Turbine blade with friction and impact vibration damping elements

A turbine blade includes an airfoil body having an outer tip and a platform; and a part-span shroud positioned between the outer tip and the platform of the airfoil body. The part-span shroud has a first opening extending through the airfoil body and having a first inner surface. The airfoil body includes a second opening extending radially from the first opening and having a second inner surface. A first elongated vibration-damping element is disposed in the first opening, and a second elongated vibration-damping element disposed radially in the second opening. The second elongated vibration-damping element includes a free radially outer end and a radially inner end coupled to the first elongated vibration-damping element. The first elongated vibration-damping element frictionally damps vibration, and the second elongated vibration-damping element damps vibration using impact within the second opening.

TECHNICAL FIELD

The disclosure relates generally to damping vibration in an article. Further, the disclosure relates to the damping of blades used in turbines.

BACKGROUND

Turbine and compressor sections within an axial flow turbine system generally include a rotor assembly comprising a rotating disk and a plurality of rotor blades circumferentially disposed around the disk. Each blade includes a base, an airfoil, and a platform positioned in the transition area between the base and the airfoil. The bases of the blades are received in complementary shaped recesses within the disk. The platforms of the blades extend laterally outward and collectively form a flow path for fluid passing through the rotor stage. The forward edge of each blade is generally referred to as the leading edge, and the aft edge as the trailing edge. Forward is defined as being upstream of aft in the gas flow through the system.

One concern in turbine operation is the tendency of the turbine blades to undergo vibrational stress during operation. For example, variations in gas temperature, pressure, and/or density can excite vibrations throughout the rotor assembly, especially within in the blade airfoils. In many installations, frequent acceleration and deceleration of the turbine subjects the blades, momentarily at least, to vibrational stresses at certain primary frequencies and, in many cases, to vibrational stresses at secondary or tertiary frequencies. During full-speed, full-load steady state operation conditions, turbine blades also often undergo vibrational stress as they are excited by the periodic, or “pulsating,” force from the upstream flow. When a blade is subjected to vibrational stress, its amplitude of vibration can readily build up to a point which may alter operations.

Blades can be damped to avoid or reduce high vibratory stress. One approach to address vibrations during operation of the turbine includes changing natural frequencies of the blades to avoid resonance, e.g., by changing the physical structure of the blades. For example, a mid-span shroud that couples adjacent blades may be used. In another example, tip shrouds may create friction between adjacent blades to dissipate the kinetic energy during operation. Changing or adding structure creates additional challenges by changing the aerodynamic performance of the blades and by adding weight and/or length.

In another example, it is known that dampers may be attached to an external surface of the airfoil. A recognized disadvantage of adding a damper to an external surface is that the damper is exposed to the harsh, corrosive environment within the engine. As soon as the damper begins to corrode, its effectiveness may be compromised. In addition, the damper may separate from the airfoil because of corrosion.

In other approaches, mechanisms to passively absorb the kinetic energy that creates the vibrations during use are employed. In one example, cavities or, in another example, baffles, may be provided adjacent an outer tip of the blade to absorb pressure variations during operation. In another case, a high pressure airflow may be directed from an upstream position into a leading edge of a blade stage.

BRIEF DESCRIPTION

A first aspect of the disclosure provides a turbine blade including: an airfoil body having an outer tip and a platform; a part-span shroud positioned between the outer tip and the platform of the airfoil body, the part-span shroud having a first opening having a first inner surface, the first opening extending through the airfoil body; a second opening in the airfoil body extending radially outward from the first opening and having a second inner surface; a first elongated vibration-damping element disposed in the first opening; and a second elongated vibration-damping element disposed radially in the second opening, the second elongated vibration-damping element including a free radially outer end and a radially inner end coupled to the first elongated vibration-damping element.

