Abstract:
A seal member for effecting a seal preventing fluid flow in an axial direction through an annular space formed between two relatively moving components including a rotatable shaft and a stator structure. The seal member includes a plurality of flexible seal strips. Each seal strip includes a planar plate extending radially through the annular space and having a radially outer end supported to the stator structure and a radially inner end defining a tip portion extending widthwise in the axial direction engaged in sliding contact with a peripheral surface of the rotatable shaft. At least one of the seal strips includes a plurality of perforations extending through the seal strip and located between a leading edge and a trailing edge of the seal strip for effecting an increased flexibility of the seal strip adjacent to the tip portion.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a seal between two relatively movable members and, more particularly, to a seal including a plurality of flexible seal strips forming an annular seal between a stationary member and a rotatable member, such as a turbine shaft. 
       BACKGROUND OF THE INVENTION 
       [0002]    In a gas turbine engine, there are fluid pressure variations between axially adjacent zones, such as adjacent zones through which the turbine shaft passes, with resulting leakage of fluid, e.g., air and/or other gases, between the zones. In particular, there is typically leakage at clearances between stationary and rotating parts of a turbine engine wherein a leakage flow occurs from a higher pressure zone to a lower pressure zone across the clearance between the rotating part and the stationary part. In order to improve the thermodynamic efficiency of the engine, the leakage flow needs to reduced or minimized, such as by means of a seal provided in the annular space between the two relatively moving parts. 
         [0003]    Generally, two types of seal are commonly used in gas turbine engines to reduce leakage between components, and in particular to reduce leakage that may occur at the rotating shaft. These seals comprise a brush seal and a leaf seal. Brush seals typically comprise a plurality of fine bristles that are held in a carrier mounted on a housing wherein the tips of the bristles wipe against the rotating shaft. Brush seals have been found to be substantially effective, providing satisfactory sealing during initial use, but experience deteriorating performance after an extended period of performance. The deterioration of performance may be due to various factors including increasing brittleness of the bristles over time and insufficient rigidity to resist flexing in the direction of a pressure gradient between axially adjacent zones, particularly in the presence of high pressure gradients. 
         [0004]    Leaf seals generally comprise a plurality of seal strips mounted to a carrier member and packed closely together in the circumferential direction. The flexible strips may bend in the circumferential direction, but exhibit a high resistance to bending in the axial direction, ensuring that the flexible strips will continue to wipe against the rotating shaft even in the presence of high pressure differentials between the axially adjacent zones. It is believed that the seal strips of leaf seals have greater durability than the bristles of brush seals and therefore provide a longer service life. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention is directed to leaf seals having increased flexibility in the circumferential direction. The increased flexibility provided by the invention is believed to provide additional durability to the leaf seal and/or provide reduced leakage axially across the leaf seal between adjacent zones at different pressures. 
         [0006]    In accordance with one aspect of the invention, a seal member is provided for effecting a seal preventing fluid flow in an axial direction through an annular space formed between two relatively moving components comprising a rotatable shaft and a stator structure. The seal member comprises a plurality of flexible seal strips. 
         [0007]    Each seal strip comprises a planar plate extending radially through the annular space and having a radially outer end supported to the stator structure and a radially inner end comprising a tip portion extending widthwise in the axial direction engaged in sliding contact with a peripheral surface of the rotatable shaft. At least one of the seal strips comprises a plurality of perforations extending through the at least one seal strip and located between a leading edge and a trailing edge of the at least one seal strip for effecting an increased flexibility of the at least one seal strip adjacent to the tip portion. 
