Abstract:
Methods and apparatus are provided for a fan containment system for a gas turbine engine having a plurality of fan blades includes a cylindrical casing with an inner surface surrounding the plurality of fan blades and an opposing outer surface; a first layer of fabric material positioned on the exterior surface of the cylindrical casing; and a shear thickening fluid impregnated within the first layer of fabric material.

Description:
TECHNICAL FIELD 
       [0001]    The present invention generally relates to fan containment systems in gas turbine engines, and more particularly relates to fan containment systems in gas turbine engines with improved impact structures. 
       BACKGROUND 
       [0002]    A gas turbine engine is used to power various types of vehicles and systems. A particular type of gas turbine engine that may be used to power aircraft is a turbofan gas turbine engine. A turbofan gas turbine engine may include, for example, five major sections: a fan section, a compressor section, a combustor section, a turbine section, and an exhaust section. 
         [0003]    The fan section is positioned at the inlet section of the engine and includes a fan that induces air from the surrounding environment into the engine and accelerates a fraction of this air toward the compressor section. The compressor section raises the pressure of the air it receives from the fan section and directs a majority of the high pressure air into the combustor section. In the combustor section, the high pressure air is mixed with fuel and combusted. The high-temperature combusted air is then directed into the turbine section where it expands through and rotates each turbine to drive various components within the engine or aircraft. The air is then exhausted through a propulsion nozzle disposed in the exhaust section. 
         [0004]    At times, portions of the fan may become detached from a fan blade or rotor. It is known to provide a fan containment system with a casing surrounding the fan section to prevent these portions from escaping the engine. It is generally desirable to maximize the strength of these fan casings. However, the fan casing is usually fabricated from a metallic material, and increasing the thickness of the casing, adding additional structures, or other strengthening mechanisms may increase the overall weight of the engine, which may undesirably decrease engine efficiency. 
         [0005]    Accordingly, it is desirable to provided fan containment systems with improved impact resistance without unduly increasing the weight of the fan section and the engine. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
       BRIEF SUMMARY 
       [0006]    In accordance with an exemplary embodiment, a fan containment system for a gas turbine engine having a plurality of fan blades includes a cylindrical casing with an inner surface surrounding the plurality of fan blades and an opposing outer surface; a first layer of fabric material positioned on the exterior surface of the cylindrical casing; and a shear thickening fluid impregnated within the first layer of fabric material. 
         [0007]    In accordance with another exemplary embodiment, a method is provided for providing impact protection in a fan section of a gas turbine engine. The method includes providing a first layer of fabric material; applying a shear thickening fluid to the first layer of fabric material; and installing the first layer of fabric material with the shear thickening fluid onto a fan casing of the fan section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein 
           [0009]      FIG. 1  is a partial, cross-sectional view of a gas turbine engine in accordance with an exemplary embodiment; 
           [0010]      FIG. 2  is a close-up cross-sectional view of a portion of the gas turbine engine of  FIG. 1 ; and 
           [0011]      FIG. 3  is a more detailed schematic cross-sectional view of a fan containment system of the gas turbine engine of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
         [0013]    Broadly, exemplary embodiments discussed herein provide improved fan containment systems for gas turbine engines. An exemplary fan containment system includes a casing that surrounds the fan section of the engine and an impact structure mounted on an exterior or outer surface of the casing. The impact structure is made up of a number of material layers impregnated with a shear thickening fluid for improving impact absorption. 
         [0014]      FIG. 1  is a partial, cross-sectional view of a gas turbine engine  100  in accordance with an exemplary embodiment with the remaining portion of the gas turbine engine  100  being axi-symmetric about a longitudinal axis  140 . In the depicted embodiment, the gas turbine engine  100  is an annular multi-spool turbofan gas turbine jet engine  100  within an aircraft, although other arrangements and uses may be provided. 
         [0015]    The engine  100  includes fan section  102 , a compressor section  104 , a combustor section  106 , a turbine section  108 , and an exhaust section  110 . The fan section  102  includes a fan  112  mounted on a rotor  114  that draws air into the engine  100  and accelerates it. A portion  200  of the fan section  102  is discussed in greater detail below. A fraction of the accelerated air exhausted from the fan  112  is directed through a bypass section  116  and the remaining fraction of air exhausted from the fan  112  is directed into the compressor section  104 . 
         [0016]    In the embodiment of  FIG. 1 , the compressor section  104  includes an intermediate pressure compressor  120  and a high pressure compressor  122 . However, in other embodiments, the number of compressors in the compressor section  104  may vary. In the depicted embodiment, the intermediate pressure compressor  120  and the high pressure compressor  122  sequentially raise the pressure of the air and directs a majority of the high pressure air into the combustor section  106 . A fraction of the compressed air bypasses the combustor section  106  and is used to cool, among other components, turbine blades in the turbine section  108 . 
