Patent Publication Number: US-2016229543-A1

Title: Icephobic Flowpath for a Nose Cone and Method Therefor

Description:
TECHNICAL FIELD OF THE DISCLOSED EMBODIMENTS 
     The present disclosures relate generally to a gas turbine engine and, more particularly, to an icephobic flowpath for a nose cone of a gas turbine engine. 
     BACKGROUND OF THE DISCLOSED EMBODIMENTS 
     During flight, a gas turbine engine of an aircraft is exposed to low temperatures that may result in the formation of ice. Under icing conditions, ice will accrete (build up) on exposed surfaces of the airframe and engine components. This accretion disrupts air flow, thereby reducing aerodynamic efficiency. When the ice reaches a certain size and geometry, it sheds and is sent downstream by the air flow, posing a hazard to downstream components. 
     Often, the nose cone of the gas turbine engine may be coated with icephobic materials. However, icephobic materials tend to be more expensive and less durable than conventional materials. Another solution to ice buildup is to circulate hot air through the forward sections of the gas turbine engine. Unfortunately, hot air must be taken from the high pressure compressor and piped forward. Additional piping adds weight and complexity to the gas turbine engine. Additionally, piping hot air through to the forward sections of the gas turbine engine adds to the aerodynamic load on the gas turbine engine. Moreover, the engine components must be able to handle the added pressure and temperature from the hot air. Another solution to ice formation is to cover portions of the gas turbine engine with electro-thermal blankets. Generally, electro-thermal blankets add weight and cost to the gas turbine engine and must be electrically connected to the engine. In addition, the electro-thermal blankets must be physically in contact with and attached to the component that the blanket is warming. Accordingly, the blankets are difficult to repair and/or replace. 
     SUMMARY OF THE DISCLOSED EMBODIMENTS 
     In one aspect, a nose cone for a gas turbine engine is provided, wherein the nose cone is symmetrically disposed about an axis. The nose cone includes a leading edge and a base. A forward section is disposed between the leading edge and the base and has a radius at any axial location defined by a first equation. A transition section is disposed between the forward section and the base and has a radius at any axial location defined by a second equation. The first equation is different than the second equation. 
     In a further embodiment of the above, the transition section is defined by a Von Karman profile. 
     In a further embodiment of any of the above, the nose cone includes a length measured along the axis between the leading edge and the base, wherein the transition section is defined by the equation: 
     
       
         
           
             
               R 
               = 
               
                 
                   
                     R 
                     0 
                   
                   
                     π 
                   
                 
                  
                 
                   
                     θ 
                     - 
                     
                       
                         sin 
                          
                         
                           ( 
                           
                             2 
                              
                             
                                 
                             
                              
                             θ 
                           
                           ) 
                         
                       
                       2 
                     
                   
                 
               
             
             , 
           
         
       
     
     wherein 
     
       
         
           
             
               θ 
               = 
               
                 
                   cos 
                   
                     - 
                     1 
                   
                 
                  
                 
                   ( 
                   
                     1 
                     - 
                     
                       
                         2 
                          
                         
                           x 
                           * 
                         
                       
                       L 
                     
                   
                   ) 
                 
               
             
             , 
           
         
       
     
     wherein R 0  is a radius of the base of the nose cone, L is the length of the nose cone, x* is a position along the length of the nose cone, and R is a radius of the nose cone at the position x*. 
     In a further embodiment of any of the above, the forward section has a spherical profile. 
     In a further embodiment of any of the above, the forward section has a blunt profile. 
     In a further embodiment of any of the above, the nose cone is coated with an icephobic material. 
     In a further embodiment of any of the above, the nose cone is formed from a metallic material. 
     In a further embodiment of any of the above, the nose cone is formed from a non-metallic material. 
     In one aspect, a gas turbine engine is provided having a fan for circulating airflow through the gas turbine engine. The fan has a hub and a nose cone is positioned on the hub of the fan. The nose cone is symmetrically disposed about an axis. The nose cone includes a leading edge and a base. A forward section is disposed between the leading edge and the base and has a radius at any axial location defined by a first equation. A transition section is disposed between the forward section and the base and has a radius at any axial location defined by a second equation. The first equation is different than the second equation. 
     In a further embodiment of the above, the transition section of the nose cone is defined by a Von Karman profile. 
     In a further embodiment of any of the above, the nose cone includes a length measured along the axis between the leading edge of the nose cone and the base of the nose cone, and the transition section is defined by the equation: 
     
       
         
           
             
               R 
               = 
               
                 
                   
                     R 
                     0 
                   
                   
                     π 
                   
                 
                  
                 
                   
                     θ 
                     - 
                     
                       
                         sin 
                          
                         
                           ( 
                           
                             2 
                              
                             θ 
                           
                           ) 
                         
                       
                       2 
                     
                   
                 
               
             
             , 
           
         
       
     
     wherein 
     
       
         
           
             
               θ 
               = 
               
                 
                   cos 
                   
                     - 
                     1 
                   
                 
                  
                 
                   ( 
                   
                     1 
                     - 
                     
                       
                         2 
                          
                         
                           x 
                           * 
                         
                       
                       L 
                     
                   
                   ) 
                 
               
             