         [0008]    In accordance with another aspect of the invention, a seal member is provided for effecting a seal preventing fluid flow in an axial direction through an annular space formed between two relatively moving components comprising a rotatable shaft and a stator structure. The seal member comprises a plurality of flexible seal strips. Each seal strip comprises a planar plate extending radially through the annular space and having a radially outer end supported to the stator structure and a radially inner end comprising a tip portion extending widthwise in the axial direction engaged in sliding contact with a peripheral surface of the rotatable shaft. The seal strips comprise a plurality of elongated perforations wherein each seal strip includes at least one of the perforations. The perforations extend through the seal strips and are located between leading edges and trailing edges of the seal strips. The perforations have a direction of elongation extending radially in a predetermined region of the seal strips between the radially outer end and the radially inner end for effecting an increased flexibility of the seal strips adjacent to the tip portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein: 
           [0010]      FIG. 1  is a cross-sectional perspective view illustrating a seal member in accordance with an embodiment of the present invention; 
           [0011]      FIG. 2  is cross-sectional view of the seal member taken along line  2 - 2  in  FIG. 1 ; 
           [0012]      FIG. 3  is a cross-sectional view of the seal member taken along line  3 - 3  in  FIG. 2 ; 
           [0013]      FIG. 4  is a diagrammatic view of a seal member, taken in the axial direction, and illustrating forces applied to the seal member; 
           [0014]      FIG. 5  is a plan view of a seal strip illustrating an embodiment of the invention; 
           [0015]      FIG. 6  is a plan view of a seal strip illustrating another embodiment of the invention; 
           [0016]      FIG. 7  is a plan view of a seal strip illustrating another embodiment of the invention; 
           [0017]      FIG. 8  is a plan view of a seal strip illustrating another embodiment of the invention including aspects of the embodiments of  FIGS. 5 and 7 ; 
           [0018]      FIG. 9  is a plan view of a seal strip illustrating another embodiment of the invention; 
           [0019]      FIG. 10  is plan view of a seal strip illustrating an embodiment comprising a variation of the embodiment of  FIG. 9 ; 
           [0020]      FIG. 11  is a plan view of a seal strip illustrating another embodiment of the invention; and 
           [0021]      FIG. 12  is an elevational view, taken in the axial direction, illustrating an embodiment of the seal member combining two types of seals. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, specific preferred embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. 
         [0023]    Referring to  FIGS. 1-4 , a first embodiment of the invention is illustrated.  FIGS. 1 and 2  show a seal member  10  comprising a leaf seal mounted in a housing  12  of a gas turbine engine in order to separate a high-pressure zone or region A 1  from a low-pressure zone or region A 2  within a chamber or annular space  14  ( FIG. 2 ) located between the housing  12  and a shaft  16 . 
         [0024]    The shaft  16  extends through a bore of the housing  12  with a clearance gap therebetween. The shaft  16  and the housing  12  are subject to relative movement, where the shaft  16  is intended to rotate at relatively high rotational rates, such as is typically found in gas turbine engines. The housing  12  may comprise an annular groove  18 , and the seal member  10  is received and mounted within the annular groove  18 . In particular, the seal member  10  comprises a stator structure or carrier  20  supporting a plurality of leaves or seal strips  22 . For example, the seal strips  22  may be attached to the carrier  20  at a braze or weld connection  24  formed at a radially outer end  26  of the seal strips  22 . The carrier  20  may include a backing plate  28 , a high-pressure side end plate  30  adjacent to a leading edge  38  of the seal strips  22 , and a low-pressure side end plate  32  adjacent to a trailing edge  40  of the seal strips  22 . The end plates  30 ,  32  extend radially inwardly, i.e., toward the shaft  16 , from the backing plate  28  and may be formed integrally with the backing plate  28  or may be attached as separate elements to the backing plate  28 . The carrier  20  provides a mounting structure that fits within the groove  18  of the casing  12  to substantially rigidly support the plurality of seal strips  22  such that a radially inner end  36  comprising a tip portion of the seal strips  22  is positioned in close proximity to a peripheral surface  34  of the shaft  16 . It should be noted that during operation of the turbine, the inner ends  36  of the seal strips  22  are generally positioned out of contact with the shaft  16 , as is seen in  FIGS. 2-4  and described further below. However, the inner ends  36  may rest in engagement with the shaft  16  with a predetermined biasing force when the turbine is not operating. Further, it should be understood that, within the spirit and scope of the invention, other stator structures may be provided for substantially rigidly supporting the seal strips  22  in engagement with the shaft  16 . 
         [0025]    The seal strips  22  comprise relatively thin planar plate members formed of a metallic material, such as stainless steel or Haynes  25 , and also may comprise a non-metallic material such as aramid. The seal strips  22  are formed with a significantly greater axial width dimension than the thickness of the seal strips  22 . An exemplary seal strip  22  for use in the present invention may have the following dimensions: a radial length of about 7.6 mm to about 38 mm, an axial width of about 3.8 mm to about 13 mm, and a thickness in the circumferential direction of about 0.08 mm to about 0.5 mm. The described materials and dimensions are provided as an exemplary description of the invention, and other materials and dimensions may be incorporated within the scope of the invention. 
