Patent Description:
Airfoils are present in many aerodynamic applications including, but not limited to, turbines of gas turbine engines. These turbine airfoils each have a root, a tip, pressure and suction surfaces that extend from root to tip and leading and trailing edges at leading and trailing sides of the pressure and suction surfaces. In a turbine, the turbine airfoils or turbine blades can aerodynamically interact with high temperature and high pressure fluids to cause a rotor to rotate.

During operations, gas turbine engines ingest dirt and this dirt travels through the compression system and the combustor and into the cores of the turbine blades where the dirt and air is flung or pumped to the outer diameters or tips of the turbine blades. Typically, the majority of the dirt particles are extremely fine and flows within the cooling air streams that are used to cool the internals of the turbine blades. However, in some cases, the dirt particles are too large to make the abrupt turns inside the internal passages of the turbine blades and they adhere to the outermost surfaces of the turbine blade internals. This can result in an accumulation of dirt on those outermost surfaces and, at given temperatures, can cause premature metallurgical degradation as well as create unwanted insulated areas within the airfoil. The accumulation of dirt can also tend to increase the tip pull of the turbine blades thus reducing the structural integrity of the blade root and disk lugs and altering the expected structural and vibration responses of the turbine blade.

Therefore, it is common practice to have at least one relatively large hole at the tip of the core of each turbine blade. This hole allows entrained relatively large dirt particles to escape out of the turbine blade and into the gas path and out the back of the gas turbine engine.

The holes are typically cast using alumina or quartz rods.

During turbine blade investment casting processes, the alumina or quartz rods can also be used as core position control features to assist in casting. Cores of turbine blades (or blade cores) shift around during the casting process so it is necessary to provide tip features that allow control of blade core shift in all directions. This is especially important in multi-core blade designs where both hot and cold walls and internal blade core ribs must be protected. Tip rods can be used as blade core locators to control radial, axial and tangential shifts of blade cores. When one blade core has multiple tip rods extending out of the tip, they are often connected by a tip plenum that extends outside of the final machined part. The tip plenum helps to provide core stability by controlling internal blade core ribs and can also be used as a blade core locator in conjunction with the tip rods.

Blade core leaching is also a concern in complex blade core designs with multiple dead end cavities. Alumina or quartz rods can be used to assist by being embedded into dead end cavities and extending outside of the finished casting. This creates a path for the ceramic blade core to exit the part during leaching. If rods cannot be used, internal core ties are often required that connect multiple blade core cavities together that would alter the cooling scheme of the turbine blade and, due to sizing requirements, may negatively impact part durability.

Alumina and quartz tip rods should meet specific sizing requirements in order to ensure cast-ability. These requirements include meeting a minimum rod diameter (e.g., about <NUM>" (<NUM>) for quartz rods), meeting a maximum unsupported length (e.g., about <NUM>. 5x the rod diameter) and the fact that rods should be embedded into blade core material by a minimum distance (e.g., about <NUM>" - <NUM>" (<NUM> - <NUM>)). In addition, rods must be surrounded by. <NUM>" (<NUM>) of blade core thickness.

In turbine blade airfoils with a sweep at the tip, radially oriented rods often do not meet producible tip rod sizing criteria, such as specifically embedded length and core thickness requirements, due to the curvature of the blade cores at the tip. The tip rods that are incorporated and that do not meet sizing criteria are highly likely to break during casting causing increased scrap.

Accordingly, it is necessary to devise tip rod geometry that can be used in turbine blades with an airfoil sweep that meets producible tip rod sizing criteria.

<CIT> discloses prior art angled tip rods in a casting core for a turbine blade.

<CIT> discloses a turbine blade casting with a strongback core.

According to a first aspect of the present invention, there is provided an airfoil as set forth in claim <NUM>.

According to a further aspect of the present invention, there is provided a method of forming an airfoil of a blade structure as set forth in claim <NUM>.

Further embodiments are provided as set forth in claims <NUM> to <NUM> and <NUM>.

