Abstract:
A hydrostatic seal and vibration damping apparatus for a gas turbine engine adapted to reduce vibrations during cold engine start-ups is disclosed. In one disclosed configuration, the vibration damping apparatus is comprised of a temperature sensitive control ring having a relatively high coefficient of thermal expansion adapted to expand quickly at relatively low temperatures to protect the hydrostatic seal during such gas turbine engine startups. At operational temperatures, the control ring is adapted to become separated from the hydrostatic sea.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This patent application is a US National Stage under 35 U.S.C. §371, claiming priority to International Application No. PCT/US2013/75978 filed on Dec. 18, 2013, which claims priority under 35 U.S.C. §119(e) to U.S. Patent Application Ser. No. 61/800,075 filed on Mar. 15, 2013. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure generally relates to gas turbine engines and, more particularly, relates to vibration damping apparatus for seal assemblies of gas turbine engines. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    With a gas turbine engine, a number of different components rotate relative to fixed components under extremely tight tolerances. For example, the compressor and turbine sections of a gas turbine engine include radially outwardly extending blades, which collectively form a rotor. Such rotors rotate relative to a fixed engine case which forms a stator, with a very small annular gap between the rotor and stator. To increase the efficiency and operation of the gas turbine engine, it is important that such gaps be maintained so as to allow for proper rotation, but do so at as small a dimension as necessary to limit air leakage through the gap. 
         [0004]    In order to minimize leakage through such gaps, seals are employed in gas turbine engines. Such seals can be contacting seals such as labyrinth or brush seals, or non-contacting seals such as hydrostatic seals. While labyrinth seals can be effective they require that all parts be manufactured and maintain at extremely tight tolerances, and can generate significant amounts of heat at the knife edge and seal rub interface. Brush seals can also be effectively, but can be prone to coking and are largely uni-directional in their sealing capability. Hydrostatic seals, on the other hand, employ a plurality of circumferentially spaced shoes extending from spring elements mounted to the stator. Such spring biased movement afforded to the shoes enables the gap between the rotor and stator to be properly maintained at all times as the velocity of the air flowing through the gap increases and decreases. 
         [0005]    While hydrostatic seals are effective, as gas turbine engine are subjected to extreme temperature ranges from start-up through maximum speed, particularly in the hot sections of the engine such as the turbine and diffuser, significant vibrations in the seal can be encountered. Such vibrations may be particularly harsh during engine cold starts, wherein the seals can become damaged by such vibrations, in some cases to the extent that overall sealing effectiveness may be compromised. 
         [0006]    It can therefore be seen that apparatus for damping such vibrations in hydrostatic seals of gas turbine engines are needed. 
       SUMMARY OF THE DISCLOSURE 
       [0007]    In accordance with one aspect of the disclosure, a hydrostatic seal and vibration damping assembly for a gas turbine engine is disclosed. The assembly may comprise a hydrostatic seal having a shoe, and a vibration damping apparatus operatively associated with the shoe, wherein the vibration damping apparatus has a different coefficient of thermal expansion than the hydrostatic shoe. 
         [0008]    In a refinement, the vibration damping apparatus may be annular in shape. 
         [0009]    In another refinement, the vibration damping apparatus is oval in shape. 
         [0010]    In another refinement, the vibration damping apparatus is a discontinuous loop. 
         [0011]    In yet another refinement, the vibration damping apparatus comprises an Inconel material. 
         [0012]    In another refinement, the vibration damping apparatus is an Inconel 718 material. 
         [0013]    In another refinement, the vibration damping apparatus has a circular cross-section. 
         [0014]    In another refinement, the vibration damping apparatus has a rectangular cross-section. 
         [0015]    In yet another refinement, the vibration damping apparatus has an extended oval cross-section. 
         [0016]    In another refinement, the vibration damping apparatus is positioned against a radially outer diameter of the shoe. 
         [0017]    In accordance with another aspect of the disclosure, a gas turbine engine is disclosed. The engine may comprise a stator, a rotor rotating within the stator and defining a circumferential gap therebetween, a hydrostatic seal positioned within the circumferential gap and including a plurality of spring-biased shoes; and a vibration damping apparatus operatively associated with the hydrostatic seal to limit vibrations of the shoe. 
         [0018]    In a refinement, the vibration damping apparatus is formed so as to engage the shoe and limit vibration of the shoes during a cold start-up of the gas turbine engine, and disengage from the shoe after the gas turbine engine reaches an operational temperature. 
         [0019]    In a refinement, the vibration damping apparatus is manufactured from a material having a different coefficient of thermal expansion than the shoes. 
         [0020]    In another refinement, the vibration damping apparatus is one of circular and oval in shape. 
         [0021]    In another refinement, the vibration damping apparatus is a discontinuous loop. 
