Patent ID: 12228052

DETAILED DESCRIPTION

FIG.1schematically depicts a turbofan engine A which, as an example, illustrates the application of the described subject matter. The turbofan engine A includes a nacelle10, a low pressure spool assembly which includes at least a fan12and a low pressure turbine14connected by a low pressure shaft16, and a high pressure spool which includes a high pressure compressor18and a high pressure turbine20connected by a high pressure shaft22, extending about a central longitudinal axis CL. The engine A further comprises a combustor26. The fan12, the high pressure compressor18, the high pressure turbine20and the low pressure turbine14, for the purposes of the present description include rotors represented by the blades30inFIG.1. WhileFIG.1illustratively depicts engine A as a turbofan engine, other types of gas turbine engines, as well as hybrid-electric engines, may be contemplated.

The rotors, for instance the fan12or the high pressure compressor18, may be provided in the form of blisks, that is, in the form of integrally bladed rotors (IBR). Referring toFIGS.2and3, a rotor B for engine A is shown. Rotor B may, for instance, be high pressure compressor18, although other rotors of engine A may be contemplated, such as fan12, high pressure turbine20, or low pressure turbine14. Rotor B includes a circumferential array of blades30integrally formed with and extending from a rotor hub34in a unitary construction. Each blade30comprises an airfoil32extending from a gas path side (shown inFIGS.2and3) of an annular platform34a, also referred to as a rim, formed at the periphery of the rotor hub34. The number and shape of the blades30may vary, for instance based on the engine A type and/or rotor B type. The hub34includes a radially inner portion34bwith a central bore36configured for mounting to an engine shaft, for instance low pressure shaft16or high pressure shaft22.

As the rotor B rotates about the axis CL, various loads may cause damage to its various components. For instance, low-cycle fatigue (LCF) loads such as centrifugal forces and thermal loads, and high-cycle fatigue (HCF) loads such as dynamic loading occurring at resonance conditions due to aerodynamic excitation may undesirably cause cracks in the blades30. In an integrally bladed rotor such as rotor B, additional concerns may result if the cracks in the blades30were to propagate to the hub34. Additionally or alternatively, cracks may initiate and/or propagate on the hub34itself, for instance due to interactions between LCF and HCF loads, and/or due to foreign object damage (FOD). Referring toFIGS.3and4, to address this and other concerns, a projection38, also referred to as a stiffening rib, extends radially inwardly from an interior side34dof the platform34a. As will be discussed in further detail below, the projection38is configured for increasing the bending stiffness of the platform34a, thereby reducing the risk of crack formation and propagation in the rotor B. By increasing the bending stiffness at areas susceptible to crack formation and/or propagation (e.g., at the base of an airfoil32), the bending stresses ensuing from HCF-derived modes may be minimized, reducing the risk that the crack would form and/or propagate. The projection38may be disposed beneath or adjacent a critical location of the rotor B (i.e., where a crack is most likely to form), thereby providing additional stiffness where it may needed most.

Referring toFIG.4, the stiffening rib or projection38is shown to be spaced axially inwardly from a front edge34cof the platform34aand is axially aligned with a leading edge32aof the airfoil32. According some applications, a projection38could be similarly disposed underneath the trailing edge of the airfoil32at an axial distance inboard from the aft edge of the platform34a. In some cases, such projections or ribs may extend in a direction generally normal to the interior side of the platform34a, although other directions may be contemplated. Various shapes and sizes of the projection38are contemplated. In the shown case, the platform34ahas a local radial thickness Tat the axial location of the projection38. The leading edge32aof the airfoil32meets the platform34aat an axial distance L1from the front edge34cof the platform34a. The projection38has an axial thickness t, a radial height h from the interior side34dof the platform34a, and an axial distance L2from the front edge34cof platform34a. In cases where the axial thickness t of the projection varies (e.g., tapers) along its radial height h, the axial thickness t may refer to its average axial thickness, although other reference thicknesses (e.g., its maximum axial thickness) may be contemplated.

To provide the platform34awith the desired additional stiffness to mitigate crack formation and/or crack propagation, the projection38may respect the following ranges for the following ratios:

0.2≤Tt≤51≤ht≤1⁢00≤L2L1≤1⁢0

In various embodiments, the projection38may additionally respect one or more of the following sub-ranges:

0.5≤Tt≤3.2≤ht≤8.2≤L2L1≤8.

Other nested sub-ranges for the above parameters and ratios may be contemplated.

