Abstract:
A turbo-machine having a means for attaching the blade ring to the casing at a plurality of alternative radial positions to provide for a plurality of alternative clocking angles for a stage of stationary airfoils. The blade ring is provided with a plurality of notches that may selectively be aligned with a pin inserted through the casing. By rotating the blade ring so that a selected notch aligns with the pin, a selected clocking position may be achieved. Assembly with a different clocking angle is achieved by aligning the pin with a different notch. The notches may be provided at any location around the blade ring so long as they are separated by a radial distance which is a non-integer multiple of the segment angle.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to the field of turbo-machines, and in particular to an apparatus and method for clocking of a second stage of stationary vanes in relation to the position of a first stage of stationary vanes in a turbine engine. 
     BACKGROUND OF THE INVENTION 
     Turbo-machines are known to include rows or stages of stationary airfoils, commonly called vanes or stationary blades, inter-spaced between stages of rotating airfoils, commonly called blades. Turbo-machines are known to include an outer casing, a blade ring affixed to the casing, and a plurality of stationary blades affixed to the blade ring, as shown in U.S. Pat. No. 4,699,566, dated Oct. 13, 1987. As a working fluid passes through the turbine, a wake is formed in the working fluid by a first stage of vanes. This wake is known to pass through the following rotating stage of blades and on to the second stage of vanes. Similar interaction occurs between subsequent stages of the machine. 
     U.S. Pat. No. 5,486,091 dated Jan. 23, 1996, teaches that the relative positioning of two rows of vanes, also known as the clocking of the vanes, can affect the efficiency of a turbine engine. 
     The clocking effect is known to exist in various types of turbo-machines, including steam turbines, gas or combustion turbines and compressors. U.S. Pat. No. 5,681,142 dated Oct. 28, 1997, teaches that there exists a class of vibratory modes known as the clocking modes in the stator of a compressor. This patent teaches that there is a need to dampen and/or to minimize the magnitude of these clocking mode forces. 
     It is known to provide for the adjustment of the stationary blades of a gas turbine, as taught in U.S. Pat. No. 5,215,434 dated Jun. 1, 1993. That patent shows an apparatus for adjustment of the pitch of the vanes, i.e. the angle of attack of the airfoil relative to the direction of flow of the working fluid. It does not, however, teach or suggest an apparatus for adjusting the clocking of the stationary vanes. 
     The above mentioned U.S. Pat. Nos. 4,699,566; 5,486,091; 5,681,142; and 5,215,434 are incorporated by reference herein. 
     As turbine and compressor designs advance, there is a need to ensure that the optimum clocking is achieved in each machine in order to maximize the overall efficiency of the machine. Further, there is a need to adjust the clocking of stationary vanes in a machine subsequent to the initial operation of the machine in order to affect the efficiency and/or the vibration characteristics of the machine. 
     SUMMARY 
     Accordingly, it is an object of this invention to provide a turbo-machine having a mechanism to facilitate the adjustment of the clocking of the rows of stationary vanes. It is a further object of this invention to provide a method of assembling a turbo-machine that provides for the clocking of the rows of stationary vanes. 
     In order to achieve the above and other objects of the invention, a turbo-machine according to one aspect of this invention includes a casing that defines a gas flow path therethrough; a blade ring; a means for attaching the blade ring to the casing within the gas flow path; wherein the means for attaching further comprises a means for attaching the blade ring to the casing in a plurality of alternative radial positions. 
     In accordance with another aspect of this invention, a method is provided for assembling a turbo-machine having a casing defining a gas flow path, a blade ring disposed within the gas flow path and attached to the casing by a pin passing through the casing and contacting the blade ring, the method comprising the steps of: calculating a desired clocking angle for the blade ring; providing a first notch in the blade ring at a first radial location corresponding to the desired clocking angle; providing a second notch in the blade ring, the radial location of the second notch corresponding to a second clocking angle; and assembling the turbo-machine by inserting an end of the pin into the first notch. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of a turbo-machine in accordance with this invention. 
     FIG. 2 is a cross sectional view of a blade ring flange affixed to a turbo-machine casing as is known in the prior art. 
     FIG. 3 is a radial view of two adjacent rows of stationary airfoils in three alternative clocking locations. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a blade ring  12  of a turbo-machine  10  such as a steam turbine, gas or combustion turbine, or compressor. The blade ring  12  is formed with an upper portion  14  and a lower portion  16  to facilitate the assembly of the turbo-machine. Removeably affixed to the blade ring  12  are N airfoils or vanes  18 , only two of which are shown in FIG. 1 for the sake of clarity. The number N varies from machine to machine, but may typically be 32 or 48 for a gas turbine engine. The radial distance between adjacent airfoils is called a segment of P degrees. One segment P is equal to 360 degrees divided by N. 
     A single blade ring  12  and its N airfoils define a stage when installed in a gas flow path within the casing  20  of the turbo-machine  10 . The casing  20  is also formed with an upper portion  22  and a lower portion  24 . The flow path (not shown) would be in a direction perpendicular to the plane of the page of FIG.  1 . The number of stages varies from machine to machine. By example, a typical gas turbine or compressor may have 4-6 stages, and a typical steam turbine may have 6-8 stages. 
