Abstract:
Embodiments for a compressor stator vane assembly in a gas turbine engine are disclosed. In an embodiment of the present invention a stator vane assembly is provided having a plurality of vanes each with an attachment and channels machined into the forward and aft walls of the attachment. A forward hook ring segment is pressfit into the channel in the forward wall of the attachment and an aft hook ring is pressfit into the channel in the aft wall of the attachment. The hook ring segments join a plurality of vanes together so as to provide a uniform engagement of mounting slots in the compressor case. Such an arrangement increases the contact area between the hook rings and the compressor case such that damping of individual vane vibrations are improved and operating stresses are reduced.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable. 
       TECHNICAL FIELD 
       [0003]    The present invention relates to gas turbine engines. More particularly, embodiments of the present invention relate to a stator vane assembly for use in a compressor of a gas turbine engine. 
       BACKGROUND OF THE INVENTION 
       [0004]    Gas turbine engines are typically utilized to provide thrust to an aerial vehicle or mechanical power to drive an electrical generator. Gas turbine engines comprise at least a compressor, a combustion system, and a turbine, with the turbine coupled to the compressor through a shaft. 
         [0005]    A typical compressor comprises a plurality of axially spaced and alternating rows of rotating and stationary airfoils. The rotating airfoils in the compressor are commonly referred to as blades and stationary airfoils are referred to as vanes or stators. Each stage of the blades and vanes decrease in radial height through the compressor as the volume of space decreases. As a result, the air compresses and pressure increases through each stage. The vanes serve to redirect the airflow onto the next stage of blades at the correct incidence angle. 
         [0006]    Compressor vanes have an attachment for mounting the individual vanes in the compressor casing. The compressor blades are mounted by an attachment to the rotor while the compressor vanes are mounted by an attachment to the compressor casing. This configuration can be better understood with reference to  FIG. 1 , which depicts a portion of a typical gas turbine engine in cross section. The engine  10  includes an inlet  12 , a compressor  14 , a plurality of can-annular combustors  16 , a turbine  18 , a diffuser  20 , and a shaft  22  (not shown) that lies generally coaxial to a centerline A-A. A closer, more detailed view of the compressor section  14  is shown in  FIG. 2 . 
         [0007]      FIG. 2  depicts a series of alternating rows of blades  24  and vanes  26 . The blades  24  are attached to a disk  28  and extend radially outward towards a compressor case  30  whereas the vanes  26  are attached to the compressor case  30  and extend radially inward towards the centerline A-A. 
         [0008]    An example of a prior art compressor vane  26  used in the compressor  14  is shown in  FIG. 3 . The compressor vane  26  in  FIG. 3  includes two straight hooks  32  located as part of the attachment  34  for mounting the vane  26  in the compressor case  30 . However, the compressor case  30  is annular in shape and the slots  36  extend circumferentially about the case. Therefore, with the vane  26  having straight hooks  32  and the vanes being placed into circumferential slots  36  in the case, the hooks did not sit completely flush in the slots  36 , and as a result a concentrated load occurs at the ends of the hooks  32 . 
         [0009]    This straight hook configuration is ideal for manufacturing due to its simple machining techniques and set-up required. Since all surfaces are straight and perpendicular, each vane can be individually machined. However, this arrangement is not ideal for engine operation due to the mismatch between the hooks and slots and the high localized stress that occurs due to this mismatch. As a result of this configuration the compressor vanes vibrate and rattle during engine operation. Any damping that does occur for this design is limited due to the stators being individual (low mass/low inertia) and having limited contact area with the slots for reacting displacement forces. As a result of the increased stress and limited damping, significant wear is exhibited at the compressor vane attachment hooks as well in the circumferential slot of the case. This wear requires premature replacement of the vanes and repair to the case. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides embodiments for a compressor stator vane assembly in a gas turbine engine that addresses the limited damping capability of the prior art vane configuration. In an embodiment of the present invention a stator vane assembly is provided having a plurality of vanes, each vane having an attachment and channels machined into forward and aft walls of the attachment. A forward hook ring segment is pressfit into the channel in the forward wall of the attachment and an aft hook ring segment is pressfit into the channel in the aft wall of the attachment. The hook ring segments in turn engage the grooves in the compressor case, such that the contact area between the hook rings and the compressor case are significantly improved. 
         [0011]    In an alternate embodiment, a method of forming a compressor vane assembly is disclosed. The method disclosed provides a means for assembling a plurality of vanes together with a forward hook ring segment pressfit into a channel in the forward face of the attachment and an aft hook ring segment pressfit into a channel in the aft face of the attachment. 