The fan section <NUM> drives air along a bypass flow path B in a bypass duct, while the compressor section <NUM> drives air along a core flow path C for compression and communication into the combustor section <NUM> and then expansion through the turbine section <NUM>.

The exemplary gas turbine engine <NUM> generally includes a low speed spool <NUM> and a high speed spool <NUM> mounted for rotation about an engine central longitudinal axis A relative to an engine static structure <NUM> via several bearing systems <NUM>.

A combustor <NUM> is arranged in the gas turbine engine <NUM> between the high pressure compressor <NUM> and the high pressure turbine <NUM>. The engine static structure <NUM> is arranged generally between the high pressure turbine <NUM> and the low pressure turbine <NUM>. The engine static structure <NUM> further supports the bearing systems <NUM> in the turbine section <NUM>.

The core airflow is compressed by the low pressure compressor <NUM> and then the high pressure compressor <NUM>, is mixed and burned with fuel in the combustor <NUM> and is then expanded over the high pressure turbine <NUM> and the low pressure turbine <NUM>. The high and low pressure turbines <NUM> and <NUM> rotationally drive the low speed spool <NUM> and the high speed spool <NUM>, respectively, in response to the expansion. For example, geared architecture <NUM> may be located aft of the combustor section <NUM> or even aft of the turbine section <NUM>, and the fan section <NUM> may be positioned forward or aft of the location of geared architecture <NUM>.

The gas turbine engine <NUM> in one example is a high-bypass geared aircraft engine. In a further example, the gas turbine engine <NUM> bypass ratio is greater than about six (<NUM>), with an example embodiment being greater than about ten (<NUM>), the geared architecture <NUM> is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM> and the low pressure turbine <NUM> has a pressure ratio that is greater than about five. In one disclosed embodiment, the gas turbine engine <NUM> bypass ratio is greater than about ten (<NUM>:<NUM>), the fan diameter is significantly larger than that of the low pressure compressor <NUM>, and the low pressure turbine <NUM> has a pressure ratio that is greater than about five <NUM>:<NUM>. The geared architecture <NUM> may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM>:<NUM>. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present disclosure is applicable to other gas turbine engines including direct drive turbofans.

The fan section <NUM> of the gas turbine engine <NUM> is designed for a particular flight condition--typically cruise at about <NUM> Mach and about <NUM>,<NUM> feet (<NUM>,<NUM> meters).

As will be described below, a tip rod geometry is provided for use in turbine blades with an airfoil sweep that meets producible tip rod sizing criteria. The tip rods are made of alumina or quartz and are located at the tip of a blade core at an angle. In locations where embedded rod lengths can be met but core thicknesses around the rod are not met, additional core support features, such as bumpers, can be used to meet producibility criteria and to add additional wall thickness controls.

With reference to <FIG> and <FIG>, a turbine blade <NUM> is provided for use in at least the compressor section <NUM> and the turbine section <NUM> of the gas turbine engine <NUM> of <FIG>.

The turbine blade <NUM> includes a root <NUM> with a dovetail or fir tree cross-section, an airfoil <NUM> and a platform <NUM> that is radially interposed between the root <NUM> and the airfoil <NUM>. The airfoil <NUM> extends radially outwardly from the platform <NUM> and includes a pressure surface <NUM>, a suction surface <NUM> opposite the pressure surface <NUM>, leading and trailing edges <NUM> and <NUM> extending along leading and trailing ends of the pressure and suction surfaces <NUM> and <NUM> and a tip shelf <NUM> at a distal, radially outboard end of the airfoil <NUM>. The tip shelf <NUM> has a first sweep configuration <NUM>, which is characterized as a sweep of the tip shelf <NUM> relative to the rest of the airfoil <NUM> (see <FIG>), and a wall <NUM>. The airfoil <NUM> is formed to define internal channels <NUM> (see <FIG>), which will be described below, and the wall <NUM> is formed to define obliquely-angled through-holes <NUM> (see <FIG>), which will also be described below. The obliquely-angled through-holes <NUM> are defined at an oblique angle α (see <FIG>) relative to a normal angle of the wall <NUM>.

