1. Field
The present invention relates to gas turbine engines, and more specifically to a removably attachable snubber assembly for a turbine blade.
2. Description of the Related Art
In an industrial gas turbine engine, hot compressed gas is produced. The hot gas flow is passed through a turbine and expands to produce mechanical work used to drive an electric generator for power production. The turbine generally includes multiple stages of stator vanes and rotor blades to convert the energy from the hot gas flow into mechanical energy that drives the rotor shaft of the engine. Turbine inlet temperature is limited to the material properties and cooling capabilities of the turbine parts. This is especially important for upstream stage turbine vanes and blades since these airfoils are exposed to the hottest gas flow in the system.
A combustion system receives air from a compressor and raises it to a high energy level by mixing in fuel and burning the mixture, after which products of the combustor are expanded through the turbine.
Since the turbine vanes and blades are exposed to the hot gas flow discharged from combustors within the combustion system, cooling methods are sometimes used to obtain a useful design life cycle for the turbine blade or vane. Blade and vane cooling is accomplished by extracting a portion of the compressed air from the compressor and directing it to the turbine section, thereby bypassing the combustors. After introduction into the turbine section, this cooling air flows through passages formed in the airfoil portions of the blades and vanes.
Gas turbines are becoming larger, more efficient, and more robust. Large blades and vanes are being produced, especially in the hot section of the engine system. Of particular challenge is the last stage blade. Traditionally the last stage blade has been solid, tip shrouded and uncooled. This configuration has limitations as the blades require more robustness as the gas path diameters increase and the gas path temperatures increase.
In order to allow for increasing the gas path diameter, turbine blades may be hollow, cooled, curve root attached blades with integral part span snubbers as seen in
The snubber creates an assembly challenge due to the potential interference between the attachment engagement and snubber contact surface engagement as can be seen in
In current assemblies, the snubbers will connect with each other once the turbine is up and running at a particular rotational speed. The blade untwists as a functional of rotational speed. The airfoil will also have radial growth at increased rotational speeds. Once the blades have sufficiently untwisted, the snubbers come into contact through their contact surfaces once that particular rotational speed is met as shown in
Aeromechanical systems for snubbers and tip shrouds consider the vibratory mode shape to define the bearing angle and contact pressure to achieve the required level of mechanical constraint and damping. Additionally, these systems try to achieve minimum weight to reduce the stress on the blade. There has been no significant reduction in the snubber aerodynamic penalty because of the mechanical requirements for blade support and part life.
In one aspect of the present invention, a removably attachable snubber assembly for turbine blades comprises: a turbine blade airfoil comprising a trailing edge and a leading edge joined by a pressure side and a suction side to provide an outer surface extending in a radial direction to a tip; at least one snubber attachment platform integrally formed onto the outer surface of the turbine blade airfoil, wherein the at least one snubber attachment platform comprises an interlocking mechanism; and a snubber comprising a first end, a second end, a trailing edge, a leading edge, a snubber length, and a snubber width, wherein the snubber is removably attachable to the at least one snubber attachment platform, wherein the snubber comprises a removable attachment mechanism on at least one of the first end and the second end, wherein the removable attachment mechanism on the snubber connects with the interlocking mechanism on the at least one snubber attachment platform, the interlocking mechanism constructed to provide a contact surface for the snubber and a clearance gap for operational blade movement.
In another aspect of the present invention, a rotor assembly comprises: a disc comprising a plurality of elongated channels provided therein and spaced along a disc periphery; a plurality of turbine blade airfoils, each comprising a trailing edge and a leading edge joined by a pressure side and a suction side to provide an outer surface extending in a radial direction to a tip, wherein each turbine blade airfoil is installed in each of the elongated channels on the disc; at least one snubber attachment platform integrally formed onto the outer surface of each turbine blade airfoil, wherein the at least one snubber attachment platform comprises an interlocking mechanism; and a plurality of snubbers each comprising a first end, a second end, a trailing edge, a leading edge, a snubber length, and a snubber width, wherein each snubber is removably attachable to at least one snubber attachment platform, wherein each snubber comprises a removable attachment mechanism on at least one of the first end and the second end, wherein each removable attachment mechanism on each snubber connects with the interlocking mechanism on each of the at least one snubber attachment platform, the interlocking mechanism constructed to provide a contact surface for the snubber and a clearance gap for operational blade movement.
