Field of Invention
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This invention relates to a bladed disk for a driven rotor of an engine of an aircraft propulsion unit, a propulsion unit for an aircraft comprising an engine comprising the bladed disk, and an aircraft comprising the propulsion unit.
Background
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A rotating disk component of an engine of an aircraft propulsion unit, such as a fan, a rotor, a compressor disk, a turbine disk, or a propeller (hereafter generically referred to as 'a bladed disk' or simply 'disk'), can fail under the high stresses induced by a combination of loads (such as pressure, inertial forces due to rotation, and impact) and mechanical weak points in the bladed disk (such as cracks, material defects, dents, and geometrical features inducing a stress concentration).
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Bladed disks can release a very high energy when they fail which can damage or injure to the surrounding systems or people. In the case of an aircraft propulsion unit, a disk failure may cause catastrophic damage to the surrounding components of the aircraft.
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Typically, it is considered that the worst-case scenario, in which the maximum energy is released in a disk burst event, is where a third of the disk breaks off (i.e., an angular sector of 120°) and is released from the disk. Such a scenario is consistent with the way that cracks typically propagate through a bladed disk.
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Existing solutions to protect against disk burst events include: (1) identifying the likely path of debris breaking off the bladed disk and designing the aircraft without any critical system in this path (2) increasing the manufacturing and lifetime controls on the bladed disk, including: careful material selection, non-destructive testing in service, and removal after a fixed in-service hours/cycles and (3) surrounding the bladed disk with a casing, such as a containment ring, strong enough to contain any debris thereby preventing debris from escaping radially and causing damage.
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However, these existing solutions lead to a number of disadvantages. In particular, solution (1) leads to increased design complexity, solution (2) leads to more costly manufacturing and operating costs, and onerous maintenance requirements, and solution (3) leads to increased mass due to the containment risk, which in turn reduces the possible payload to be carried by the aircraft.
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The present invention seeks to at least partly ameliorate these disadvantages.
Summary of the Invention
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Aspects and embodiments of the present invention are set out in the appended claims. These and other aspects and embodiments of the invention are also described herein.
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According to at least one aspect described herein, there is provided a bladed disk for a driven rotor of an engine of an aircraft propulsion unit, the bladed disk comprising: a hub, a plurality of blades extending radially from the hub, and at least one retaining element, wherein the at least one retaining element extends circumferentially to the hub and is coupled to the hub to retain a segment of the bladed disk in the event of a failure of the bladed disk.
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The term "hub" is used to mean a central body of the bladed disk from which the blades extend. The hub comprises at least an outer rim and an inner web. The outer rim forms the outermost part of the hub, and the plurality of blades extend from the outer rim. The inner web is located within the outer rim of the hub and extends radially inward from the outer rim towards the centre of the hub. The outer rim and the inner web are formed together as a single piece to make up the hub.
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The term "coupled to the hub" is used to mean that the at least one retaining element is attached, either directly or indirectly, to a part of the hub. This includes the retaining element being coupled to an exterior or interior surface of any part of the hub. For example, the retaining element may include a retaining element that is coupled to an interior or exterior part of the outer rim of the hub. Alternatively, or additional, the at least one retaining element may include a retaining element that is coupled to the web of the hub.
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Advantageously, the at least one retaining element prevents a sector of the disk being released in the event that the bladed disk bursts. In this way, the retaining element acts as a redundant alternative load path to contain the burst disk against the centrifugal force. As a consequence of the retaining element, the containment ring can be reduced in thickness as it would no longer be required to withstand an entire sector of the disk being released, such as a third of the disk being released, in a disk failure. The containment ring may still be required to protect surrounding systems or people in the event that a blade becomes detached from the disk, but since the release of a single blade has a much lower energy then the release of a sector of the disk, the containment ring need not be so thick. In some cases, it might even be possible to remove the containment ring entirely. In this way, the weight of the propulsion unit can be reduced, which in turn means that that the payload carried by the aircraft can be increased.