A further aspect of the disclosure provides an article including: an airfoil body having an outer tip and a platform; a part-span shroud positioned between the outer tip and the platform of the airfoil body, the part-span shroud having a first opening having a first inner surface, the first opening extending through the airfoil body; a first elongated vibration-damping element disposed in the first opening and frictionally engaging the first inner surface for frictionally damping vibrations; and a second elongated vibration-damping element disposed radially in a second opening in the airfoil body, the second elongated vibration-damping element having a radially inner end coupled to the first elongated vibration-damping element and a free radially outer end for damping vibrations by impacting a second inner surface of the second opening.

Another aspect of the disclosure provides a method of damping vibration in a turbine blade, the method comprising: damping vibration by friction in a part-span shroud positioned between an outer tip and a platform of an airfoil body of the turbine blade, the part-span shroud having a first opening having a first inner surface and a first elongated vibration-damping element disposed in the first opening and frictionally engaging the first inner surface; and damping vibration by impact of a second elongated vibration-damping element disposed radially in a second opening in the airfoil body, the second elongated vibration-damping element having a radially inner end coupled to the first elongated vibration-damping element and a radially outer end capable of damping vibrations by impacting with an inner surface of the second opening.

DETAILED DESCRIPTION

In addition, several descriptive terms may be used regularly herein, and it should prove helpful to define these terms at the onset of this section. These terms and their definitions, unless stated otherwise, are as follows. As used herein, “downstream” and “upstream” are terms that indicate a direction relative to the flow of a fluid, such as the working fluid through the turbine system or, for example, the flow of air through the combustor or coolant through one of the turbine's component systems. The term “downstream” corresponds to the direction of flow of the fluid, and the term “upstream” refers to the direction opposite to the flow. It is recognized that in an opposed flow configuration, upstream and downstream directions may change depending on where one is in the turbine system. The terms “forward” and “aft,” without any further specificity, refer to directions, with “forward” referring to the front end of the turbine system, and “aft” referring to the rearward of the turbine system.

It is often required to describe parts that are at differing radial positions with regard to a center axis. The term “radial” refers to movement or position perpendicular to an axis. In such cases, if a first component resides closer to the axis than a second component, it will be stated herein that the first component is “radially inward” or “inboard” of the second component. If, on the other hand, the first component resides further from the axis than the second component, it may be stated herein that the first component is “radially outward” or “outboard” of the second component. The term “axial” refers to movement or position parallel to an axis. Finally, the term “circumferential” refers to movement or position around an axis. It will be appreciated that such terms may be applied in relation to the center axis of the turbine system, e.g., an axis of a rotor thereof.

In addition, several descriptive terms may be used regularly herein, as described below. The terms “first”, “second”, and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components.

Embodiments of the disclosure provide an article or turbine blade with a vibration damping system that includes frictional and impact vibration damping elements. The article or turbine blade may include an airfoil body having an outer tip and a platform; and a part-span shroud positioned between the outer tip and the platform of the airfoil body. The part-span shroud has a first opening having a first inner surface therein. The airfoil body includes a second opening extending radially from the first opening and having a second inner surface. A first elongated vibration-damping element is disposed in the first opening, and a second elongated vibration-damping element is disposed radially in the second opening. The second elongated vibration-damping element includes a free radially outer end and a radially inner end coupled to the first elongated vibration-damping element. The first elongated vibration-damping element frictionally damps vibration, and the second elongated vibration-damping element damps vibration using impact within the second opening. The vibration damping system including the vibration damping elements reduces blade vibration with a simple arrangement and does not add extra mass to the blade so that it does not add additional centrifugal force to the blade root or require a change in blade configuration.

Referring to the drawings,FIG. 1is a schematic view of an illustrative machine including a turbine(s) to which teachings of the disclosure can be applied. InFIG. 1, a turbomachine90in the form of a combustion turbine or gas turbine (GT) system100(hereinafter, “GT system100”), is shown. GT system100includes a compressor102and a combustor104. Combustor104includes a combustion region105and a fuel nozzle section106. GT system100also includes a turbine108and a common compressor/turbine shaft110(hereinafter referred to as “rotor110”).

