Turbine airfoil attachment with serration profile

An attachment root for a blade includes a symmetric serration profile with multiple lobes. Contact surfaces of each lobe form equal contact angles with a line normal to a symmetry plane of the serration profile. Non-contact surfaces of lobes form angles greater than three degrees relative to the line that increase in a radially inward direction.

BACKGROUND

Gas turbine engines produce work by introducing fuel into a compressed air flow produced by one or more compressor stages, combusting the air-fuel mixture in a combustor, and expanding the exhaust flow across one or more turbine stages. Rotors of compressor stages and turbine stages include airfoils that rotate to compress the airfoil or extract work from the airfoil during operation of the gas turbine engine. The airfoils can be attached to the rotors by an attachment root. During operation, the attachment root restrains the airfoil against centripetal force, which imposes relatively high stress levels within the attachment root. High stress levels may accelerate wear and tear on the airfoil particularly when combined with high temperatures.

SUMMARY

An attachment root according to an example embodiment of this disclosure includes a serration profile and a first lobe. The serration profile is symmetric about a plane that bisects the serration profile. The first lobe is spaced from the plane and described relative to a line that is normal to the plane. The first contact surface of the first lobe defines a first acute angle between the first contact surface and the line that is equal to forty-five degrees. The first non-contact surface of the first lobe defines a second acute angle between the first non-contact surface and the line that greater than three degrees.

DETAILED DESCRIPTION

FIG.1is a schematic view of gas turbine engine10in accordance with an example embodiment of this disclosure. Gas turbine engine10extends about centerline axis12and includes low-pressure spool14, high-pressure spool16, inlet18, bypass duct20, and combustor21, and outlet22. Low-pressure spool14includes fan24, low-pressure compressor26, low-pressure turbine28, and shaft30. High-pressure spool16includes high-pressure compressor32, high-pressure turbine34, and shaft36. Gas turbine engine10includes one or more casing sections generally represented at38. Each of low-pressure spool14and high-pressure spool16can be supported by casing38in a lateral direction with respect to centerline axis12via two or more bearings and axially along centerline axis12by at least one bearing. For example, forward bearing40A and aft bearing40B support low-pressure spool14while forward bearing42A and aft bearing42B support high-pressure spool16. Low-pressure spool14and high-pressure spool16rotate independently from each other about centerline axis12and, thus, may rotate at different speeds.

Each of low-pressure compressor26, low-pressure turbine28, high-pressure compressor32, and high-pressure turbine34include one or more stages, each stage including one or more rows of blades operatively associated within one or more rows of vanes. As shown, low-pressure compressor26includes three stages, each stage formed by rows of low-pressure compressor blades44and corresponding rows of low-pressure compressor vanes46. Low-pressure turbine28includes three stages formed by alternating rows of low-pressure turbine blades48and low-pressure turbine vanes50. Similarly, high-pressure compressor32includes seven stages formed by rows of high-pressure compressor blades52and high-pressure compressor vanes54. High-pressure turbine34includes two stages formed by rows of high-pressure turbine blades56and high-pressure turbine vanes58.

FIG.2is an isometric view of high-pressure turbine blade56that includes airfoil68, platform70, and attachment root100. Airfoil68extends outward from platform70while attachment root100extends inward from an opposite side of platform70relative centerline axis12when installed within gas turbine engine10. Airfoil68includes pressure side surface72and suction side surface74extending outward along a spanwise direction from platform70to tip73. Pressure side surface72and suction side surface74extend from leading edge76to trailing edge78in a chordwise direction.

Attachment root100includes serration profile102, leading edge end face104, and trailing edge end face106. Serration profile102extends from leading edge end face104to trailing edge end face106to form sides of attachment root100. Serration profile102is symmetric about plane108to form pressure side profile110and suction side profile112, which is a mirror image of pressure side profile110. Pressure side profile110is associated with pressure side surface72of airfoil68, and suction side surface112is associated with suction side surface74of airfoil68. Leading edge end face104is associated with leading edge76while trailing edge end face106is associated with trailing edge78.

