Patent Publication Number: US-2018051582-A1

Title: Rotating brush slea with bristle shield

Description:
BACKGROUND OF THE INVENTION 
     Embodiments of the invention relate generally to brush seals and, more particularly, to a rotating brush seal attached to a rotating component wherein the bristles of the brush seal protected by a bristle shield, more than circumferentially. 
     Known brush seals are typically mounted or attached to a stationary component of a turbomachine, where only the flexible bristle tips of the brush seal engage a rotating component during operation of the turbomachine to form a dynamic seal. Known brush seals also typically include bristles that are angled circumferentially with respect to the rotating component. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a brush seal for use between a rotating component and a stationary component in a turbomachine is provided. The brush seal includes a set of flexible bristles having a fixed end and a free end. The free end of the set of flexible bristles seals against a radially inward surface of the stationary component. The set of flexible bristles are angled axially at an axial angle of about 15 degrees to about 70 degrees with respect to the rotating component. The set of flexible bristles are also angled circumferentially at an angle that is less than the axial angle. A frusto-conical retaining plate extends radially outward from the rotating component at least partially along a length of the set of flexible bristles, such that the retaining plate is configured to at least partially support the set of flexible bristles on a radially inner surface of the retaining plate from centrifugal loading in an operative state of the turbomachine. A bristle shield extends radially outward from the rotating component at least partially along a length of the set of flexible bristles, such that the bristle shield is configured to at least partially shield the set of flexible bristles from flow during an operative state of the turbomachine. The set of flexible bristles is located between the retaining plate and the bristle shield. A circumferential groove is in the rotating component, and the circumferential groove has a downstream side and an upstream side. A side plate is attached to the upstream side of the circumferential groove. The fixed end of the set of flexible bristles is attached to the upstream side of the circumferential groove by the side plate, and the retaining plate is attached to both the downstream and upstream side of the circumferential groove. The retaining plate is attached to the upstream side of the circumferential groove by the side plate in the rotating component. 
     In another aspect, a turbomachine includes a rotating component having a circumferential groove therein. The circumferential groove has an upstream side and a downstream side. A side plate is attached to the circumferential groove. The turbomachine also includes a stationary component and a brush seal for use between the rotating component and the stationary component. The brush seal includes a set of flexible bristles having a fixed end and a free end. The fixed end of the set of flexible bristles is attached to the circumferential groove by the side plate. The free end of the set of flexible bristles seals against a radially inward surface of the stationary component. The set of flexible bristles are angled axially at an axial angle of about 15 degrees to about 70 degrees with respect to the rotating component. A retaining plate extends at least partially along a length of the set of flexible bristles, such that the retaining plate is configured to at least partially support the set of flexible bristles from centrifugal loading in an operative state of the turbomachine. The retaining plate is attached to the circumferential groove in the rotating component. A bristle shield extends radially outward from the rotating component at least partially along a length of the set of flexible bristles, such that the bristle shield is configured to at least partially shield the set of flexible bristles from flow during an operative state of the turbomachine. The set of flexible bristles are located between the retaining plate and the bristle shield. 
     In yet another aspect, a brush seal is provided for use between a rotating component and a stationary component in a turbomachine. A circumferential groove is in the rotating component, and a side plate is attached to the circumferential groove. The brush seal includes a set of flexible bristles having a fixed end and a free end. The fixed end of the set of flexible bristles is attached to the circumferential groove by the side plate. The free end of the set of flexible bristles seals against a radially inward surface of the stationary component. The set of flexible bristles are axially angled at an angle of about 15 degrees to about 70 degrees with respect to the rotating component. The set of flexible bristles are circumferentially angled at an angle that is less than the axial angle. A retaining plate is attached to the circumferential groove by a dovetail assembly. The retaining plate extends radially outward from the rotating component at least partially along a length of the set of flexible bristles, such that the retaining plate is configured to at least partially support the set of flexible bristles on a radially inner surface of the retaining plate from centrifugal loading in an operative state of the turbomachine. A bristle shield extends radially outward from the rotating component at least partially along a length of the set of flexible bristles, such that the bristle shield is configured to at least partially shield the set of flexible bristles from flow during an operative state of the turbomachine. The set of flexible bristles are located between the retaining plate and the bristle shield. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which: 
         FIG. 1  shows a partial cross-sectional view of a turbomachine including a brush seal as known in the art. 