In accordance with embodiments, the angle α can be about <NUM> degrees or slightly less, <NUM>-<NUM> degrees inclusive or about <NUM> degrees or slightly more.

As shown in <FIG>, the tip shelf <NUM> can be curved to maintain a substantially uniform depth of about <NUM>" (<NUM>) or the tip shelf <NUM> can be flat or straight with a maximum depth of about <NUM>" (<NUM>) and a minimum depth of <NUM>" (<NUM>) at a central point in the tip shelf <NUM>, a maximum depth of about <NUM>" (<NUM>) and a minimum depth of <NUM>" (<NUM>) at the leading edge <NUM> and a maximum depth of about <NUM>" (<NUM>,<NUM>) and a minimum depth of <NUM>" (<NUM>) at the trailing edge <NUM>. In any case, the tip shelf <NUM> is formed to define a squealer pocket <NUM> with an optional <NUM>" (<NUM>) step. The obliquely-angled through-holes <NUM> can be defined adjacent to a wall <NUM> surrounding the squealer pocket <NUM> and along the pressure surface <NUM>. The wall <NUM> extends radially outwardly from the tip shelf <NUM> and delimits a periphery of the squealer pocket <NUM>.

In accordance with embodiments, the wall <NUM> at the pressure surface <NUM> can have a substantially uniform thickness T1 (of about <NUM>" (<NUM>) nominal, <NUM>" (<NUM>) minimal) from an upstream portion <NUM> thereof, which is disposed axially between the through-holes <NUM> and the leading edge <NUM>, to a downstream portion <NUM> thereof, which is disposed axially between the through-holes <NUM> and the trailing edge <NUM>. To achieve this substantially uniform thickness T1, the wall <NUM> curves inwardly into the squealer pocket <NUM> around each of the through-holes <NUM> to form notched or convex sections <NUM>. The wall <NUM> can also include a straight or flat section <NUM> between the notched or convex sections <NUM>.

In accordance with further embodiments, while the wall <NUM> has the substantially uniform thickness T1 from the upstream portion <NUM> to the downstream portion <NUM>, the wall <NUM> can continue around an entirety of the squealer pocket <NUM> and can have varying thicknesses at several different sections. For example, the wall <NUM> can have a slightly increased thickness at or near the leading edge <NUM> and a significantly increased thickness at or near the trailing edge <NUM>. In addition, the wall <NUM> at the suction surface <NUM> can have varying thicknesses T2 that each exceed the magnitude of the substantially uniform thickness T1. In some cases, the wall <NUM> can have a wedge-shape <NUM> (see <FIG>) at the suction surface <NUM>. The wedge-shape <NUM> allows for more material to be provided to the wall <NUM> during installing and initial operations. At a base of the wedge-shape <NUM>, the wall <NUM> can have a thickness of about <NUM>" (<NUM>) nominal or about <NUM>" (<NUM>) minimum.

Notably, when blades and blade outer air seals (BOAS) interact, a goal is for the BOAS to lose material and the blades to remain intact. However, if the blade is too solid at the tip, there will be too much material to cool during engine operation and the tip will oxidize. Due to the tip bow and squealer pocket design in this case, there is more material at the tip during initial engine operation (when the blades and BOAS "break in") but less material to cool on the blade tips once any rub has occurred.

With continued reference to <FIG> and <FIG> and with additional reference to <FIG>, a core <NUM> is provided for use in fabricating an airfoil of a blade, such as the turbine blade <NUM> of <FIG> and <FIG>, to include the features of the airfoil <NUM> described above using casting processes which will be described below. The core <NUM> includes channel sections <NUM> and tip rods <NUM>. The channel sections <NUM> are configured to form the internal channels <NUM> (see <FIG>) within the airfoil <NUM> by the casting processes. The tip rods <NUM> are disposed to extend from respective portions of the channel sections <NUM> that are located proximate to a location of the tip shelf <NUM> once the tip shelf <NUM> is eventually formed by the casting processes. That is, the tip rods <NUM> extend radially outwardly from distal ends of the respective portions of the channel sections <NUM>. The respective portions of the channel sections <NUM> have a second sweep configuration <NUM> that corresponds to the first sweep configuration <NUM> (see <FIG>). The tip rods <NUM> are configured to extend from the respective portions of the channel sections <NUM> or the internal channels <NUM> (see <FIG>) and through the wall <NUM> once the tip shelf <NUM> and the wall <NUM> are eventually formed by the casting processes at the oblique angle α (i.e., about <NUM> degrees) relative to a normal angle of the wall <NUM> during the casting processes. The tip rods <NUM> cause the obliquely-angled through-holes <NUM> to form in the wall <NUM>.