On each side of plane108, serration profile102includes one or more lobes114. As depicted, attachment root100includes lobes114A,114B,114C on pressure side profile110and lobes114D,114E, and114F of suction side profile112. Each lobe114includes contact surface116and non-contact surface118. Contact surfaces116form a radially outward facing surface of each lobe114and are configured to mate with corresponding surfaces of a rotor (i.e., a rotor off high pressure turbine34). Contact surfaces116restrain blade56against centrifugal force and acrodynamic loading on airfoil68during operation of gas turbine engine10. Non-contact surfaces118form a radially inward facing surface of each lobe114and are configured to maintain clearance between attachment root100and the rotor (i.e., the rotor of high-pressure turbine34). Lobes114A,114B, and114C include respective contact surfaces116A,116B,116C and non-contact surfaces118A,118B, and118C. Lobes114D,114E, and114F include respective contact surfaces116D,116E, and116F and respective non-contact surfaces118D,118E, and118F. Contact surfaces116A-116F and non-contact surfaces118A-118F are discussed in greater detail below. In some examples, attachment root100can include pressure side bevel120and suction side bevel122(not shown), which are discussed in greater detail below.

FIG.3is a plan view of attachment root100taken along section A-A inFIG.2. As shown, serration profile102extends between leading edge end face104and trailing edge end face106along symmetry plane108. Symmetry plane108forms bearing angle A1relative to centerline axis12of gas turbine engine10. Bearing angle A1may range from zero degrees (i.e., no bearing angle) to a non-zero, positive angle. In some examples, bearing angle A1can be greater than zero degrees and less than or equal to ten degrees. For instance, bearing angle A1equals ten degrees in the depicted example. Leading edge end face104and trailing edge end face106are parallel while edges of serration profile102extend parallel to symmetry plane108such that the projected view of attachment root100forms a rhombus characterized by obtuse included angles α and acute included angles β. Pressure side bevel120, if present, is formed at the intersection of pressure side serration profile110and leading edge end face104(i.e., adjacent to obtuse included angle α). Likewise, suction side bevel118is formed at the intersection of suction side serration profile112and trailing edge end face106when attachment root100includes leading edge bevel118. Pressure side bevel120and suction side bevel122are parallel and form relief angle B1with respect to centerline axis12of gas turbine engine10. The profile of pressure side bevel120is identical to pressure side profile110, and the profile of suction side bevel122is identical to suction side profile112. The depth of pressure side bevel120and suction side bevel122can be defined by perpendicular distance D measured from leading edge face104or trailing edge end face106. In some examples, distance D is less than or equal to eight percent of a perpendicular distance from leading edge end face104and trailing edge end face106.

Bearing angle A1and relief angle B1can be expressed by plane angle A2and bevel angle B2, respectively, taken relative to leading edge end face104or relative to trailing edge face106. Plane angle A2and bevel angle B2are adjacent angles to bearing angle A1and relief angle B1and, accordingly, can be used to define features of attachment root100expressed by bearing angle A1and relief angle B1. For instance, plane angle A2equals ninety degrees minus bearing angle A1. Accordingly, plane angle A2can be equal to ninety degrees (i.e., no bearing angle) or a nonzero angle less than ninety degrees and greater than zero degrees. In some instances, plane angle A2is less than ninety degrees and greater than or equal to eighty degrees. Similarly, bevel angle B2equals ninety degrees minus relief angle B1. In some examples, the bevel angle B2equals ninety degrees (i.e., no bevel). In other examples, bevel angle B2is less than ninety degrees and greater than or equal to seventy degrees. In all examples, the bevel angle B2is always less than the plane angle A2. Whether relief angle B1or bevel angle B2are used, the length of the pressure side bevel120and suction side bevel122can be expressed by distance D described above.

Nonzero relief angles β1, or corresponding bevel angles β2, relieve peak contact pressure imposed on attachment root100at or near leading edge end face104and trailing edge end face106. Contact forces between attachment root100and the rotor to have a pressure component that is normal to symmetry plane108. For nonzero relief angles β1, centrifugal force reacted by attachment root100imposes moment M about point C of attachment root100, which is a point on symmetry plane108equidistant between leading edge end face104and trailing edge end face106. Pressure side bevel120and suction side bevel122remove regions of serration profile102and act to redistribute contact pressure along contact surfaces116A-116F, lowering peak contact pressure at or near leading edge end face104and at or near trailing edge end face106.

