Patent Description:
In certain operating conditions, aircraft engines, such as turbofan engines, may be subjected to foreign object damage (FOD). FOD may occur when a foreign object (e.g., ice) is ingested by the engine and damages an airfoil of a rotor or a stator. The damaged airfoil is typically impacted at its leading edge. This may result in performance loss, imbalance, and so on. Improvements are therefore sought.

<CIT>, discloses a tandem turbine-blade cascade with at least two rows of blades disposed essentially one immediately behind the other in the rotor or stator of a turbo-engine, a power engine or other machine. The cascade of the second or following row of blades has a larger number of blades than the preceding row.

<CIT>, discloses a stator of the compressor section of the gas turbine engine. The stator includes a plurality of individual vanes, wherein said vanes can be manufactured in groups of several vanes connected to an integral shroud portion.

<CIT>, discloses a multiple of Nozzle Guide Vanes (NGVs) arranged asymmetrically, the multiple of NGVs clocked around a <NUM> degree circumference with respect to multiple of fuel nozzles.

In one aspect of the invention, there is provided an aircraft engine, comprising: an upstream stator having upstream stator vanes circumferentially distributed about a central axis; and a downstream stator having downstream stator vanes circumferentially distributed about the central axis, the downstream stator located downstream of the upstream stator relative to an airflow flowing within a core gaspath of the aircraft engine, a number of the upstream stator vanes being different than a number of the downstream stator vanes, the downstream stator vanes including: a first vane made of a first material, a major portion of a leading edge of the first vane circumferentially overlapped by one of the upstream stator vanes, and a second vane made of a second material having a greater stiffness, strength, and/or ductility than that of the first material, a major portion of a leading edge of the second vane exposed via a spacing defined between two of the upstream stator vanes.

The aircraft engine as defined above and described herein may further include any one or more of the following features, in whole or in part, and in any combination.

In some embodiments, the major portion of the leading edge include at least <NUM>% of a span of the downstream stator vanes.

In some embodiments, the major portion is a radially-outer portion.

In some embodiments, the major portion includes a tip section.

In some embodiments, the first material is aluminum and the second material is steel.

In some embodiments, zones are circumferentially distributed about the central axis where major portions of leading edges of the downstream stator vanes are exposed via the spacing, the first vane located between two of the zones, the second vane located within one of the zones.

In some embodiments, the stiffness of the second material is at least two times greater than that of the first material.

In some embodiments, the downstream stator includes vane segments distributed about the central axis, each of the vane segments having one or more of the downstream stator vanes.

In some embodiments, the vane segments include a first vane segment each including the first vane, and a second vane segment including the second vane.

Further, there is provided a stator assembly, comprising: an upstream stator having upstream stator vanes circumferentially distributed about a central axis; and a downstream stator having downstream stator vanes circumferentially distributed about the central axis, the downstream stator located downstream of the upstream stator relative to an airflow flowing through the stator assembly, a number of the upstream stator vanes being different than a number of the downstream stator vanes, the downstream stator vanes including: a first vane made of a first material, a major portion of a leading edge of the first vane circumferentially overlapped by one of the upstream stator vanes, and a second vane made of a second material having a greater stiffness, strength, and/or ductility than that of the first material, a major portion of a leading edge of the second vane exposed via a spacing defined between two of the upstream stator vanes.

The stator assembly as defined above and described herein may further include any one or more of the following features, in whole or in part, and in any combination.

In some embodiments, the major portion of the leading edge includes at least <NUM>% of a span of the downstream stator vanes.

In some embodiments, the vane segments include a first vane segment including the first vane, and a second vane segment including the second vane.