         [0017]    In the combustor section  106 , which includes an annular combustor  124 , the high pressure air is mixed with fuel and combusted. The high-temperature combusted air is then directed into the turbine section  108 . In the embodiment of  FIG. 1 , the turbine section  108  includes three turbines disposed in axial flow series, namely, a high pressure turbine  126 , an intermediate pressure turbine  128 , and a low pressure turbine  130 . However, it will be appreciated that the number of turbines, and/or the configurations thereof, may vary. In the embodiment depicted in  FIG. 1 , the high-temperature combusted air from the combustor section  106  expands through and rotates each turbine  126 ,  128 , and  130 . The air is then exhausted through a propulsion nozzle  132  disposed in the exhaust section  110 . As the turbines  126 ,  128 , and  130  rotate, each drives equipment in the engine  100  via concentrically disposed shafts or spools. Specifically, the high pressure turbine  126  drives the high pressure compressor  122  via a high pressure spool  134 , the intermediate pressure turbine  128  drives the intermediate pressure compressor  120  via an intermediate pressure spool  136 , and the low pressure turbine  130  drives the fan  112  via a low pressure spool  138 . 
         [0018]      FIG. 2  is a close-up cross-sectional view of the portion  200  of the fan section  102  of the engine  100  of  FIG. 1 . As discussed above, the fan section  102  includes an array of fan blades  202  extending radially outward from a rotor  114  ( FIG. 1 ). As the fan blades  202  rotate, air is drawn into the engine  100 . 
         [0019]    During operation, portions of the fan blades  202  may become detached from the fan blades  202  or rotor  114  ( FIG. 1 ) of the fan section  102 . To prevent these portions from escaping the fan section  102 , a fan containment system  250  is provided. The fan containment system  250  generally includes a casing  260  and an impact structure  270 . The casing  260  has an inner surface  262  and an outer surface  264  and is cylindrically shaped to circumscribe the rotating fan blades  202 . The casing  260  may extend the entire axial length of the fan section  102  or only a portion thereof. Typically, the casing  260  is fabricated from a metallic material, although other materials may be used. Although not shown, one or more stiffening rings may also be provided. 
         [0020]    The impact structure  270  is mounted on or otherwise secured to the outer surface  264  of the casing  260 . As described below, the impact structure  270  and casing  260  cooperate to absorb at least some of the kinetic energy of any detached fan portions, thereby reducing the likelihood of these portions traveling out of the fan section  102 , particularly in a radial direction out of the engine  100 . The impact structure  270  may have an axial length  275  that is greater than the axial length of the fan blade  202 , particularly in the aft direction, which is also the area where a detached portion of the fan blade  202  will likely impact. In other embodiments, the impact structure  270  has an axial length  275  approximately equal to the axial length of the fan blade  202 . In an alternate embodiment, the impact structure  270  (or an additional impact structure) is mounted on the inner surface  262  of the casing  260 . During a fan detachment event, the impact structure  270  may deform radially outward to absorb kinetic energy. Additionally, although  FIG. 2  depicts the impact structure  270  mounted directly (or connected) to the casing  260 , other embodiments may include the impact structure  270  indirectly attached to the casing  260  via intermediate layers or structures. In any event, the impact structure  270  is coupled to the casing  260  to absorb kinetic energy. The coupling may be rigid, flexible or rotatable. 
         [0021]      FIG. 3  is a more detailed schematic cross-sectional view of the fan containment system  250  of the engine  100  of  FIG. 1 . As shown in  FIG. 3 , the impact structure  270  is made up of a stack of radially disposed material layers (or windings)  271 ,  272 ,  273 , and  274 . The term material layer describes a planar arrangement of non-woven or woven fibers or yarns that have been consolidated into a single unitary structure, i.e. a single ply. Such layers may include weaves, braids, windings and unidirectional forms. In one exemplary embodiment, each layer is uni-directional material lightly stitched together and was conducive to a modified filament winding setup. Although not shown, the material layers  271 ,  272 ,  273 , and  274  of the impact structure  270  may be enclosed or partially enclosed by a housing structure, for example, with a metallic or plastic skin. In one particular embodiment, the material layers  271 ,  272 ,  273 , and  274  of the impact structure  270  may be enclosed or partially enclosed by the fan containment housing (not shown). 