         [0026]    Referring to  FIG. 3 , the seal strips  22  are closely arranged adjacent to each other, substantially minimizing the leaf-to-leaf spacing between adjacent seal strips  22  to minimize axial flow through the seal member  10  between the high-pressure region A 1  and adjacent low-pressure region A 2 . Further, the seal strips  22  comprise flexible elements, having a relatively high degree of flexibility in the circumferential direction and having a relatively high rigidity in the axial direction of the shaft  16 . Referring to  FIG. 4 , the length of the seal strips  22  is preferably greater than a radial distance between an inner surface  42  of the backing plate  28  of the carrier  20  and the peripheral surface  34  of the shaft  16 . The seal strips  22  are angled from their attachment to the backing plate  28  at the radially outer end  26  in the direction of rotation of the shaft  16  to form an angle α between the peripheral surface  34  and the plane of the seal strips  22  at the radially inner end  36 . The angle α may be selected, along with the length of the seal strips  22 , to provide a predetermined pre-load pressure P P  between the radially inner end  36  of the seal strips  22  and the peripheral surface  34  of the shaft  16 . The pre-load pressure P P  may additionally be adjusted by adjusting the flexibility of the seal strips  22  through selection of the thickness of the seal strips  22 , as well as by selection of the material of the seal strips  22 . 
         [0027]    In addition, it should be understood that during operation of the turbine engine, the rotating shaft  16  may cause a hydrodynamic pressure D P  to be applied to a first side  44  of each seal strip  22 , which acts on the seal strips  22  in a direction opposite from the pre-load pressure P P . A further lifting pressure L P  applies a lifting force to each seal strip  22 , opposite to the pre-load pressure P P , due to a pressure differential between the first side  44  of the seal strip  22  and an opposite second side  46  of the seal strip  22 . The hydrodynamic pressure D P  and lifting pressure L P  operate against the pre-load pressure P P  during rotation of the shaft to cause the radially inner ends  36  of the seal strips  22  to lift from the shaft  16 , such that wear on the tip portions of the seal members  22  at the radially inner ends  36  may be reduced. As noted above, the flexibility of the seal strips  22  to permit movement of the radially inner ends  36  radially outwardly relative to the shaft  16  may be controlled or adjusted by selection of the thickness of the seal strips  22 . Further, in accordance with an aspect of the present invention described in detail below, the flexibility of the seal members  22  in the circumferential direction may be increased by providing one or more perforations, extending between the first and second sides  44 ,  46 , to provide a mechanism for adjusting the circumferential flexibility of the seal strips  22  substantially independently of the thickness of the seal strips  22  while substantially maintaining the rigidity of the seal strips  22  in the axial direction. 
         [0028]    Referring to  FIG. 5 , a seal strip  22  illustrating the invention includes a row of perforations  48 A, illustrated by a row of six substantially uniformly spaced perforations  48 A extending through the seal strip  22  located and extending axially between the leading edge  38  and the trailing edge  40 . The row of perforations  48 A define an axially extending hinge location and increase the flexibility of the seal strip  22  in the circumferential direction to effect an increased flexing movement of the tip portion at the radially inner end  36  of the seal strip  22 . The perforations  48 A in the illustrated embodiment comprise simple closed figures, depicted as circles. It should be understood that the perforations  48 A may comprise other simple closed figures, such as polygons or other shapes. In an exemplary embodiment of the invention, the diameter of the perforations  48 A shown in  FIG. 5  may be in the range of from about 0.2 mm to about 0.8 mm. 
         [0029]    The row of perforations  48 A in  FIG. 5  is shown located in a radially outer portion of the seal strip  22 , closer to the radially outer end  26  than to the radially inner end  36 , for increasing the flexibility of the seal strip  22  in the circumferential direction at the radial location of the row of perforations  48 A. However, the row of perforations  48 A may be located at other radial locations along the seal strip  22  to obtain flexibility at a desired radial location along the seal strip  22 . Further, the number and size of the perforations  48 A may be increased or decreased to effect the desired degree of flexibility. 