         FIGS. 2 and 3  show cross-sectional views of a brush seal as known in the art. 
         FIGS. 4-8  show cross-sectional views of brush seals according to aspects of this invention. 
         FIG. 9  shows an axial cross-sectional view of a portion of a brush seal according to an aspect of this invention. 
         FIGS. 10-12  show exploded views of gaps between arcuate segments of a brush seal according to aspects of this invention. 
         FIGS. 13-14  illustrate top, cross-sectional views of the flexible bristles and the bristle shield, according to aspects of this invention. 
     
    
    
     It is noted that the drawings of the invention are not necessarily to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings,  FIG. 1  shows a cross-sectional view of a conventional brush seal  15 , as known in the art, in use in a turbomachine  1 . Two additional views of brush seal  15  are shown in  FIGS. 2 and 3 . As illustrated in  FIGS. 2 and 3 , brush seal  15  comprises a set of bristles for use between a rotating component  10  (also referred to as a rotor) and a stationary component  20  of turbomachine  1  (e.g., a gas turbine, steam turbine, etc.). It is understood that brush seal  15  forms a ring when installed in turbomachine  1 , and typically brush seal  15  comprises a series of arcuate segments forming the complete ring when installed. As known in the art, brush seal  15  has a fixed end  14  mounted or attached to stationary component  20 , and a flexible free end  16  that extends towards rotating component  10  to form a dynamic seal. A backing plate  22  can also be included (mounted on stationary component  10 ), that acts to support flexible free end  16  as it is pressed against backing plate  22  by pressure loading while turbomachine  1  is in an operative state. As shown by arrow R in  FIG. 2 , in an operative state, rotating component  10  rotates in the direction of arrow, R. As shown in  FIGS. 2 and 3 , the bristles of brush seal  15  are angled circumferentially with respect to an axial axis, A axial , and a radial axis, A radial , of rotating component  10 . The angled bristles are easy to deflect and will move radially as rotating component  10  undergoes excursion or vibration. 
     As illustrated by angle, a, in  FIG. 2 , the bristles of brush seal  15  are angled circumferentially with respect to the axial and radial axes (A axial  and A radial , shown in  FIGS. 2 and 3 ) of rotating component  10 . Since the bristles are angled along the same circumferential direction as rotational direction, R, of rotating component  10 , the bristle tips can ride on the surface of rotating component  10  without causing buckling or locking up. The circumferential angle, a, of the bristles, also called the “cant angle” or “lay angle,” is orientated such that free end  16  extends in the same direction as rotational direction, R, of rotating component  10 . 
       FIG. 4  illustrates a cross-sectional view of a brush seal  100  according to aspects of this invention. Brush seal  100  is used to form a dynamic seal between a rotating component  102  and a stationary component  104  in turbomachine  1  ( FIG. 1 ). Brush seal  100  comprises a set of bristles  110  and forms a ring when installed. For example, brush seal  100  can comprise a series of arcuate segments forming a complete ring when installed. In addition, the set of bristles  110  has a fixed end  112  and a free end  114 . However, brush seal  100  differs from known seals in the art in several aspects. For example, as discussed in more detail herein, fixed end  112  is mounted, or attached, to rotating component  102 , not stationary component  104 . Also, the set of bristles  110  is angled substantially axially, not mainly circumferentially (as in known systems), with respect to rotating axis, A rotating , of rotating component  102 . A bristle shield  140  is placed adjacent to the bristles  110 , and the bristle shield  140  both protects and shields the bristles from flow during an operative state of the turbomachine. 
     As shown in  FIG. 4 , brush seal  100  further includes a conical or frusto-conical retaining plate  116  that at least partially supports, i.e., bears a partial load of, the set of bristles  110 . Frusto-conical retaining plate  116  extends at least partially along a radial length of the set of bristles  110  such that, in an operative state of the turbomachine, retaining plate  116  at least partially supports the set of bristles  110  from centrifugal loading. 