In another aspect of the present invention, a method for attaching snubbers to a rotor assembly comprises: installing a plurality of turbine blades onto a disc comprising a plurality of elongated channels provided therein and spaced along a disc periphery, wherein the plurality of turbine blades each comprise an airfoil, a trailing edge and a leading edge joined by a pressure side and a suction side to provide an outer surface extending in a radial direction to a tip, wherein the plurality of turbine blades are installed in each of the elongated channels on the disc, wherein at least one snubber attachment platform is integrally formed onto the outer surface of each turbine blade airfoil, wherein the at least one snubber attachment platform comprises an interlocking mechanism; and removably attaching a plurality of snubbers, each snubber removably attached into each of the at least one snubber attachment platforms each snubber comprising a first end, a second end, a trailing edge, a leading edge, a snubber length, and a snubber width, wherein each snubber comprises a removable attachment mechanism on at least one of the first end and the second end, wherein each removable attachment mechanism on each snubber connects with the interlocking mechanism on each of the at least one snubber attachment platform, the interlocking mechanism constructed to provide a contact surface for the snubber and a clearance gap for operational blade movement.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
The invention is shown in more detail by help of figures. The figures show preferred configurations and do not limit the scope of the invention.
In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention.
Broadly, an embodiment of the present invention provides a removably attachable snubber assembly for turbine blades that includes a turbine blade airfoil including a trailing edge and a leading edge joined by a pressure side and a suction side to provide an outer surface extending in a radial direction to a tip. At least one snubber attachment platform is integrally formed onto the outer surface of the turbine blade airfoil. At least one snubber attachment platform includes an interlocking mechanism. A snubber is removably attachable to the at least one snubber attachment platform, the snubber including a first end, a second end, a trailing edge, a leading edge, a snubber length, and a snubber width. The snubber also includes a removable attachment mechanism on at least one of the first end and the second end that connects with the interlocking mechanism on the at least one snubber attachment platform.
A gas turbine engine may comprise a compressor section, a combustor and a turbine section. The compressor section compresses ambient air. The combustor combines the compressed air with a fuel and ignites the mixture creating combustion products comprising hot gases that form a working fluid. The working fluid travels to the turbine section. Within the turbine section are circumferential rows of vanes and blades, the blades being coupled to a rotor. Each pair of rows of vanes and blades forms a stage in the turbine section. The turbine section comprises a fixed turbine casing, which houses the vanes, blades and rotor. A blade of a gas turbine receives high temperature gases from a combustion system in order to produce mechanical work of a shaft rotation.
Damping is an important benefit that a snubber may provide for a turbine blade. The damping occurs when there is direct contact between adjacent blade snubbers. An aspect of the level of damping is a contact surface. The contact surface is the area of contact between each component. Another phenomena that occurs once the blades are at a certain rotational speed, is that there is radial growth of the airfoil as well as an untwisting at operating conditions.
Improved damping may occur with a snubber that is able to be removed from the blade itself. The snubber, as will be discussed in detail below, may be able to provide a bridge between blades through sliding onto snubber attachment platforms integral to the blades.
As is shown in
The at least one snubber attachment platform 12 may be integrally formed along the outer surface 14 of the blade airfoil. In certain embodiments, the at least one snubber attachment platform 12 may be positioned along the airfoil at a distance that may equate to a snubber span radius (R) of a conventional snubber blade assembly at a zero speed. The at least one snubber attachment platform 12 may provide the areas of contact and constraint between the plurality of airfoils 10 and a plurality of snubbers 16. The at least one snubber attachment platform 12 may have one of several different shapes in order to fit an application as shown in
The shape of the snubber 16 may also vary depending on mechanical and aerodynamic requirements.
The plurality of blades 10, may be placed and installed on the wheel. The wheel may include a rotating disc. The disc may include a plurality of elongated channels provided therein and spaced along a disc periphery. Each of the blades 10 may be installed in each of the elongated channels on the disc. The plurality of blades 10 may define a passage 34, having a passage length and a passage width between each blade 10. The snubber 16 may be supported at the airfoils with snubber attachment platform 12 in the passage 34. It may be possible to reduce the aerodynamic blockage of the conventional snubber with a thinner snubber 16. The snubber 16 may have a variable width or thickness in the passage 34 along a circumferential direction. The snubber 16 may have a variable tangential camber within the passage 34 as is shown in
Each snubber 16 may include a first end 22, a second end 24, a trailing edge 28, a leading edge 26, a snubber chordwise width 30, and a snubber thickness 32.