In one embodiment, GT system100is a 7HA.03 engine, commercially available from General Electric Company, Greenville, S.C. The present disclosure is not limited to any one particular GT system and may be implemented in connection with other engines including, for example, the other HA, F, B, LM, GT, TM and E-class engine models of General Electric Company and engine models of other companies. More importantly, the teachings of the disclosure are not necessarily applicable to only a turbine in a GT system and may be applied to practically any type of turbine, e.g., steam turbines, jet engines, compressors (as inFIG. 1), turbofans, turbochargers, etc. Hence, reference to turbine108of GT system100is merely for descriptive purposes and is not limiting.

FIG. 2shows a cross-sectional view of an illustrative portion of turbine108. In the example shown, turbine108includes four stages L0-L3that may be used with GT system100inFIG. 1. The four stages are referred to as L0, L1, L2, and L3. Stage L0is the first stage and is the smallest (in a radial direction) of the four stages. Stage L1is the second stage and is disposed adjacent the first stage L0in an axial direction. Stage L2is the third stage and is disposed adjacent the second stage L1in an axial direction. Stage L3is the fourth, last stage and is the largest (in a radial direction). It is to be understood that four stages are shown as one example only, and each turbine may have more or less than four stages.

A plurality of stationary vanes or nozzles112may cooperate with a plurality of rotating turbine blades114(hereafter “blades114”) to form each stage L0-L3of turbine108and to define a portion of a working fluid path through turbine108. Blades114in each stage are coupled to rotor110(FIG. 1), e.g., by a respective rotor wheel116that couples them circumferentially to rotor110(FIG. 1). That is, blades114are mechanically coupled in a circumferentially spaced manner to rotor110, e.g., by rotor wheels116. A static nozzle section115includes a plurality of stationary nozzles112circumferentially spaced around rotor110(FIG. 1). Each nozzle112may include at least one endwall (or platform)120,122connected with airfoil124. In the example shown, nozzle112includes a radially outer endwall120and a radially inner endwall122. Radially outer endwall120couples nozzle(s)112to a stationary casing124of turbine108.

With reference toFIGS. 1 and 2, in operation, air flows through compressor102, and pressurized air is supplied to combustor104. Specifically, the pressurized air is supplied to fuel nozzle section106that is integral to combustor104. Fuel nozzle section106is in flow communication with combustion region105. Fuel nozzle section106is also in flow communication with a fuel source (not shown inFIG. 1) and channels fuel and air to combustion region105. Combustor104ignites and combusts fuel. Combustor104is in flow communication with turbine108within which gas stream thermal energy is converted to mechanical rotational energy by directing the combusted fuel, e.g., working fluid, into the working fluid path to turn blades114. Turbine108is rotatably coupled to and drives rotor110. Compressor102is rotatably coupled to rotor110. At least one end of rotor110may extend axially away from compressor102or turbine108and may be attached to a load or machinery (not shown), such as, but not limited to, a generator, a load compressor, and/or another turbine.

FIGS. 3 and 4show perspective and side views, respectively, of a blade114of the type for which embodiments of a vibration damping system128of the present disclosure may be employed. Each of the plurality of blades114includes a root or base130by which blade114attaches to rotor110(FIG. 1). Base130may include a dovetail132configured for mounting in a corresponding dovetail slot in the perimeter of a rotor wheel116(FIG. 2) of rotor110(FIG. 1). Base130may further include a shank134that extends between dovetail132and a platform136, which is disposed at the junction of airfoil body138and base130and which defines a portion of the inboard boundary of the working fluid path (FIG. 2) through turbine108. It will be appreciated that airfoil body138is the active component of blade114that intercepts the flow of working fluid and that induces rotor110(FIG. 1) to rotate. It will be seen that airfoil body138of blade114includes a concave pressure side (PS) outer wall140and a circumferentially or laterally opposite convex suction side (SS) outer wall142extending axially between opposite leading and trailing edges144,146, respectively. Sidewalls140and142also extend in the radial direction from platform136to an outer tip148. Hence, airfoil body138extends from platform136to outer tip148.