With regards to the ratio T/t, the radial thickness T of the platform34amay be said to be an independent parameter of a given rotor B, whereas the axial thickness t of the projection38may be subsequently selected based on the radial thickness T for a pre-selected stiffness of the platform34a. As such, a T/t ratio below 0.2 may result in a platform34awith an increased stiffness but a non-negligible weight increase, thereby potentially minimizing the practicality of the projection38. On the other hand, a T/t ratio above 5 may result in a lighter projection38, albeit potentially providing less stiffness gain than desired. A T/t ratio between 0.2 and 5 may thus provide a balance between weight gain and increased stiffness. Other ranges may be contemplated, for instance based on the number and type of projections38and the selected materials.

With regards to the ratio h/t, an h/t ratio below 1 may, in some applications, provide a minimal increase in stiffness to the platform34a, whereas an h/t ratio above 10 may create a discernable weight increase. A h/t ratio between 1 and 10 may thus provide a balance between weight gain and increased stiffness. Other ranges may be contemplated, for instance based on the number and type of projections38and the selected materials.

With regards to the ratio L2/L1, the additional stiffness may be provided where a crack is most likely to initiate, which may be at the L1location. As such, a L2/L1ratio of approximately 1 (i.e., the projection38axially aligned with the leading edge32aof the airfoil32) may provide adequate stiffness to the platform34a. In other cases, the location where stress concentrations would be highest may vary (for instance, based on the size and/or shape of the airfoil), and as such the preferred L2/L1ratio may vary from 0 (i.e., the projection38axially disposed at the edge34cof the platform34a) to 10 (i.e., the projection38disposed near a web of the hub34). Other L2/L1ratios may be contemplated, for instance based on the number and type of projections38and the selected materials.

The projection38may be integrally formed with the platform34a. In the shown embodiment, the projection38is circumferentially continuous about the inner side34dof the platform34a. Cutouts38b, illustratively circumferentially spaced-apart scalloped-shaped cutouts38b, may be provided in the radially inner edge of the projection38for increased balancing and/or reduced weight. Additionally or alternatively, one or more axial through holes may be provided through the projection38. The circumferential locations of the cutouts38b(or holes) may be selected, for instance, to be misaligned with the blades30(i.e., circumferentially disposed between adjacent blades30), for instance to ensure full projection38thickness (and thus structural integrity) at the locations of the blades30. In other embodiments, a plurality of circumferentially spaced apart projections38(for instance, identically sized and shaped projections38) may be provided in annular alignment, interrupted by circumferential voids or spaces. In such embodiments, the projections38may be circumferentially aligned with the blades30so as to provide structural reinforcement at the circumferential locations of the blades30. Other locations for the projections38and the voids may be contemplated.

In other embodiments, two or more rows of projections38, i.e., axially spaced apart from one another from the edge34cof the platform34a, may be provided. The rows of projections38may be configured to provide additional stiffness at desired locations of the platform34a. In some embodiments, a first row of projections38may be continuous about its circumference, while a second row of projections38may include a plurality of circumferentially spaced apart projections38in annular alignment, interrupted by voids or spaces. Oher combinations of continuous and non-continuous projections38may be contemplated.

In accordance with one or more embodiments of the present disclosure, there is provided a method for increasing the stiffness of an integrally bladed rotor B for an aircraft engine A. The integrally bladed rotor B includes a circumferential array of blades30extending from a hub34, each blade30having an airfoil32extending from a gaspath side of a platform34aprovided at a periphery of the hub34, the platform34ahaving a radial thickness T, an edge32aof the airfoil32disposed at an axial distance L1from an adjacent axial edge34cof the platform34a. The method includes providing a projection38extending radially inwardly from an interior side34dof the platform34a, the projection38having an axial thickness t, a radial height h from the interior side34dof the platform34a, and an axial distance L2from the adjacent axial edge34cof the platform34d, wherein

0.2≤Tt≤5,1≤ht≤10,and⁢0≤L2L1≤1⁢0.

In the present disclosure, when a specific numerical value is provided (e.g. as a maximum, minimum or range of values), it is to be understood that this value or these ranges of values may be varied, for example due to applicable manufacturing tolerances, material selection, etc. As such, any maximum value, minimum value and/or ranges of values provided herein (such as, for example only, the above-noted ranges for the ratios T/t, h/t and L2/L1), include(s) all values falling within the applicable manufacturing tolerances. Accordingly, in certain instances, these values may be varied by ±5%. In other implementations, these values may vary by as much as ±10%. A person of ordinary skill in the art will understand that such variances in the values provided herein may be possible without departing from the intended scope of the present disclosure, and will appreciate for example that the values may be influenced by the particular manufacturing methods and materials used to implement the claimed technology.

The embodiments described in this document provide non-limiting examples of possible implementations of the present technology. Upon review of the present disclosure, a person of ordinary skill in the art will recognize that changes may be made to the embodiments described herein without departing from the scope of the present technology. Yet further modifications could be implemented by a person of ordinary skill in the art in view of the present disclosure, which modifications would be within the scope of the present technology.