US3649133A

US3649133A - Rotor blade coupler arrangement

Info

Publication number: US3649133A
Application number: US71177A
Authority: US
Inventors: John T Wagner
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1970-09-10
Filing date: 1970-09-10
Publication date: 1972-03-14
Anticipated expiration: 1989-03-14
Also published as: JPS4946647B1

Abstract

Rotor blade vibrations in an axial flow elastic fluid machine are controlled by mechanically connecting all the blades in an annular row of blades. The blades are connected by means of links secured to the upstream face and the downstream face of each blade by rivets projecting from the faces. Each link is connected to two blades to alternately connect the blades in pairs, but the links are so staggered that each blade is connected to the adjacent blade on one side by a link on the upstream face and to the adjacent blade on the other side by a link on the downstream face, thereby forming a chain completely around the row of blades.

Description

[ 5] Mar. 14, 1972 Unite tates atent Wagner [54] ROTOR BLADE COUPLER ARRANGEMENT [72] Inventor: John T. Wagner, Lansdowne, Pa. [73] Assignee: Westinghouse Electric Corporation, Pittsburgh, Pa.

[22] Filed: Sept. 10, 1970 [2]] Appl. No.: 71,177

[52] U.S.Cl ..4l6/l90,4l6/l94,416/196, 4l6/500 [51] Int. Cl ..F0ld 5/10, FOld 5/22 [58] Field of Search ..416/l90-196, 500

[56] References Cited UNITED STATES PATENTS 3,367,630 2/1968 Saunders ..416/19O Att0meyA. T. Stratton, F. P. Lyle and F. Cristiano, Jr.

[5 7] ABSTRACT Rotor blade vibrations in an axial flow elastic fluid machine are controlled by mechanically connecting all the blades in an annular row of blades. The blades are connected by means of links secured to the upstream face and the downstream face of each blade by rivets projecting from the faces. Each link is connected to two blades to alternately connect the blades in pairs, but the links are so staggered that each blade is connected to the adjacent blade on one side by a link on the upstream face and to the adjacent blade on the other side by a link on the downstream face, thereby forming a chain completely around the row of blades 16 Claims, 9 Drawing Figures I t' lz Patented March 14, 1972 2 Sheets-Sheet l FIG.

INVENTOR John T. Wagner WITNESSES M) 941% Patented March 14, 1972 2 Sheets-Sheet 2 v m ma MY NM Am FIG.

ROTOR BLADE COUPLER ARRANGEMENT BACKGROUND OF THE INVENTION This invention relates, generally, to axial flow elastic fluid machines, and, more particularly, to a coupler arrangement for controlling vibrational stresses in the rotor blades of machines, such as steam or gas turbines.

Heretofore, blade shrouds which span large circumferential arcs have been utilized in turbines of certain types to control blade vibrations. However, the danger of excessive thermal stresses which exists when shrouds of conventional and other proposed structures are used for long spans has limited this practice.

In systems with relatively weak coupling, which have also been utilized in turbomachines, differences in the natural frequencies and damping of blades can cause high amplitudes in some blades. With stronger coupling, damping anywhere in the system absorbs energy from blades with low damping and prevents unusually high amplitudes. This amplitude equalization effect is particularly advantageous in partial admission stages, where the amplitude of the blade or a lashed group of blades entering or leaving the admission are is ordinarily much greater than the average amplitude.

In the structure disclosed in US. Pat. No. 3,367,629, issued Feb. 6, I968 to A. J. Partington and assigned to the same assignee as this invention, the outer ends of all the blades of an annular row of turbine rotor blades are attached to a continuously connected segmented shroud which comprises two annular concentric layers of staggered arcuate segments alternately connecting the blades in pairs. Each blade is connected to the adjacent blade on one side by a segment in the outer layer and to the adjacent blade on the other side by a segment in the inner layer of the two concentric layers. Each blade has an integrally formed rivet which extends radially through the two layers to secure the segments in position. The patented structure requires shrouding the blades and it can result in excessive thermal stresses since radial expansion can be accommodated only by stretching the segments.

