Abstract:
A gas turbine fan blade containment assembly includes a fan case having an inner surface surrounding a jet engine fan and an outer surface. Mounted on the inner surface and across a blade containing region of the fan case is a load spreader layer for initially receiving a point load from a fan blade release (a “blade-out event”). A band layer is mounted to an outer surface of the fan case for carrying at least a portion of a hoop tensile load on the fan case resulting from the blade-out event, and separator film layer is mounted between the outer surface of the fan case and the band layer to retard the formation of stress concentrations in the band layer. In one embodiment, the load spreader layer includes a plurality of circumferentially-arrayed load spreader layer segments.

Description:
GOVERNMENT INTEREST 
       [0001]    The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms Contract No. NAS 3 02160, awarded to A&amp;P Technology, Inc. by the National Aeronautics and Space Administration. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to gas turbine jet engines, and more particularly, to fan case systems for containment of gas turbine jet engines during a blade-out event. 
       BACKGROUND OF THE INVENTION 
       [0003]      FIG. 1  provides a perspective view of a conventional commercial airliner  1  having gas turbine jet engines  2 .  FIG. 2  presents an enlarged view of a cut-away section of the jet engine  2  of  FIG. 1 , including a fan containment case  4  that surrounds rotary blades  6  of the jet engine  2 . 
         [0004]    In rare instances, one or more of the blades  6  in the jet engine  2  may be caused to release, for example, as a result of the ingestion of a foreign object. In such an event, the released fan blade must be contained so as not to penetrate the fan case  4 . In addition, the fan case  4  must retain its structural integrity while the jet engine  2  shuts down in order to prevent further potentially catastrophic damage. Under these circumstances, a high strength fan containment case becomes critically necessary. 
         [0005]    The mechanisms of fan blade release are further illustrated with reference to  FIGS. 3-5 .  FIG. 3  presents a cut-away sectional view of the fan containment case  4  along the lines  3 - 3  of  FIG. 2 . Blades  6  are shown at the intake side of the case  4 .  FIG. 4  presents a front view of the fan containment case  4  looking aft down a longitudinal axis defined by fan hub  8  of the engine  2  at which the blades  6  are secured. 
         [0006]    During normal operation of the jet engine  2 , the blades  6  rotate around the fan hub  8 . Due to the engine rotation, centrifugal forces are generated on each blade  6  that is supported by the fan hub  8 . During a blade-out event, blade  6   a  (as shown in  FIG. 5 ) disengages from the fan hub  8  to become a pointed projectile which can impact the interior of the fan case  4  and cause the generation of a point load at the location of impact. As illustrated in  FIG. 5 , with the dislodging of blade  6   a , a hoop tensile load is generated at the area of impact of the blade  6   a . The resulting point load at the interior of the fan case  4  also results in a distortion in the symmetry of fan case  4 , as shown by the displacement  13  in the case  4  of  FIG. 5 . 
         [0007]    Two approaches for containing a released fan blade within the fan case  4  have been successfully used previously. In a first approach (the “softwall” fan case), a metal casing is over-wound with dry aramid fibers. A broken blade is allowed to pierce and pass through the metal layer, where it is stopped and contained within the external aramid wrap. In the second approach (the “hardwall” fan case), a single metal hardwall casing is designed to reflect the broken blade back into the engine. The hardwall approach enables designers to improve engine aerodynamics by building a fan case with a smaller radial envelope, since there is no “dead space” required for absorbing the broken blade. However, hard wall fan cases tend to be comparatively heavy, and still maintain some risk that the blade may pass completely through the fan case. 
         [0008]    Accordingly, it would be desirable to overcome the drawbacks of prior art methods used for containing fan blades in jet engines during “blade-out” events. 
