Abstract:
A method enables a structural cover for a gas turbine engine to be manufactured. The method includes forming a torroidial body including an integrally-formed windage cover portion and a seal flange portion, and forming a plurality offastener openings extending from a forward side of the torroidial body to an aft side of the torroidial body, such that when installed in the gas turbine engine, the windage cover portion facilitates shielding the fastener openings from a gas flow path.

Description:
This is a divisional of application Ser. No. 09/733,447, filed Dec. 8, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to gas turbine engines, and more specifically to structural covers used with gas turbine engine bolted flanges. 
     At least some known gas turbine engines include a core engine having, in serial flow arrangement, a high pressure compressor which compresses airflow entering the engine, a combustor which burns a mixture of fuel and air, and a turbine which includes a plurality of rotor blades that extract rotational energy from airflow exiting the combustor. 
     Often components within the gas flowpath are coupled together using bolted flanges. Because of the velocity of air within the gas flow path, exposed fasteners in the bolted flanges may cause undesirable disruptions in the flow path downstream from the bolted flange. Such disruptions commonly known as windage, may adversely affect engine performance. 
     To facilitate eliminating windage caused by exposed fasteners, at least some known bolted flanges include a separate windage cover which extends over the heads or nuts of the fasteners to facilitate minimizing fastener exposure to the gas flowpath. However, because of the thickness of the covers, longer fasteners and an additional alignment flange must be used in comparison to those bolted flanges which do not include the covers. As such, installing such covers increases overall manufacturing assembly time, parts count, engine weight, and overall manufacturing costs. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect of the invention, a method for manufacturing a structural cover for a gas turbine engine is provided. The method comprises forming a torroidial body including an integrally-formed windage cover portion and a seal flange portion, and forming a plurality of fastener openings extending from a forward side of the torroidial body to an aft side of the torroidial body, such that when installed in the gas turbine engine, the windage cover portion facilitates shielding the fastener openings from a gas flow path. 
     In another aspect of the invention, a structural cover for a gas turbine engine is provided. The cover includes a torroidial body including an integrally-formed windage cover portion, a seal flange portion, and at least one fastener opening extending therethrough, wherein the windage cover portion is for shielding a fastener from a gas flow path. 
     In a further aspect of the invention, a gas turbine including a torrodial structural cover is provided. The cover includes an integrally-formed windage cover portion, a seal flange portion, and a plurality of fastener openings extending therethrough. The windage cover portion is configured to facilitate sheilding fasteners extending through the fastener openings from a gas flow path. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is schematic illustration of a gas turbine engine; 
     FIG. 2 is a perspective view of a structural cover that may be used with the gas turbine engine shown in FIG. 1; 
     FIG. 3 is a cross-sectional view of the structural cover shown in FIG.  2  and taken along line  3 — 3 ; 
     FIG. 4 is a cross-sectional view of the structural cover shown in FIG.  2  and taken along line  4 — 4 ; 
     FIG. 5 is a partial cross-sectional view of a gas turbine engine including the structural cover shown in FIG.  2  and taken along line  3 — 3 ; and 
     FIG. 6 is a cross-sectional view of a known windage cover that may be used with the gas turbine engine shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a schematic illustration of a gas turbine engine  10  including a fan assembly  12 , a high pressure compressor  14 , and a combustor  16 . Engine  10  also includes a high pressure turbine assembly  18  and a low pressure turbine assembly  20 . Engine  10  has an intake side  28  and an exhaust side  30 . In one embodiment, engine  10  is a CF34 engine commercially available from General Electric Aircraft Engines, Cincinnati, Ohio. 
     In operation, air flows through fan assembly  12  and compressed air is supplied to high pressure compressor  14 . The highly compressed air is delivered to combustor  16 . Airflow from combustor  16  drives turbines  18  and  20 , and turbine  20  drives fan assembly  12 . Turbine  18  drives high pressure compressor  14 . 