     FIG. 2 illustrates how the blade ring  12  is affixed to the casing  20  of the turbo-machine  10 . Identical structures are numbered consistently in FIGS. 1 and 2. The blade ring lower portion  16  is supported in the vertical and horizontal directions within the casing lower portion  24 . A key  26  is affixed to the blade ring lower portion by bolt  28 . The upper portion  14  of the blade ring  12  rests on and is supported in the vertical direction by the lower portion  16  of the blade ring  12 . The upper portion  22  of the casing  20  is then positioned over the blade ring  12  and onto the casing lower portion  24 , capturing the key  26  therebetween. The interference between the key  26  and the casing upper and lower portions  22 , 24  provides radial support for the blade ring  12 . 
     As further illustrated in FIG. 1, torque pins  28 , 30  penetrate openings  32 , 34  in the casing upper and lower portions  22 , 24  respectively. The torque pins  28 , 30  are operable to be inserted into the casing  20  so that the ends of the pins  28 , 30  are received by notches  36 , 38  formed in the outer surface of the blade ring upper and lower portions  14 , 16 . Torque pins  28 , 30  and notches  36 , 38  are known in the art. The alignment of notches  36 , 38  with torque pins  28 , 30  defines the radial position of the blade ring  12 , and thereby the clocking position of that stage of the turbo-machine  10 . 
     In accordance with this invention, blade ring  12  is provided with at least one and preferably a plurality of additional notches  40 , 42 , and the casing is provided with clocking pins  44 . Notches  40  are located a radial distance of A degrees clockwise from a reference position, and notches  42  are located a radial distance of B degrees counter-clockwise from a reference position. As illustrated in FIG. 1, the reference position corresponds to the alignment of known pins  28 , 30  and notches  36 , 38 . 
     In order to change the clocking angle of the stage of vanes shown in FIG. 1, the blade ring  12  is rotated within the casing  20  until the clocking pins  44  align with notches  40  or  42 , and torque pins  28 , 30  align with notches  40  or  42 . Rotation of the blade ring  12  in either radial direction to a maximum of P degrees will change the clocking angle of the stage. Due to the symmetry of the arrangement of the airfoils  18  around the blade ring  12 , a rotation of exactly P degrees results in the same clocking angle as the original position. It may be desirable, therefore, to rotate the blade ring  12  in any amount from 0 to P degrees. 
     The notches  36 , 40 , 42  must be designed to have a certain finite size based upon the calculated forces, material selection, and other mechanical design considerations. Due to the size of the notches and the stress concentration in the blade ring caused by the notches and the loads imposed by the pins, the notches  36 , 40 , 42  must be spaced a calculated distance apart from each other. Therefore, it may not be possible to form the desired number of notches corresponding to the desired number of clocking angles in a space of one segment of P degrees on the blade ring  12 . Notches may, however, be formed in other segments of the blade ring  12  at a distance from the reference position equal to the desired change in clocking angle plus an integer multiple of the segment angle P. Similarly, a desired rotation in the clockwise direction may be achieved by forming a notch in the counterclockwise direction at a radial distance of P degrees minus the desired rotation angle. 
     FIG. 1 illustrates a turbo-machine having a means for attaching the blade ring to the casing at three alternative radial positions; i.e. at a reference position, at A degrees clockwise from the reference position, and at B degrees counterclockwise from the reference position. Radial distances A and B as well as the combination of A plus B are each non-integer multiples of the segment angle P, and A and B are non-integer multiples of each other, thereby providing three alternative clocking angles for the assembly of this segment of the turbo-machine. By way of example, A may be an angle less than P degrees and B may be an angle greater than P degrees. As long as A and B are not equal to each other and are each non-integer multiples of P and non-integer multiples of each other, three distinct clocking angles may be provided in the embodiment of FIG.  1 . 
     To assemble a turbo-machine  10  in accordance with this invention, the designer may first calculate a desired clocking angle for the blade rings  12  of the various stages of the machine  10 . A notch  36 , 38  is provided in the blade ring  12  at a reference radial location that corresponds to the location of pin  28 , 30  when the blade ring  12  is at the desired clocking angle. Additional notch  40  is provided in the blade ring  12 . Additional notch  40  is located at a radial location A degrees counterclockwise from the reference notch  36 , 38 . As long as A is a non-integer multiple of P, the blade ring will be clocked to a second clocking angle when additional notch  40  is aligned with pin  28 , 30 , 44 . The turbo-machine may first be assembled with notches  36 , 38  aligned with pins  28 , 30 , then if a second clocking angle is desired as a result of performance testing, modified operating conditions, or other reason, the turbo-machine  10  may be disassembled and re-assembled with notches  40  aligned with pins  28 , 30 , 44  to provide the second clocking angle. 
     As can be seen in FIG. 2, pin  26  must be removed to permit the rotation of the blade ring  12  to the alternative clocking angle positions. To provide additional support for the blade ring  12  after pin  26  is removed, clocking pins  44  are provided. The ends of clocking pins  44  are received by notches  40 , 42  after pin  26  is removed and the blade ring  12  is rotated. When the blade ring is in the reference position wherein pins  28 , 30  are aligned with notches  36 , 38  and key  26  is installed, the ends of pins  44  may be retracted as shown in FIG. 1, or may be inserted into additional notches (not shown) formed in the blade ring  12 . 
     Providing the turbo-machine  10  with a third notch  42  allows the machine to be disassembled and re-assembled with the blade ring  12  at a third clocking angle, so long as the third notch  42  is provide at a radial distance B which is equal to a non-integer multiple of P and a non-integer multiple of A. 
     Other aspects, objects and advantages of this invention may be obtained by studying the figures, the disclosure, and the appended claims.