       SUMMARY OF THE INVENTION 
       [0009]    In the present invention, a fan blade containment assembly for a gas turbine engine includes a fan case having an inner surface for surrounding a jet engine fan mounted for rotation about an engine axis and an outer surface. Mounted on the inner surface and across a circumferentially and axially extending blade containing region of the fan case are one or more load spreader layers. In the event that one or more of the fan blades releases (a “blade-out event”), each load spreader layer acts as a point load spreader to isolate and distribute a point load generated on the load spreader layer by a released fan blade to the fan case. In addition, the load spreader layer acts to mitigate cutting and/or gouging of the inner surface of the fan case that may otherwise be caused by sharp features on the released fan blade. Each load spreader layer may be made from a wide variety of suitable materials including, for example, fiber-reinforced polymers, non-reinforced polymers, ceramics and metals. 
         [0010]    The fan blade containment assembly may further include one or more band layers mounted to an outer surface of the fan case and extending across the blade containing region. Each band layer is capable of carrying at least a portion of a hoop tensile load on the fan case that results from a blade-out event, thereby enabling the strength, cost and thickness of individual load spreader segments to be further reduced. The band layers may be made from a wide variety of suitable materials including, for example, fiber-reinforced polymers, carbon braid, cloth fiber or triaxial braid including carbon fibers, quartz fibers or glass fibers. 
         [0011]    The fan blade containment assembly including one or more band layers may further include a separator film layer mounted between the outer surface of the fan case and the band layers. The separator film layer acts to retard the formation of stress concentrations in the band layer as a result of the blade-out event and may be made, for example, from a fluoropolymer such as polytetrafluoroethylene (PTFE). 
         [0012]    In one embodiment of the present invention, the load spreader layer is configured within the blade-containing region as a plurality of circumferentially-arrayed load spreader layer segments, the plurality of segments defining a plurality of gaps between ends of adjacent ones of the plurality of load spreader segments. In another embodiment, the load spreader layer is configured as a single, circumferentially-continuous structure rather than as a plurality of circumferentially-arrayed segments. 
         [0013]    In embodiments of the present invention having more than one load spreader layer or more than one band layer, the individual layers may be formed from different materials to meet particular performance requirements. For example, in an embodiment having first and second load spreader layers, the first load spreader layer may be formed from a polymer or polycarbonate material, and the second load spreader segments may be formed from a steel or ceramic material. In a fan blade containment assembly having at least two layers of load spreader segments, the segment layers may be positioned so that ends of segments in one layer lie along the arcuate lengths of segments in another layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention will become more readily apparent from the Detailed Description of the Invention, which proceeds with reference to the drawings, in which: 
           [0015]      FIG. 1  is a perspective view of a conventional jet airliner having jet engines; 
           [0016]      FIG. 2  provides a cut-away view of one of the jet engines illustrated in  FIG. 1 ; 
           [0017]      FIG. 3  provides a sectional view of the jet engine illustrated in  FIG. 2 ; 
           [0018]      FIG. 4  provides a front view of the jet engine illustrated in  FIG. 2 ; 
           [0019]      FIG. 5  provides another front view of the jet engine illustrated in  FIG. 2 ; 
           [0020]      FIG. 6   a  provides a front view of the jet engine illustrated in  FIG. 2  that has been adapted according to principles of the present invention; 
           [0021]      FIG. 6   b  provides another view of the jet engine illustrated in  FIG. 6   a  that has been further adapted according to principles of the present invention; 
           [0022]      FIG. 7   a  provides an enlarged view of a segment of a containment layer as illustrated in  FIG. 6 ; 
           [0023]      FIG. 7   b  provides a sectional view of the container layer segment of  FIG. 7   a;    
           [0024]      FIG. 8  shows a sectional view of the jet engine of  FIG. 6  along a longitudinal axis of the jet engine; 
           [0025]      FIG. 9   a  provides a front view of the jet engine illustrated in  FIG. 2  that has been adapted according to principles of the present invention; and 
           [0026]      FIG. 9   b  provides another view of the jet engine illustrated in  FIG. 9   a  that has been further adapted according to principles of the present invention. 
       
    
    
       [0027]    In the drawings, like reference numerals designate corresponding parts throughout the several depicted views. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    Referring now to  FIG. 6   a , there is shown an exemplary portion of a fan containment case  4  according to principles of the present invention. The fan case  4  includes three generally concentric layers  14 ,  16  and  18  that effectively and efficiently reinforce the fan case  4  to accommodate loads resulting from blade-out events. 