Blade114may also include a part-span shroud150extending from each outer wall140,142. Part-span shroud150is positioned radially between outer tip148and platform130of airfoil body138, i.e., radially outboard of platform136. As understood, part-span shrouds150may be located along a radial span of blade114and may interact or mate with a part-span shroud150of an adjacent blade to, among other things, reduce vibrations in each blade114. In one example, part-span shroud150is positioned more than half way radially outboard on airfoil body138from platform136so as to be closer to outer tip148than to platform136, which is especially advantageous on longer blades to provide increased vibration damping near outer tip148. However, part-span shroud150may be positioned at any radial location between outer tip148and platform136. While an illustrative blade114has been described, it will be appreciated that blades may vary in structure across different types of turbines.

As noted, during operation of a turbine, blades114may be excited into vibration by a number of different forcing functions. Variations in, for example, working fluid temperature, pressure, and/or density, can excite vibrations throughout the rotor assembly, especially within the blade airfoils and/or outer tips. Gas exiting upstream of the turbine and/or compressor sections in a periodic, or “pulsating,” manner can also excite undesirable vibrations. Embodiments of the disclosure aim to reduce the vibration of a large rotating turbine blade114without significant change of blade design.

FIG. 5shows an enlarged perspective view of blade114in the vicinity of part-span shroud150and including outer tip148, andFIG. 6shows a top down, cross-sectional view of blade114along view line6-6inFIG. 5. As noted, part-span shroud150is positioned between outer tip148and platform136(FIG. 3) of airfoil body138. Typically, part-span shroud150is a solid material or includes small cooling passages therein. In accordance with embodiments of the disclosure, part-span shroud150includes a first opening160having a first inner surface162. First opening160extends in a substantially linear fashion along most, if not all, of a longitudinal length of part-span shroud150and extends through the airfoil body138. Blade114also includes a second opening164in airfoil body138extending radially outward from first opening160and having a second inner surface166. Second opening164opens to and is aligned with first opening160. That is, first and second opening160,164intersect one another, e.g., at a radial outer extent168(FIG. 5) of first opening160. The user may define the location along a length of first opening160where the two openings meet, e.g., based on desired vibration damping and/or airfoil body138internal structure. First and second openings160,164may be formed using any now known or later developed technique, e.g., machining (such as drilling), additive manufacture, etc.

Second opening164may be positioned in a number of ways in airfoil body138. In one example, as shown inFIG. 3, airfoil body138may include a solid block of material in which case second opening164extends radially within the block of material. In another example, shown inFIG. 6, airfoil body138includes an internal rib or wall169defining an elongated internal cavity170extending inwardly from outer tip148of airfoil body138. As appreciated in the field, internal wall169and elongated internal cavity170can take a variety of forms to provide the desired structural integrity to blade114and/or the desired coolant delivery to keep the blade cool. In the example shown inFIG. 6, second opening164extends radially within internal wall170. Because the internal structure of blades114can vary significantly, it will be appreciated that second opening164may extend in a variety of alternative internal structures in blade114other than those illustrated.

Vibration damping system128and blade114may also include a first elongated vibration-damping element176disposed in first opening160, and a second elongated vibration-damping element178disposed radially in second opening164. First elongated vibration-damping element176(hereinafter “first damping element176”) engages at least a portion of first inner surface162of first opening160, allowing first damping element176to damp vibrations through frictional engagement with first inner surface162of first opening160. The extent of frictional engagement between first damping element176and first inner surface162can be user defined to provide any desired amount of frictional damping.

Second elongated vibration-damping element178(hereinafter “second damping element178”) includes a radially inner end180(FIG. 5) coupled to first damping element176, i.e., near intersection of openings160,164. Consequently, first damping element176and second damping element178may collectively have an upside-down T shape in airfoil body138. The T shape may or may not be symmetrical, depending on the location of the second opening164. Second damping element178may be coupled to first damping element176in a number of ways. In one embodiment, radially inner end180of second damping element178is threadably coupled in an opening182(FIG. 5) in first damping element176. In alternative embodiments, they may be fastened together in any manner with sufficient strength to prevent radial movement of second damping element178, e.g., press fit.

