Abstract:
A stator for a turbo-machine having a plurality of airfoils extending radially therefrom has a base from which the airfoils depend, and slits disposed in the base, each slit disposed adjacent a pair of airfoils, wherein a first set of adjacent slits and a distance between a second set of adjacent slits varies

Description:
BACKGROUND 
       [0001]    Gas turbine engines include alternating stages of rotating blades and stationary vanes. Each vane stage comprises a plurality of stator segments. A segment could include a plurality of vanes extending between an outer platform and an inner platform. Stator segments are commonly formed by casting or by brazing. 
         [0002]    To relieve any build-up of stress caused by temperature gradients in the vanes and platforms during engine operation, the inner platform typically includes relief slits between adjacent vanes. These relief slits also help isolate vanes from vibration modes of adjacent vanes. The stator segment also includes a damper to reduce vibration amplitudes, thereby helping prevent vane cracking. 
       SUMMARY 
       [0003]    According to an embodiment shown herein, stator for a turbo-machine having a plurality of airfoils extending radially therefrom has a base from which the airfoils depend, and slits disposed in the base, each slit disposed adjacent a pair of airfoils, wherein first set of adjacent slits and a distance between a second set of adjacent slits varies. 
         [0004]    According to a further embodiment shown herein, a gas turbine engine stator having a plurality of airfoils depending radially inwardly therefrom has a base from which the airfoils depend, and slits disposed in the base, each slit disposed between a pair of airfoils, first set of adjacent slits and a distance between a second set of adjacent slits varies. 
         [0005]    According to a still further embodiment shown herein, method for creating a stator having a plurality of blades depending therefrom includes the steps of designing slits, each slit disposed between a set of adjacent blades, wherein the slits have varying distances therebetween wherein a first area between a first set of the slits has a first frequency mode that is not in tune with a second area between a second set of the slits having a second frequency mode, and creating the slits within the stator. 
         [0006]    Although different examples have the specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components of another of the examples. 
         [0007]    These and other features disclosed herein can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic view of a gas turbine engine that incorporates an embodiment disclosed herein. 
           [0009]      FIG. 2  is a top, segmented, view of a portion of  FIG. 1  taken along the lines  2 - 2 . 
           [0010]      FIG. 3  is a bottom view of  FIG. 2 . 
           [0011]      FIG. 4  shows a method of determining spacing within the embodiment shown in  FIGS. 2 and 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Referring to  FIG. 1 , an example turbo-machine, such as a gas turbine engine  10 , is circumferentially disposed about an axis A. The gas turbine engine  10  includes a fan  14 , a low pressure compressor section  16 , a high pressure compressor section  18 , a combustion section  20 , a high pressure turbine section  22 , and a low-pressure turbine section  24 . Other example turbo-machines may include more or fewer sections and different arrangements. 
         [0013]    During operation, air is compressed in the low pressure compressor section  16  and the high pressure compressor section  18 . The compressed air is then mixed with fuel and burned in the combustion section  20 . The products of combustion are expanded across the high pressure turbine section  22  and the low pressure turbine section  24 . 
         [0014]    The low pressure compressor section  16  and the high pressure compressor section  18  include low pressure rotors  28  and high pressure rotors  30 , respectively. The high pressure turbine section  22  and the low pressure turbine section  24  each include high pressure rotors  36  and low pressure rotors  38 , respectively. The rotors  36  and  38  rotate in response to the expansion to rotatably drive the high pressure compressor section  18  and the low pressure compressor section  16 . 
         [0015]    The rotor  36  is coupled to the low pressure rotor  28  with a spool  44 , and the rotor  38  is coupled to the rotor  30  with a spool  46 . Bearings rotatably support the spools  44  and  46  during operation of the gas turbine engine  10 . 
         [0016]    A plurality of vanes, for instance, low pressure compressor vanes  48 , high pressure compressor vanes  50 , high pressure turbine vanes  52  and low pressure turbine blades  54  are interspersed between the rotors  28 ,  30 ,  36 ,  38  to direct air as it passes between sections of the engine  10 . The blades may also be referred to as airfoils. 