         [0029]    The first layer  14  comprises a load spreader layer. The load spreader layer  14  operates to distribute a point load generated by the liberated pointed projectile blade  6   a  of  FIG. 5  as it strikes the load spreader layer  14  into the second layer  16 . In addition, the load spreader layer acts to mitigate cutting and/or gouging of an inner surface of the second layer  16  that may otherwise be caused by sharp features on the released blade. 
         [0030]    By distributing the point load into the second layer  16  and mitigating cutting and or gouging of the second layer  16  at the impact location, the stress concentration in the second layer  16  may be diminished at the impact location, thus enabling the second layer  16  to more easily carry the impact load of a projectile blade  6   a . First layer  14  can be produced from a variety of materials including conventional fiber reinforced or non-reinforced polymers, ceramic or metals (for example, stainless steel and other ductile metals with high impact strength), as permitted according to cost and weight requirements. 
         [0031]    The second layer  16  defines a casing portion of the fan casing  4 , which may be produced, for example, from a conventional fiber reinforced polymer (FRP). The third or band layer  18  defines a band surrounding the fan casing portion  16 , and may also be produced from a FRP. The third layer  18  encapsulates the first and second layers  14  and  16 , and is selected to have strength and stiffness properties in accordance with the energy absorbing needs of the containment system. 
         [0032]    Alternatively, one or more of layers  16  and  18  may be produced from a FRP braided material. A single selected braid material can be used in each of layers  16 ,  18 , or different types of braid may be used in each layer. In addition, a fiber reinforcement, including braid and other types of reinforcement such as cloth fiber, can be symmetrically distributed for example in all directions on the layers  16  and  18 , around the circumference of the fan case  2 , along a longitudinal axis backward from the hub  8 , or asymmetrically distributed along the same or other directions. A suitable reinforced braid may include carbon fiber, quartz fiber or glass fiber, in an equiaxed braid having fibers arranged in at least three different fiber directions (for example, 0 degrees and +/−60 degrees). 
         [0033]    In addition, a fourth or separator film layer  20  may be applied as film separating the second and third layers, and can be produced, for example, from a fluoropolymer such as PTFE. Separator film layer  20  may act for example to discourage the formation of stress concentrations in the third layer  18  at an impact location. As in the case of layers  16  and  18 , specifications for separator film layer  20  will vary in accordance with the specifications of the fan case  4 , as dictated for example by particular performance, weight and cost requirements, and therefore do not limit the scope of the present invention. 
         [0034]    Referring next to  FIG. 6   b , there is shown an exemplary portion of another fan containment case  4  according to principles of the present invention. As illustrated in  FIG. 6   a , the fan case  4  once again includes three generally concentric layers  14 ,  16  and  18  that effectively and efficiently reinforce the fan case  4  to accommodate loads resulting from blade-out events. However, in contrast to the fan case  4  of  FIG. 6   a , the load spreader layer  14  is not formed as a continuous ring, but rather as a series of distinct, circumferentially-arrayed load spreader segments  14   a . Typically, the load spreader layer  14  may include between 2 and 14 distinct segments. In the example illustrated by  FIG. 6   b , twelve segments  14   a  define the load spreader layer  14 . 
         [0035]    The segmentation of load spreader layer  14  into load spreader segments  14   a  prevents the accumulation of hoop tensile loads in the load spreader layer  14 , because generated loads are contained within the individual segment or segments  14   a  that are directly impacted by the liberated blade  6   a  of  FIG. 5 , rather than being transferred around the inner perimeter of the case  4  (as would be the case for load spreader layer  14  of  FIG. 6   a ). By preventing the transfer and accumulation of hoop tensile loads in the segmented layer  14 , the load spreader segments  14   a  may for example be produced from a less ductile material than materials typically selected to produce the load spreader layer  14  of  FIG. 6   a.    