In accordance with embodiments, thickness of the tip shelf <NUM> can vary. For example, the thickness of the tip shelf <NUM> at or around the obliquely-angled through-holes <NUM> can be about <NUM>" (<NUM>) and the thickness of the tip shelf <NUM> within the squealer pocket <NUM> can be about <NUM>" (<NUM>) maximum, to about <NUM>" (<NUM>) minimum at the leading edge <NUM> or about <NUM>" (<NUM>) minimum at the trailing edge <NUM>.

In addition to the obliquely-angled through-holes <NUM>, the tip shelf <NUM> can be further formed to define additional holes <NUM> within the squealer pocket <NUM>. These holes <NUM> can be provided for permitting fluid communication, e. g, a flow of coolant outwardly from an interior of the airfoil <NUM> or, more particularly, from one or more of the internal channels <NUM> to the squealer pocket <NUM> as shown in <FIG>. The additional holes <NUM> can be arranged in various formations including, but not limited to, the formation <NUM> that is illustrated in <FIG>. The additional holes <NUM> have a linear grouping of additional holes <NUM> that become increasingly staggered with increasing distance from the trailing edge <NUM>, at least one or more additional hole <NUM> located between the notched or convex sections <NUM> and at least one or more additional hole <NUM> proximate to the leading edge <NUM>.

In accordance with embodiments, the tip rods <NUM> can include at least one or more of alumina and quartz.

In accordance with further embodiments, the channel sections <NUM> can include a bumper <NUM> proximate to an internal end of at least one of the tip rods <NUM>.

With reference to <FIG>, a plenum body <NUM> can be provided and external ends <NUM> of the tip rods <NUM> can be coupled to the plenum body <NUM>.

With continued reference to <FIG> and with additional reference to <FIG>, a method of assembling the core <NUM> (see <FIG>) is provided. As shown in <FIG>, the method includes forming the channel sections <NUM> such that the channel sections <NUM> are configured to form the internal channels <NUM> (see <FIG>) within the airfoil <NUM> by casting processes (block <NUM>), disposing the tip rods <NUM> to extend from the respective portions of the channel sections <NUM> proximate to the location of the tip shelf <NUM> (block <NUM>) and executing the casting processes to cast the blade whereby the tip rods <NUM> extend from the internal channels <NUM> and through the wall <NUM> at the oblique angle α relative to the normal angle of the wall <NUM> to form the obliquely-angled through-holes <NUM> in the wall <NUM> (block <NUM>). The method can further include forming the squealer pocket <NUM> in the tip shelf <NUM> (block <NUM>).

The executing of the casting processes of block <NUM> can include executing an investment casting process to cast the blade around the core <NUM> and to subsequently remove the core <NUM> from the blade once the blade is cast. This can be achieved by known methods and processes for casting and results in the definition and the formation of the airfoil <NUM> and the internal channels <NUM>. The method can further include removing the tip rods <NUM> from the blade via the obliquely-angled through-holes <NUM> in the wall <NUM> upon completion of the investment casting process (block <NUM>).

In accordance with embodiments, the method can also include forming the bumper <NUM> proximate to the internal end of at least one of the tip rods <NUM> and coupling the external ends of the tip rods <NUM> to the plenum body <NUM>.

Except as provided herein, the squealer pocket <NUM> of <FIG> and the wall <NUM> can be formed by various additional or alternative processes. These include, but are not limited to, electro-dynamic machining (EDM). In some cases, where the squealer pocket <NUM> is formed by EDM, the additional holes <NUM> can be formed by cast processes or by further EDM processing.

