Abstract:
A seal member for effecting a seal preventing fluid flow in an axial direction through an annular space formed between a rotatable shaft and a stator structure. The seal member includes a plurality of flexible seal strips 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 for engaging in sliding contact with a peripheral surface of the rotatable shaft. The seal strips are mounted to the stator structure with the tip portions of the seal strips at an angle to the axial direction. Each of the tip portions are formed with a curvature in a radially extending plane between a leading edge and a trailing edge of each seal strip.

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 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]    A seal for limiting leakage across the annular space may comprise a leaf seal. 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 be positioned closely adjacent to the rotating shaft even in the presence of high pressure differentials between the axially adjacent zones. 
       SUMMARY OF THE INVENTION 
       [0004]    In accordance with an 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 a rotatable shaft and a stator structure defining two relatively moving components. The seal member may comprise a plurality of flexible seal strips, each seal strip comprising 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 for engaging in sliding contact with a peripheral surface of the rotatable shaft. The seal strips are mounted to the stator structure with the tip portions of the seal strips at an angle to the axial direction. Each of the tip portions are formed with a curvature in a radially extending plane between a leading edge and a trailing edge of each seal strip. 
         [0005]    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 a rotatable shaft and a stator structure defining two relatively moving components. The seal member may comprise a plurality of flexible seal strips, each seal strip comprising 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 for engaging in sliding contact with a peripheral surface of the rotatable shaft. Each of the seal strips comprises a leading edge and a trailing edge. The seal strips are mounted to the stator structure with the tip portions of the seal strips at an angle to the axial direction. The seal strips are arranged in a plurality of axially adjacent rows. The seal strips of at least one of the rows being angled in the axial direction with the leading edge being located aft of the trailing edge with reference to a rotation direction of the rotatable shaft, and the seal strips of another of the rows being angled in an opposite direction with the trailing edge being located aft of the leading edge. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    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: 
           [0007]      FIG. 1  is a cross-sectional perspective view illustrating a seal member in accordance with an embodiment of the present invention; 
           [0008]      FIG. 2  is cross-sectional view of the seal member taken along line  2 - 2  in  FIG. 1 ; 
           [0009]      FIG. 3  is a cross-sectional view of the seal member taken along line  3 - 3  in  FIG. 2 ; 
           [0010]      FIG. 4  is a view of an outer end of a seal including a plurality of seal strips oriented at an axial angle; 
           [0011]      FIG. 5  illustrates a sealing effect of the seal of  FIG. 4 ; 
           [0012]      FIG. 6  is a view of an outer end of a seal including a plurality of seal strips at an axial angle opposite to that illustrated in  FIG. 4 ; 
           [0013]      FIG. 7  is a view of an outer end of an alternative arrangement of a seal member including a combination of the seals of  FIGS. 4 and 6 ; 
           [0014]      FIG. 8  is a plan view of a seal strip in accordance with the present invention; 
           [0015]      FIG. 9  illustrates an embodiment for an additional flow inhibiting feature for the seal; 
           [0016]      FIG. 10  illustrates another embodiment of an additional flow inhibiting feature for the seal; and 
           [0017]      FIGS. 11 and 12  illustrate a further embodiment of an additional flow inhibiting feature for the seal. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    In the following detailed description of the preferred embodiment, 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, a specific preferred embodiment 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. 
         [0019]    Referring to  FIGS. 1-3 , an 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 . 
         [0020]    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 an annular seal  21  comprising 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 or tip portion  36  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. 2-3 . 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 . 
         [0021]    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 5 mm to about 40 mm, an axial width of about 5 mm to about 30 mm, and a thickness in the circumferential direction of about 0.05 mm to about 1 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. 
         [0022]    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 . It may be noted that 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 a radial angle between the peripheral surface  34  and the plane of the seal strips  22  at the radially inner end  36 . The radial angle may be selected, along with the length of the seal strips  22 , to provide a predetermined pre-load pressure between the radially inner end  36  of the seal strips  22  and the peripheral surface  34  of the shaft  16 . 
