US20120141259A1

US20120141259A1 - Blade segment and fluid flow machine

Info

Publication number: US20120141259A1
Application number: US13/310,939
Authority: US
Inventors: Alexander Boeck
Original assignee: MTU Aero Engines GmbH
Current assignee: MTU Aero Engines AG
Priority date: 2010-12-03
Filing date: 2011-12-05
Publication date: 2012-06-07
Also published as: EP2460979B1; ES2401350T3; EP2460979A1

Abstract

A blade segment (1) for a fluid flow machine (2), including: a first blade (3); a first shroud (7) attached to the tip of the first blade (3) and having a contact face (11); a second blade (3′); and a second shroud (7′) attached to the tip of the second blade (3′) and having a counter-contact face (12′) for engagement with the contact face (11) of the first shroud (7) in the radial direction (R) in such a way that a friction lock (RF) can be created between the contact face (11) and the counter-contact face (12′).

Description

This claims the benefit of European Patent Application EP 101 93 687.0, filed Dec. 3, 2010 and hereby incorporated by reference herein.
The present invention relates to a blade segment and to a fluid flow machine.

BACKGROUND

It is known, for example, from Japanese Patent Publication JP 2007154695 A, to torsionally bias turbine blades. This has a favorable effect on the damping behavior of the turbine blades during operation thereof. The torsional bias is maintained by the turbine blades each being provided on their tips with shrouds that are tied together by Z-shaped interlock notches, which are also referred to as Z-shrouds.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an alternative or complementary approach for coupling at least two blades of a blade segment so as to achieve a favorable damping behavior.
The present invention provides a blade segment for a fluid flow machine, including: a first blade; a first shroud attached to the tip of the first blade and having a contact face; a second blade; and a second shroud attached to the tip of the second blade and having a counter-contact face for engagement with the contact face of the first shroud in the radial direction in such a way that a friction lock can be created between the contact face and the counter-contact face.
Also provided is a fluid flow machine, in particular a turbomachine, having the blade segment according to the present invention.
The present invention can arrange the shrouds of the respective blades in the manner of roof tiles so that the shrouds rest against each other in the radial direction in such a way that a friction lock is created between mutually overlapping shrouds at least during operation of the blade segment (or also when it is at rest). The friction lock causes the shrouds, and respectively the blades, to be coupled to each other, which is favorable in terms of damping behavior.
Advantageous embodiments will become apparent from the dependent claims.
The resting of the contact face against the counter-contact face in the radial direction is understood herein to mean that a vector perpendicular to the plane in which the contact face and the counter-contact face rest against each other has at least one radial component.
“Circumferential direction” is understood herein to mean a direction along a circle whose centerline coincides with the axis of rotation of the blade segment in the fluid flow machine. “Radial” is understood herein to refer to a direction perpendicular to the axis of rotation of the blade segment in the fluid flow machine. “Axial” is understood herein to refer to a direction along the axis of rotation of the blade segment in the fluid flow machine.
In one embodiment of the blade segment of the present invention, the center of gravity of the first shroud is spaced in the circumferential direction from a centerline of the first blade in such a way that during operation of the blade segment, the first blade bends under the action of the centrifugal forces so as to create the friction lock between the contact face and the counter-contact face. Thus, during operation of the blade segment, a bending moment is produced under the action of the centrifugal forces, said bending moment tending to tilt the blade together with the shroud in the circumferential direction. However, such tilting is prevented by the contact face of the first shroud and the counter-contact face of the second shroud. In doing so, the contact face presses radially against the counter-contact face in such a way that a friction lock is created between the contact face and the counter-contact face.