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Preferably, the at least one retaining element is located forward of the blades in an axial direction of the bladed disk. In other words, the at least one retaining element is located on the bladed disk further towards the front of the aircraft (in use) then the blades. Advantageously, locating the retaining element in this way reduces the risk that the retaining element interferes with the blades of the disk. In this case, the retaining element may be located externally or internally to the hub. The retaining element nonetheless extends circumferentially to the hub, whether it is external or internal to the hub. The retaining element located forward of the blades may be the only retaining element on the bladed disk, or it may be provided in addition to other retaining elements on the bladed disk.
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Alternatively, or additionally, the at least one retaining element is located after the blades in an axial direction of the bladed disk. In other words, the at least one retaining element is located on the bladed disk further towards the aft of the aircraft (in use) then the blades. Advantageously, locating the retaining element in this way reduces the risk that the retaining element interferes with the blades of the disk. In this case, the retaining element may be located externally or internally to the hub. The retaining element nonetheless extends circumferentially to the hub, whether it is external or internal to the hub. The retaining element located after the blades may be the only retaining element on the bladed disk, or it may be provided in addition to other retaining elements on the bladed disk.
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Preferably, the at least one retaining element is located to be radially aligned with the blades extending from the hub. In other words, the retaining element may be located on a line between the centre of the hub and the base of the blades. In this case, the retaining element may be located externally or internally to the hub. In the case where the retaining element is located internally, this may include a retaining element located within a cylindrical volume defined by the blades' leading and trailing edges, inside the hub. Advantageously, locating the retaining element in this way reduces the distance between the retaining element and the centre of mass of the bladed disk, which reduces the lever arm of the retaining element, thereby reducing any moment generated by load through the retaining element. In the case where the retaining element is located within the hub, the retaining element may be coupled to the web of the hub. In this case, the retaining element may extend circumferentially to the hub following an annular shape around the web within the hub. In the case where the retaining element is located outside the hub, the retaining element may be coupled to the outer rim of the hub, between the blades. The retaining element located radially aligned with the blades may be the only retaining element on the bladed disk, or it may be provided in addition to other retaining elements on the bladed disk.
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Preferably, the at least one retaining element comprises a first retaining element located forward of the blades in an axial direction of the bladed disk, and a second retaining element located after the blades in an axial direction of the bladed disk. The first and second retaining elements are preferably spaced apart from the blades in such a way that each retaining element generates an approximately equal lever arm on the hub. Preferably, the first and second retaining elements are spaced apart from the blades such that each retaining element generates an approximately equal lever arm on the hub, more preferably wherein the first and second retaining elements are spaced equidistantly from the blades. This is advantageous because the first and second retaining elements located on opposing sides of the blades (forward and after the blades), so they approximately balance any moments that might be generated by load through the retaining elements.
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Preferably, the at least one retaining element is located within the hub. In particular, the at least one retaining element may be located within the hub, and extending circumferentially around the interior of the hub. In this case, the retaining element may be located forward of, after, or radially aligned with the blades. Locating the retaining element(s) within the hub in advantageous because it hides the retaining element, which may provide an improved surface finish on the exterior of the bladed disk, which may be aerodynamically preferable.
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Alternatively, or additionally, the at least one retaining element is located outside the hub, extending circumferentially around the hub. Locating the retaining element(s) outside the hub can provide simplified manufacturing of the hub, as well as simplified attachment of the retaining element to the hub.
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Preferably, the at least one retaining element is arranged to fit around the hub so as to be in contact with the hub when the bladed disk is not rotating. Such a contact fit reduces the extent to which the bladed disk can expand and contract during use, which can prolong the life of the disk since repeated expansion and contraction of the disk can cause cracks to begin to form in the disk. A contact fit may also enable the bladed disk to continue in use, at least for a short period, even after it has burst, because the retaining element may maintain the general structure of the disk even after it has burst.
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Alternatively, or additionally, the at least one retaining element is arranged to fit around the hub with a clearance between the at least one retaining element and the hub when the bladed disk is not rotating. In this case, the bladed disk may comprise at least one rib located between the at least one retaining element and the hub. Such a clearance fit provides space to allow the bladed disk to expand, which may happen when the disk is rotating at high speed. This can prolong the life of the retaining element by reducing fatigue on the retaining element that might otherwise occur when the disk repeatedly bears against the retaining element as the disk expands during use.