     The bristles  110  are sandwiched between the retaining plate  116  and the bristle shield  140 . As shown in  FIG. 4 , the bristle shield  140  extends radially outward from the rotating component and at least partially along a length of the set of flexible bristles  110 . The bristle shield  140  extends radially outward or past the retaining plate  116 , as shown in  FIG. 4 . However, the bristle shield may extend all the way to the radially inward surface of the stationary component  104  (as shown in  FIG. 6 ), or to about the same outer radial distance as the retaining plate  116  (as shown in  FIG. 5 ). The amount of shielding and protection provided by the bristle shield  140  may be adjusted by the “height” of the bristle shield. Higher bristle shields may be desired in applications where bristle protection is a priority, whereas lower bristle shields may be more desirable where larger rotational clearances between the rotating and stationary components are specified. 
     The bristle shield  140  may be comprised of a second set of thicker and stiffer bristles than the bristles in flexible bristles  110 . As one example only, the flexible bristles  110  may be comprised of bristles having a diameter of about 2.5 mils to about 4 mils. The bristles in the bristle shield  140  may have a diameter of about 5 mils to about 10 mils, so it can be seen that the bristles in bristle shield  140  are thicker and stiffer than the bristles in flexible bristles  110 . The thinner bristles  110  are better at sealing, but are more susceptible to damage or deformation from flow or flow disturbances. The thicker bristles in bristle shield  140  are less effective at sealing, but are better at resisting damage from flow. The combination of thick/thin bristles as described results in a more robust and better sealing brush seal. 
     As referenced above, embodiments of this invention include a brush seal  100  having a fixed end  112  mounted, or attached to, rotating component  102 .  FIGS. 4-8  show various examples of how fixed end  112  of bristles  110  can be mounted or attached to rotating component  102 . As shown in  FIGS. 4-8 , a circumferential groove  103  can be included in rotating component  102 . Circumferential groove  103  has a first, front, side  103   a  and a second, back, side  103   b  ( FIG. 4 ). Frusto-conical retaining plate  116  and fixed end  112  of the set of bristles  110  can be inserted into groove  103 , and attached to rotating component  102  as desired. In a first example, shown in  FIG. 4 , retaining plate  116  can be attached to back (or downstream side) side  103   b  through the use of caulks and/or welds. Caulk  120  and/or welds along faces of retaining plate  116  contact groove  103 , and fixed end  112  can be attached to front (or upstream) side  103   a  and retaining plate  116  through the use of a side plate  118 . It is also understood that brazed or soldered joints can be used in conjunction with, or in place of, the caulk and welded joints discussed herein. 
     In a second example, shown in  FIG. 5 , the set of bristles  110  is bent such that fixed end  112  is axially displaced with respect to free end  114 . Therefore, retaining plate  116  is similarly bent, such that retaining plate  116  extends along at least a portion of the length of the set of bristles  110 . Again, as in  FIG. 4 , retaining plate  116  and the set of bristles  110  can be attached to groove  103  through the use of caulks and welds. An electron beam weld  122 , shown in  FIG. 5 , is another example of how the set of bristles  110  may be attached to retaining plate  116 . The bristle shield  140  extends radially outward to about the same radial distance as the retaining plate  116 . Even in this configuration, the bristle shield  140  still shields and protects a majority of the bristles  110 . 
     In  FIG. 6 , the set of bristles  110  is bent as in  FIG. 5 , but in this example, a screw  124  (e.g., a grub screw) is used to attach retaining plate  116  to rotating component  102 . Screw  124  can be screwed through retaining plate  116  into rotating component  102 , in addition to, or in place of, the caulk/friction combination that is used in  FIGS. 4 and 5 . It is also understood that other fasteners, other than a screw, can be used, for example, a bolt, a pin, etc. The bristle shield  140  has an end that is adjacent to the radially inward surface of the stationary component  104 . This configuration will provide maximum shielding and protection for the bristles  110 , and may be desirable in applications were clearances are minimal. 
     As shown in  FIG. 7 , a dovetail assembly can be used to attach retaining plate  116 , bristle shield  140  and the set of bristles  110  to rotating component  102 . In this example, groove  103  includes a retaining feature  126  which holds retaining plate  116  (which is attached to the set of bristles  110  through the use of a weld  122  and side plate  118  in this example) in place once the set of bristles  110  is slid circumferentially into groove  103 . In order to facilitate sliding the set of bristles  110  into groove  103 , an entry dovetail slot  128  can be used (illustrated by dotted line in  FIG. 7 ). The bristle shield  140  extends radially outward of the end of the retaining plate  116 , and a substantial majority of the bristles  110  are shielded and protected by bristle shield  140 . 