     FIG. 2 is a perspective view of a structural cover  40  that may be used with gas turbine engine  10 . FIG. 3 is a cross-sectional view of structural cover  40  taken along line  3 — 3 , and FIG. 4 is a cross-sectional view of structural cover  40  taken along line  4 — 4 . FIG. 5 is a partial cross-sectional view of gas turbine engine  10  including structural cover  40  taken along line  3 — 3 . In the exemplary embodiment, structural cover  40  is a forward outer seal flange and is coupled within engine  10  to high pressure turbine assembly  18  downstream from combustor  16 . More specifically, combustor  16  includes a liner  46  that extends downstream to a turbine nozzle  48 , such that airflow from combustor  16  is discharged through turbine nozzle  48 . Structural cover  40  is coupled radially inward from turbine nozzle  48  and upstream from a first stage of high pressure turbine blades  50 . 
     Structural cover  40  is annular and includes a torrodial body  52  that extends radially between an inner perimeter  54  and an outer perimeter  56 . Body  52  also extends axially between a forward side  58  and an aft side  60 . Torrodial body  52  is frusto conical, such that when coupled within engine  10 , outer perimeter  56  is radially outward from, and axially-downstream from, inner perimeter  54 . 
     Body  52  includes an integrally-formed windage cover portion  70  and a seal flange portion  72 . More specifically windage cover portion  70  extends from inner perimeter  58  to outer perimeter  56 , and seal flange portion  72  extends from windage cover portion  70  arcuately along portions  78  of outer perimeter  56 . 
     Cover inner perimeter  54  is defined by an arcuate lip  80  that extends to a body seal portion  82 . Body seal portion  82  facilitates forming a seal  83  with a high pressure turbine seal member  84 , and extends between lip  80  and a body coupling portion  86 . In the exemplary embodiment, when cover  40  is coupled within engine  10 , because body  52  is frusto-conical, cover seal portion  82  extends obliquely from lip  80  with respect to an engine centerline axis of symmetry (not shown). Additionally, in the exemplary embodiment, structural cover seal portion  82  includes a plurality of cooling openings  88  extending therethrough. More specifically, cover coupling portion  86  extends from cover seal portion  82  to body outer perimeter  56  and facilitates coupling structural cover  40  within engine  10 . In the exemplary embodiment, cover coupling portion  86  is substantially perpendicular with respect to the engine centerline axis of symmetry. 
     A plurality of fastener bosses  90  are spaced circumferentially along body outer perimeter  56  within cover coupling portion  86 . Each fastener boss  90  includes at least one fastener opening  92  extending therethrough between cover forward side  58  to cover aft side  60 . More specifically, openings  92  are sized to receive a fastener  96  therethrough for coupling cover  40  within engine  10 . In the exemplary embodiment, openings  92  extend axially through bosses  90  and are substantially parallel to the engine centerline axis of symmetry. 
     Adjacent fastener bosses  90  are separated along body outer perimeter  56  by at least one scalloped pocket  110 . More specifically, scalloped pockets  110  are spaced circumferentially along body outer perimeter within cover coupling portion  86 . Each scalloped pocket  110  is arcuate in shape and extends radially inwardly from cover outer perimeter  56  to a radially inner pocket surface  112 . More specifically, each scalloped pocket  110  extends from cover forward side  58  towards cover aft side  60 . Accordingly, scalloped pockets  110  do not penetrate cover aft side  60 , but instead facilitate reducing an overall weight of structural cover  40 , thus facilitating an overall improvement in engine performance. 
     Seal flange portion  72  extends from windage cover portion  70  arcuately along portions  78  of outer perimeter  56  and facilitates alignment of cover  40  within engine  10 . More specifically, seal flange only extends along outer perimeter  56  adjacent each fastener boss  90 , such that each fastener boss  90  defines a portion of seal flange portion  72 . Furthermore, because seal flange portion  72  is integrally formed with windage cover portion  70  and bosses  90 , a thickness T 1  of seal flange portion  72  does not necessitate an increased length  114  of fastener  96  when cover  40  is coupled within engine  10 . 