The rotor blade coupler arrangement herein disclosed produces the desired effects without danger of excessive thermal stresses. Furthermore, it reduces vibratory amplitudes by increasing system damping without danger of severe wear and eventual failure that exists with frictional damping devices which incorporate loose parts. Also, the present coupler arrangement facilitates improved scaling to control leakage of the motive fluid past the blades as there is no interference between the coupler members and the seal members.

Vibratory mode shapes (deflection patterns) are altered in such a manner that excitation by the flow of some of the lowest frequency modes, which cause the most trouble, becomes difficult or impossible. In any one of the lowest frequency modes, all blades resonate at the same frequency despite differences in dimensions and material properties. This facilitates the tuning of the system to avoid resonance at usual operating speeds. Thus, it is possible to tune short, stiff blades where slight differences in root geometry would otherwise cause excessive frequency differences.

SUMMARY OF THE INVENTION In accordance with one embodiment of the invention, each blade in an annular row of turbine rotor blades has an integral cover or shroud at the outer end of the vane portion of the blade. All of the blades in the row are mechanically connected by means of annular rows of links secured to the upstream face and the downstream face of each shroud by fastening means, such as rivets, projecting generally axially from the faces. Each link is connected to two blades to alternately connect the blades in pairs, but the links are so staggered that each blade is connected to the adjacent blade on one side by a link on the upstream face and to the adjacent blade on the other side by a link on the downstream face. In this manner, the shrouds and the links form a continuous chain completely around the row of blades which acts as a continuous shroud and provides the desired coupling. The fundamental tangential mode cannot be excited in such a system by the flow in a turbine and the excitation of higher frequency modes is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the nature and objects of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a view, in plan, of a portion ofa turbine rotor having a blade coupler arrangement constructed in accordance with the present invention;

FIG. 2 is a view, in elevation, of the portion of the rotor shown in FIG. 1;

FIG. 3 is a view, partly in elevation and partly in section, taken along the line III-III in FIG. 2;

FIG. 4 is a view, similar to FIG. 2, of a portion of a turbine rotor showing a second embodiment;

FIG. 5 is a view, partly in elevation and partly in section, taken along the line V-V in FIG. 4;

FIG. 6 is a view, similar to FIG. 3, of a rotor blade and coupler arrangement showing a third embodiment;

FIG. 7 is a view, similar to FIG. 1, but showing a fourth embodiment in which a modified arrangement is provided for attaching the links of the blade coupler;

FIG. 8 is a view, similar to FIG. 1, ofa fifth embodiment of a blade shroud and coupler arrangement; and

FIG. 9 is a view, partly in elevation and partly in section, taken along the line IX-IX in FIG. 8.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to the drawings, particularly to FIGS. 1, 2 and 3, there is shown therein a portion of a turbine rotor 10 which includes an annular row of rotor blades 11 secured in a rotor (not shown) in a suitable manner for rotation about the central axis of the turbomachine. Each blade 11 has an integral cover or shroud 12 at the outer end of the vane portion of the blade. The turbine is of the axial flow type and the blades 11 are driven by energy extracted from an elastic motive fluid, such as steam, in a manner well known in the art.

In order to control vibration in the turbomachine blades 11, a blade coupler arrangement 13 is provided. The coupler arrangement 13 comprises an annular row of links 14 secured to the upstream face 15 of each shroud 12 and a similar row of links 14 secured to the downstream face 16 of each shroud. The links are secured by fastening means, such as rivets 17, formed integrally with the shrouds and projecting generally axially from the faces of the shrouds.

As shown more clearly in FIG. 3, the links 14 are rectangular in cross section and they are attached to the faces of the shrouds flatwise. Each link is connected to two blades to alternately connect the blades in pairs, but the links are so staggered that each blade is connected to the adjacent blade on one side by a link on the upstream face and to the adjacent blade on the other side by a link on the downstream face of the shroud. In this manner the shrouds and the links form a continuous chain completely around the row of blades which acts as a continuous shroud and provides the desired coupling. The fundamental tangential mode cannot be excited in such a system by the flow in a turbine and the excitation of higher frequency modes is reduced.