         [0022]    Each of the material layers  271 ,  272 ,  273 , and  274  may be wound around the exterior of the casing  260 . As shown, material layer  271  is mounted directly on the casing  260 , material layer  272  is attached to material layer  271 , material layer  273  is attached to material layer  272 , and material layer  274  is attached to material layer  273 . Although four material layers  271 ,  272 ,  273 , and  274  are illustrated, any number of material layers may be provided based on weight and performance considerations. The layers  271 ,  272 ,  273 , and  274  can be attached in several ways including any combination of the following: mechanical fastening of layer(s) to casing(s), adhesive bonding of layer(s) to casing(s), adhesive bonding along longitudinal edge(s) of one layer to an adjacent layer over a given area, adhesive bonding of one layer to an adjacent layer over a given area and spaced over a given distance in the axial direction (normal to the longitudinal direction), or no adhesive bonding between layer(s), i.e., held together by pressure or friction upon assembly. 
         [0023]    As noted above, the material layers  271 ,  272 ,  273 , and  274  may be fabricated as a network of fibers that have been formed into a fabric material. In particular, the material layers  271 ,  272 ,  273 , and  274  are made up of high strength and high modulus fibers. For example, the fibers that make up the material layers  271 ,  272 ,  273 , and  274  may be para-aramid synthetic fibers, such as KEVLAR fibers, which are sold by E.I. duPont de Nemours and Company. Non-limiting examples of other high strength fibers include metal fibers, ceramic fibers, glass fibers, carbon fibers, boron fibers, p-phenylenetherephtalamide fibers, aromatic polyamide fibers, silicon carbide fibers, graphite fibers, nylon fibers, and mixtures thereof. Another example of suitable fibers includes ultra high molecular weight polyethylene, such as SPECTRA fibers manufactured by Honeywell International Inc. The material layers  271 ,  272 ,  273 , and  274  may be identical or different in composition or arrangement. In one exemplary embodiment, the material layers  271 ,  272 ,  273 , and  274  may include, for example, 30 layers of para-aramid fabric wrapped in one continuous piece around the outside of the casing  260 . 
         [0024]    Typically, the fibers of the material layers  271 ,  272 ,  273 , and  274  may have high tensile strength and high modulus that are highly oriented, thereby resulting in very smooth fiber surfaces exhibiting a low coefficient of friction. Such fibers, when formed into a fabric layer, generally exhibit poor energy transfer to neighboring fibers during an impact event. Unless addressed, this lack of energy transfer may correlate to a reduced efficiency in dissipating the kinetic energy of a moving object, thereby necessitating the use of more material to achieve full dissipation. 
         [0025]    Accordingly, one or more of the material layers  271 ,  272 ,  273 , and  274  is respectively impregnated with a shear thickening fluid  281 ,  282 ,  283 , and  284  to improve the impact resistance of the impact structure  270 . In the exemplary embodiment, all of the material layers  271 ,  272 ,  273 , and  274  are respectively impregnated with the shear thickening fluid  281 ,  282 ,  283 , and  284  throughout the entire thicknesses. In other embodiments, only a portion of the material layers  271 ,  272 ,  273 , and  274  or only certain material layers  271 ,  272 ,  273 , and  274  are impregnated with the shear thickening fluid  281 ,  282 ,  283 , and  284 . For example, in one exemplary embodiment, only the outermost material layer (e.g., material layer  274 ) and/or the innermost material layer (e.g., material layer  271 ) may be impregnated with shear thickening fluid  281 . 
         [0026]    In general, the shear thickening fluid  281 ,  282 ,  283 , and  284  is non-Newtonian, dilatant, and flowable liquid containing particles suspended in a carrier whose viscosity increases with the deformation rate. These characteristics increase the energy transfer between the fibers within the material layers  271 ,  272 ,  273 , and  274  as the rate of deformation increases. Such energy transfer may be embodied as strain, strain rate, vibration, both frequency and magnitude dependent, pressure, energy (i.e. low force over large distance and high force over short distance both induce a response) as well as energy transfer rate (higher rates induce greater response). As such, at low deformation rates, the material layers  271 ,  272 ,  273 , and  274  with the shear thickening fluids  281 ,  282 ,  283 , and  284  may deform as desired for handling and installation. However, at high deformation rates, such as during an impact or damage event, the material layers  271 ,  272 ,  273 , and  274  with the shear thickening fluids  281 ,  282 ,  283 , and  284  transition to more viscous, in some cases rigid, materials with enhanced protective properties. Accordingly, the material layers  271 ,  272 ,  273 , and  274  impregnated with the shear thickening fluids  281 ,  282 ,  283 , and  284  advantageously provide an impact structure  270  that is workable, light and flexible during installation, but that is rigid and protective during impact. 