         [0022]    In yet another refinement, the vibration damping apparatus comprises an Inconel material. 
         [0023]    In another refinement, the vibration damping apparatus comprises an Inconel 718 material. 
         [0024]    In another refinement, the vibration damping apparatus has one of a circular, rectangular, and extended oval cross-section. 
         [0025]    In yet another refinement, the hydrostatic seal further comprises a spacer plate and a front plate which cooperate with the shoe to define a channel, and the vibration damping apparatus is positioned within the channel. 
         [0026]    In accordance with yet another aspect of the disclosure, a method of damping vibrations in a hydrostatic seal of a gas turbine engine is disclosed. The method may comprise positioning a hydrostatic seal between a rotor and a stator of the gas turbine engine, extending a shoe of the hydrostatic seal into a gap between the rotor and the stator, engaging the shoe with a vibration damping apparatus when the gas turbine engine initiates a cold start-up, and disengaging the shoe from the vibration damping apparatus when the gas turbine engine reaches an operational temperature. 
         [0027]    In a refinement, the hydrostatic seal further includes a front plate and spacer plate which cooperate to form a channel, and the method further includes positioning the vibration damping apparatus within the channel. 
         [0028]    In another refinement, the method further includes manufacturing the vibration damping apparatus from a material having a different coefficient of thermal expansion than the shoe. 
         [0029]    In another refinement, the method further includes manufacturing the vibration damping apparatus from an Inconel material. 
         [0030]    These and other aspects and features of the present disclosure will be better understood in light of the following detailed description when read in light of the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  is a side cross-sectional view of a gas turbine engine constructed in accordance with the teachings of this disclosure. 
           [0032]      FIG. 2  is a plan view of a hydrostatic seal and vibration damping apparatus of the gas turbine engine of  FIG. 1 , and constructed in accordance with the teachings of this disclosure; 
           [0033]      FIG. 3  is a fragmentary plan view of one section of the hydrostatic seal and vibration damping apparatus of  FIG. 2 ; 
           [0034]      FIG. 4  is a cross-sectional view of the hydrostatic seal and vibration damping apparatus of  FIG. 2  taking along line  4 - 4  of  FIG. 2 ; 
           [0035]      FIG. 5  is a plan view of one embodiment of a vibration damping apparatus constructed in accordance with the teachings of this disclosure; 
           [0036]      FIG. 6  is a cross-sectional view of the vibration damping apparatus of  FIG. 5 , taken along line  6 - 6  of  FIG. 5 ; 
           [0037]      FIG. 7  is a plan view of a second embodiment of a vibration damping apparatus constructed in accordance with the teachings of this disclosure; 
           [0038]      FIG. 8  is a cross-sectional view of the vibration damping apparatus of  FIG. 7 , taken along line  8 - 8  of  FIG. 7 ; 
           [0039]      FIG. 9  is a plan view of a third embodiment of a vibration damping apparatus constructed in accordance with the teachings of this disclosure; 
           [0040]      FIG. 10  is a cross-sectional of the vibration damping apparatus of  FIG. 9 , taken along line  10 - 10  of  FIG. 9 ; and 
           [0041]      FIG. 11  is a flowchart depicting a sample sequence of steps which may be practiced in accordance with the present disclosure. 
       
    
    
       [0042]    It should be understood that the drawings are not to scale, and that the disclosed embodiments are illustrated only diagrammatically and in partial views. It should also be understood that this disclosure is not limited to the particular embodiments illustrated herein. 
       DETAILED DESCRIPTION 
       [0043]    Referring now to the drawings, and with initial reference to  FIG. 1 , a gas turbine engine constructed in accordance with the teachings of the present disclosure is generally referred to reference numeral  20 . As shown, the gas turbine engine  20  includes a fan  22 , a compressor  24 , a diffuser  26 , a combustor  28 , and a turbine  30  axially aligned along a longitudinal shaft(s)  31 . As the functionality of a gas turbine engine is well known to those of ordinary skill in the art, its operation will not be discussed in detail herein. However, it is important to note, that the engine  20  includes a number of rotors  32  rotating within fixed stators  34 . For example, as shown, the compressor  24  and turbine  30  include a plurality of radially outwardly extending blades  36  which collectively form rotors  32 , which rotate within sections of an engine case  38 , forming stators  34 . 
         [0044]    To allow the rotors  32  to rotate within the stators  34 , circumferential air gaps  40  are maintained therebetween as shown in  FIGS. 1 and 4 . Moreover, in order to limit leakage of air through the gap  40 , a hydrostatic seal  44  such as the one shown in  FIGS. 2 and 3 , is operatively associated with each gap  40 . As shown in  FIG. 4 , the hydrostatic seal  44  includes a seal carrier or housing  46  mounted directly to the stator  34 . The seal carrier  46  holds a main or primary seal  48 , along with a secondary seal  50  situated downstream of the primary seal  48 . A seal cartridge  52  is employed to encapsulate and support the main or primary seal  48  and secondary seal  50  in a single structure for ease of manufacture and/or installation. 