The snubber 16 may be removably attached to the snubber attachment platform 12 in multiple embodiments. In certain embodiments, at the first end 22 and the second end 24 of each snubber 16 may be a removable attachment mechanism 36 such as access slots as shown in
In certain embodiments, the snubber attachment platform 12 may provide an interlocking mechanism 42 such as an interlocking hook with a similar feature on the snubber 16 such as shown in
The method of removable attachment may prevent the snubber 16 from sliding off of the support at least one snubber attachment platform 12 during operation. The method may not restrict the airfoil motion, however, for untwisting or radial growth. There are no special fitting requirements between the snubbers 16 of adjacent blades 10. Instead, the snubbers 16 may simply be installed between the blades 10 along the snubber attachment platforms 12. As is illustrated in
In certain embodiments, the trailing edge 28 of the snubber 16 may be plastically deformed. The first end 22, the second end 24, or both may be plastically deformed to prevent the snubber 16 from sliding off of the snubber attachment platform 12 as is shown in
The snubbers 16 may have a superior aerodynamic shape compared to snubbers that are integral with the blades 10. Integral snubbers, by their nature, must have a large interface with the contacting snubber in the adjacent blade 10 and that causes aerodynamic losses. As mentioned above, the snubber thickness may be reduced and be provided with a very thin profile. A thinner midsection profile may also reduce aerodynamic blockage.
In certain embodiments, the snubber 16 may have an airfoil-like cross section such as shown in section C-C of
In certain embodiments, the blade 10 may include an air flow cooling circuit. The snubber 16 may be cooled by providing cooling air flow 48 from the blade 10 through the snubber attachment platforms 12 to the snubber 16 as presented in
In all embodiments, blade 10 to blade 10 contact is maintained for all operating speeds. There is no need for special tools in order to properly set and assemble the plurality of snubbers 16 in place for proper contact. The plurality of blades 10 may be placed in the wheel, and each snubber 16 may be placed into each snubber attachment platform 12. Once each snubber 16 is placed into each snubber attachment platform 12, there is blade 10 to blade 10 contact. The blade 10 to blade 10 contact may be maintained at all operating speeds, including no speed and at high speeds. Therefore, damping may be available at all operating speeds.
Since the snubber 16 is removable, the snubber 16 may be easily replaced. In certain embodiments, a one interval uncooled part may be placed in position along the snubber attachment platform 12 for temporary placement. Additional cooling flow savings may also be produced with this one interval part.
A thinner snubber 16 than conventionally used may be used and therefore provide improved aerodynamic performance. The thickness necessary in a conventional snubber 16 for contact surface may not be necessary when the snubber 16 may be removably attached to the snubber attachment platform 12, since the snubber attachment platform 12/snubber 16 connection provides the contact surface. The portion of the snubber 16 that is in between the blades 10 may be as thin as possible for the application. The thickness may also be variable for various possibilities such as shown in
Servicing of the blades 10 and snubbers 16 may improve with the ability to change out the removably attached snubbers 16. Differently shaped snubbers 16 may be placed in service to update or improve performance of the turbine. Instead of having to replace a full blade 10, the snubber 16 alone may be removed and replaced. The easy replacement of snubbers 16 may allow for reduced part life designs that may not require active cooling.
Aeromechanical tuning may be provided for the blades 10 with adjustments to the snubbers 16, or replacement of the snubbers 16 with ease. If problems occur while in service, an individual snubber 16 may be replaced with a different snubber 16 with more damping and or improved shape per the specific application.
As mentioned above, the size and shape of each snubber attachment platform 12 and snubber 16 may be determined by mechanical and aerodynamic requirements. The size of the snubber 16 used in a turbine application may be changed since the snubber 16 may be removed. The contact surface for damping may be reduced due to the change in configuration from the conventional integral snubber. The amount of airfoil radial growth and untwist during operating conditions may change the requirements for the size and shape of the snubber attachment platform 12 and snubber 16.
Optimization may occur with proper testing of the turbine. Mistuning may be used to reduce blade vibration responses. A removably attachable snubber 16 may provide multiple methods to mistune the vibratory response of the blades 10. There may be two or more snubber 16 configurations distributed in the blade passages 34 in order to interfere with coupled blade-to-blade vibration as seen in the formation of a nodal diameter pattern. Each snubber 16 in the turbine blade assembly may be of a different shape, may each have different removable attachment mechanisms 36, or the like. Different snubbers 16 may also change blade natural frequencies. Some of the snubbers 16 may be removed that may eliminate the formation of a coherent nodal diameter pattern.
While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternative to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims, and any and all equivalents thereof.
Development of this invention was supported in part by the United States Department of Energy, Contract No. DE-FE0023955. Accordingly, the United States Government may have certain rights in this invention.
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Number | Date | Country | |
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