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Preferably, the at least one retaining element may comprise: a first retaining element located forward of the blades in an axial direction of the bladed disk; a second retaining element located after the blades in an axial direction of the bladed disk; and a third retaining element located within the hub, preferably located to be radially aligned with the blades extending from the hub. Any of the three retaining elements may be located externally or internally to the hub. Preferably at least one of the retaining element is located externally and at least one of the retaining elements is located internally to the hub. Multiple retaining elements provide additional security for mitigating the effects of a disk burst event.
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Preferably, the at least one retaining element is formed as a separate component from the hub and/or blades. The separate retaining element(s) may nonetheless be coupled to the bladed disk. Where the at least one retaining element is formed as a separate component from the hub, the retaining element may have a dual purpose. For example, the retaining element may be formed as a fairing over the hub of the bladed disk. In this way, the retaining element could act jointly as a spinner of the bladed disk, and also as a sleeve over a part of the hub so as to mitigate the effects of a disk burst event. Advantageously, forming the retaining element from a separate component from the hub and/or blades may reduce the probability that both the bladed disk and the retaining element fail at the same time. This is because a crack will typically stop at the point where two components interface with one another. Therefore, forming the retaining element as a separate component from the other parts of the bladed disk may reduce the ability for a crack to propagate through the bladed disk.
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Preferably, the at least one retaining element is formed from a separate material from the hub and/or blades. Advantageously, forming the retaining element from a different material from the hub and/or blades may reduce the probability that both the bladed disk and the retaining element fail at the same time. This is partly because different materials will have different lifetimes and partly because a crack will typically stop at the point where two different materials interface with one another. Therefore, forming the retaining element from a different material to the other parts of the bladed disk may reduce the ability for a crack to propagate through the bladed disk. Preferably, if the hub/blades are formed from titanium or aluminium, or a combination thereof, the retaining element(s) are formed from composite carbon fibres, such as carbon fibre reinforced plastic (CFRP). Preferably, if the hub/blades are formed from composite carbon fibres, such as carbon fibre reinforced plastic (CFRP), the retaining element(s) are formed from either titanium or aluminium, or a combination thereof.
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Preferably, the at least one retaining element is coupled to the hub by: an adhesive bond between the retaining element and the hub; and/or the retaining element being fastened to the hub; and/or the retaining element being wrapped around the hub; and/or the retaining element being press-fit around the hub, such as by pins; and/or by being glued to the hub; and/or by being bolted to the hub.
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According to at least one aspect described herein, there is provided a propulsion unit for an aircraft, the propulsion unit comprising an engine comprising a bladed disk as aforementioned. The bladed disk may be attached to a driven rotor of the engine. As described above, a propulsion unit which includes the bladed disk as aforementioned can have containment ring with a reduced thickness as the containment ring would no longer be required to withstand an entire sector of the disk being released, such as a third of the disk being released, in a disk failure. In some cases, it might even be possible to remove the containment ring entirely (for example, the containment ring may be replaced by a standard ducting). Advantageously, the weight of the propulsion unit can thereby be reduced.
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According to at least one aspect described herein, there is provided an aircraft comprising a propulsion unit as aforementioned. The propulsion unit may be a ducted fan engine. As described above, where the propulsion unit which includes the bladed disk as aforementioned, the thickness of the containment ring can be reduced which in turn reduces the weight of the propulsion unit. Advantageously, the aircraft can thereby carry an increased payload.
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Any apparatus feature as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure.
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Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Furthermore, any, some and/or all features in one aspect can be applied to any, some and/or all features in any other aspect, in any appropriate combination. It should also be appreciated that particular combinations of the various features described and defined in any aspects of the invention can be implemented and/or supplied and/or used independently.
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Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure, such as a suitably programmed processor and associated memory. Furthermore, features implemented in hardware may generally be implemented in software, and vice versa. Any reference to software and hardware features herein should be construed accordingly.