FIG.4is a cross section that depicts serration profile102of attachment root100taken along section B-B ofFIG.3, which is perpendicular to symmetry plane108. Pressure side profile110includes lobes114A,114B, and114C. Lobe114A is closest to platform70and airfoil68(i.e., the radially outermost lobe). Lobe114C is farthest from platform70and airfoil68and accordingly may be referred to as the radially innermost lobe. Lobe114B is positioned between lobe114A and lobe114C and may be referred to as an intermediate lobe. Suction side profile112includes lobes114D,114E, and114F, which correspond to lobes114A,114B, and114C, respectively. While features of serration profile102may be described with respect to pressure side profile110or suction side profile112, it shall be understood to apply to both pressure side profile110and suction side profile112.

Contact faces116A-116F of respective lobes114A-114F define respective contact angles123A-123F with respect to line124, which intersects serration profile102and is perpendicular to symmetry plane108. In the example shown, contact angles123A-123F are positive, nonzero, acute angles, each of contact angles123A-123F equal to forty-five degrees. Non-contact surfaces118A-118F define respective non-contact angles125A-125F with respect to line124. Non-contact angles125A-125F are positive, nonzero, acute angles. In some examples, each of non-contact angles125A-125F is greater than three degrees and less than or equal to fifty degrees.

Referring to pressure side profile110, non-contact angles125A,125B, and125C of lobes114A,114B, and114C increase with each successive lobe in the radially inward direction (i.e., in a direction moving away from platform70). In the depicted example, non-contact angle125A of lobe114A is less than non-contact angle125B of lobe118B. Similarly, non-contact angle125B of lobe114B is less than non-contact angle125C of lobe114C. In some examples, non-contact angle125A of lobe114A is greater than three degrees and less than twelve degrees. In the same example, non-contact angle125B of lobe114B is less than or equal to seventeen degrees and greater than or equal to twelve degrees, and non-contact angle125C of lobe114C is less than or equal to fifty degrees and greater than or equal to forty-five degrees. In yet other examples, non-contact angles125A,125B, and125C are equal to seven degrees, twelve degrees, and fifty degrees for lobes114A,114B, and114C, respectively.

Airfoils of gas turbine engine10experience centrifugal forces from rotation about centerline axis12during operation of gas turbine engine. Contact forces between attachment root100and the rotor impose a bending moment on each lobe114(e.g., lobes114A-114F) of serration profile102. As shown inFIG.4, tensile stress zones154are created at the inboard or proximal ends of lobes114A-114F on the contact surfaces116A-116F, and compressive stress zones156are created at the inboard or proximal end of lobes114A-114F on the non-contact surfaces118A-118F. By increasing the non-contact angles125A,125B, and125C of respective lobes114A,114B, and114C greater than three degrees, peak compressive stresses in zones156are reduced. Especially when combined with pressure side bevel120and suction side bevel122, serration profiles102in which non-contact angles125A,125B, and125C are greater than three degrees or have progressively increasing non-contact angles125A,125B, and125C in the radially inward direction can withstand higher compressive stresses from centrifugal loading. Compressive stress capacity is particularly relevant in high temperature operation, such as experienced by blades of high-pressure turbine34.

Discussion of Possible Embodiments

Attachment Root

An attachment root according to an example embodiment of this disclosure includes, among other possible things, a serration profile and a first lobe define relative to a plane and a line. The plane bisects the serration profile, and the serration profile is symmetric about the plane. The line intersects the serration profile that is normal to the plane. The first lobe is spaced from the plane. The first lobe includes a first contact surface and a first non-contact surface. The first contact surface defining a first acute angle between the first contact surface and the line. The first acute angle equal forty-five degrees. The first non-contact surface defines a second acute angle between the first non-contact surface and the line. The second acute angle is greater than three degrees.

The attachment root of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components.

A further embodiment of the foregoing attachment root can further include a second lobe of the serration profile.

A further embodiment of any of the foregoing attachment roots, wherein the second lobe can include a second contact surface defining a third acute angle between the second contact surface the line.

A further embodiment of any of the foregoing attachment roots, wherein the third acute angle can equal forty-five degrees.

A further embodiment of any of the foregoing attachment roots, wherein the second lobe can include a second non-contact surface defining a fourth acute angle between the second non-contact surface and the line.

A further embodiment of any of the foregoing attachment roots, wherein the fourth acute angle can be greater than the first acute angle.