         [0045]    A front plate  54  is adapted to secure the primary and secondary seals  48 ,  50  within the cartridge  52 . The front plate  54  may be threadedly or otherwise secured to the cartridge  52  in a manner that permits the front plate  54  to maintain tight securement and positioning of both the primary and secondary seals  48 ,  50 , respectively. 
         [0046]    In order to maintain the integrity of the primary and secondary seals  48 ,  50  within the seal cartridge  52 , a spacer plate  56  is adapted to assure independent operation of the primary seal  48  and the secondary seal  50 , even though the two may be relatively tightly axially juxtaposed by the front plate  54 . In the disclosed embodiment, an anti-rotation pin  58  is adapted to constrain the secondary seal  50  against any relative rotation within the seal cartridge  52 . A retaining ring  60 , axially secured against the front plate  54 , assures a tertiary retention aspect for the fully assembled seal cartridge  52 , i.e. to assure containment of the primary and secondary seals  48 ,  50 , within the seal carrier  46 . 
         [0047]    In the disclosed embodiment, the primary seal  48  is a hydrostatic non-contacting seal, having a plurality of circumferentially spaced and segmented shoes  62 . As shown best in  FIGS. 2 and 3 , the shoes  62  are integral with the primary seal  48  by way of spring elements  64 . Employing such a spring-biased arrangement, the shoes  62  are adapted to hydrostatically float relative to the gap  40  between the shoes  28  and the rotor  32 . More specifically, as the seal carrier  46  is mounted to the stator  34 , a limit to the radially outer movement of the shoes  62  is provided. To limit the radially inner movement of the shoes  62 , one or more arms  66  are provided which are adapted to engage shoulders  68 . In so doing, the shoes  62  cannot completely close the gap  40  and detrimentally engage the rotor  32 . 
         [0048]    In order to limit the vibration of the shoes  62 , the present disclosure provides a vibration damping apparatus  70  in operative association with the hydrostatic seal  44 . The vibration damping apparatus  70 , when mounted to the hydrostatic seal  44 , collectively form a hydrostatic seal and vibration damping assembly  71 . In the depicted embodiment of  FIG. 5 , the vibration damping apparatus  70  is provided in the form of a vibration control ring or annulus  72 , but in the embodiments of  FIGS. 7-10 , non-circular shapes, such as but not limited to, ovals and non-continuous loops are possible, as will be described in further detail herein. 
         [0049]    As shown best in  FIG. 4 , the vibration damping apparatus  70  is situated within a channel  74  defined between the shoe  62 , the spacer plate  56 , and the front plate  54 . Alternatively, the vibration control ring  72  may be situated on the radially inner, rather than radially outer, circumference of the shoe  62 . The vibration control ring  72  can be effective to dampen vibrations, and/or particularly undesirable resonance modes thereof, that can occur during engine operation, especially during cold engine startups, as may be appreciated by those skilled in the art. 
         [0050]    More specifically, within hot sections of gas turbine engines, hydrostatic seals may be particularly sensitive to cold start vibrations; i.e. vibrations incurred prior to the full thermal expansion of parts achieved at hot section operating temperatures. During periods of rising temperatures, i.e. from cold start to normal operating temperatures, the vibration control ring  72  provides damping to protect the shoes  62 , while becoming essentially inert at normal gas turbine engine operating temperatures. This may be accomplished by manufacturing the vibration control ring  72  from a material having coefficient of thermal expansion which is higher than the coefficient of thermal expansion of the hydrostatic seal  44 . For example, a nickel alloy may provide a relatively high coefficient of thermal expansion, permitting the vibration control ring  72  to expand rapidly upon startup for providing immediate damping from ambient temperature up through about 200 degrees Fahrenheit. In so doing, when cold, e.g, at engine start-up, the vibration control ring  72  engages the shoes  62  and limits vibration thereof. Beyond about 200° F., however, the vibration control ring  72  expands away from the shoes  62  and offers no functional input, i.e., neither benefit nor burden. 
         [0051]    In other embodiments, the vibration damping apparatus  70  may be manufactured from other materials including, but not limited to, an Inconel material such as Inconel 718. It should be noted, in addition, that the vibration damping apparatus  70  does not need to be manufactured from a material having a higher coefficient of thermal expansion than the hydrostatic seal  44 , and that it is the difference in thermal expansion coefficients between the two components that provides the benefit. Depending on the geometry and the environmental conditions at which the vibrations occur, the material of the vibration damping apparatus could be selected such that its thermal expansion coefficient otherwise alters its geometry sufficiently to damp vibrations. 