         [0036]      FIG. 7   a  presents an enlarged front view of a single segment  14   a  from the load spreader layer  14 , as a cut-away section of  FIG. 6   b . As earlier described in reference to the load spreader layer  14  of  FIG. 6   a , spreader segments  14   a  may be produced from a variety of conventional non-reinforced polymers, ceramics or metals, among other materials. The load spreader segments  14   a  as illustrated in  FIGS. 6   b  and  7   a  have an arcuate length of approximately 30 degrees, and may be configured with ends that are canted (for example, at an angle ranging between 30 and 50 degrees). 
         [0037]    The inventors of the present invention have found that canting the ends of the individual segments helps to reduce the probability that a liberated blade  6   a  as illustrated in  FIG. 5  directly reaches the second layer  16  by striking a point between and at the ends of load spreader segments  14   a , as well as the probability that the liberated blade  6   a  striking a load spreader segment  14   a  at an end of the segment  14   a  will dislodge it. Consistent with the principles of the present invention, the ends of segments  14   a  may be canted at any angle greater than 0 degrees and less than 90 degrees, and more preferably, at angles ranging from 30 to 50 degrees. 
         [0038]    Referring now to  FIG. 9   a , there is shown another exemplary portion of a fan containment case  4  according to principles of the present invention. In  FIG. 9   a , two load spreader layers  14 ,  15  are applied to the fan case  4 . As a result, the fan case  4  of  FIG. 9   b  includes five generally concentric layers ( 14 ,  15 ,  16 ,  20  and  18 ) that reinforce the fan case  4  to accommodate loads resulting from blade-out events. Alternatively, one or more of these layers may be omitted (for example, layers  20  and  18 ), or additional layers may be added (for example, a third load spreader layer applied on the interior circumference of load spreader layer  15 ), according to particular cost, weight and performance requirements for the fan case  4 . 
         [0039]    Referring now to  FIG. 9   b , one more example is shown providing an exemplary portion of a fan case  4  according to principles of the present invention. In the fan case  4  of  FIG. 9   b , load spreader layers  14 ,  15  are respectively provided as circumferentially-arrayed load spreader segments  14   a ,  15   a . Load spreader layers  14 ,  15  are arranged so that ends of the load spreader segments  14   a  in load spreader layer  14  overlap load spreader segments  15   a  in load spreader layer  15 . This arrangement limits the probability that a liberated blade will pass through both load spreader layers  14 ,  15  to strike second layer  16 . 
         [0040]    As shown in  FIG. 9   b , the segments  15   a  of the inner layer  15  are positioned such that the ends of the segments  15   a  lie at points along the arcuate lengths of the segments  14   a . As a result, spaces between the underlying segments  14   a  are effectively obstructed by overlying segments  15   a , and spaces between the overlying segments  15   a  are effectively backed by the underlying segments  14   a . In this manner, the liberated blade  6   a  must strike at least one of a load spreader segment  15   a  or  14   a  along its arcuate length, thereby distributing the point load to the struck load spreader segment before it reaches the second layer  16 . 
         [0041]    In the configuration illustrated by  FIG. 9   b , segments  15   a  are symmetrically positioned with respect to segments  14   a , such that spaces between the segments  15   a  are essentially located at the center of the arcuate lengths of the segments  14   a . In alternative embodiments, the ends of segments  15   a  may be selected to be located at any point along the arcuate length of segments  14   a , as long as the selected locations cause the spaces between the segments  14   a  to be obstructed by segments  15   a.    
         [0042]      FIG. 7   b  presents a side sectional view of a segment  14   a  along the axial length of the jet engine; as shown along line  7   b - 7   b  in  FIG. 7   a . As previously noted, segments  14   a  can be produced from a variety of materials including conventional fiber reinforced or non-reinforced polymers, ceramics or metals (for example, steel or other suitable metals), as permitted according to cost and weight requirements. 