A further embodiment of any of the foregoing attachment roots can further include a third lobe of the serration profile.

A further embodiment of any of the foregoing attachment roots, wherein the third lobe can include a third contact surface defining a fifth acute angle between the third contact surface and the line.

A further embodiment of any of the foregoing attachment roots, wherein the fifth acute angle can equal forty-five degrees.

A further embodiment of any of the foregoing attachment roots, wherein the third lobe can include a third non-contact surface defining a sixth acute angle between the third non-contact surface and the line.

A further embodiment of any of the foregoing attachment roots, wherein the sixth acute angle can be greater than forth-five degrees.

A further embodiment of any of the foregoing attachment roots, wherein the second acute angle can be at least seven degrees.

A further embodiment of any of the foregoing attachment roots, wherein the second acute angle can be less than twelve degrees.

A further embodiment of any of the foregoing attachment roots, wherein the fourth acute angle can be at least twelve degrees.

A further embodiment of any of the foregoing attachment roots, wherein the fourth acute angle can be less than seventeen degrees.

A further embodiment of any of the foregoing attachment roots can further include a first end face and a second end face. The serration profile extends from the first end face to the second end face.

A further embodiment of any of the foregoing attachment roots, wherein the plane can define a plane angle with the first end face that is greater than or equal to eighty degrees and less than ninety degrees.

A further embodiment of any of the foregoing attachment roots can further include a first bevel and a second bevel. The first bevel is located at the intersection of the serration profile and the first end face. The second bevel is located at the intersection of the serration profile and the second end face parallel that is parallel to the first bevel.

A further embodiment of any of the foregoing attachment roots, wherein the first bevel can define a bevel angle with the first end face greater than or equal to seventy degrees and less than or equal to seventy-five degrees.

A further embodiment of any of the foregoing attachment roots, wherein the plane extends between the first bevel and the second bevel.

Rotor Blade

A rotor blade according to an example embodiment of this disclosure includes, among other possible things, a platform, an airfoil, and an attachment root. The airfoil extends from the platform in a spanwise direction to a tip and in a chordwise direction from a leading edge to a trailing edge. The attachment root extends from the platform opposite the airfoil. The attachment root includes a serration profile and a first lobe defined relative to a plane and a line. The plane bisects the serration profile, and the serration profile is symmetric about the plane. The line intersects the serration profile that is normal to the plane. The first lobe is spaced from the plane. The first lobe includes a first contact surface and a first non-contact surface. The first contact surface defining a first acute angle between the first contact surface and the line. The first acute angle equal forty-five degrees. The first non-contact surface defines a second acute angle between the first non-contact surface and the line. The second acute angle is greater than three degrees.

A further embodiment of the foregoing rotor blade, wherein the attachment root can include a second lobe of the serration profile.

A further embodiment of any of the foregoing rotor blades, wherein the second lobe can include a second contact surface defining a third acute angle between the second contact surface the line.

A further embodiment of any of the foregoing rotor blades, wherein the third acute angle can equal forty-five degrees.

A further embodiment of any of the foregoing rotor blades, wherein the second lobe can include a second non-contact surface defining a fourth acute angle between the second non-contact surface and the line.

A further embodiment of any of the foregoing rotor blades, wherein the fourth acute angle can be greater than the first acute angle.

A further embodiment of any of the foregoing rotor blades, wherein the attachment root can include a third lobe of the serration profile.

A further embodiment of any of the foregoing rotor blades, wherein the third lobe can include a third contact surface defining a fifth acute angle between the third contact surface and the line.

A further embodiment of any of the foregoing rotor blades, wherein the fifth acute angle can equal forty-five degrees.

A further embodiment of any of the foregoing rotor blades, wherein the third lobe can include a third non-contact surface defining a sixth acute angle between the third non-contact surface and the line.

A further embodiment of any of the foregoing rotor blades, wherein the sixth acute angle can be greater than forth-five degrees.

A further embodiment of any of the foregoing rotor blades, wherein the second acute angle can be at least seven degrees.

A further embodiment of any of the foregoing rotor blades, wherein the second acute angle can be less than twelve degrees.

A further embodiment of any of the foregoing rotor blades, wherein the fourth acute angle can be at least twelve degrees.

A further embodiment of any of the foregoing rotor blades, wherein the fourth acute angle can be less than seventeen degrees.