“Centerline” is understood herein to mean the axis of the first blade that is positioned in such a way that if the center of gravity of the first shroud coincided with this axis, no or only an insignificant bending moment would be introduced from the shroud into the first blade. This applies similarly to the centerline of the second blade.
In one embodiment of the blade segment of the present invention, the contact face of the first shroud and/or the counter-contact face of the second shroud is/are configured with an interference dimension in the radial direction for bending the first blade about its root point in the circumferential direction to thereby create the friction lock between the contact face and the counter-contact face. The term “interference dimension” is understood to mean that the contact face and/or the counter-contact face is/are thickened in the radial direction so as to produce a contact pressure and, thus, a friction lock between the contact face and the counter-contact face. This embodiment may be provided alternatively or in addition to the previous embodiment, where the center of gravity of the first shroud is spaced in the circumferential direction from a centerline of the first blade.
In another embodiment of the blade segment of the present invention, the friction lock is adapted to produce a reaction torque in a direction about the centerline of the first and second blades. This is favorable for the purpose of compensating for the tendency of radially twisted rotor blade airfoils to untwist.
In a further embodiment of the blade segment of the present invention, the first and/or second blade has/have a basic tilt in the axial direction, which is defined by a basic tilt axis; the contact face and the counter-contact face being arranged obliquely, in particular at an angle between 45 and 135 degrees, with respect to the basic tilt axis in the axial direction of the first and second blades. The basic tilt is also called “lean”. The basic tilt is usually used to allow the gas forces, which occur during the operation of the fluid flow machine and produce corresponding bending moments on the blades, to be substantially compensated for, at least in certain operating ranges of the fluid flow machine. Depending on the design of the fluid flow machine, the basic tilt is typically between 0 and 2 degrees. The oblique arrangement of the contact face and the counter-contact face results in a twisting moment being produced around the centerline of a respective blade, said twisting moment being capable of counteracting the untwisting of the respective blade. Here, two mirror-image configurations are possible. This twisting moment increases with the force with which the contact face presses against the counter-contact face.
In another embodiment of the blade segment of the present invention, the contact and counter-contact faces have an engagement element and a receiving element which engage with one another in the circumferential direction. In this manner, the first and second shrouds are supported on one another even better; i.e., in addition to the friction lock. In particular, this embodiment prevents untwisting of the blades when no friction lock is created (for example, when in the embodiment where the center of gravity of the shroud is offset in the circumferential direction, the blade segment is at rest.)
In a further embodiment of the blade segment of the present invention, the first and/or second blade is/are torsionally biased. When the blades are in engagement with one another via the aforedescribed engagement and receiving elements, it is also possible, for example, to torsionally bias the blades such that sufficient coupling between the blades is achieved even at low speeds, which results in a favorable damping behavior. At low speeds, the friction lock resulting from the offset of the center of gravity of a respective shroud may not suffice to achieve such a sufficient coupling between the shrouds.
In a further embodiment of the blade segment of the present invention, the first and second blades are rotor blades.
In yet another embodiment of the blade segment of the present invention, the first and second blades are made of a strongly creeping material. “Strongly creeping materials” are understood to be materials which creep more strongly than current nickel materials.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in more detail below with reference to exemplary embodiments and the accompanying drawings, in which:

FIG. 1 is a schematic view, looking in the axial direction, of a blade segment according to an exemplary embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1;

FIG. 3 is a cross-sectional view taken along line B-B in FIG. 1;

FIG. 4 is a perspective view of the blade segment of FIG. 1, seen obliquely from below; and

FIG. 5 is a schematic view, looking in the axial direction, of a blade segment according to another exemplary embodiment of the present invention.

DETAILED DESCRIPTION

In the Figures, like reference numerals designate like or functionally equivalent components, unless stated otherwise.
FIG. 1 schematically shows a blade segment 1 according to an exemplary embodiment of the present invention, looking in the axial direction.
Blade segment 1 forms part of a fluid flow machine, in particular a turbomachine, which is generally designated by reference numeral 2. The turbomachine is preferably an aircraft engine.
Blade segment 1 includes two blades 3 and 3′. Blades 3 and 3′ are preferably rotor blades. Blades 3 and 3′ are mounted by their respective roots 4, 4′ in a rotor 5 (see FIG. 4), for example by means of a fir-tree connection. Rotor 5 rotates about an axis 6, the blades 3, 3′ interacting with a fluid passing through fluid flow machine 2. The terms of “in the circumferential direction”, “in the radial direction” and “in the axial direction” will be used below with reference to axis 6. It should be noted that in reality, axis 6 is significantly further away from blades 3, 3′ than is shown in FIG. 1.
At the radially outer periphery, blades 3, 3′ have shrouds 7, 7′ attached to their respective tips. Blades 3, 3′ and their roots 4, 4′ and shrouds 7, 7′ are arranged adjacent to each other in circumferential direction U, preferably forming a closed ring. The partial view of FIG. 1 shows only two such blades 3, 3′. Shrouds 7, 7′ are placed on each other in the manner of roof tiles in the axial direction.
Shrouds 7, 7′ each have a center of gravity S, respectively S′, which is spaced by a distance D, D′ from a centerline M, M′, of a blade 3, 3′, respectively. Centerlines M, M′ pass through axis 6, which cannot be seen in FIG. 1 because of the highly schematic nature of the representation. Further, centerline M passes through a center of gravity SB of blade 3 (see FIG. 2). Center of gravity SB is the center of gravity of the airfoil of blade 3. This applies similarly to centerline M′ of blade 3′.
A respective shroud 7, 7′ has a contact face 11, 11′ and an opposite counter-contact face 12, 12′. Contact faces 11, 11′ and counter-contact faces 12, 12′ may be formed on respective ends of shrouds 7, 7′ in circumferential direction U.
When blade segment 1 is at rest or rotates at low speed, there are no or almost no centrifugal forces acting on blades 3, 3′ and their shrouds 7, 7′. Blades 3, 3′ and their shrouds 7, 7′ are then in the position that is shown in FIG. 1 in dashed lines for left blade 3 only. As the speed of blade segment 1 increases, a bending moment of shroud 7 about a root point F of the blade increases as well. This is because center of gravity S is spaced by distance D from centerline M and center of gravity SB of blade 3. The resulting bending moment is denoted in FIG. 1 by BM. Bending moment BM causes blade 3 to tilt; i.e, bend, along with shroud 7 from its dashed line position to its solid line position in FIG. 1. Above a certain speed, contact face 11 comes into contact with counter-contact face 12′ in radial direction R, which means that a vector 9 (see FIG. 3) perpendicular to plane 10, in which contact face 11 and counter-contact face 12′ rest against each other, has at least one component in radial direction R. As a result, a friction lock is created between contact face 11 and counter-contact face 12′. From this point on, blade 3 is frictionally coupled to blade 3′, which has a favorable effect on the damping behavior thereof.
FIG. 2 shows a cross-sectional view taken along line A-A in FIG. 1.
In FIG. 2, it can be seen that friction lock RF between contact face 11 and counter-contact face 12′ can be created in such a way that it produces a reaction torque TM about centerline M, which prevents blade 3 from oscillating about the centerline in an undesired manner.
FIG. 3 shows a cross-sectional view taken along line B-B in FIG. 1.
As can be seen from FIG. 3, contact face 11 and counter-contact face 12′ can be arranged obliquely at an angle W′ of, for example, 93 degrees with respect to a basic tilt axis G′. The term “obliquely” refers to an angle W′ not equal to 90 degrees and preferably between 45 and 135 degrees. Basic tilt axis G′ of blade 3′ may be tilted, for example, 1 degree in the direction of axis of rotation 6.
Under the action of centrifugal forces and a corresponding untwisting of blade 3, a contact force AK is produced between contact face 11 and counter-contact face 12′. Due to the oblique arrangement of contact face 11 and counter-contact face 12′, contact force AK results in a reaction force RK1 and a reaction force RK2 acting on blade 3. RK2 acts along basic tilt axis G′, and RK1 acts perpendicular thereto.
This is also shown in FIG. 2. Here, it can be seen that RK1 produces an additional twisting moment TR about center of gravity SB and centerline M of blade 3, which counteracts untwisting E of blade 3.
FIG. 4 shows the blade segment of FIG. 1 in an oblique perspective view from below.
As illustrated in FIG. 4, shrouds 7, 7′ are preferably provided, at their opposite ends, with engagement elements 13, 13′ and receiving elements 14, 14′ in the region of contact faces 11, 11′ and counter-contact faces 12, 12′. Engagement element 13′ of shroud 7′ engages with receiving element 14 of shroud 7 in the circumferential direction. This produces an interlock in the axial direction, which prevents blades 3, 3′ from untwisting when blade segment 1 is at rest or rotates at low speed, which is when friction lock RF is still too weak to couple blades 3, 3′ to one another.
FIG. 5 schematically shows a blade segment 1 according to another exemplary embodiment of the present invention, looking in the axial direction.
Blade segment 1 differs from that shown in FIGS. 1 through 4 only in the manner in which friction lock RF is created. Apart from that, the explanations given for FIGS. 1 through 4 apply equally to the blade segment shown in FIG. 5.
In blade segment 1 of FIG. 5, contact face 11 of shroud 7 is configured with an interference dimension P in radial direction R for bending first blade 3 about its root point F in circumferential direction U to thereby create friction lock RF between contact face 11 and counter-contact face 12′. Of course, the same applies to the other blades of the blade segment.
In the exemplary embodiment of FIG. 5, friction lock RF is not, or only to an insignificant extent, dependent on the speed of rotation.
The embodiments shown in FIGS. 1 through 4 and in FIG. 5 may also be combined with one another.
Although the present invention has been described above with reference to preferred exemplary embodiments, it is not limited thereto but can be modified in many ways.