         [0023]    As seen in  FIGS. 1 and 4 , the seal strips  22  are oriented at an angle to the axial direction, i.e. relative to an axis of rotation  15  of the shaft  16 , as is illustrated by an angle β of the tip portion  36  relative to a line  37  parallel to the axis of rotation  15  of the shaft  16 . Specifically, in the present embodiment, the seal strips  22  are angled in the axial direction with the leading edge  38  located aft of the trailing edge  40  with reference to the direction of rotation of the shaft  16 . It is believed that orienting the seal strips  22  at the angle β may increase the sealing effect of the seal member  10  by effecting a further restriction to leakage flow F L  between adjacent strips  22 . In particular, the angled seal strips  22  are formed with a greater axial width than a distance between the high-pressure side end plate  30  and the low-pressure side end plate  32 , in a direction parallel to the axis of rotation  15  of the shaft  16 , thereby increasing the length of the leakage flow path and increasing the resistance to leakage flow F L  along the leakage flow path defined between adjacent seal strips  22 . 
         [0024]    The leakage flow F L  is further reduced by a hydrodynamic pressure related to a cavity flow F C  produced by friction between the shaft surface  34  and the air in the cavity adjacent to the seal  21  due to rotation of the shaft  16 . The cavity flow F C  has a component in the direction of rotation of the shaft  16 , and may operate to increase the dynamic head in the low pressure area A 2 . That is, the cavity flow F C  produced in the low pressure area A 2  by the rotation of the shaft  16  tends to flow into the spaces between the adjacent seal strips  22  at the trailing edges  40  of the seal strips  22 , creating an increased back pressure for counteracting leakage flow F L  entering at the leading edges  38  of the seal strips  22 . 
         [0025]    In addition, in the embodiment shown in  FIG. 4 , the cavity flow F C  will tend to act against a forward face  44  of the seal strips  44 , and will be turned or deflected to flow generally parallel to the seal strips  22 . The force required to deflect the direction of the cavity flow F C  comprises a circumferentially directed force that tends to bias and move the seal strips  22  circumferentially into engagement with each other, as is depicted in  FIG. 4  by movement in the direction, d s , of a seal strip  22   a  into engagement with an adjacent seal strip  22   b . The movement of the seal strips  22  toward each other may further increase the sealing between adjacent seal strips  22  to reduce the leakage flow F L . 
         [0026]    Referring to  FIG. 6 , a further seal  21 ′ comprising an alternative orientation of the seal strips  22  is illustrated, where the seal strips  22  of the seal  21 ′ are angled relative to the rotational axis  15  of the shaft  16  at an axial angle opposite to that of the seal plates  22  of the seal  21 , as depicted by an angle β′ relative to the line  37  parallel to the rotational axis  15  of the shaft  16 . The seal strips of the seal  21 ′ are angled in the axial direction with the trailing edge  40  located aft of the leading edge  38  with reference to the direction of rotation of the shaft  16 . It is believed that the orientation of the seal strips  22  in the seal  21 ′ permit the cavity flow F C  to enter the seal  21 ′ at the leading edges  38  between the seal strips  22 , where the leakage flow F L  may accelerate the cavity flow F C . The acceleration of the cavity flow F C  as it passes between the seal strips  22  may increase a hydrodynamic pressure on the forward face  44  of the seal strips  22  to facilitate lifting the seal strips  22  radially away from the surface  34  of the shaft  16 , reducing friction at the shaft  16 . 
         [0027]    Referring to  FIG. 7 , an alternative arrangement for the seals is illustrated in which a seal member  110  may comprise a plurality of the seals  21 ,  21 ′. In particular, the seal strips  22  of the seals  21 ,  21 ′ are arranged in axially adjacent rows with the orientation, i.e., the angle relative to the axial direction, of each row of seal strips  22  alternating relative to the orientation of seal strips  22  of immediately adjacent rows of the seal strips  22 . The alternating arrangement of the seals  21 ,  21 ′ may be provided to obtain the advantages of the respective seals  21 ,  21 ′, as described above. The particular combination of the seals  21 ,  21 ′ may vary from the configuration shown herein. For example, a seal member may be configured with the seal  21 , located as a first row of seal strips  22 , followed by seal strips  22  oriented as shown for the seal  21 ′. Further, any number of the rows of seal strips  22  arranged as shown for the seals  21  and  21 ′ may be provided in a seal member. 