         [0030]    In addition to increasing the flexibility of the seal strip  22  in the circumferential direction when pushed and/or lifted by forces applied to the first side  44 , such as forces from the hydrodynamic pressure D P  and the lifting pressure L P , it is believed that the described perforations  48 A further reduce axial flow leakage. In particular, it is believed that the perforations  48 A provide areas where the leakage flow will expand and contract, such as by flowing between the opposite sides  44 ,  46  of the seal strip  22 , resulting in greater flow resistance to flow of fluids moving in the axial direction from the high-pressure area A 1  to the low-pressure area A 2 . 
         [0031]    Referring to  FIG. 6 , an alternative embodiment depicting the invention is shown where elements corresponding to elements of the embodiment of  FIG. 5  are identified with the same reference numeral increased by 100. The seal strip  122  includes a first row of perforations  148 A similar to those described above for the embodiment of  FIG. 5 . A second row of perforations  148 B is also provided extending between the leading edge  138  and the trailing edge  140  and spaced radially inwardly from the first row of perforations  148 A. 
         [0032]    The second row of perforations  148 B comprises five substantially uniformly spaced perforations  148 B that may be larger than the perforations  148 A of the first row. The first and second perforations  148 A,  148 B in the embodiment of  FIG. 6  comprise simple closed figures, depicted as circles. However, the perforations  148 A,  148 B may comprise other simple closed figures, such as polygons or other shapes. In an exemplary embodiment of the invention, the diameter of the perforations  148 A and  148 B shown in  FIG. 6  may be in the range of from about 0.2 mm to about 1 mm. 
         [0033]    In addition, the perforations  148 B of the second row may be positioned axially in between the axial locations of the perforations  148 A of the first row. The second row of perforations  148 B provide an additional amount of flexibility to seal strip  122  in the circumferential direction, such as may be desired for thicker seal strips  122 , to effect an increased flexing movement of the tip portion at the radially inner end  136  of the seal strip  122 . Further, the second row of perforations  148 B provides an additional area along the seal strip  122  for controlling the flexibility of the seal strip  122 , such as by selecting the number and size of the perforations  148 B. As in the embodiment of  FIG. 5 , the perforations  148 A,  148 B shown in  FIG. 6  may reduce the axial flow across the seal strip  122 , in that the second row of perforations  148 B may provide additional areas for causing expansion and contraction of the fluid flow passing across the seal strip  122  to increase the resistance to the fluid flow. 
         [0034]    Referring to  FIG. 7 , an alternative embodiment depicting the invention is shown where elements corresponding to elements of the embodiment of  FIG. 5  are identified with the same reference numeral increased by 200. The seal strip  222  includes a row of perforations  248 C, illustrated by a row of six substantially uniformly spaced perforations extending through the seal strip  222  located and extending axially between the leading edge  238  and the trailing edge  240 . The row of perforations  248 C increase the flexibility of the seal strip  222  in the circumferential direction to effect an increased flexing of the tip portion at the radially inner end  236  of the seal strip  222 . The perforations  248 C in the illustrated embodiment comprise simple closed figures, depicted as radially elongated rectangles. It should be understood that the perforations  248 C may comprise other simple closed figures, such as for example an elongated oval. In an exemplary embodiment of the invention, the perforations  248 C shown in  FIG. 7  may have a radial length of about 3.8 mm to about 19 mm, and an axial width of about 0.1 mm to about 0.5 mm. 
         [0035]    The perforations  248 C in  FIG. 7  each comprise a radially inner terminal end  250  and a radially outer terminal end  252 . The radially outer terminal ends  252  of the perforations  248 C are preferably spaced radially inwardly from the radially outer end  226  of the seal strip  222 , and the radially inner terminal ends  250  of the seal strip  222  are spaced radially outwardly from the inner end  236  of the seal strip  222 . The perforations  248 C may extend along a substantial portion of the radial length of the seal strip  222 . For example, the radially outer terminal ends  252  of the perforations  248 C may be located radially outwardly from the midpoint of the seal strip  222 , adjacent to the radially outer end  226  of the seal strip  222 , and the radially inner ends  250  of the perforations  248 C may be located radially inwardly from the midpoint of the seal strip  222 , adjacent to the radially inner end  236  of the seal strip  222 . The row of perforations  248 C increases the flexibility of the seal strip  222  in the circumferential direction to effect an increased flexing movement of the tip portion at the radially inner end  236  of the seal strip  222 . The particular length and radial location, as well as the number of the perforations  248 C, may be selected to obtain a desired degree of flexibility. 