LIST OF REFERENCE NUMERALS

1 blade segment
2 fluid flow machine
3 blade
3′ blade
4 root
4′ root
5 rotor
6 axis of rotation
7 shroud
7′ shroud
9 vector
10 plane
11 contact face
11′ contact face
12 counter-contact face
12′ counter-contact face
13 engagement element
13′ engagement element
14 receiving element
14′ receiving element
D distance
F root point
G′ basic tilt axis
M centerline
M′ centerline
R radial direction
S center of gravity
S′ center of gravity
U circumferential direction
AK contact force
BM bending moment
RF frictional force or lock
RK1 reaction force
RK2 reaction force
SB center of gravity of the blade
TM reaction torque
TR twisting moment
E untwisting

Claims

1. A blade segment for a fluid flow machine comprising:

a first blade;

a first shroud attached to a tip of the first blade and having a contact face;

a second blade; and

a second shroud attached to a second tip of the second blade and having a counter-contact face for engagement with the contact face of the first shroud in a radial direction to permit creation of a friction lock between the contact face and the counter-contact face.

2. The blade segment as recited in claim 1 wherein a center of gravity of the first shroud is spaced in a circumferential direction from a centerline of the first blade, and during operation of the blade segment, the first blade bending under action of centrifugal forces to create the friction lock between the contact face and the counter-contact face.

3. The blade segment as recited in claim 1 wherein at least one of the contact face of the first shroud and the counter-contact face of the second shroud is configured with an interference dimension in the radial direction for bending the first blade about a root point in a circumferential direction to create the friction lock between the contact face and the counter-contact face.

4. The blade segment as recited in claim 1 wherein the friction lock is adapted to produce a reaction torque in a direction about a centerline of at least one of the first and second blades.

5. The blade segment as recited in claim 1 wherein at least one of the first and second blades has a basic tilt in an axial direction defined by a basic tilt axis, the contact face and the counter-contact face being arranged obliquely with respect to the basic tilt axis.

6. The blade segment as recited in claim 5 wherein the contact face and counter-contact face are arrange at an angle between 45 and 135 degrees to the basic tilt axis.

7. The blade segment as recited in claim 1 wherein the contact face and the counter-contact face have an engagement element and a receiving element engaging one another in a circumferential direction.

8. The blade segment as recited in claim 1 wherein at least one of the first and second blades is torsionally biased.

9. The blade segment as recited in claim 1 wherein the first and second blades are rotor blades.

10. The blade segment as recited in claim 1 wherein at least one of the first and second blades is made of a strongly creeping material.

11. A fluid flow machine comprising the blade segment as recited in claim 1.

12. A turbine comprising the blade segment as recited in claim 1.