In another aspect of the invention, there is provided a method of manufacturing a downstream stator of a stator assembly, the stator assembly including an upstream stator and the downstream stator located downstream of the upstream stator, the method comprising: determining circumferential positions around a central axis of the stator assembly where vanes of the downstream stator are at least partially exposed between vanes of the upstream stator thereby susceptible to foreign object damage; installing a first vane of the downstream stator between two of the circumferential positions, the first vane made of a first material; and installing a second vane of the downstream stator at one of the circumferential positions, the second vane made of a second material having a greater stiffness, strength, and/or ductility than that of the first material of the first vane.

The method as defined above and described herein may further include any one or more of the following features, in whole or in part, and in any combination.

In some embodiments, the installing of the first vane includes installing the first vane made of aluminum, the installing of the second vane includes installing the second vane made of steel.

In some embodiments, the installing of the second vane includes installing the second vane having the stiffness two times greater than that of the first vane.

In some embodiments, the downstream stator includes vane segments distributed about the central axis, each of the vane segments having one or more of the downstream stator vanes, the vane segments including a first vane segment including the first vane and a second vane segment each including the second vane, the installing of the second vane at the one of the circumferential positions including installing the second vane segment at the one of the circumferential position.

<FIG> illustrates an aircraft engine depicted as a gas turbine engine <NUM> of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan <NUM> through which ambient air is propelled, a compressor section <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section <NUM> for extracting energy from the combustion gases. The fan <NUM>, the compressor section <NUM>, and the turbine section <NUM> are rotatable about a central axis <NUM> of the gas turbine engine <NUM>. In the embodiment shown, the gas turbine engine <NUM> comprises a high-pressure spool having a high-pressure shaft <NUM> drivingly engaging a high-pressure turbine 18A of the turbine section <NUM> to a high-pressure compressor 14A of the compressor section <NUM>, and a low-pressure spool having a low-pressure shaft <NUM> drivingly engaging a low-pressure or power turbine 18B of the turbine section <NUM> to a low-pressure compressor 14B of the compressor section <NUM> and drivingly engaged to the fan <NUM>.

Although illustrated as a turbofan engine, the gas turbine engine <NUM> may alternatively be another type of engine, for example a turboshaft engine, also generally comprising in serial flow communication a compressor section, a combustor, and a turbine section, and a fan through which ambient air is propelled. A turboprop engine may also apply. In addition, although the engine <NUM> is described herein for flight applications, it should be understood that other uses, such as industrial or the like, may apply. The engine may have one or more spools.

Still referring to <FIG>, in the embodiment shown, a fan stator <NUM> is located within a core gaspath <NUM> of the gas turbine engine <NUM>. The fan stator <NUM> is located downstream of the fan <NUM> relative to a flow within the core gaspath <NUM>. The low-pressure compressor 14B also referred to as a boost compressor, includes successive rows of stators 14C and rotors 14D. A first rotor 14D of the low-pressure compressor 14B may be located downstream of the fan stator <NUM> and upstream of a first stator 14C of the low-pressure compressor 14B. The first stator 14C may be the first stator the flow within the core gaspath <NUM> meets after it leaves the fan stator <NUM>. The fan stator <NUM> and the low-pressure compressor 14B are located within the core gaspath <NUM>, which is defined between an inner wall <NUM> and an outer wall <NUM>. This core gaspath <NUM> is located radially inwardly of an annular gaspath that extends around an engine core. Each of the core stator <NUM>, and the rotors 14D and stators 14C include airfoils extending through the core gaspath <NUM>.

For the remainder of the present disclosure, the fan stator <NUM> will be referred to as an upstream stator <NUM> and the first stator 14C of the low-pressure compressor 14B will be referred to as a downstream stator <NUM>. It will be understood that the principles of the present disclosure may apply to any combinations of two stators in serial flow communication with each other. These two stators may be located at any suitable locations along the core gaspath <NUM>. Any pair of stators may benefit from the present disclosure.