         [0012]    In a further embodiment, a method of modifying prior art individual vanes into a compressor stator vane assembly is provided. The method utilizes modifying existing individual vanes having a pair of straight hooks to provide a channel in the forward face of the attachment and a channel in the aft face of the attachment. The method further comprises placing a forward hook ring segment into the channel and an aft hook ring segment into the channel such that each of the hook ring segments are pressfit into the attachment of the vanes to form a vane assembly. 
         [0013]    Additional advantages and features of the present invention will be set forth in part in a description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from practice of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0014]    The present invention is described in detail below with reference to the attached drawing figures, wherein: 
           [0015]      FIG. 1  depicts a partial cross section view of a typical gas turbine engine of the prior art; 
           [0016]      FIG. 2  depicts a partial cross section view of a portion of the compressor of the prior art; 
           [0017]      FIG. 3  depicts a perspective view of a series of vanes installed in the case of the prior art; 
           [0018]      FIG. 4  depicts a perspective view of a vane assembly installed in a case in accordance with a preferred embodiment of the present invention; 
           [0019]      FIG. 5  depicts a partial cross section view of a vane assembly in accordance with a preferred embodiment of the present invention; 
           [0020]      FIG. 6  depicts a partial cross section view of the attachment portion of a vane assembly in accordance with a preferred embodiment of the present invention; and 
           [0021]      FIG. 7  depicts a perspective view of a hook ring segment in accordance with a preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    The subject matter of the present invention is described with specificity herein to meet statutory requirements. However, the description itself is not intended to limit the scope of this patent. Rather, the inventors have contemplated that the claimed subject matter might also be embodied in other ways, to include different steps or combinations of steps similar to the ones described in this document, in conjunction with other present or future technologies. Moreover, although the terms “step” and/or “block” may be used herein to connote different elements of methods employed, the terms should not be interpreted as implying any particular order among or between various steps herein disclosed unless and except when the order of individual steps is explicitly described. 
         [0023]    Referring now to  FIGS. 4-7 , the present invention provides a vane assembly  50  for reducing operating stresses and vibrations in individual vanes. The vane assembly of the present invention comprises a plurality of vanes  52 , each vane having an airfoil  54  and an attachment  56 . The attachment  56  has a first surface  58  adjacent the airfoil  54  and a second surface  60  spaced a distance from the first surface. In the embodiment shown in  FIGS. 4-7 , the first surface  58  is generally parallel to the second surface  60 . However, depending on the actual attachment geometry, these surfaces could each have a radius of curvature. 
         [0024]    Extending between the first surface  58  and the second surface  60  is a pair of generally parallel and axially extending sidewalls  62  and  64  and a forward wall  66  and aft wall  68 , with the forward and aft walls  66  and  68  being generally perpendicular to the plurality of sidewalls  62  and  64 . Another feature of the attachment  56  is a forward channel  70  in the forward wall  66  and an aft channel  72  in the aft wall  68 . As it can be noted from  FIG. 6 , the forward channel  70  and aft channel  72  both have a general “C” shape cross section. Furthermore, the channels  70  and  72  are generally arc-shaped in the direction along the forward and aft walls such that the channels have a radius of curvature. In addition, the channels  70  and  72  are located at approximately the same radial position along the attachment. 
         [0025]    The vane assembly  50  also comprises a forward hook ring segment  74  which has a circumferential length and an axially extending hook  76  and an aft hook ring segment  78  which also has a circumferential length and an axially extending hook  80 . The aft hook ring segment  78  is shown in  FIG. 7 . The hook ring segments  74  and  78  are used to join the plurality of vanes  52  together into vane assembly  50 . This is possible since the hook ring segments are generally arc-shaped with a radius of curvature corresponding to the arc-shaped channels  70  and  72 . 
         [0026]    In order to join the vanes together, the forward hook ring segment  74  is pressfit into the forward channel  70  and the aft hook ring segment  78  is pressfit into the aft channel  72  of the attachment  56 . To assist in the assembly of the hook ring segments  74  and  78  into the attachment, the hook ring segments each have chamfers at approximately a 45 degree angle at the corners of the surfaces that are first inserted into the channels  70  and  72 . The outside edges  70   a  and  72   a  of the channels are also chamfered. 