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The invention extends to methods, system and apparatus substantially as herein described and/or as illustrated with reference to the accompanying figures.
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One or more aspects will now be described, by way of example only and with reference to the accompanying drawings having like-reference numerals.
- Figures 1a and 1b show bladed disks for an engine of an aircraft propulsion unit to indicate the problem solved by the present invention. In particular, Figure 1a is a front view of a bladed disk for an engine of an aircraft propulsion unit, indicating the worst-case scenario where a third of the disk is released in a disk burst event. Figure 1b is a cross section view of a bladed disk for an engine of an aircraft propulsion unit, surrounded by a containment ring, which is one existing solution for mitigating the effects of a disk burst event.
- Figure 2 is a cross sectional view of the bladed disk according to a first example of the invention.
- Figure 3 is a cross sectional view of the bladed disk according to a second example of the invention.
- Figure 4 is a cross sectional view of the bladed disk according to a third example of the invention.
- Figure 5 is a cross sectional view of the bladed disk according to a fourth example of the invention.
- Figure 6 is a perspective cross sectional view of the bladed disk according to the third example of the invention.
Detailed description
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Figures 1a and 1b show bladed disks for an engine of an aircraft propulsion unit to indicate the problem solved by the present invention.
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Figure 1a is a front view of a bladed disk 10 for an engine of an aircraft propulsion unit, indicating the worst-case scenario where a third of the disk is released in a disk burst event. Figure 1b is a cross section view of a bladed disk 10 for an engine of an aircraft propulsion unit, where the bladed disk 10 is surrounded by a containment ring 20, which is one existing solution for mitigating the effects of a disk burst event.
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In Figures 1a and 1b, the bladed disk 10 comprises a hub 12 and a plurality of blades 14 extending radially from the hub. The hub 12 forms a central body of the bladed disk, and couples (either directly or indirectly) to a means for rotating the disk. The hub 12 comprises at least an outer rim 16 and an inner web 18. The outer rim 16 forms the outermost part of the hub 12, and the plurality of blades 14 extend from the outer rim 16. The inner web 18 is located within the outer rim of the hub and extends radially inward from the outer rim 16 towards the centre of the hub. The outer rim 16 and the inner web 18 are formed together as a single piece. An axial direction may be defined as the direction running through the centre of the hub. A radial direction may be defined as a direction from the centre of the hub away from the centre of the hub towards or through the rim.
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The dashed lines in Figure 1a indicate a third of the bladed disk 10 (i.e., an angular sector of 120°). Typically, it is considered that the worst-case disk burst scenario, in which the maximum energy is released in a disk burst event, is the case where a third of the disk breaks off and is released from the disk. Such a scenario is consistent with the way that cracks typically propagate through a bladed disk.
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Figure 1b shows one existing solution for mitigating the effects of a disk burst event, which is to surround the bladed disk 10 with a containment ring 20. The containment ring acts as a casing that is strong enough to contain any debris released in a disk burst event, thereby preventing the debris from escaping radially and causing damage or injury to nearby systems or people. A problem with this solution is that, for the containment ring to be sufficiently strong as to contain high energy debris, it must be thick and therefore heavy. The increased mass of the containment risk increases the mass of the aircraft, which in turn reduces the possible payload that the aircraft can carry. The examples of the invention shown in the following drawings seek to at least partly ameliorate these disadvantages.
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Figure 2 is a cross sectional view of the bladed disk 100 according to a first example of the invention. The bladed disk 100 comprises a hub 102 and a plurality of blades, of which one blade 104 is visible, extending radially from the hub. The hub 102 forms a central body of the bladed disk, and couples (either directly or indirectly) to a means for rotating the disk. The hub 102 comprises at least an outer rim 106 and an inner web 108. The outer rim 106 forms the outermost part of the hub 102, and the plurality of blades extend from the outer rim 106. The inner web 108 is located within the outer rim of the hub and extends radially inward from the outer rim 106 towards the centre of the hub. The outer rim 106 and the inner web 108 are formed together as a single piece. In this example, the inner web also includes an arm 110 which branches off from the web 108 such that a gap is formed between the distal part of the web 108 (distal from the rim 106) and the arm 110.