         [0017]    The examples described in this disclosure are not limited to the two-spool gas turbine architecture described, however, and may be used in other architectures, such as the single-spool axial design, a three-spool axial design, and still other architectures. That is, there are various types of gas turbine engines, and other turbo-machines, that can benefit from the examples disclosed herein. 
         [0018]    Referring now to  FIGS. 2 and 3 , an example stator  56  has a plurality of segments  70  (one of which is shown in  FIG. 2 ) that abut each other to form a ring (shown in  FIG. 1 ). An example stator  56  may have seven or eight such segments  70  connected end-to-end to each other. Each segment has a radially curved base  75  having forward end  80  and aft end  85 . A forward side wall  90  and an aft sidewall  95  each extend radially upwardly from forward end  80  and aft end  85  of the base  75  respectively. Forward brim  100  extends forward axially from side wall  90  and aft brim  105  extends aft from side wall  95  such that the brims  100 ,  105  do not extend over the base  75 . A sheet (not shown), usually made of a shaped metal, may be placed against the base  75  between the sidewalls  90 ,  95  to damp structural vibrations in the segments. 
         [0019]    Depending downwardly from the base  75 , a plurality of vanes  50  (e.g., blades or airfoils) extend. The vanes  50  and the segment  70  may be formed together as clusters to minimize the costs of manufacturing a segment. The vanes  50  have a curved cross-sectional shape  110  that is contained on the base  75 . Each vane  50  has a forward end portion  115  and an aft end portion  120 . The vanes  50  may be angled relative to Axis A as may be required by the requirements of the engine  10 . 
         [0020]    It has been discovered by the Applicants herein, that a segment  70  made in a cluster and that has multiple vanes or airfoils may have very similar vibratory modes to other segments, which can result in resonance or mistuning that could shorten the life of a segment. Harmonious vibratory modes may be destructive to a lifespan of a segment  70 . 
         [0021]    Between each vane  50 , a slit  125  is disposed (e.g., cut or formed or the like) that extends through aft brim  105 , aft side wall  95  and into the base  75  at an angle corresponding to the disposition of the vanes  50  from the base  75 . The slits  125  are not regularly spaced and the distance or widths W between slits  125  differ. For instance width W (including an area including a vane/airfoil and a piece of the base  75 ) may be different from width W 2  or width W 3  or width W n . The depth of each slit  125  may vary though they may extend to the forward end portion  115  of the airfoil/vane  50 . The width of each slit  125  may also vary though they may be kept uniform for ease of construction. The slits  125  may be filled with a damping material  127  such as an elastomer or the like, which may further limit vibratory modes and act to minimize the flow of air through the slits  125 . The slits  125  may also be mechanically blocked by a damping sheet  127  (see  FIG. 2 ) or the like. The slits  125  extend radially through the base  75  from a top  130  to a bottom  135  thereof. There may be a slit  125  between or adjacent to each vane  50 . The slits  125  may be skewed relative to each other to improve the (dis)harmonics of each width W. 
         [0022]    Though the segment  70  demonstrated herein is used in the high pressure compressor section  18  of the engine  10 , one of ordinary skill in the art recognizes that the teachings herein may be used in other sections of the engine  10 . 
         [0023]    Referring now to  FIG. 4 , a method of creating a segment using widths W n  is shown. The varying widths/distance W n  that create discordant resonant frequencies are determined that deliberately mistune each width relative to other widths (step  205 ), operation of the segment  70  with varied widths is simulated (step  210 ), the efficacy of chosen widths as to the life of the segment  70  (e.g., minimize damage to the segment  70 ) in reaction to the chosen widths W n  is determined (step  215 ) and the slits are created if appropriate (step  220 ). In essence, each width is a tuning fork with given vibratory modes that might combine with other modes that may damage the segment  70 . By varying each width W n  and each width&#39;s attendant vibratory modes thereby, a non-destructive discordance is created. 
         [0024]    Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments. 
         [0025]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.