         [0028]    Referring to  FIG. 8 , the seal members  22  are preferably configured with the inner edge tip portion  36  formed with a curvature in a radially extending plane, i.e., a plane defined by either the forward face  44  or a rearward face  46  ( FIG. 5 ) of the seal strips  22 , extending between a leading edge  38  and a trailing edge  40  of the seal strips  22 . The curvature of the inner edge tip portion  36  is configured to match the curvature of the shaft  16  along the portion of the shaft  16  where the tip portion  36  contacts the surface  34  of the shaft  16 , and comprises an elliptical shape, i.e., a section of an ellipse. The elliptical shape of the tip portion  36  provides a substantially uniform engagement or spacing between the tip portion  36  and the surface  34  of the shaft  16 , effecting a substantially uniform sealing between the tip portion  36  and the shaft  16  across the width of the seal strip  22 . The curvature of the tip portion  36  may be greater or lesser than that shown, depending on the angle β of the tip portion  36  relative to the rotational axis  15  of the shaft  16 . 
         [0029]    Further, the outer edge  26  of the seal strip  22  may include a curvature, depicted by the dotted line  27  in  FIG. 8 , generally parallel to the tip portion of the inner edge  36 . Although not necessary for the present invention, the outer edge  26  may be formed as an elliptical curved edge to match a curvature of the carrier  20  adjacent to the outer edge  36  at the connection  24 . 
         [0030]    Referring to  FIG. 9 , the seal strips  22  may include additional flow inhibiting features, inhibiting leakage flow F L  between the adjacent seal strips  22 . In particular, the rearward face  46  of the seal strip  22  may be formed with a flow inhibiting feature at the trailing edge  40  comprising a tapered portion  48 . The tapered portion  48  cooperates with the forward face  44  of an adjacent seal strip  22  to define a diffuser section  50  that facilitates passage of the cavity flow F C  into the gaps between the adjacent seal strips  22  to increase the back pressure between the seal strips  22 . The increased back pressure inhibits and reduces the leakage flow F L  in the direction from the leading edge  38  toward the trailing edge  40  of the seal strips  22 . 
         [0031]    Referring to  FIG. 10 , another flow inhibiting feature is illustrated and comprises one of the leading and trailing edges  38 ,  40  of the seal strips  22  comprising a turned portion  52  to form an angle transverse to the forward and rearward faces  44 ,  46  of the seal strips  22 . As shown in  FIG. 10 , the turned portion  52  comprises the leading edge  38  turned at a substantially perpendicular angle extending away from the rearward face  46 , i.e., directed generally facing toward the cavity flow F C . The turned portions  52  require the leakage flow F L  to turn as it passes into the spaces between the seal strips  22 , producing pressure losses in the flow field of the leakage flow F L  and thereby reducing the leakage flow F L . The turned portions  52  may be provided at either or both the leading edge  38  and/or the trailing edge  40  to increase the flow losses in the leakage flow F L  at either or both edges of the seal strips  22 . 
         [0032]    Referring to  FIGS. 11 and 12 , a further flow inhibiting feature comprises a rough surface coating  54  that may be applied to one or both of the forward and rearward facing surfaces  44 ,  46 . A surface roughness of the surface coating  54  effects flow pressure losses in the leakage flow F L  between the adjacent seal strips  22  to reduce the leakage flow F L . The surface roughness may comprise a depth D of surface features  56  formed by discrete variations in the depth of the surface coating  54 . For example, the depth D of the surface features  56  in the surface coating  54  may be in a range from about 5 μm to about 50 μm. The surface coating  54  may comprise a metallic coating applied to the forward and rearward faces  44 ,  46  of the seal strips  22 . Alternatively, for lower temperature applications, i.e., applications in which the seal strips  22  operate near ambient air temperatures, the surface coating  54  may comprise a plastic coating material applied to the forward and rearward faces  44 ,  46  to form a surface roughness on the seal strips  22 . 
         [0033]    It should be understood that any one or combination of the flow inhibiting features described in  FIGS. 9-12  may be incorporated into any of the seals  21  or  21 ′ described above. 
         [0034]    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.