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The bladed disk 100 in this example comprises at least one retaining element 200a. The retaining element 200a extends circumferentially to the hub 102 and is coupled to the hub to retain a segment of the bladed disk 100 in the event of a failure of the bladed disk. In this example, these is a single retaining element 200a. The retaining element 200a is located outside the hub 102, specifically outside of the outer rim 106 of the hub, and extends circumferentially around the outside of the hub so as to form a sleeve around the hub. To accommodate the sleeve, the outer rim 106 may include a seat to accommodate the retaining element, so that when the retaining element is attached to the outer rim and seated in the seat it is flush with the outer surface of the hub, which may provide improved aerodynamic performance.
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In this way, in the event that the bladed disk 100 bursts, the retaining element prevents a sector of the disk being released. In this way, the retaining element acts as a redundant alternative load path to contain the burst disk against the centrifugal force. As a consequence of the retaining element, the containment ring can be reduced in thickness as it would no longer be required to withstand a sector, such as a third, of the disk being released in a disk failure. The containment ring may still be required to protect surrounding systems or people in the event that a blade becomes detached from the disk, but since the release of a single blade has a much lower energy then the release of a sector of the disk, the containment ring need not be so thick. In some cases, it might even be possible to remove the containment ring entirely. In this way, the weight of the propulsion unit can be reduced, which in turn means that that the payload carried by the aircraft can be increased.
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In this example, the retaining element 200a is located forward of the blades in an axial direction of the bladed disk, in the sense that it is located on the bladed disk further towards the front of the aircraft (in use) than the blades. Locating the retaining element 200a in this way ensures that the retaining element does not interfere with the blades of the disk. This example, which uses only a single retaining element 200a, is advantageous because it involves adding the least amount of weight to the bladed disk (as compared to, for example, the third or fourth examples described with reference to Figures 4 and 5).
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In this example, the at least one retaining element 200a is arranged to fit around the hub 102 so as to be in contact with the hub when the bladed disk is not rotating. In other examples, the retaining element 200a may be arranged to fit around the hub 102 with a clearance between the at least one retaining element 200a and the hub 102 when the bladed disk is not rotating. In this latter case, the bladed disk 100 may comprise at least one rib located between the retaining element 200a and the hub 102, the ribs acting the space the retaining element from the hub. The clearance fit and the contact fit of the retaining element have respective advantages. A clearance fit provides space to allow the bladed disk to expand, which is does when rotating at high speed. This can prolong the life of the retaining element by reducing fatigue on the retaining element that might otherwise occur when the disk repeatedly expands and contracts against the retaining element use time the disk is used. A contact fit, however, does not allow the bladed disk to expand and contract so easily, which can prolong the life of the disk, since repeated expansion and contraction of the disk can cause cracks to begin to form in the disk. A contact fit may also enable the bladed disk to continue in use, at least for a short period, even after it has burst, because a tight-fitting retaining element will maintain the general structure of the disk.
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Figure 3 is a cross sectional view of the bladed disk according to a second example of the invention. This example differs from the first example in that the retaining element 200b is located after the blades in an axial direction of the bladed disk, in the sense that it is located on the bladed disk further towards the aft of the aircraft (in use) then the blades. Locating the retaining element 200a in this way ensures that the retaining element does not interfere with the blades of the disk. This example, which again uses only a single retaining element 200b, is advantageous because it involves adding the least amount of weight to the bladed disk (as compared to, for example, the third or fourth examples described with reference to Figures 4 and 5).
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The retaining element 200b extends circumferentially to the hub 102 and is coupled to the hub to retain a segment of the bladed disk 100 in the event of a failure of the bladed disk, in the same way as in the previous example. In this example, however, the retaining element 200b is located inside the hub 102. Specifically, the retaining element 200b is located within an annual groove formed within the hub. In this example, the annual groove is formed in a part of the outer rim 106 of the hub, and extends circumferentially around the inside of the hub. In this way, in the event that the bladed disk 100 bursts, the retaining element prevents a sector of the disk being released by maintaining an interior connection between all parts of the hub. In other examples, the retaining element make be coupled to an interior surface of the outer rim 106 of the hub 102, rather than located within a groove formed within the hub.