         [0027]    As noted above, the shear thickening fluid  281 ,  282 ,  283 , and  284  generally includes particles suspended in a solvent. Any suitable concentration may be provided, and in one example, the shear thickening fluid  281 ,  282 ,  283 , and  284  includes at least about  50  percent by weight particles. Exemplary particles may include fumed silica, kaolin clay, calcium carbonate, and titanium dioxide, and exemplary solvents include water and ethylene glycol. The particles of the shear thickening fluid  281 ,  282 ,  283 , and  284  may be any suitable size to impregnate between the fibers of the material layers  271 ,  272 ,  273 , and  274 . For example, the particles may be nanoparticles, having an average diameter ranging from about 1 to about 1000 nanometers, or microparticles, having an average diameter ranging from about 1 to about 1000 microns. 
         [0028]    Further examples of the particles of the shear thickening fluid  281 ,  282 ,  283 , and  284  include polymers, such as polystyrene or polymethylmethacrylate, or other polymers from emulsion polymerization. The particles may be stabilized in solution or dispersed by charge, Brownian motion, adsorbed. Particle shapes may include spherical particles, elliptical particles, or disk-like particles. 
         [0029]    The solvents are generally be aqueous in nature (i.e. water with or without added salts, such as sodium chloride, and buffers to control pH) for electrostatically stabilized or polymer stabilized particles. The solvents may be organic (such as ethylene glycol, polypropylene glycol, glycerol, polyethylene glycol, ethanol) or silicon based (such as silicon oils, phenyltrimethicone). The solvents can also be composed of compatible mixtures of solvents, and may contain free surfactants, polymers, and oligomers. The solvent of the shear thickening fluid  281 ,  282 ,  283 , and  284  is generally stable so as to remain integral to the material layers  271 ,  272 ,  273 , and  274 . For a general preparation, the solvent, particles, and, optionally, a setting or binding agent are mixed and any air bubbles are removed. 
         [0030]    The shear thickening fluid  281 ,  282 ,  283 , and  284  may be embedded into the material layers  271 ,  272 ,  273 , and  274  in a number of ways. For example, the shear thickening fluid  281 ,  282 ,  283 , and  284  may be applied by individually coating the material layers  271 ,  272 ,  273 , and  274  with techniques such as knife-over-roller, dip, reverse roller screen coaters, application and scraping, spraying, and full immersion. The material layers  271 ,  272 ,  273 , and  274  may undergo further operations, such as reaction/fixing (i.e. binding chemicals to the substrate), washing (i.e. removing excess chemicals and auxiliary chemicals), stabilizing, and drying. For example, the fibers of the material layers  271 ,  272 ,  273 , and  274  may be bound with the shear thickening fluid  281 ,  282 ,  283 , and  284  with a thermosetting resin that may be cured with ultraviolet (UV) or infrared (IR) radiation. Generally, such curing will not result in the hardening of the material layers  271 ,  272 ,  273 , and  274  and the shear thickening fluid  281 ,  282 ,  283 , and  284 , such that the material layers  271 ,  272 ,  273 , and  274  remain workable until installation. Additional coatings may be provided, such as to make the material layers  271 ,  272 ,  273 , and  274  fireproof or flameproof, water-repellent, oil repellent, non-creasing, shrink-proof, rot-proof, non-sliding, fold-retaining, antistatic, or the like. 
         [0031]    The material layers  271 ,  272 ,  273 , and  274  may be impregnated with the shear thickening fluid  281 ,  282 ,  283 , and  284  prior to installation, for example, as a prepreg in which the impregnated with shear thickening fluid packaged and sold as a roll of continuous material. A length of the material layers  271 ,  272 ,  273 , and  274  may be sized, cut and installed, and as many layers as desired may follow. Because the shear thickening fluid  281 ,  282 ,  283 , and  284  is flowable and deformable, it can fill complex volumes and accommodate bending and rotation. These materials provide flexible and conformable protective impact structures  270 . 
         [0032]    Accordingly, exemplary embodiments of the fan containment system  250  dissipate the kinetic energy of moving objects, thereby preventing or reducing the likelihood of those moving objects exiting the fan section  102 . The impact structure  270  thus provides the designer of an aircraft engine with the ability to optimize containment performance and weight with improved impact resistance and damage tolerance properties. Additionally, a designer may be able to reduce the number of material layers of fabric while achieving such improved containment performance. The use of fewer layers has the advantage of reducing the weight that is carried by the engine for improved engine performance and reduced fuel consumption. 
         [0033]    While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.