The disclosure relates generally to gas turbine engines and, more particularly, to hybrid vanes for gas turbine engines.
Compressor vanes and other airfoils in aero gas turbine engines are generally designed to have low maintenance costs. This is typically achieved by: designing the vane to be field replaceable; designing the vane such that repair is as simple as possible; and designing the vane such that it is sufficiently robust and not prone to foreign object damage (FOD) and erosion. Usually, gas turbine vanes are manufactured from aluminum, steel or other metal and/or metal alloys. More recently, composite-based vanes have been used to reduce weight and increase strength, however limitations exist with existing composite vanes. The cost and lead times of manufacturing existing composite vanes is greater when compared to forged metal stampings that were historically used in gas turbine engines.
Accordingly, improvements are desirable.
In one aspect, there is provided a hybrid vane for a gas turbine engine, the hybrid vane comprising an airfoil having an inner core composed of a fiber-reinforced thermoplastic composite, a longitudinal axis of the hybrid vane extending between a vane root and a vane tip, and a metallic outer layer at least partially covering the inner core.
In a further aspect, there is provided a method of manufacturing a hybrid vane for a gas turbine engine, the method comprising forming an airfoil out of a fiber-reinforced thermoplastic composite to form an inner core, a longitudinal axis of the hybrid vane extending between a vane root and a vane tip, and applying at least one layer of a metal coating onto the inner core, the metal coating at least partially covering the inner core and defining an outer structural surface of the vane.
In a further aspect, there is provided a method of dynamically tuning a hybrid vane for a gas turbine engine, the vane including an airfoil having an inner core composed of a fiber-reinforced thermoplastic composite and a metallic outer layer at least partially covering the inner core, the method comprising varying a thickness of the inner core and/or a thickness of the metallic outer layer to avoid a natural frequency of the vane at engine operating conditions.
Reference is now made to the accompanying figures in which:
Referring to
Hybrid vane 30 has a vane root 32, a vane tip 34, and an airfoil portion 36 extending therebetween. Various shapes for the airfoil portion 36 may be contemplated such as a foot (not shown) at the vane root 32 and/or at the vane tip 34, integrated inner and/or outer platforms, etc. In some embodiments, for instance where the vane 30 is included among other vanes 30, forming an annular array of vanes, in vane assembly 20 within the bypass duct 22, but not necessarily the case in all embodiments, the vane root 32 may be retained in an inner shroud (not shown) of the vane assembly 20 while the vane tip 34 may be retained in an outer shroud (not shown) of the vane assembly 20. Other configurations for the installation of the vane 30 within different vane assemblies in the gas turbine engine 10 may be contemplated as well. For instance, in an alternate embodiment, a plurality of vanes 30 may be installed in a circumferential array, to collectively form a stator and/or a vane pack, which may be positioned in the compressor 14 or elsewhere in the gas turbine engine 10. The airfoil portion 36 of each vane 30 defines a leading edge 38 and a trailing edge 40, which may be relatively sharp in comparison with a mid-span thickness of the vane, such that a passing airflow, for instance coming from the blades of the fan 12 or compressor 14, flows over the vane airfoil 36 from the leading edge 38 to the trailing edge 40.