Second damping element178, however, is not frictionally engaged within second opening164. Rather, second damping element178is free to move within second opening164and, in particular, includes a free radially outer end184that is unencumbered other than by second opening164to impact inner surface166, i.e., to vibrate, within second opening164. In this regard, as shown for example in a cross-sectional view inFIG. 7, second opening164may have a dimension D1greater than a corresponding outer dimension D2of second damping element178. This structure allows second damping element178a limited movement range within second opening164for damping vibrations through impact with second inner surface166of second opening164, and allowing fastening of second damping element178to first damping element176. The amount of movement allowed can be user defined to provide any desired amount of impact damping. In one non-limiting example, dimension D1of second opening164may be 1.8 centimeters (0.7 inch), and a largest dimension D2of second damping element178may be 1.6 centimeters (0.6 inch). The spacing between second opening164and second damping element178need not be consistent around the element178and can vary depending on a number of factors such as, but not limited to, the anticipated direction of vibration, the amount of vibration, etc. In any event, the dimensions D1, D2allow sufficient space to allow fastening of second damping element178to first damping element176, e.g., rotation for threading, spacing for press fit, etc.

First and second damping elements176,178may be made of the same material as airfoil body138, e.g., a superalloy, or they may be made of other materials. In any event, damping elements176,178are typically configured to add as little additional mass as possible. While openings160,164and damping elements176,178are illustrated with either a circular or elliptical/oval (FIG. 7) cross-section, it is emphasized that either element can have practically any desired cross-section, including in addition to those shown, polygonal cross-sections (as inFIG. 8). Hence, damping element176or178may take the form of a rod or pin of any desired cross-sectional shape. In one embodiment, second opening164has a circular cross-sectional shape, and second damping element178has a cross-sectional shape selected from the group consisting of a circle (FIG. 6), an ellipse having a major and a minor axis of different lengths (FIG. 7), and a polygon (FIG. 8). As noted, second opening164has sufficient width to allow second damping element178to allow fastening, e.g., turning for threading, into first damping element176regardless of cross-sectional shape.

Openings160,164and damping elements176,178can be customized to provide the desired damping according to a wide variety of factors such as, but not limited to: anticipated vibration magnitude and/or direction, blade size, blade internal structure, existence of a tip shroud, and/or part-span shroud150size and/or shape. Damping elements176,178can be inserted into openings160,164in any manner. For example, first damping element176may be forcibly and frictionally fit into first opening160, while second damping element178can be inserted into second opening164through outer tip end148and coupled to first damping element176, e.g., by turning element178to thread end180into first damping element176. Second damping element178may be inserted into second opening164, for example, prior to closing of outer tip end148with a tip plate and/or tip rail (not shown).

Embodiments of the disclosure also provide a method of damping vibration in a turbine blade114, i.e., using damping vibration system128. In operation, turbine blade114is operated in a normal fashion within turbine108(FIG. 2). However, damping vibration by friction is carried out in part-span shroud150positioned between outer tip148and platform136of airfoil body138of turbine blade114by frictional engagement of first damping element176in first opening160. As noted, first opening160has first inner surface162in which first damping element176is disposed such that first damping element176frictionally engages first inner surface162of first opening160. Simultaneously or contemporaneously, damping vibration is carried out by impact of second damping element178disposed radially in second opening164in airfoil body138. As noted, second damping element178has radially inner end180coupled to first damping element176and radially outer end184capable of damping vibrations by impacting with inner surface166of second opening164.

While embodiments of the disclosure have been described herein as a blade that is part of a turbine, it is noted that the teachings of the disclosure may be applied to a variety of other applications for an article including an airfoil.

Embodiments of the disclosure provide two different damping mechanisms combined in a T-shaped pin design. First damping element176, which is generally horizontal, dissipates the energy by friction with inner surface162of first opening160, and second damping element178, which is radially extending, dissipates the energy by impact with inner surface166of second opening164. Embodiments of the disclosure thus retain blade114pull load and the original configuration of the blade and rotor, while reducing the blade flex vibration effectively and with a simple design.