     In any of the embodiments discussed herein, retaining plate  116  can be integrally machined into rotating component  102  or can comprise a separate element that is welded or otherwise attached to rotating component  102 . If retaining plate  116  is integral to rotating component  102 , as discussed herein, an entry groove/slot (similar to slot  128  shown in  FIG. 7 ) can be used to insert the set of bristles  110  and bristle shield  140  into rotating component  102 . In this embodiment, a relatively small entry slot  128  can be used, and this embodiment could result in a relatively more compliant brush seal  100  because the set of bristles  110  and bristle shield  140  could be bent as they are fed into the groove/slot. Bending the set of bristles  110  and bristle shield  140  in this way could result in less gap leakages between the segments of brush seal  100 , as well as minimize the issues of holding the set of bristles  110  in the area of the entry slot. This embodiment would further reduce the total rotating mass of brush seal  100  as an additional back plate would not be necessary. 
     In  FIG. 8 , a modification of the configurations shown in  FIGS. 6 and 7  is shown. In this embodiment, a retaining feature  126  (similar to  FIG. 7 ) can be used along with a pin or grub screw  124  (similar to  FIG. 6 ), where one or more pins  124  can act as anti-rotation mechanisms for brush seal  100  elements. A variety of configurations for pins  124  are possible (and applicable to any embodiments shown herein including pins  124 ). For example, (1) one anti-rotation pin  124  per segment can be used, with pins  124  either at a middle section of a segment, or just inboard of the end of the segment to limit segment movement which could lead to imbalance, (2) one anti-rotation pin  124  can be used, positioned on each side of the entry slot  128  ( FIG. 7 ), or (3) one anti-rotation pin  124  can be used, positioned between the two adjacent segment ends, and centered in the middle of entry slot  128  ( FIG. 7 ). The bristle shield  140  extends close to, but does not touch, the radially inward surface of the stationary component. 
     Regardless of how brush seal  100  is mounted to rotating component  102 , the axial angle of the set of bristles  110  and/or bristle shield  140  of brush seal  100  assists in allowing brush seal  100  to seal effectively. Since brush seal  100  rotates with rotating component  102 , if the set of bristles  110  were angled substantially circumferentially, the centrifugal loading would tend to straighten the bristles out and cause bending stress at the root of the bristles. In addition, if the set of bristles  110  are allowed to straighten out, the bristles will not move inward easily, and can buckle or be damaged when brush seal  100  moves toward stationary component  104  during rotor excursion or vibration. Therefore, a large cant angle is not desirable for rotating brush seal  100  according to embodiments of this invention. 
     Therefore, as discussed herein, the set of bristles  110  is not angled substantially circumferentially as in prior art brush seals, but rather is mainly angled axially, and is supported by retaining plate  116  and shielded/protected by bristle shield  140 . This is further illustrated in  FIG. 9 , showing a partial axial cross-sectional view of brush seal  100 , showing the set of bristles  110  are not substantially circumferentially angled. When the turbomachine is in an operative state, the set of bristles  110  is pressed against retaining plate  116  by centrifugal force. Angling the set of bristles  110  axially, in accordance with embodiments of this invention, will cause the bristles to bend forward and away from retaining plate  116  if seal  100  is pushed by stationary component  104 . 
     As also shown in  FIG. 9 , brush seal  100  can comprise a series of arcuate segments (three segments S 1 , S 2 , S 3  are partially shown in  FIG. 9 , but it is understood that in practice, brush seal  100  can comprise a plurality of arcuate segments that will form a complete ring.) As shown in  FIG. 9 , gaps  132  are typically included between segments, referred to as butt gaps  132 . As shown in  FIG. 9 , a spring  134  can be inserted in one or more butt gaps  132 . Springs  134  can act to allow for thermal expansion due to brush seal  100  heating faster than rotating component  102  on startup as well as to account for different coefficients of thermal expansion between rotating component  102  and brush seal  100 . Springs  134  also act to keep pressure on the segments to damp aeromechanical vibration. Springs  134  can comprise thin and stiff springs, such as wave springs, of any shape desired. Three examples of different shapes and configurations of springs  134  are shown in the exploded views of gaps  132  in FIGS.  10 - 12 .  FIG. 9  further shows an anti-rotation grub screw  124  (as discussed in connection with  FIG. 8 ), with grub screw  124  position in the middle of segment S 2 . 