Referring now to <FIG>, a front view of a section of the gas turbine engine <NUM> is presented and illustrates the upstream stator <NUM> in foreground and the downstream stator <NUM> in background. The upstream stator <NUM> includes upstream stator vanes <NUM> circumferentially distributed about the central axis <NUM>. The upstream stator vanes <NUM> extend in a direction having a radial component relative to the central axis <NUM> from the inner wall <NUM> to the outer wall <NUM>. The downstream stator <NUM> has downstream stator vanes <NUM> circumferentially distributed about the central axis <NUM>. The downstream stator vanes <NUM> extend in a direction having a radial component relative to the central axis from the inner wall <NUM> to the outer wall <NUM>. For the sake of clarity, in <FIG>, outlines of the downstream stator vanes <NUM> are shown with dashed lines. The downstream stator <NUM> and its downstream stator vanes <NUM> are located rearward of the upstream stator <NUM> and the upstream stator vane <NUM>. Thus, the airflow meets the upstream stator <NUM> before it meets the downstream stator <NUM>.

A number of the upstream stator vanes <NUM> may be different (e.g., more, less) than a number of the downstream stator vanes <NUM>. The number of the upstream stator vanes <NUM> may not be a multiple of the number of the downstream stator vanes <NUM> and vice versa. Consequently, some of the downstream stator vanes <NUM> may be exposed (e.g. visible) via spacing <NUM> defined between circumferentially adjacent upstream stator vanes <NUM>. As shown in <FIG>, some of the downstream stator vanes <NUM> are visible through the upstream stator <NUM>. In other words, some of the downstream stator vanes <NUM> have areas exposed and visible via the spacing <NUM> defined between the upstream stator vanes <NUM>. Because of the different numbers in upstream stator vanes <NUM> and downstream stator vanes <NUM>, some of the downstream stator vanes <NUM> may be more susceptible to foreign object damage (FOD) because sensitive sections of those downstream stator vanes <NUM> may become exposed to FOD via the spacing <NUM> between the upstream stator vanes <NUM>. In <FIG>, the downstream stator vanes <NUM> located at a plurality of circumferential positions, herein, at <NUM> o'clock, <NUM> o'clock, <NUM> o'clock, <NUM> o'clock, <NUM> o'clock, and <NUM> o'clock, may be most susceptible to FOD. Circumferential positions of the downstream stator vanes <NUM> susceptible to FOD may vary as a function of a number of the upstream stator vanes <NUM> and as a function of a number of the downstream stator vanes <NUM>.

The sensitive areas of the downstream stator vanes <NUM> may correspond to leading edges of the downstream stator vanes <NUM>. In some cases, the sensitive areas may correspond to the trailing edges. The thinner areas of the airfoils may correspond to the sensitive areas. More specifically, tip sections of the leading edges of the downstream stator vanes <NUM> may be particularly prone to FOD. Herein, the expression tip sections may include a radially-outer <NUM>% of a span of the downstream stator vanes <NUM>. In some cases, the outer section of the span may include from <NUM>% to <NUM>% of the span. It may include all of the span in some cases. In some embodiments, base sections of the downstream stator vanes <NUM> may be the sensitive areas; the base sections extending from <NUM>% to <NUM>% span from the radially-inner ends. In some cases, the tip sections includes a radially-outer <NUM>%, or a radially-outer <NUM>% in some cases, of the span. In some other cases, the tip sections includes a radially-outer <NUM>% of the span. The tip sections of the leading edges of the downstream stator vanes <NUM> may be more sensitive to FOD because the downstream stator vanes <NUM> may decrease in both chord and thickness towards tips of the downstream stator vanes <NUM>. This, in turn, may result in the tip sections of the downstream stator vanes <NUM> less stiff than a remainder of the downstream stator vanes <NUM> and, consequently, more susceptible to FOD. In some embodiments, the thickness distribution of the vane is constant along their spans. In the embodiment shown, the exposed part of the vanes is increasing from inner ends to outer ends. In this case, for the lower part, only small ice pellet may impact. For the higher part bigger ice pellets may impact. Small ice pellets may have less energy and may make less damage than bigger ice pellets closer to the tip. This may be engine-dependant. Some engine will fly at low speed and may be susceptible to FOD near the tip. Some other engine will fly much faster and may be susceptible to FOD closer to the radially inner ends of the vane. Small ice pellet at high speed might cause more damage than big pellets at low speed.

