Abstract:
An apparatus for use in a gas turbine engine includes a wall defining an exterior face, a first film cooling passage extending through the wall for providing film cooling to the exterior face of the wall, and a second film cooling passage extending through the wall adjacent to the first film cooling passage for providing film cooling to the exterior face of the wall. The first film passage includes a first vortex-generating structure for inducing a vortex in a first rotational direction in a cooling fluid passing therethrough, and the second film passage includes a second vortex-generating structure for inducing a vortex in a second rotational direction in a cooling fluid passing therethrough. The first and second rotational directions are substantially opposite one another.

Description:
BACKGROUND 
       [0001]    The present invention relates to film cooling, and more particularly to structures and methods for providing vortex film cooling flows along gas turbine engine components. 
         [0002]    Gas turbine engines utilize hot fluid flows in order to generate thrust or other usable power. Modern gas turbine engines have increased working fluid temperatures in order to increase engine operating efficiency. However, such high temperature fluids pose a risk of damage to engine components, such as turbine blades and vanes. High melting point superalloys and specialized coatings (e.g., thermal barrier coatings) have been used to help avoid thermally induced damage to engine components, but operating temperatures in modern gas turbine engines can still exceed superalloy melting points and coatings can become damaged or otherwise fail over time. 
         [0003]    Cooling fluids have also been used to protect engine components, often in conjunction with the use of high temperature alloys and specialized coatings. One method of using cooling fluids is called impingement cooling, which involves directing a relatively cool fluid (e.g., compressor bleed air) against a surface of a component exposed to high temperatures in order to absorb thermal energy into the cooling fluid that is then carried away from the component to cool it. Impingement cooling is typically implemented with internal cooling passages. However, impingement cooling alone may not be sufficient to maintain suitable component temperatures in operation. An alternative method of using cooling fluids is called film cooling, which involves providing a flow of relatively cool fluid from film cooling holes in order to create a thermally insulative barrier between a surface of a component and a relatively hot fluid flow. Problems with film cooling include flow separation or “liftoff”, where the film cooling flow lifts off the surface of the component desired to be cooled, undesirably allowing hot fluids to reach the surface of the component. Film cooling fluid liftoff can necessitate additional, more closely-spaced film cooling holes to achieve a given level of cooling. Cooling flows of any type can present efficiency loss for an engine. The more fluid that is redirected within an engine for cooling purposes, the less efficient the engine tends to be in producing thrust or another usable power output. Therefore, fewer and smaller cooling holes with less dense cooling hole patterns are desirable. 
         [0004]    The present invention provides an alternative method and apparatus for film cooling gas turbine engine components. 
       SUMMARY 
       [0005]    An apparatus for use in a gas turbine engine includes a wall defining an exterior face, a first film cooling passage extending through the wall for providing film cooling to the exterior face of the wall, and a second film cooling passage extending through the wall adjacent to the first film cooling passage for providing film cooling to the exterior face of the wall. The first film passage includes a first vortex-generating structure for inducing a vortex in a first rotational direction in a cooling fluid passing therethrough, and the second film passage includes a second vortex-generating structure for inducing a vortex in a second rotational direction in a cooling fluid passing therethrough. The first and second rotational directions are substantially opposite one another. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a perspective view of an exemplary film cooled turbine blade. 
           [0007]      FIG. 2A  is a cross-sectional view of a portion of a film cooled gas turbine engine component. 
           [0008]      FIGS. 2B-2E  are cross-sectional views of portions of the film cooled gas turbine engine component taken along lines B-B, C-C, D-D and E-E, respectively, of  FIG. 2A . 
           [0009]      FIG. 3  is a schematic view of a pair of film cooling passages. 
           [0010]      FIGS. 4A-4C  are cross-sectional views of exemplary embodiments of vortex-generating structures. 
           [0011]      FIG. 5  is a schematic view of another embodiment of a film cooling passage. 
           [0012]      FIG. 6A  is a cross-sectional view of a portion of another embodiment of a film cooled gas turbine engine component. 
           [0013]      FIGS. 6B and 6C  are cross-sectional views of a portion of the film cooled gas turbine engine component, taken along lines B-B and C-C, respectively, of  FIG. 6A . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The present invention, in general, relates to structures and methods for generating a counter-rotating vortex film cooling flow along a surface of a component for a gas turbine engine exposed to hot gases, such as a turbine blade, vane, shroud, duct wall, etc. Such a film cooling flow can provide a thermally insulative barrier between the gas turbine engine component and the hot gases. According to the present invention, a pair of film cooling passages have closely-spaced outlets at an exterior surface (or face) of the component that is exposed to the hot gases. A vortex-generating structure is positioned within each film cooling passage of the pair to generate a vortex flow. The vortex flow generated within a first of the pair of film cooling passages rotates in a first rotational direction therein, prior to reaching an outlet, and the vortex flow generated within a second of the pair of film cooling passages rotates in a substantially opposite direction (i.e., counter-rotates with respect to the first rotational direction). In one embodiment of the present invention, the vortex-generating structures can comprise helical ribs (or rifling), with the helical ribs of the first and second film cooling passages winding in opposite directions. Additional features and benefits of the present invention will be recognized in light of the description that follows. 