A further embodiment of any of the foregoing rotor blades, wherein the attachment root can include a first end face and a second end face. The serration profile extends from the first end face to the second end face.

A further embodiment of any of the foregoing rotor blades, wherein the plane can define a plane angle with the first end face that is greater than or equal to eighty degrees and less than ninety degrees.

A further embodiment of any of the foregoing rotor blades, wherein the attachment root can include a first bevel and a second bevel. The first bevel is located at the intersection of the serration profile and the first end face. The second bevel is located at the intersection of the serration profile and the second end face parallel that is parallel to the first bevel.

A further embodiment of any of the foregoing rotor blades, wherein the first bevel can define a bevel angle with the first end face greater than or equal to seventy degrees and less than or equal to seventy-five degrees.

A further embodiment of any of the foregoing rotor blades, wherein the plane extends between the first bevel and the second bevel.

A high-pressure turbine according to an example embodiment of this disclosure includes, among other possible things, a rotor, an airfoil, and an attachment root. The attachment root couples the airfoil to the rotor. The attachment root includes a serration profile and a first lobe defined relative to a plane and a line. The plane bisects the serration profile, and the serration profile is symmetric about the plane. The line intersects the serration profile that is normal to the plane. The first lobe is spaced from the plane. The first lobe includes a first contact surface and a first non-contact surface. The first contact surface defining a first acute angle between the first contact surface and the line. The first acute angle equal forty-five degrees. The first non-contact surface defines a second acute angle between the first non-contact surface and the line. The second acute angle is greater than three degrees.

The high-pressure turbine of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components.

A further embodiment of the foregoing high-pressure turbine, wherein the attachment root can include a second lobe of the serration profile.

A further embodiment of any of the foregoing high-pressure turbines, wherein the second lobe can include a second contact surface defining a third acute angle between the second contact surface the line.

A further embodiment of any of the foregoing high-pressure turbines, wherein the third acute angle can equal forty-five degrees.

A further embodiment of any of the foregoing high-pressure turbines, wherein the second lobe can include a second non-contact surface defining a fourth acute angle between the second non-contact surface and the line.

A further embodiment of any of the foregoing high-pressure turbines, wherein the fourth acute angle can be greater than the first acute angle.

A further embodiment of any of the foregoing high-pressure turbines, wherein the attachment root can include a third lobe of the serration profile.

A further embodiment of any of the foregoing high-pressure turbines, wherein the third lobe can include a third contact surface defining a fifth acute angle between the third contact surface and the line.

A further embodiment of any of the foregoing high-pressure turbines, wherein the fifth acute angle can equal forty-five degrees.

A further embodiment of any of the foregoing high-pressure turbines, wherein the third lobe can include a third non-contact surface defining a sixth acute angle between the third non-contact surface and the line.

A further embodiment of any of the foregoing high-pressure turbines, wherein the sixth acute angle can be greater than forth-five degrees.

A further embodiment of any of the foregoing high-pressure turbines, wherein the second acute angle can be at least seven degrees.

A further embodiment of any of the foregoing high-pressure turbines, wherein the second acute angle can be less than twelve degrees.

A further embodiment of any of the foregoing high-pressure turbines, wherein the fourth acute angle can be at least twelve degrees.

A further embodiment of any of the foregoing high-pressure turbines, wherein the fourth acute angle can be less than seventeen degrees.

A further embodiment of any of the foregoing high-pressure turbines, wherein the attachment root can include a first end face and a second end face. The serration profile extends from the first end face to the second end face.

A further embodiment of any of the foregoing high-pressure turbines, wherein the plane can define a plane angle with the first end face that is greater than or equal to eighty degrees and less than ninety degrees.

A further embodiment of any of the foregoing high-pressure turbines, wherein the attachment root can include a first bevel and a second bevel. The first bevel is located at the intersection of the serration profile and the first end face. The second bevel is located at the intersection of the serration profile and the second end face parallel that is parallel to the first bevel.

A further embodiment of any of the foregoing high-pressure turbines, wherein the first bevel can define a bevel angle with the first end face greater than or equal to seventy degrees and less than or equal to seventy-five degrees.

A further embodiment of any of the foregoing high-pressure turbines, wherein the plane extends between the first bevel and the second bevel.