Still referring to <FIG>, the downstream stator vanes <NUM> may be divided in two groups: a first group including first vanes and a second group include at least a second vane. Major portions of leading edges 41A of the first vanes may be circumferentially overlapped by the upstream stator vanes <NUM>. That is, the major portions of the leading edges of the first vanes may be not visible when looking in a direction parallel to the central axis <NUM> and parallel to a direction of an air flow flowing through the gas turbine engine <NUM>. The first vanes may be substantially shielded or protected against FOD by the upstream stator vanes <NUM>. In other words, major portions of the first vanes may not be visible via the spacing <NUM> defined between the upstream stator vanes <NUM>. In some embodiments, major portions of the leading edges 41A of the first vanes may not be visible via the spacing <NUM> defined between the upstream stator vanes <NUM>. Herein, the expression "major portions" may include <NUM>% or more of a span of the downstream stator vanes <NUM>. In some embodiments, major portions include <NUM>%, <NUM>%, or <NUM>% of the span of the vane. Major portions may include radially-outer <NUM>% of the span. The major portions may include tip sections of the downstream stator vanes <NUM>. The tip sections may include the outer <NUM>% of the span of the downstream stator vanes <NUM>. Since the first vanes of the downstream stator vanes <NUM> have their leading edges 41A substantially overlapped, and thus covered, by the upstream stator vanes <NUM>, they may be less susceptible of being impacted by a foreign object. The first vanes of the downstream stator vanes <NUM> are labelled with reference numeral <NUM> in <FIG>. The at least second vane of the downstream stator vanes <NUM> is exposed to FOD because a major portion of its leading edges 41A is visible via the spacing <NUM> defined between the upstream stator vanes <NUM>. The second vanes of the downstream stator vanes <NUM> are labelled with reference numeral <NUM> in <FIG>.

Still referring to <FIG>, each of the downstream stator vanes <NUM> may be thin at its leading edge 41A and increase to a maximum thickness along a chord before tapering back down towards its trailing edge 41B. A downstream stator vane <NUM> may be considered at risk of FOD if the downstream stator vane <NUM> is exposed (e.g., visible within one of the spacing between two upstream stator vanes <NUM>) anywhere along the chord from its leading edge 41A to a location of maximum thickness. In other words, the major portions of the leading edges may correspond to leading edge sections extending along chords of the downstream stator vanes <NUM> from the leading edges 41A to locations of maximum thickness. The leading edge sections at spanwise locations closer to tips of the downstream stator vanes <NUM>, for instance at the tip sections of the downstream stator vanes <NUM>, may be more prone to FOD. Hence, the downstream stator vanes <NUM> having their leading edge sections along their tip sections (e.g., outer <NUM>% of their span) exposed within the spacing <NUM> may be susceptible to FOD and may be considered a second vane <NUM>.

The downstream stator vanes <NUM> may have their trailing edges 41B visible via the spacing <NUM> between the upstream stator vanes <NUM>. However, the trailing edges 41B, because they are not facing the incoming flow, may be less susceptible to FOD. Moreover, if a trailing edge of a downstream stator vane <NUM> is impacted, it may have less impact on overall aerodynamic performance of the downstream stator <NUM> than if a leading edge were impacted.

In the embodiment shown, the first vanes <NUM> are made of a first material and the second vanes <NUM> are made of a second material having a better ability to withstand impact without fracture than the first material. Any property of the second material, such as its stiffness, strength, or ductility may be increased to improve impact resistance. The first material may be aluminum and the second material may be steel. The stiffness, strength, and/or ductility of the second material may be at least about <NUM>%, <NUM>%, <NUM>%, or <NUM>% greater than that of the first material. The stiffness of the second material may be about two to three times that of the first material. The strength of the second material may be about from two to three times that of the first material. Herein, the expression "about" implies variations of plus or minus <NUM>%.