Thermal expansion is accommodated by twisting of the blades 11 and bending of the links 14 flatwise. Twisting of the blades is caused by a link on one side pushing in one direction and a link on the other side pushing in the opposite direction during expansion of the blade and coupler. Differences between the temperatures of the blades and the rotor cause the action. When the blades and shroud are hotter than the rotor, the shroud band expansion is restrained because of the rotor, causing the links to push. Expansion gaps 18 are provided between the shrouds 12 of the blades and similar gaps 19 are provided between the ends of the links in each annular row of links. The expansion gaps are opened or closed as the as sembly stretches or contracts in accordion fashion.

An additional advantage of the present coupler arrangement over conventional shrouds is that the rivet holes can be accurately sized and shaped. Installation of a conventional shroud requires oversize rivet holes and deformation of the shroud and sometimes the blade. This may result in radial misalignment and improper loading of the blade roots, particularly in stiff blades. This could be a factor in the vibratory failures that have been experienced with stiff blades having roots of the fir-tree type.

In the modification of the invention shown in FIGS. 4 and 5, the blades 11a are unshrouded and each blade has a root 21 of the fir-tree type slidably disposed in an axial groove in a rotor 22. Each blade has an extension 23 extending from the top of the root 21 to the bottom of a platform 24 having upstream faces and downstream faces to which links 14a are secured by means of rivets 17 projecting axially from the faces of the platform 24. Such a coupling arrangement is effective in the tangential modes, but less effective in axial modes. However, unshrouded and unlashed blades are likely to have only one axial mode which may be troublesome, while groups of blades connected by conventional shrouds or lashing wires have two or more such modes.

The links 14a can be extended inwardly toward the rotor 22 at least beyond the tops of the roots 21 to lock the blades in place, thereby eliminating other locking devices and forming passages 25 for any blade or rotor coolant. If necessary, the torsional flexibility of the root extension 23 can be increased by providing one or more slots 26 in the extension.

If the blades are too short to have the torsional flexibility required by the coupler arrangement shown in FIG. 1, blade twist can be accommodated by sliding of the root 21 in the rotor groove or by dividing the blade 11b lengthwise into two sections and utilizing a through rivet 17a to hold the pieces together as shown in FIG. 6. Such an assembly has an increased torsional flexibility and increased damping. In order to reduce the axial length of the structure, the links 14 can be mounted in recessed faces a and 16a in the upstream side and the downstream side, respectively, of the shroud portion 12 ofeach blade as also shown in FIG. 6. This recessed mounting arrangement for the links also reduces the possibility of slipping and pivoting of the links about round rivets. The recessed arrangement may also be used with the embodiment shown in FIG. 1.

As shown in FIG. 7, the distance between the two rivets 17 for each link can be increased to more than one blade pitch by moving the rivets toward the ends of the link. This minimizes the possibility of a complete thermal fatigue failure. This result can also be obtained by providing two or more layers of parallel-connected links 14 in each annular row of links as shown in FIG. 8.

lf the gaps 18a between blade shrouds or platforms cannot be parallel to the turbomachine axis, washers 28 having skewed faces can be utilized to facilitate riveting by keeping the rivet seats 29 on the upstream and downstream faces perpendicular to a common axis 30 which is parallel to the gaps 18a. This construction maintains maximum flexibility in the links and adds interfaces for frictional damping. With some loss of flexibility and damping, the seats 29 could be formed directly on the links.

As shown in FIG. 9, recesses 31 can be formed in the shroud 12a to provide a lightweight shroud structure suitable for long steam turbine exhaust blades. The use of a shroud having a relatively large angle 32 on its underside, as shown in FIG. 9, permits a compact and thermodynamically efficient machine.

The link members of the coupling arrangements herein described can be riveted by means of a machine with the blades in place. To rivet by hand when one face of the shroud or platform is inaccessible and the blade roots are of the straight fir-tree type with axial grooves, the blades can be installed with upstream and downstream faces reversed. The

links can then be riveted to the exposed face. The connected pairs of blades can then be removed and installed in the correct position. The links can then be riveted to the face then exposed. Another possibility is to utilize threaded fasteners instead of rivets to secure the links in position.