         [0043]    In the configuration shown in  FIGS. 9   a  and  9   b , layers  14  and  15  may be constructed of the same or of different materials. For example, layer  15 , which is closer to the blades  6  than layer  14 , may be constructed using a relatively stiff material, such as steel or ceramic. A softer material may then be selected for layer  14 , such as a polymer or polycarbonate. 
         [0044]    In the configuration illustrated by  FIG. 9   b , the spacing in between adjacent load spreaders  14   a ,  15   a  in layers  14 ,  15  can be as small, for example, as 0.015 inches, and may vary within each of the layers  14 ,  15 , and between the layers  14 ,  15 . The number, design, and dimensions of the load spreader segments  14   a  within layer  14  and/or segments  15   a  within layer  15 , as well as the materials used to produce the load spreader segments  14   a ,  15   a , will vary according to product specifications providing performance, weight and cost requirements. 
         [0045]    As previously noted, the second layer  16  as illustrated in  FIGS. 6   a ,  6   b ,  8 ,  9  and  9   b  can be constructed from a variety of materials (for example, including a conventional FRP material) to form the base of the fan case  4 . Alternatively, the second layer  16  may be constructed from a braided FRP or other similar material. The specifications for layer  16  will vary according to particular performance, weight and cost requirements, and therefore do not limit the scope of the present invention. 
         [0046]      FIG. 8  shows a side sectional view of the fan containment case  4  along the longitudinal axis of the jet engine  2  (and along lines  8 - 8  shown in  FIG. 6   b ). Layers  14  and  16  are applied to the fan case  4  in proximity to an air intake end of the jet engine  2 , and are oriented to frame a blade containing region around the blades  6  in order to coincide with the area of the fan case  4  where point and tensile hoop loads are generated during a blade-out event. 
         [0047]    As shown in  FIG. 8 , a third layer  18  is applied to the fan case  4  in proximity to the blade containing region. As previously noted, third layer  18  can be produced from a variety of materials (including, for example, conventional FRP material) in order to help to carry the hoop tensile loads that accumulates during a blade-out event. The inventors have determined that the principal failure mode of the fan case  4  during a blade-out event is a tensile failure resulting as the released blade  6   a  is slowed by the fan case  4 . The orientation of the associated tensile load in the fan case  4  is primarily in the radial direction, as shown in  FIG. 5  by arrows  12 . The tensile load resulting from the blade-out event also causes a substantial hoop stress to be circumferentially generated in the fan case  4 . 
         [0048]    The specifications for layer  18  will vary in accordance with the specifications for the fan case  4 , as dictated for example by particular performance, weight and cost requirements, and therefore do not limit the scope of the present invention. 
         [0049]      FIGS. 6   a ,  6   b ,  8 ,  9   a  and  9   b  also show a separator film layer  20  that is applied in between layer  16  and layer  18 . As previously noted, separator film layer  20  may comprise a fluoropolymer such as PTFE, and act to discourage the formation of stress concentrations in the third layer  18  at an impact location. As in the case of layers  16  and  18 , specifications for separator film layer  20  will vary in accordance with the specifications of the fan case  4 , as dictated for example by particular performance, weight and cost requirements, and therefore do not limit the scope of the present invention. 
         [0050]    It should be noted that many variations in the number of load spreader layers  14 ,  15 , band layers  18  and separator film layers  20  applied to the blade containing region of fan case  4  are possible, will be determined by performance, cost and weight requirements, and are all fully contemplated within the scope of the present invention. For example, in addition to applying two or more load spreader layers  14 ,  15  to the second layer  16 , two or more band layers  18  may be applied to the second layer  16 , with or without a separator film layer  20 . The number, configurations and specifications of layers for the inventive fan case  2  design therefore do not limit the scope of this invention. 
         [0051]    Numerous details have been set forth in this description, which is to be taken as a whole, to provide a more thorough understanding of the invention. In other instances, well-known features have not been described in detail, so as to not obscure unnecessarily the invention. 
         [0052]    The invention includes all combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. The following claims define certain combinations and subcombinations, which are regarded as novel and non-obvious. Additional claims for other combinations and subcombinations of features, functions, elements and/or properties may be later presented in this or a related application.