Referring to
The core 50 of the vane 30 is made from a fiber-reinforced thermoplastic composite and thus includes a plurality of fibers 52 embedded within one or more thermoplastic polymers 54. In various embodiments, such a core composition may make the core 50 easier to mold, for instance via compression molding, which may reduce manufacturing costs when compared to machining a metal core (e.g. aluminum), while offering a comparatively lighter and stronger vane 30. In various embodiments, the fibers 52 may be carbon fibers, glass fibers, and/or polyaramid fibers, although other fiber types may be contemplated as well. Various polymer resins may be used to form the thermoplastic polymer(s) 54 such as Polyaryletherketone (PAEK), Polyether ether ketone (PEEK), Polyetherketoneketone (PEKK) and/or Polyphenylene sulfide (PPS). Other thermoplastics may be considered as well. In other embodiments, a thermoset epoxy may be used as a fiber-reinforced polymer in the core, rather than a thermoplastic. In certain embodiments, the use of one or more thermoplastic polymers 54 may improve ductility and erosion resistance compared to typical vane core materials. Additionally, such thermoplastic polymers used for the core may also, in certain embodiments, reduce the required molding or cure time. Additionally, a core formed of a thermoplastic polymer may also be more easily repairable, for instance by compression molding, as thermoplastics may be processed repeatedly above their melting temperatures. The fibers 52 in the core 50 may all be aligned in a single direction, for instance parallel to a longitudinal axis L of the vane 30 (the longitudinal axis L of the fane extending from the vane root 32 to the vane tip 34), or alternatively different layers or plies of fibers 52 may be oriented differently, as will be discussed in further detail below. The core 50 of the vane 30 further includes a vane thickness T that may be variable between the leading edge 38 and trailing edge 40. In the depicted embodiment, although not necessarily in all contemplated embodiments, the vane thickness T is measured in a direction substantially normal to the longitudinal axis, i.e. forming an angle of 90 degrees plus/minus manufacturing tolerances applicable to each particular embodiment, application and/or manufacturing process.
It is understood that gas turbine vanes are typically long and slender, making dynamic resonance an issue if the vane is not sufficiently stiff. As well, the fan inlet and compressor vane must be able to withstand impact and foreign object damage (FOD), including so-called soft FOD caused by ice, hail, and the like. The skilled reader will also understand that the requirement to have a stiff vane for dynamics and deflection control under aerodynamic loading, while remaining tough enough to withstand FOD, is not currently attainable with conventional short fibre polymer technologies.
In some cases, in order to provide adequate stiffness for the vane 30 formed of a fiber-reinforced thermoplastic core 50, and in some cases in order to allow the vane 30 to be dynamically tuned as required. For example, in certain embodiments this tuning may be performed to avoid a natural frequency of the vane at engine operating conditions. The vane 30 includes a single layer of a metal outer coating 60 which at least partially covers or completely encapsulates the polymer core 50, as is illustrated in
In a particular embodiment, the metallic outer coating 60 includes a single layer of electroless plating. Such electroless plating may be desirable for its uniform plating thickness, i.e. to maintain an airfoil profile shape unchanged by the plating, whereas an electroplating includes a buildup edge, thus changing the shape of the leading edge 38 of the airfoil portion 36, which may affect the airfoil portion's 36 aerodynamic performance. In other cases, a multilayer outer coating 60 including two or more layers, for instance an electroplating as well as electroless plating, may be used. In cases, processing steps and methods to minimize the built-up edge due to the electroplating may be implemented. In such cases, multiple metallic plating layers having different mechanical properties may provide additional degrees of freedom to tune the vane dynamics, for instance by varying the thickness of each layer as needed. In a particular embodiment, the overall thickness of a multilayer metallic outer coating 60 may not exceed 0.008 inches (plus/minus manufacturing tolerances applicable to each particular embodiment, application and/or manufacturing process), whereas the thickness of an individual metallic plate may be as thin as 0.0005 inches or less. Other thicknesses may be contemplated as well. In various cases, the electroless plating layer(s) may include nickel, copper, or combinations thereof. If present, the electroplating layer(s) may include nickel, copper, iron, cobalt, or combinations thereof. Other metals may be contemplated as well.
In order to reduce the effects of thermal cycling on the vane, the selection of the thermoplastic polymer(s) 54 for the core 50 and metal for the coating 60 may involve selecting a combination which minimizes differential thermal expansion and thermal stresses between both materials. Additionally, the selection may be made to choose material combinations that have the highest bond strength. Doing so may assist in impeding the occurrence of debonding between the coating 60 and the core 50.
The metal coating 60 may be applied to the core 50 regardless of the complexity of the shape of the airfoil 36, and also allows the leading edge 38 to be very sharp, e.g. 0.001 inch thick (0.0254 mm), such as to minimize the boundary layer effect and as such may improve performance.
In a particular embodiment, the metal coating 60 is a plated coating, i.e. is applied through a plating process in a bath, to apply the metallic coating to the non-metallic substrate, such as to be able to accommodate complex vane geometries with a relatively low fabrication cost. Any suitable coating process can be used. Any suitable number of plating layers may also be provided. In other cases, the metal coating 60 may be applied to the core 50 via another suitable application process, such as by vapour deposition of the metal coating, for example. Other application processes may be considered as well.