         [0015]      FIG. 1  is a perspective view of an exemplary film cooled turbine blade  20  having an airfoil portion  22 . Pairs of film cooling hole outlets  24  are positioned along exterior sidewall surfaces of the airfoil portion  22  (only one side of the airfoil portion  22  is visible in  FIG. 1 ). The hole outlets  24  of each pair are located at substantially the same streamwise location along the airfoil portion  22 . During operation, the pairs of film cooling hole outlets  24  eject a film cooling fluid (e.g., compressor bleed air) to provide a thermally insulative barrier along portions of the turbine blade  20  exposed to hot gases. The particular arrangement of the pairs of film cooling hole outlets  24  shown in  FIG. 1  is merely exemplary, and nearly any desired arrangement of the pairs of film cooling hole outlets  24  is possible in alternative embodiments. It should also be noted that the turbine blade  20  is shown merely as one example of a gas turbine engine component that can be film cooled according to the present invention. The present invention is equally applicable to other types of gas turbine engine components, such as vanes, shrouds, duct walls, etc. 
         [0016]      FIG. 2A  is a cross-sectional view of a portion of a wall  30  of a film cooled gas turbine engine component. The wall  30  has an exterior surface  32  that is exposed to a hot gas flow  34 . As shown in  FIG. 2A , a substantially cylindrically shaped first film cooling passage  36 A extends through the wall  30  to a first outlet  38 A located at the exterior surface  32  of the wall  30 , the first film cooling passage  36 A angled slightly toward a free stream direction of the hot gas flow  34 . The first outlet  38 A can be shaped similarly to a cross-sectional profile of an interior portion of the first film cooling passage  36 A. A substantially helically-shaped vortex generating rib  40 A is positioned along an interior surface of the first film cooling passage  36 A, and can be formed using electro-discharge machining (EDM), stem drilling, casting, or other suitable processes. A film cooling fluid  42  passes through the first film cooling passage  36 A and is ejected from the first outlet  38 A, and then forms a thermally insulative barrier along the exterior surface  32  of the wall  30  that extends downstream from the first outlet  38 A. Although only the first film cooling passage  36 A is visible in  FIG. 2A , a second film cooling passage  36 B can be positioned adjacent to the first film cooling passage  36 A and have a similar configuration. The first and second film cooling passages  36 A and  36 B respectively can be arranged substantially parallel to one another, angled toward one another (i.e., in a non-parallel arrangement), or have other configurations. Furthermore, the first and second film cooling passages  36 A and  36 B respectively can be connected to a common fluid supply manifold (not shown), or otherwise branched together opposite the first and second outlets  38 A and  38 B respectively. 
         [0017]      FIG. 2B  is a cross-sectional view of a portion of the wall  30  of the film cooled gas turbine engine component, taken along line B-B of  FIG. 2A . The pair of first and second film cooling passages  36 A and  36 B respectively have a first and second substantially helically-shaped vortex-generating ribs  40 A and  40 B, respectively. The first vortex-generating rib  40 A generates a vortex flow within the first film cooling passage  36 A in generally a first rotational direction  44  (e.g., clockwise). The second vortex-generating rib  40 B generates a vortex flow within the second film cooling passage  36 B in generally a second rotational direction  46  (e.g., counter-clockwise). It should be noted that the cross-section of  FIG. 2B  is taken at a location within the wall  30 , upstream from the first and second outlets  38 A and  38 B respectively of the film cooling passages  36 A and  36 B (see  FIG. 2A ), and vortex flows are present within the film cooling passages  36 A and  36 B upstream from the first and second outlets  38 A and  38 B respectively. 