         [0036]    As in the previous embodiments, the perforations  248 C shown in  FIG. 7  may reduce the axial flow across the seal strip  222 , in that the row of perforations  248 C may provide areas for causing expansion and contraction of the fluid flow passing across the seal strip  222  to increase the resistance to the fluid flow. In this regard, the width of the perforations  248 C in the axial direction may be adjusted to increase the flow resistance. 
         [0037]    Referring to  FIG. 8 , an alternative embodiment depicting the invention is shown wherein elements of the embodiments of  FIGS. 5 and 7  are combined. Elements of the embodiment of  FIG. 8  corresponding to elements of the embodiment of  FIG. 5  are identified with the same reference numeral increased by 300, and elements corresponding to elements of the embodiment of  FIG. 7  are labeled with the same reference numeral increased by 100. The seal strip  322  includes a first row of perforations  348 A similar to those described above for the embodiment of  FIG. 5 . A second row of perforations  348 C is also provided extending between the leading edge  338  and the trailing edge  340  and spaced radially inwardly from the first row of perforations  348 A. 
         [0038]    The first row of perforations  348 A comprises a plurality of perforations  348 A similar to those of  FIG. 5  and arranged in an axially extending row adjacent to the radially outer end  326  of the seal strip  322 . The second row of perforations  348 C comprises a plurality of elongated perforations  348 C similar to those of  FIG. 7  and arranged in an axially extending row. Each of the perforations  348 C extend radially from a location adjacent to the first row of perforations  348 A to a location adjacent to the radially inner end  336  of the seal strip  322 . 
         [0039]    The first and second rows of perforations  348 A,  348 C each provide flexibility to the seal strip  322  in the circumferential direction to effect an increased flexing movement of the tip portion at the radially inner end  336  of the seal strip  322 . Further, the perforations  348 A,  348 C shown in  FIG. 8  may reduce the axial flow across the seal strip  322 , as discussed above with regard to the embodiments of  FIGS. 5 and 7 . In particular, the second row of perforations  348 C may provide a reduction in axial flow along a substantial radial extent of the seal strip  322 , providing additional areas for causing expansion and contraction of the fluid flow passing across the seal strip  322  to increase the resistance to the fluid flow. 
         [0040]      FIGS. 9-11  illustrate embodiments of the invention comprising partially segregated seal strips wherein perforations extend radially outwardly from the tip portions to form independently movable end portions. Referring to  FIG. 9 , a seal strip  422  depicting an alternative embodiment of the invention is shown and comprises a row of perforations  448 D, illustrated as a row of three substantially uniformly spaced perforations  448 D extending through the seal strip  422  located and extending axially between the leading edge  438  and the trailing edge  440 . Further, the perforations  448 D comprise radially elongated perforations  448 D, such as rectangular perforations, extending radially outwardly from radially inner terminal ends  450 , comprising openings at the tip portion of the radially inner end  436  of the seal strip  422 , to radially outer terminal ends  452 . The radially outer terminal ends  452  of the perforations  448 D may be located radially inwardly from a midpoint between the radially inner end  436  and radially outer end  426  of the seal strip  422 . The perforations  448 D may comprise slits extending radially into the seal strip  422  from the tip portion at the radially inner end  436  of the seal strip  422  to the radially outer terminal ends  452 , distal from the radially outer end  426  of the seal strip  422 . 
         [0041]    The perforations  448 D define a plurality of leaves  454  adjacent to the radially inner end  436  of the seal strip  422 , increasing the flexibility of the tip portion at the radially inner end  436  of the seal strip  422 . In particular, each of the leaves  454  may move in the circumferential direction independently of the other leaves  454  of the seal strip  422 , facilitating sealing of the radially inner end  436  to the rotating shaft  16 . For example, as one leaf  454  flexes circumferentially away from contact with shaft  16 , one or more of the other leaves  454  may be in a radially closer position to the shaft  16 . Hence, the present configuration for the seal strip  422  may provide a wider profile to axial flow from the high pressure area A 1  to the low pressure area A 2 , as the leaves spread circumferentially. The perforations  448 D and relative movement between the leaves  454  of the seal strip  422  may further create a reduction in axial flow along the seal strip  422  by providing areas for causing expansion and contraction of the fluid flow passing across the seal strip  422  to increase the resistance to the fluid flow. 
