, the first and second wires were embedded in glass fiber reinforced plastic to demonstrate shape recovery. The wires were heated by passing electrical current of about 2 Amps through the wires. Both the wires were found to demonstrate shape recovery.
[0088] In yet another set of experiments, a 1.6 mm NiTi wire was trained to remember a bent shape in hot condition. Later this pre-trained wire was deformed in cold condition of approximately 25ºC temperature, and heated using hot air blower to approximately about 60ºC temperature. The NiTi alloy wire demonstrated shape recovery. The above-mentioned tests were repeated multiple times on different wires and foils to demonstrate the shape recovery.
[0089] The foregoing embodiments are selected embodiments from a manifold of all possible embodiments of the claimed invention. The foregoing embodiments are therefore to be considered in all respects as illustrative rather than limiting. The claimed invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. While only certain features of the claimed invention have been illustrated and described herein, it is to be understood that one skilled in the art, given the benefit of this disclosure, will be able to identify, select, optimize or modify suitable conditions/parameters for using the methods in accordance with the principles of the present disclosure, suitable for these and other types of applications. This written description uses some examples to disclose the claimed invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The scope of the claimed invention may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the appended claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.