     In one embodiment of the invention, the pressure loading is from left to right referring to  FIGS. 4-8 , with the bristle shield  140  facing a higher pressure side of the brush seal, while retaining plate  116  is exposed to a downstream side of the brush seal with lower pressure. In such an arrangement, both the pressure force and centrifugal force act to press the set of bristles  110  against retaining plate  116  and balance the pressure loading. In another embodiment of the invention, the pressure loading can be from right to left (or vice versa, depending on the orientation of the turbomachine), where the retaining plate  116  is exposed to the higher pressure side, and the bristle shield  140  faces the lower pressure side. 
     The axial angle of the set of bristles  110  can be set to achieve desired flexibility without requiring excessive axial space. In one embodiment, the set of bristles  110  can be angled in an axial direction with respect to rotating component  102  at an axial angle of approximately 15 degrees to approximately 70 degrees, for example, at approximately 30 to 45 degrees. 
     As discussed herein, a circumferential angle of the set of bristles  110  is not necessary to make brush seal  100  flexible. However, a small circumferential angle, substantially less than the axial angle, may be beneficial for seal  100 , not for flexibility reasons, but for operability, for example, in the range of approximately 0 to 15 degrees. Therefore, a small cant angle in a circumferential direction can be used, where the set of bristles  110  will contract owing to the cant angle, opening up clearance between seal  100  and stationary component  104  at no or low speed to avoid rub during transient. As speed goes up to operating condition, the set of bristles  110  will stretch out, reducing the cant angle, thus closing up the gap between the tips of the set of bristles  110  and stationary component  104 . 
     An additional benefit of brush seal  100  according to embodiments of this invention is that the heat generated by brush seal  100  will not cause rotor bowing like conventional brush seals because the bristle tips slide on stationary component  104 . The heat generated by the rubbing of the tips of the set of bristles  110  on stationary component  104  will partly go into stationary component  104  and partly be taken away by leakage through the set of bristles  110 . Therefore, there is little to no heat going into rotating component  102 . In contrast, in conventional brush seals, the bristle tips rub the surface of the rotating component, which heats up the rotating component directly. This heating of the rotating component can cause the rotating component to bow and further increase undesirable non-uniform heating. 
     As shown in  FIGS. 4-8 , additional seals can also be used in conjunction with brush seal  100 . For example, one or more tooth seals, such as J-strip seals  130 , can be used. J-strip seals  130  can have a fixed end attached to rotating component  102  and a free end extending radially outward from rotating component  102  toward stationary component  104 . J-strip seals  130  can be positioned axially upstream and/or downstream of brush seal  100 . 
       FIG. 13  illustrates a top, cross-sectional view of brush seal  100 , according to an aspect of the present invention. The bristle shield  140  is comprised of a second set of thicker and stiffer bristles than the bristles in flexible bristles  110 . As one example only, the flexible bristles  110  may be comprised of bristles having a diameter of about 2.5 mils to about 4 mils. The bristles in the bristle shield  140  have a thicker diameter of about 5 mils to about 10 mils. The thicker and stiffer bristles  140  protect and shield the thinner and more flexible bristles  110 . Thinner bristles are better at sealing, but are more susceptible to damage or deformation from flow or flow disturbances. Thicker bristles are less effective at sealing (compared to thinner bristles), but are better at resisting damage from flow. The present combination of thick/thin bristles results in a more robust and better sealing brush seal. Both of the bristles in layers  110  and  140  may be comprised of cobalt alloys, Haynes 25, Haynes 188, or any other suitable material as desired in the specific application. 
       FIG. 14  illustrates a top, cross-sectional view of brush seal  100 , according to an aspect of the present invention. The bristle shield  1440  is comprised of sheet metal. The sheet metal may have a thickness of about 5 mils to about 10 mils, or more, and may also be made of cobalt alloys, Haynes 25, Haynes 188, or any other suitable material. The solid nature of the sheet metal provides excellent shielding and protection of flexible bristles  110 , as there are “no gaps” when compared to a bristle layer or bristle layers. However, sheet metal layer  1440  still retains flexibility and can bend radially inward if it contacts the radially inward surface of the stationary component. It most applications the radially outward edge of the sheet metal layer  1440  will be designed so it does not contact the stationary component, but still provides shielding and protection for bristles  110 . 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any related or incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.