         [0018]      FIG. 2C  is a cross-sectional view of a portion of the wall  30  of the film cooled gas turbine engine component, taken along line C-C of  FIG. 2A  just downstream from the first and second outlets  38 A and  38 B respectively (not shown in  FIG. 2C ) along the exterior surface  32  of the wall  30  (relative to the hot gas flow  34 ). As shown in  FIG. 2C , cooling fluid  42  from both the first and second film cooling passages  36 A and  36 B respectively (not shown in  FIG. 2C ) have mixed together to form a contiguous jet of the film cooling fluid  42  upon leaving the first and second outlets  38 A and  38 B, respectively (not shown in  FIG. 2C ). A boundary  48  is defined between the jet of the film cooling fluid  42  and the hot gas flow  34 . The cooling fluid  42  passes along the exterior surface  32  of the wall  30 , attached thereto, that is, the film cooling fluid  42  remains substantially in contact with the exterior surface  32  to form a barrier between the exterior surface  32  and the hot gas flow  34 . The film cooling fluid  42  includes counter-rotating vortices defined by fluid rotating in the substantially opposite first and second rotational directions  44  and  46  respectively. The first and second rotational directions  44  and  46  respectively can be arranged to generally oppose a tendency of the hot gas flow  34  to move toward the exterior surface  32  of the wall  30 , thereby reducing “liftoff” or “flow separation” that occur when a portion of the hot gas flow  34  extends between the film cooling fluid  42  and the exterior surface  32  of the wall  30 . In the illustrated embodiment, the first and second rotational directions  44  and  46  respectively are arranged to flow generally toward the exterior surface  32  at a location where the vortexes adjoin each other, and generally away from the exterior surface  32  at lateral boundaries of the jet of the film cooling fluid  42 . 
         [0019]      FIG. 2D  is a cross-sectional view of a portion of the wall  30  of the film cooled gas turbine engine component, taken along line D-D of  FIG. 2A  downstream from the cross-sectional view shown in  FIG. 2C  (relative to the hot gas flow  34 ). As shown in  FIG. 2D , the counter-rotating vortices defined by the film cooling fluid  42  rotating in the substantially opposite first and second rotational directions  44  and  46  respectively causes mixing with the hot gas flow  34  at or near the boundary  48 , which can reduce momentum of the counter-rotating vortices of the film cooling fluid  42  and also reduce or disrupt momentum of the hot gas flow  34  in a direction toward the wall  30 . This mixing can help reduce “liftoff” of the film cooling fluid  42 , such that the film cooling fluid  42  remains substantially attached to the exterior surface  32  of the wall. 
         [0020]      FIG. 2E  is a cross-sectional view of a portion of the wall  30  of the film cooled gas turbine engine component, taken along line E-E of  FIG. 2A  downstream from the cross-sectional view of  FIG. 2D . As shown in  FIG. 2E , mixing of the film cooling fluid  42  with the hot gas flow  34  (not labeled in  FIG. 2E ) has formed a mixed fluid zone  48  around the original location of the boundary  48 , which is no longer a distinct transition. The film cooling fluid  42  has lost essentially all rotational kinetic energy, meaning the counter-rotating vortices have substantially ceased to rotate. The film cooling fluid  42  still moves downstream along wall  30  substantially attached to the exterior surface  32 . The film cooling fluid  42  will inevitably degrade as it continues downstream along the exterior surface  32  of the wall  30 . However, the present invention can allow the film cooling fluid  42  to provide a relatively effective thermal barrier that is substantially attached to the exterior surface  32  for a relatively long distance along the wall  32  downstream from the first and second outlets  38 A and  38 B respectively. 
         [0021]      FIG. 3  is a schematic view of the pair of first and second film cooling passages  36 A and  36 B respectively. The first and second film cooling passages  36 A and  36 B respectively define first and second central axes  50 A and  50 B, respectively. The first and second central axes  50 A and  50 B respectively are arranged substantially parallel to one another, and are closely spaced apart by a distance S. As used herein, the term “closely spaced” means spaced from each other on the order of a few diameters. The first film cooling passage  36 A has a radius R A , and the second film cooling passage has a radius R B . In one embodiment, the radii R A  and R B  can be substantially equal. The first vortex-generating structure  40 A has a pitch P A , and the second vortex-generating structure  40 B has a pitch P B . The pitches P A  and P B  can be substantially constant (as shown in  FIG. 3 ) or variable along lengths of the first and second film cooling passages  36 A and  36 B, respectively. 
         [0022]    The first and second vortex-generating structures  40 A and  40 B respectively can have nearly any desired cross-sectional shape (or profile).  FIGS. 4A ,  4 B, and  4 C are cross-sectional views of exemplary embodiments of vortex-generating structures  140 A,  140 B, and  140 C, respectively, each defining a height H t  and a width W t . The vortex-generating structure  140 A shown in  FIG. 4A  has a substantially rectangular cross-sectional shape, the vortex-generating structure  140 B shown in  FIG. 4B  has a substantially triangular cross-sectional shape, and the vortex-generating structure  140 C shown in  FIG. 4C  has a substantially arcuate cross-sectional shape. It should be understood that further cross-sectional shapes can be utilized in alternative embodiments. 