With reference to <FIG>, a blade structure <NUM> is provided. The blade structure <NUM> is essentially an intermediate stage structure which exists during the casting processes and includes the tip rods <NUM> and the airfoil <NUM> as each is described above. The airfoil <NUM> has the first sweep configuration <NUM> and is formed to define the internal channels <NUM>. Here, the core <NUM> has already been removed by the completion of the investment casting process noted above with the airfoil <NUM> left remaining and intact whereby the core <NUM> includes the wall <NUM> as well as external passage wall components <NUM> and internal passage wall components <NUM> that were formed by the channel sections <NUM>. The tip rods <NUM> extend from the internal channels <NUM> and through the wall <NUM> at the oblique angle α relative to the normal angle of the wall <NUM> to thus form the obliquely-angled through-holes <NUM> during the casting processes and are removable via the obliquely-angled through-holes <NUM>.

With the tip rods <NUM> extending through the wall <NUM> at the oblique angle α, distances between the tip rods <NUM> and the external and internal passage wall components <NUM> and <NUM> can be maintained at or above minimum required distances with the tip rods <NUM> still having reliably producible dimensions and sizes of the obliquely-angled through-holes <NUM> being maintained at or above minimum required sizes.

In accordance with embodiments, at least one or more of the internal passage wall components <NUM> proximate to the internal end of at least one of the tip rods <NUM> can be formed to define a divot <NUM>. The divot results from the investment casting process and the formation of the bumper <NUM> (see <FIG>). To an extent the internal end of the at least one of the tip rods <NUM> is excessively close to the internal passage wall component <NUM>, the divot <NUM> serves to recapture the minimum required distance.

With reference to <FIG>, a method of forming an airfoil of a blade structure as described above is provided. The method includes casting the airfoil to include pressure and suction surfaces, leading and trailing edges extending along the pressure and suction surfaces and a tip shelf with a sweep configuration at an outboard airfoil end (<NUM>), executing the casting such that the airfoil defines internal channels and the tip shelf defines obliquely-angled through-holes (<NUM>) and machining a squealer pocket into the tip shelf with a remainder of the tip shelf forming a wall extending radially outwardly to delimit a periphery of the squealer pocket and with the obliquely-angled through-holes being adjacent to the wall (<NUM>). In accordanc with embodiments, the machining of operation <NUM> can include electro-dynamic machining (EDM).

With reference to <FIG>, tip solidity of the airfoil <NUM> described herein can vary along the chord line of the airfoil <NUM> as shown in the graph.

Benefits of the features described herein allows for the use of tip rods to produce holes for internal cavity dirt purge, core position control and casting in blades with an airfoil sweep.

Claim 1:
An airfoil (<NUM>), comprising:
pressure and suction surfaces (<NUM>, <NUM>);
leading and trailing edges (<NUM>, <NUM>) extending along the pressure and suction surfaces (<NUM>, <NUM>);
a tip shelf (<NUM>) with a sweep configuration (<NUM>) at an outboard airfoil end; and
a wall (<NUM>, <NUM>) extending radially outwardly from the tip shelf (<NUM>) to delimit a periphery of a squealer pocket (<NUM>) at the tip shelf (<NUM>),
wherein the airfoil (<NUM>) defines internal channels (<NUM>),
the tip shelf (<NUM>) defines obliquely-angled through-holes (<NUM>) adjacent to the wall (<NUM>, <NUM>),
the wall (<NUM>, <NUM>) comprises notched sections (<NUM>) that curve around the obliquely-angled through-holes (<NUM>, <NUM>), characterised in that
the tip shelf (<NUM>) defines additional holes (<NUM>) within the squealer pocket (<NUM>) to provide fluid communication between the internal channels (<NUM>) and the squealer pocket (<NUM>), and
the additional holes (<NUM>) are arranged in a linear grouping becoming increasingly staggered with increasing distance from the trailing edge (<NUM>) with at least one of the additional holes (<NUM>) being located between the notched sections (<NUM>) and with at least one of the additional holes (<NUM>) proximate to the leading edge (<NUM>).