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Figure 4 is a cross sectional view of the bladed disk according to a third example of the invention. In this example, the at least one retaining element comprises a first retaining element 200a located forward of the blades in an axial direction of the bladed disk, and a second retaining element 200b located after the blades in an axial direction of the bladed disk. Therefore, this third example represents a combination of the first and second examples described above, and the description of those examples therefore applies equally to this example.
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In this third example, the first and second retaining elements 200a, 200b are preferably spaced apart from the blades 104 in such a way that each retaining element generates an approximately equal lever arm on the hub 102. This is advantageous because the two retaining elements 200a, 200b are located on opposing sides of the blades (forward and after the blades), which balances any moments that might be generated by the forces of the retaining elements on the bladed disk. In particular, the lateral spacing of the first retaining element 200a and the second retaining element 200b from the centre of mass of the bladed disk may be carefully selected to ensure that any moments generated by one retaining element are compensated by the other retaining element. This may be by spacing first and second retaining elements 200a, 200b equidistantly from the blades, if the forces generated by each retaining element are approximately equal, or non-equidistantly if the forces are not equal.
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Figure 5 is a cross sectional view of the bladed disk according to a fourth example of the invention. In this example, the at least one retaining element comprises a first retaining element 200a located forward of the blades in an axial direction of the bladed disk, and a second retaining element 200c. The first retaining element 200a is as described in the first example above with reference to Figure 2, and the description of that example therefore applies equally to this example.
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The second retaining element 200c is located to be radially aligned with the blades extending from the hub 102. In particular, the second retaining element 200c is located within the hub and coupled to the web 108 of the hub 102 (where the web 102 extends from the outer rim 106 of the hub 102 radially inwards towards the centre of the hub, as previously described). In other words, the second retaining element 200c is located on a line between the centre of the hub and the base of the blades 104. The retaining element 200c extends circumferentially to the hub 102, within the hub, such that the retaining element takes an annular disc shape. The retaining element 200c is arranged to retain a segment of the bladed disk 100 in the event of a failure of the bladed disk, in the same way as in the previous examples. In this example, the retaining element 200c prevents a sector of the disk being released by maintaining an interior connection, via the web, between all parts of the hub in the event of a disk burst event. In other examples, the retaining element make be located within a groove formed in the web 108 of the hub 102.
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In this example, the second retaining element 200c may primarily bear the load of the bladed disk in the event of a disk burst. Because the second retaining element 200c is located so as to be radially aligned with the blades 104, it will not generate a lever arm and a moment (or, at least it will generate a minimal lever arm and moment) which is advantageous. The first retaining element 200a is provided in addition in the event that the second retaining element 200c fails or is insufficient to withstand the disk burst. Alternatively, both of the first and second retaining elements 200a, 200c may be the load of the bladed disk in the event of a burst (e.g., equally).
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Figure 6 is a perspective cross sectional view of the bladed disk according to the third example of the invention. As described above, in the third example, the at least one retaining element comprises a first retaining element 200a located forward of the blades in an axial direction of the bladed disk, and a second retaining element 200b located after the blades in an axial direction of the bladed disk. Figure 6 shows in more detail the preferred laminate structure of the retaining elements described above, in any examples. In particular, the retaining element is preferably formed from a carbon fibre reinforced polymer (CFRP) laminate.
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In addition to what is shown in the drawings, other examples of the invention are envisaged. In particular, in one other example, the bladed disk may have three retaining elements: a first retaining element 200a located forward of the blades in an axial direction of the bladed disk (as described in the first example with reference to Figure 2); a second retaining element 200b located after the blades in an axial direction of the bladed disk (as described in the second example with reference to Figure 3); and a third retaining element 200c located within the hub, preferably located to be radially aligned with the blades extending from the hub coupled to the web of the hub as described in the fourth example with reference to Figure 5. In this example, the first and second retaining elements 200a, 200b may be coupled to the outer rim 106 of the hub 102, and the third retaining element 200c may be coupled to the web 108 within the hub 102.