     Seal flange portion  72  includes a recessed opening  120  that facilitates shielding fasteners  96  and retainers  122  coupled to fasteners  96  from the gas flowpath  130  within engine  10 . Each recessed opening  120  extends from an aft side  60  of each boss  90  towards a forward side  58  of each boss  90 . Furthermore, each recessed opening  120  has a diameter D 1  which is larger than a D 2  of each fastener opening  92 . More specifically, each recessed opening  120  is positioned substantially concentrically with respect to each fastener opening  98 . Recessed opening diameter D 1  is also larger than an outer diameter D 3  of each fastener retainer  122 . Boss thickness T 1  is measured between each respective boss forward side  58  and recessed opening  120 . 
     During installation, fasteners  96  are extended through a plurality of engine structural mounting components  106  and into each respective cover fastener opening  92 . Fasteners  96  are then extended into recessed openings  120  and retainers  122  are coupled to fasteners  96  to secure cover  40  within engine  10  with respect to engine components  106 . In the exemplary embodiment, fasteners  96  are bolts, and retainers  122  are nuts threadably coupled to the bolts. Because cover  40  is integrally formed with seal flange portion  72  and windage cover portion  70 , additional flanges are not required for alignment of cover  40  with respect to engine  10 , and an additional windage cover is not necessary to facilitate shielding fasteners  96  and retainers  122 . Additionally, cover  40  facilitates fasteners  96  having a shorter length  114  than other known covers coupled to the same engine components  106 . In addition, as will become more clear below, because cover  40  is integrally formed with seal flange portion  72  and windage cover portion  70 , an overall length of engine  10  is shorter in comparison to known covers including separate seal flanges and windage covers, thus facilitating reducing an overall weight of engine  10 . 
     FIG. 6 is a cross-sectional view of a known windage cover  200 . Windage cover  200  is similar to structural cover  40  (shown in FIGS. 2,  3 ,  4 , and  5 ) and components in windage cover  200  that are identical to components of structural cover  40  are identified in FIG. 6 using the same reference numerals used in FIGS.  2 , 3 , 4 , and  5 . Accordingly, windage cover  200  includes outer and inner perimeters  56  and  54 , lip  80 , and body seal portion  82 . Windage cover  200  also includes an annular coupling portion  202  that extends between body seal portion  82  and outer perimeter  56 . More specifically, coupling portion  202  extends radially outwardly from seal portion  82  to define a shelf  204  extending between coupling portion  202  and seal portion  82 . Coupling portion  202  also includes a plurality of openings  210  extending therethrough and spaced circumferentially around windage cover  200  within coupling portion  202 . 
     Each opening  210  is sized to receive a fastener (not shown) therethrough. More specifically, a seal flange  220  is coupled against windage cover  200  and extends circumferentially adjacent cover shelf  204  such that a plurality of openings  226  extending through flange  220  are substantially concentrically aligned with respect to windage cover openings  210 . Flange  220  facilitates maintaining a proper alignment of cover  200  when cover  200  is coupled to engine mounting components  106  within engine  10 . 
     Seal flange  220  also defines a recessed area  230  that facilitates shielding fasteners and associated coupling retainers (not shown) used to mount cover  200  within engine  10 . More specifically, during assembly, the fasteners are extended through the same structural mounting components  106  (shown in FIG. 5) as fasteners  96  (shown in FIG.  5 ), however the fasteners extending through windage cover  200  have a length (not shown) that is longer than fastener length  114  (shown in FIG.  5 ). The increased fastener length is necessary to accommodate a thickness T wc  of windage cover coupling portion  202  adjacent openings  210  and an increased thickness T SF  of an annular seal flange  220  coupled between windage cover  200  and seal flange recessed area  230 . 
     The above-described structural cover is cost-effective and highly reliable. The unitary cover is integrally formed to include a windage cover portion and a seal flange portion, such that fewer assembly parts are required. The seal flange portion facilitates shielding the mounting fasteners from the gas turbine engine gas flowpath, and also facilitates proper alignment of the cover during installation. Because the cover is integrally formed, a length of mounting fasteners used is shorter than other known covers coupled to the same engine components. Furthermore, the cover includes a plurality of scalloped pockets which reduce an overall weight of the cover in comparison to other known covers coupled to the same engine components. As a result, the integral structural cover facilitates reducing manufacturing costs in a cost-effective and reliable manner. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.