As shown in <FIG>, the downstream stator <NUM> may include FOD zones Z1 circumferentially distributed about the central axis <NUM> where major portions of the leading edges 41A of the downstream stator vanes are visible via the spacing <NUM>. The first vanes <NUM> may be located between or outside the FOD zones Z1 whereas the second vanes <NUM> may be located within the FOD zones Z1. In other words, the downstream stator <NUM> may include FOD-free zones Z2 interspaced between the FOD zones Z1 and where there is a lesser risk of FOD. The first vanes <NUM> may be located within those FOD-free zones Z2.

The downstream stator <NUM> may be a segmented ring including a plurality of segments circumferentially distributed about the central axis <NUM>. The segments may include first segments <NUM> including one or more of the first vanes <NUM> and second segments <NUM> including one or more of the second vanes <NUM>. The first segments <NUM> may be located within the FOD-free zones Z2 whereas the second segments <NUM> may be located within the FOD zones Z1. The first vane segments <NUM> may be interspaced between the second vane segments <NUM>.

Referring now to <FIG>, a method of manufacturing the downstream stator <NUM> is shown at <NUM>. The method <NUM> includes determining circumferential positions around the central axis <NUM> where the vanes <NUM> of the downstream stator <NUM> are susceptible to foreign object damage via the spacing <NUM> defined between the vanes <NUM> of the upstream stator <NUM> at <NUM>; installing the first vanes <NUM> of the downstream stator <NUM> between the circumferential positions at <NUM>, the first vanes <NUM> made of a first material; and installing the second vanes <NUM> of the downstream stator <NUM> at the circumferential positions at <NUM>, the second vanes <NUM> made of a second material having a stiffness greater than that of the first vanes <NUM>.

In the present embodiment, the installing of the first vanes <NUM> includes installing the first vanes <NUM> made of aluminum and the installing of the second vanes <NUM> includes installing the second vanes <NUM> made of steel. The installing of the second vanes <NUM> may include installing the second vanes <NUM> having the stiffness, strength, and/or ductility <NUM>%, <NUM>%, <NUM>%, or <NUM>% greater than that of the first vanes <NUM>.

In the embodiment shown, the installing of the second vanes <NUM> at the circumferential positions including installing the second vane segments <NUM> at the circumferential positions where the vanes are susceptible to FOD.

More than two materials may be used. Combining the two materials may allow to minimize a weight of the downstream stator while minimizing impact on engine performance. This arrangement of two or more materials may prevent FOD while minimizing weight and costs.

Claim 1:
An aircraft engine (<NUM>), comprising:
an upstream stator (<NUM>) having upstream stator vanes (<NUM>) circumferentially distributed about a central axis (<NUM>); and
a downstream stator (<NUM>) having downstream stator vanes (<NUM>; <NUM>, <NUM>) circumferentially distributed about the central axis (<NUM>), the downstream stator (<NUM>) located downstream of the upstream stator (<NUM>) relative to an airflow flowing within a core gaspath of the aircraft engine (<NUM>), a number of the upstream stator vanes (<NUM>) being different than a number of the downstream stator vanes (<NUM>; <NUM>, <NUM>), the downstream stator vanes (<NUM>; <NUM>, <NUM>) including:
a first vane (<NUM>) made of a first material, a major portion of a leading edge (41A) of the first vane (<NUM>) circumferentially overlapped by one of the upstream stator vanes (<NUM>), and
characterized in having,
a second vane (<NUM>) made of a second material having a greater stiffness, strength, and/or ductility than that of the first material, a major portion of a leading edge of the second vane (<NUM>) exposed via a spacing (<NUM>) defined between two of the upstream stator vanes (<NUM>).