         [0042]    Referring to  FIG. 10 , an alternative configuration of the seal strip  422  illustrated in  FIG. 9  is shown, where elements of  FIG. 10  corresponding to those of  FIG. 9  are labeled by the same reference numeral primed. The seal strip  422 ′ of  FIG. 10  is substantially similar to that of  FIG. 9 , with the exception that the perforations  448 D′ of  FIG. 10  are at axially different locations than the perforations  448 D of  FIG. 9 . In the present embodiment, the seal strip  422 ′ comprises four substantially uniformly spaced perforations  448 D′. In an exemplary embodiment of the invention, the perforations  448 D and  448 D′ shown in  FIGS. 9 and 10  may extend radially from the inner end  436 ′ a radial length in the range of from about 3.8 mm to about 19 mm. 
         [0043]    The seal strips  422  and  422 ′ may be alternately positioned adjacent to each other in the seal member  10  to limit gas flow through the seal member  10  in the circumferential direction, due to the axial displacement between the perforations  448 D and  448 D′, while also restricting flow in the axial direction as described above with reference to the seal strips  422 . 
         [0044]    Referring to  FIG. 11 , a seal strip  522  depicting an alternative embodiment of the invention is shown, where elements of the seal strip  522  corresponding to the seal strip  422  of  FIG. 9  are labeled with the same reference numeral increased by 100. The seal strip  522  comprises a row of perforations  548 E, illustrated as a row of four substantially uniformly spaced perforations  548 E extending through the seal strip  522  located and extending axially between the leading edge  538  and the trailing edge  540 . 
         [0045]    In the present embodiment, the perforations  548 E comprise radially elongated notches  548 E, illustrated as inverted V-shaped notches, extending radially outwardly from radially inner terminal ends  550 , comprising openings at the tip portion of the radially inner end  536  of the seal strip  522 , to radially outer terminal ends  552 . The radially outer terminal ends  552  of the perforations  548 E may be located radially inwardly from a midpoint between the radially inner end  536  and radially outer end  526  of the seal strip  522 . 
         [0046]    The perforations  548 E define a plurality of leaves  554  adjacent to the radially inner end  536  of the seal strip  522 , increasing the flexibility of the tip portion at the radially inner end  536  of the seal strip  522 . As described above with reference to the embodiment of  FIG. 9 , each of the leaves  554  may move in the circumferential direction independently of the other leaves  554  of the seal strip  522 , facilitating sealing of the radially inner end  536  to the rotating shaft  16 . For example, as one leaf  554  flexes circumferentially away from contact with shaft  16 , one or more of the other leaves  554  may be in a radially closer position to the shaft  16 . The perforations  548 E and relative movement between the leaves  554  of the seal strip  522  may further create a reduction in axial flow along the seal strip  522  by providing areas for causing expansion and contraction of the fluid flow passing across the seal strip  522  to increase the resistance to the fluid flow. 
         [0047]    It should be understood that the seal member  10  may be formed of a combination of any of the above-described seal strips to provide a desired flexibility and sealing of the seal member  10 . In particular, the seal strips will flex and contact each other in the circumferential direction, and adjacent seal strips will affect the flexing movement of each other. It may be desirable to provide some seal strips that are more flexible in the circumferential direction than other seal strips forming the seal member  10  to provide a desired overall circumferential flexing movement of the seal strips forming the seal member  10 . Accordingly, it may be desirable to form the seal member  10  shown in  FIG. 1  by providing some seal strips as solid members, i.e., with no perforations, located between perforated seal strips, such as are described above, in order to obtain a desired flexibility in the circumferential direction. 
         [0048]    Further, it may be desirable to form the seal member  10  with other seal elements incorporated between the above-described perforated seal strips. For example, it may be desirable to include known brush seals between the perforated seal strips described herein, as is illustrated in  FIG. 12  showing brush seals  56  located between seal strips  22 . The perforated seal strips  22  provide a substantially rigid structure against flexing in the axial direction and the brush seals  56  may provide additional advantages in sealing against gas flow in the axial direction. 
         [0049]    While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.