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As discussed above, the number of layers of the core 50′ may vary, for instance due to the thickness T′ of the core 50′ at a given position between the leading edge 38′ and the trailing edge 40′ and the thickness of the layers. As discussed above, in cases where there are an odd number of layers, there may be only one central layer about which the other layers are symmetrical, i.e. the central layer represents the mid-plane M′. In addition, as the thickness T′ may vary between the leading edge 38′ and the trailing edge 40′, the number of fiber layers would vary as well. In such cases, the mid-plane M′ position would remain consistent throughout the core 50′ between the leading edge 38′ and the trailing edge 40′ while the number of layers on either side of the mid-plane M′ may vary between the leading edge 38′ and the trailing edge 40′, accounting for the differences in thickness T′ throughout the core 50′. In different cases, the relative orientations of the fibers 52′ in each layer may vary, for instance for different strength profiles of the vane, so long as the relative fiber orientations of each layer are symmetrical on either side of the mid-plane M′.
Referring to
It has been found that flightworthy vanes may be provided using fiber-reinforced thermoplastic cores having a metallic outer coating, which may result in a significant cost advantage compared to comparable composite vanes or more traditional aluminum, steel or other metal vanes typically used in gas turbine engines. Accordingly, the present vanes may be cheaper to produce and be of lighter weight than traditional solid metal vanes, while nevertheless providing comparable strength and other structural properties, and therefore offer a comparable if not improved life-span. For example, due to the improved resistance to foreign object damage (FOD) and erosion of the present vanes, reduced field maintenance of the gas turbine engine may be possible, as well as increased time between overhauls (TBO).
In various cases, the metallic outer coating 60 may have mechanical properties which are superior to those of the core 50. In effect, the outer coating 60 provides a structural member which enables the use of a lighter substrate as the core 50, resulting in a lighter overall vane 30. Additionally, the structural combination of the two materials may provide good impact resistance, which is desirable for resistance to so-called “soft” FOD caused by hail or other weather conditions, for example. Beneficially, in various cases the outer coating 60 may also provide erosion protection to the vane 30, or at a minimum provide erosion resistance comparable to conventional aluminum vanes. As such, in cases where the core 50 is completely surrounded by the metallic outer coating 60, there may be no need to apply a dedicated erosion resistance treatment to the core 50. In addition, in embodiments where the metal outer coating 60 completely surrounds the core 50, the vane 30 may benefit from the various mechanical properties of the chosen core 50 materials while ensuring that the core 50 is protected from various environmental factors such as moisture, solvents, aviation fluids etc. by the outer coating 60.
Additionally, as noted above, the thickness of the metallic outer coating 60, which provides at least some of the structural integrity for the hybrid vane 30, may be adjusted and/or varied as required on the core, for example in order to reduce stresses and stiffen the vane in order to reduce deflections in the vane 30 and to dynamically tune the vane 30 as required. In various cases, the dimensions (for instance the thicknesses) of both the core 50 and the metallic outer coating 60 may be chosen to dynamically tune the vane 30 as required. For instance, if an overall vane size is known, the individual dimensions of the core 50 and the outer coating 60 can be selected to reach a desired level of dynamic tuning, with an increase in one's sizing resulting in a decrease in the other's sizing (or vice-versa) to respect the desired overall dimension of the vane. In addition, as discussed above, the orientation of the fibers 52 on the layers in the core 50 may aid in dynamically tuning a vane 30. For instance, if the thickness of the outer coating 60 is to be minimize to reach a certain level of dynamic tuning, thus reducing the strength provided by the outer coating, the fibers 52 on the different layers may be oriented differently so that the core 50 provides added strength to the vane 30 (as discussed above). Other methods for dynamically tuning the vane 30 may be contemplated as well, for instance by choosing certain materials for the core 50 and/or outer coating 60 over others, and/or by the orientation of the fibers 52 in the core 50, and/or by the choice of materials for the outer 60 in combination with the layering thicknesses of the coating materials.
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.