         [0023]    The following are descriptions of particular dimensions and proportions for exemplary embodiments of the present invention. These embodiments are provided merely by way of example and not limitation. The first and second film cooling passages  36 A and  36 B and the first and second vortex-generating structures  40 A and  40 B can be described as having vortex generating structures with a pitch P that is a multiple of a radius R, where P represents either the pitch P A  or P B  and R represents the corresponding radius R A  or R B . The pitch P can be in the range of approximately 1 to 10 times the radius R, or alternatively in the range of approximately 1.5 to 3 times the radius R. 
         [0024]    A ratio of the height of vortex-generating structure H t  over the diameter of the associated film cooling passage (i.e., two time the radius R A  or R B ) can be between approximately 0.05 and 0.5, or alternatively between approximately 0.1 and 0.3. A ratio of the width W t  over the height H t  of the vortex-generating structures  40 A and  40 B can be between approximately 0.5 and 4, or alternatively between approximately 0.5 and 1.5. The distance S between the axes  50 A and  50 B can be less than approximately ten times the radius R, or alternatively between approximately two to six times the radius R. Furthermore, a length of the first and second film cooling passages  36 A and  36 B respectively can be at least approximately three to ten times a hydraulic diameter at the respective first and second outlets  38 A and  38 B, or alternatively at least approximately 5 to ten times the hydraulic diameter at the respective first and second outlets  38 A and  38 B (where the hydraulic diameter is four times the area divided by the perimeter). 
         [0025]      FIG. 5  is a schematic view of an alternative embodiment of a film cooling passage  36  of the present invention (applicable to either one of the pair of film cooling passages  36 A or  36 B). As shown in  FIG. 5 , the film cooling passage  36  includes two sets of helical vortex-generating ribs  46 C and  46 D that wind in the same direction, adjacent one another (the vortex-generating rib  46 C is represented by a weighted line in  FIG. 5 , for illustrative purposes). In the illustrated embodiment, the rib  46 C has a pitch P 1  and the rib  46 D has a pitch P 2 . The pitches P 1  and P 2  can be substantially equal. The pitches P 1  and P 2  can be substantially constant (as shown in  FIG. 3 ) or variable along lengths of the film cooling passage  36 . In further embodiments, still more additional ribs can be provided. 
         [0026]    The present invention provides numerous advantages. For example, while mixing of film cooling fluid jets with hot gas flows represents an efficiency loss, that loss is balanced against improved film cooling effectiveness per film cooling passage. This can permit a given level of film cooling to be provided to a given component with a relatively small number of film cooling passages for a given film cooling fluid flow rate and/or increasing spacing between pairs of cooling hole outlets. Moreover, even with the presence of paired, closely spaced cooling hole outlets, the present invention can provide film cooling to a given surface area with a relatively low density of cooling holes and a relatively low total cooling hole area. Film cooling according to the present invention can help allow gas turbine engine components to operate in higher temperature environments with a relatively low risk of thermal damage. 
         [0027]      FIGS. 6A ,  6 B and  6 C illustrate an alternative embodiment of the present invention, configured to produce a different effect from the previously described embodiments.  FIG. 6A  is a cross-sectional view of another embodiment of a portion of a wall  30  of the film cooled gas turbine engine component.  FIG. 6B  is a cross sectional view of a portion of the film cooled gas turbine engine component  30 , taken along line B-B of  FIG. 6A . In this embodiment, the first film cooling passage  36 A has a first helical vortex-generating rib  40 C, which winds in an opposite direction with respect to the first vortex-generating rib  40 A of previously-described embodiments, and a second helical vortex-generating rib  40 D, which winds in an opposite direction with respect to the second vortex-generating rib  40 B of previously-described embodiments (vortex-generating ribs  40 A and  40 B are not shown in  FIG. 6B ). In this configuration, the film cooling fluid  42  rotates in the second rotational direction  46  (e.g., counter-clockwise) within the first film cooling passage  36 A, and the film cooling fluid  42  rotates in the first rotational direction  44  (e.g., clockwise) within the second film cooling passage  36 B. 
         [0028]      FIG. 6C  is a cross sectional view of a portion of the film cooled gas turbine engine component  30 , taken along line C-C of  FIG. 6A  (i.e., downstream from an outlet of the film cooling passage  36 A). In the illustrated embodiment, the first and second rotational directions  44  and  46  are arranged to flow generally away from the exterior surface  32  at a location where the vortexes adjoin each other, and generally toward the exterior surface  32  at lateral boundaries of the jet of the film cooling fluid  42 . This configuration would essentially encourage liftoff of the fluid  42  from the exterior surface  32  (i.e., the entrainment of the hot gas flow  34  between the exterior surface  32  and the cooling fluid  42 ), which may be desirable for fluidic injection applications, etc. 
         [0029]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For instance, the particular angle of film cooling passages relative to a film cooled surface can vary as desired for particular applications. Moreover, a cross-sectional area of film cooling passages of the present invention can vary over their length (e.g., with substantially conical film cooling passages).