         [0027]    As one skilled in the art will understand, a pressfit is a means of binding two or more components together through an interference fit along mating surfaces. The exact amount of interference is a function of the design requirements, component materials, and operating conditions. For an embodiment of the present invention, the radial dimensions of the forward and aft channels  70  and  72 , respectively, are slightly undersized compared to the radial height of the forward and aft hook ring segments  74  and  78 , respectively. For the embodiment disclosed in  FIGS. 4-7 , this difference in dimension is set for up to 0.0005 inches of interference between the mating surfaces of the hook ring segment and channel. Such an interference fit was set in order to minimize stresses in the attachments  56  yet provide sufficient retention of vanes  52  in hook ring segments  74  and  78 . However, the interference fit could be slightly larger, for example up to about 0.0015 inches without exceeding the material capabilities of the vane attachments. The interference fit also serves to dampen the vibrations in the individual vanes and reduce the amount of displacement that can occur from vane-to-vane during operation. 
         [0028]    As previously stated, the hook ring segments join a plurality of vanes together. For the embodiment shown in  FIGS. 4-7 , the vane assembly  50  comprises five vanes  52  assembled together by hook ring segments  74  and  78 . However, the quantity of vanes shown in the vane assembly is meant to be merely illustrative and the actual quantity of vanes can vary depending on the engine configuration. 
         [0029]    Depending on the engine conditions and compressor case receiving the vane assemblies, it may be desirable to also apply a coating to the surfaces of the hook ring segments that contact the compressor casing. Specifically, this region is radially inward of the axially extending hooks. Applying a coating, such as an Aluminum Bronze, ensures that the wear between the hook ring segments and the compressor case will be directed towards the hook ring segments, as these components can be replaced easier than repairing the large compressor casing out in the operating field. 
         [0030]    Once the vanes are assembled with the hook ring segments into the vane assembly  50 , it is ready to be installed in the compressor casing. The vane assembly is held in the casing by the hooks  76  and  80  on the forward hook ring segment and aft hook ring segment respectively. Each vane assembly is intended to abut to an adjacent vane assembly when installed in an engine so as to provide additional damping from assembly to assembly. While it is intended that each vane assembly abuts and adjacent vane assembly, as one skilled in the art will understand, there may be small gaps between adjacent vane assemblies due to manufacturing and/or assembly tolerances. Any gaps that may be present between the vane assemblies are sealed by shim plates. 
         [0031]    In an alternate embodiment, a method of forming a compressor stator vane assembly is disclosed in which the method comprises providing a plurality vanes, with each vane having an airfoil  52  and an attachment  56  having a forward wall  66  and an aft wall  68 . Each of the forward wall and aft wall have a channel  70  and  72  therein, respectively. 
         [0032]    The method also comprises providing a circumferentially extending forward hook ring segment  74  and a circumferentially extending aft hook ring segment  78 . The method then comprises a step of inserting the forward hook ring segment  74  into the forward channel  70  and inserting the aft ring segment  78  into the aft channel  72 . By inserting the forward and aft hook ring segments into the forward and aft channels, the plurality of vanes are joined together to create a vane assembly with this vane assembly having increased damping capability. 
         [0033]    In yet another embodiment of the invention, a method of modifying individual vanes to form a compressor stator vane assembly is disclosed. In this method a plurality of vanes are provided with each vane having an airfoil  52  and an attachment  56  with the attachment having a first surface  58  and a second surface  60  spaced a distance from the first surface  58  and generally parallel thereto. Extending between the first surface  58  and the second surface  60  is a pair of generally parallel sidewalls  62  and  64  and a forward wall  66  and an aft wall  68 , with the forward and aft walls and the sidewalls being generally perpendicular to the first surface and second surface. The attachment is also initially provided with forward and aft hooks  32  (see  FIG. 3 ) that are generally parallel to the first and second surfaces. 
         [0034]    This method also comprises providing a circumferentially extending forward hook ring segment  74  and a circumferentially extending aft hook ring segment  78 . Since this vane assembly is fabricated from existing individual vane segments, the sidewalls  62  and  64  of the attachment are machined at an angle so as to taper the sidewalls and improve surface area contact between adjacent vane sidewalls. This angle is preferably radial, but can also be a compound radial/axial angle. The existing forward and aft hooks  32  are removed by machining a forward channel  70  having a radius of curvature into the forward wall  66  and machining an aft channel  72  having a radius of curvature into an aft wall  68  of the attachment. Once the vane attachment has been modified to remove the original hooks and incorporate the channels, the forward hook ring segment  74  is inserted into the forward channel  70  and the aft hook ring segment  78  is inserted into the aft channel  72 . These hook ring segments join together the individual vane segments at their attachment to form a vane assembly. 
         [0035]    The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive. Alternative embodiments will become apparent to those of ordinary skill in the art to which the present invention pertains without departing from its scope. 
         [0036]    From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects set forth above, together with other advantages which are obvious and inherent to the system and method. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and within the scope of the claims.