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In any of the examples described above, the at least one retaining element may be formed as a separate component from the hub 102 and/or the blades 104. In this example, the separate retaining element(s) may nonetheless be coupled to the bladed disk 100. In one example, where the at least one retaining element is formed as a separate component from the hub, the retaining element may have a dual purpose. For example, the retaining element could be formed as a fairing over the hub 102 of the bladed disk. In this way, the retaining element could act jointly as a spinner of the bladed disk, and also as a sleeve over a part of the hub 102 so as to mitigate the effects of a disk burst event (as described above, for example with reference to Figure 2).
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In any of the examples described above, the at least one retaining element may be formed from a separate material from the hub 102 and/or blades 104. Forming the retaining element from a different material to the hub 102 and/or blades 104 may lower the probability that both the bladed disk and the retaining element fail at the same time, because different materials will have different lifetimes and the two components (the bladed disk and the retaining element) would be manufactured separately. In addition, a crack will typically stop at the point where two materials interface with one another. Therefore, forming the retaining element from as a separate component, and preferably from a different material, from the other parts of the bladed disk may reduce the ability for a crack to propagate through the bladed disk. While many combinations of materials are envisaged, exemplary materials for the retaining element and the hub or blades of the bladed disk are as follows:
- If the hub/blades are formed from titanium or aluminium, or a combination thereof, the retaining element(s) are preferably formed from composite carbon fibres, such as carbon fibre reinforced plastic (CFRP).
- If the hub/blades are formed from composite carbon fibres, such as carbon fibre reinforced plastic (CFRP), the retaining element(s) are preferably formed from either titanium or aluminium, or a combination thereof.
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In any of the examples described above, there are a number of ways in which the at least one retaining element may be coupled to the hub. Examples of the coupling between the at least one retaining element and hub include:
- an adhesive bond between the retaining element and the hub; and/or
- the retaining element(s) being fastened to the hub; and/or
- the retaining element(s) being wrapped around the hub; and/or
- the retaining element(s) being press-fit around the hub, preferably by means of pins; and/or
- the retaining element(s) being glued to the hub; and/or
- the retaining element(s) being bolted to the hub
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In any of the examples above, where a retaining element is shown to be located outside the hub, it may instead be located inside the hub, and vice versa. For example, while in the first example described with reference to Figure 2 the retaining element 200a is shown and described as being a sleeve located externally around the hub, the retaining element 200a may instead be located internally within the hub, such as on an internal face of the outer rim of the hub (while still being forward of the blades). Similarly, while in the second example described with reference to Figure 3 the retaining element 200b is shown and described as being located inside the hub, within an annular groove, the retaining element 200b may instead be located externally as a sleeve around the hub (while still being located after the blades).
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In the fourth example, shown in Figure 5, while the second retaining element 200c is shown as being located on a face of the web 108 inside the hub 102, the retaining element 200c may instead by located in the gap between the distal end of the web 108 (distal from the outer rim 106) and the arm 110.
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In any of the examples described above, the at least one retaining element prevents a sector of the disk being released in the event that the bladed disk bursts. In this way, the retaining element acts as a redundant alternative load path to contain the burst disk against the centrifugal force. As a consequence of the retaining element, the containment ring can be reduced in thickness as it would no longer be required to withstand an entire sector of the disk being released, such as a third of the disk being released, in a disk failure. The containment ring may still be required to protect surrounding systems or people in the event that a blade becomes detached from the disk, but since the release of a single blade has a much lower energy then the release of a sector of the disk, the containment ring need not be so thick. In some cases, it might even be possible to remove the containment ring entirely. In this way, the weight of the propulsion unit can be reduced, which in turn means that that the payload carried by the aircraft can be increased.
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It will be understood that the invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.
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Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.
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Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.