         [0052]    Referring now to  FIGS. 5 and 6 , a first embodiment of the disclosed vibration damping apparatus  70  is presented. In this embodiment, the vibration damping apparatus  70  is comprised of the continuous vibration control ring or annulus  72 . In such an embodiment, as shown in  FIG. 6 , the vibration control ring  72  has a circular shape in cross-section as well, but other cross-sectional shapes as will be described in further detail below are possible as well. The circular cross-section may provide particular flexibility benefits with respect to manufacture and/or installation of the vibration control ring  72  in the hydrostatic seal  44 . 
         [0053]    A second embodiment of the vibration damping apparatus  70  is depicted in  FIGS. 7 and 8 . As disclosed, the vibration damping apparatus  70  may be elliptical in shape. Such an elliptical shape may offer a resilient biasing force to facilitate initial tolerance control, for example. In such an embodiment, the vibration damping apparatus  70  may have a rectangular shape in cross-section as shown in  FIG. 8 , but other cross-sectional shapes such as the aforementioned circular shape are possible in such an embodiment as well. Such a rectangular cross-section may provide particular benefits with respect to damping within some hydrostatic seals  44  that may be subjected to particular vibrational harmonics or resonance modes, for example. 
         [0054]      FIGS. 9 and 10  depict a third embodiment of the vibration damping apparatus  70  comprised of a discontinuous loop. The loop may, also have an elliptical shape for reasons already provided with respect to the second embodiment, or may be ring-like or annular as with the first embodiment. The discontinuity of the vibration damping apparatus  70  may facilitate installation thereof within the hydrostatic seal  44 , for example. In such an embodiment, the vibration damping apparatus  70  may have an elongated oval cross-section. Such a cross-sectional shape may provide particular benefits for damping within some hydrostatic seals  44  to accommodate certain geometrical challenges with respect to spacing, as one example. Of course the cross-sectional shape of the discontinuous loop embodiment may be circular or rectangular as well. 
         [0055]    Beyond the geometries and cross-sectional shapes of the vibration damping apparatus  70  presented above, numerous and various other geometries and/or shapes, including cross-sections, may fall within the spirit and scope of this disclosure. 
         [0056]    An exemplary method of damping vibrations in a hydrostatic seal adapted for use in gas turbine engines  20  is depicted in flow chart format in  FIG. 11 . As shown, the method may include a first step  100  of providing the primary seal  48 . In a second step  102 , the secondary seal  50  may be secured to the primary seal  48  in an axially juxtaposed orientation. In a third step  104 , the sealing shoe  62  may be positioned radially inwardly of the primary and secondary seals  48 ,  50 , to provide a hydrostatic sealing gap  40  with relative to the rotor  32 . The vibration damping apparatus  70  is then mounted within the hydrostatic seal  44 , as shown in a step  106 . Since the vibration damping apparatus  70  has a coefficient of expansion greater than the shoe  62 , during cold start-up of the engine  20 , the vibration damping apparatus  70  engages the shoe  62  and limits vibration thereof during a step  108 . However, as the vibration damping apparatus  70  heats up, it expands at a different rate than the shoe  62  and thus separates from the shoe  62  when the engine  20  reaches an operating temperature, as indicated in a step  110 . 
       INDUSTRIAL APPLICABILITY 
       [0057]    From the foregoing, it may be appreciated that the technology disclosed herein may have industrial applicability in a variety of settings, such as, but not limited to, damping enhancements that may protect hydrostatic seals, such as shoes used in gas turbine engine hydrostatic seals, during cold startups. 
         [0058]    Indeed, such technology may be expanded in some cases to provide for either continuous or intermittent damping, depending on particular system requirements. For example, for continuous damping the vibration damping apparatus may be made of the same material as the base material of the hydrostatic seal to provide for suitable pairing under thermal growth. In such cases, the fit of the control ring relative to the shoes could be sized to permit only controlled relative movements, for example, by restricting deflections greater than a set or predetermined threshold. 
         [0059]    In environments requiring intermittent damping, the vibration damping apparatus material may be selected to control damping at desired operating conditions, based on relative growth of associated parts. As one example, a gas turbine engine hydrostatic seal made of a nickel-chromium super alloy material may require damping from ambient or cold start temperature, up through about 200-300 degrees Fahrenheit. If such a seal were damped by a vibration damping apparatus formed of, for example, an Inconel 718 alloy, the vibration damping apparatus would have a relatively higher coefficient of thermal expansion. As the seal heats up, the vibration damping apparatus thus expands away from the shoes to avoid contact/damping at temperatures in a normalized range, or at steady-state operating temperatures, of the hot section of a gas turbine engine. In other instances, in which damping may be desired at higher temperatures rather than low temperatures, reverse material selections may be used to provide for appropriate material pairings to accommodate desired objectives.