From the foregoing description it is now apparent that the invention provides a rotor blade coupler arrangement which produces strong vibratory coupling between the rotating blades in a row of blades, thereby controlling vibration in the blades. Thermal expansion is accommodated without causing excessive thermal stresses in the blades, and without loose parts subject to wear. The coupler arrangement is susceptible of many modifications and can be economically manufactured and installed in an axial flow elastic fluid machine.

I claim as my invention:

1. In an axial flow elastic fluid machine having a central axis, in combination,

an annular row of rotor blades each one of which has an upstream face and a downstream face,

fastening means projecting generally axially from said faces,

annular rows of links secured to said faces by the fastening means to mechanically connect all of the blades in the row of blades, and

each link being connected to two blades to alternately connect the blades in pairs.

2. The combination defined in claim 1, wherein each blade is connected to the adjacent blade on one side by a link on the upstream face and to the adjacent blade on the other side by a link on the downstream face.

3. The combination defined in claim 2, wherein the fastening means comprises rivets formed integrally with each blade.

4. The combination defined in claim 1, wherein each blade has an integral shroud portion at its outer end,

and

said upstream faces and downstream faces are on said shroud portions.

5. The combination defined in claim 4, wherein the links are generally rectangular in cross section and are secured to said faces flatwise.

6. The combination defined in claim 1, wherein each blade has a root portion at its inner end and a platform portion between the root portion and the outer end of the blade, and

said upstream faces and downstream faces are on said platform portions.

7. The combination defined in claim 6, wherein the links extend inwardly beyond the tops of the root portions.

8. The combination defined in claim 6, wherein each blade has an extension portion between the root portion and the platform portion, and

the links extend inwardly beyond the extension portion.

9. The combination defined in claim 8, wherein the extension portion has a radially extending slot therein.

10. The combination defined in claim 2, wherein each blade is divided lengthwise into two sections, and

the fastening means extends through the two sections to hold them together.

1 l. The combination defined in claim 5, wherein each link is secured by two rivets, and

the distance between said two rivets is greater than one blade pitch.

12. The combination defined in claim 1, wherein each row of links includes at least two layers of parallel-connected links.

13. The combination defined in claim 4, wherein expansion gaps are provided between adjacent shrouds and between the ends of the links in each row of links.

14. The combination defined in claim 13, wherein the expansion gaps between shrouds are not parallel to the machine axis, and

the fastening means on opposite sides of each shroud have a common axis parallel to the expansion gaps.

15. The combination defined in claim 14, wherein each shroud has recesses formed therein to provide a lightweight shroud structure. 16. The combination defined in claim 5, wherein the shroud faces have recesses therein, and 5 the links are mounted in said recesses.

Claims

1. In an axial flow elastic fluid machine having a central axis, in combination, an annular row of rotor blades each one of which has an upstream face and a downstream face, fastening means projecting generally axially from said faces, annular rows of links secured to said faces by the fastening means to mechanically connect all of the blades in the row of blades, and each link being connected to two blades to alternately connect the blades in pairs.

4. The combination defined in claim 1, wherein each blade has an integral shroud portion at its outer end, and said upstream faces and downstream faces are on said shroud portions.

5. The combination defined in claim 4, wherein the links are generally rectangular in cross-section and are secured to said faces flatwise.

6. The combination defined in claim 1, wherein each blade has a root portion at its inner end and a platform portion between the root portion and the outer end of the blade, and said upstream faces and downstream faces are on said platform portions.

8. The combination defined in claim 6, wherein each blade has an extension portion between the root portion and the platform portion, and the links extend inwardly beyond the extension portiOn.

10. The combination defined in claim 2, wherein each blade is divided lengthwise into two sections, and the fastening means extends through the two sections to hold them together.

11. The combination defined in claim 5, wherein each link is secured by two rivets, and the distance between said two rivets is greater than one blade pitch.

14. The combination defined in claim 13, wherein the expansion gaps between shrouds are not parallel to the machine axis, and the fastening means on opposite sides of each shroud have a common axis parallel to the expansion gaps.

15. The combination defined in claim 14, wherein each shroud has recesses formed therein to provide a lightweight shroud structure.

16. The combination defined in claim 5, wherein the shroud faces have recesses therein, and the links are mounted in said recesses.