             , 
           
         
       
     
     wherein R 0  is a radius of the base of the nose cone, L is the length of the nose cone, x* is a position along the length of the nose cone, and R is a radius of the nose cone at the position x*. 
     In a further embodiment of any of the above, the forward section of the nose cone has a spherical profile. 
     In a further embodiment of any of the above, the forward section of the nose cone has a blunt profile. 
     In a further embodiment of any of the above, the nose cone is coated with an icephobic material. 
     In a further embodiment of any of the above, the nose cone is formed from a metallic material. 
     In a further embodiment of any of the above, the nose cone is formed from a non-metallic material. 
     In one aspect, a nose cone for a gas turbine engine is provided. The nose cone is symmetrically disposed about an axis. The nose cone includes a leading edge and a base. A forward section is disposed between the leading edge and the base and has a first shape. A transition section is disposed between the forward section and the base and has a second shape. The first shape is less aerodynamic than the second shape, whereby streamlines of air flowing past the nose cone are closer to the transition section than to the forward section such that ice accretion is minimized on the forward section. 
     In a further embodiment of the above, the second shape is defined by a Von Karman profile. 
     In a further embodiment of any of the above, the nose cone includes a length measured along the axis between the leading edge and the base, wherein the second shape is defined by the equation: 
     
       
         
           
             
               R 
               = 
               
                 
                   
                     R 
                     0 
                   
                   
                     π 
                   
                 
                  
                 
                   
                     θ 
                     - 
                     
                       
                         sin 
                          
                         
                           ( 
                           
                             2 
                              
                             θ 
                           
                           ) 
                         
                       
                       2 
                     
                   
                 
               
             
             , 
           
         
       
     
     wherein 
     
       
         
           
             
               θ 
               = 
               
                 
                   cos 
                   
                     - 
                     1 
                   
                 
                  
                 
                   ( 
                   
                     1 
                     - 
                     
                       
                         2 
                          
                         
                           x 
                           * 
                         
                       
                       L 
                     
                   
                   ) 
                 
               
             
             , 
           
         
       
     
     wherein R 0  is a radius of the base of the nose cone, L is the length of the nose cone, x* is a position along the length of the nose cone, and R is a radius of the nose cone at the position x*. 
     In a further embodiment of any of the above, the first shape has a spherical profile. 
     Other embodiments are also disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments and other features, advantages and disclosures contained herein, and the manner of attaining them, will become apparent and the present disclosure will be better understood by reference to the following description of various exemplary embodiments of the present disclosure taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a sectional view of a gas turbine engine in an embodiment; and 
         FIG. 2  is a schematic of stagnant air formed upstream from a nose cone having a pointed forward end. 
         FIG. 3  is a schematic view of stagnant air formed upstream from a nose cone having a blunt forward end. 
         FIG. 4  is a graph showing ice formation along a nose cone having a pointed forward end. 
         FIG. 5  is a graph showing ice formation along a nose cone having a blunt forward end. 
         FIG. 6  is a graph illustrating the dimensions of various nose cones. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS 
     For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of this disclosure is thereby intended. 
       FIG. 1  shows a gas turbine engine  20 , such as a gas turbine used for power generation or propulsion, circumferentially disposed about an engine centerline, or axial centerline axis A. The gas turbine engine  20  is disclosed herein as a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . Alternative engines might include an augmentor section (not shown) among other systems or features. The fan section  22  drives air along a bypass flow path B in a bypass duct, while the compressor section  24  drives air along a core flow path C for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures. 
     The exemplary engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided, and the location of bearing systems  38  may be varied as appropriate to the application. 
     The low speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low pressure compressor  44  and a low pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a speed change mechanism, which in exemplary gas turbine engine  20  is illustrated as a geared architecture  48  to drive the fan  42  at a lower speed than the low speed spool  30 . The high speed spool  32  includes an outer shaft  50  that interconnects a high pressure compressor  52  and high pressure turbine  54 . A combustor  56  is arranged in exemplary gas turbine  20  between the high pressure compressor  52  and the high pressure turbine  54 . An engine static structure  36  is arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The engine static structure  36  further supports bearing systems  38  in the turbine section  28 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A which is collinear with their longitudinal axes. 
     The core airflow is compressed by the low pressure compressor  44  then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , then expanded over the high pressure turbine  54  and low pressure turbine  46 . The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. It will be appreciated that each of the positions of the fan section  22 , compressor section  24 , combustor section  26 , turbine section  28 , and fan drive gear system  48  may be varied. For example, gear system  48  may be located aft of combustor section  26  or even aft of turbine section  28 , and fan section  22  may be positioned forward or aft of the location of gear system  48 . 
     The engine  20  in one example is a high-bypass geared aircraft engine. In a further example, the engine  20  bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture  48  is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine  46  has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine  20  bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor  44 , and the low pressure turbine  46  has a pressure ratio that is greater than about five 5:1. Low pressure turbine  46  pressure ratio is pressure measured prior to inlet of low pressure turbine  46  as related to the pressure at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. The geared architecture  48  may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans. 
     A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section  22  of the engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet (10,688 meters). The flight condition of 0.8 Mach and 35,000 ft. (10,688 meters), with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of 1 bm of fuel being burned divided by 1 bf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/(518.7° R)] 0.5 . The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second (350.5 m/sec). 
       FIG. 2  is a schematic of stagnant airflow  100  formed upstream from a nose cone  102  having a pointed forward end  104 . Generally, the thickest ice accumulation occurs at a leading edge  106  of a nose cone  102  independent of the shape of the nose cone  102 . In the embodiment illustrated of  FIG. 2 , the sharp point of the forward end  104  of the nose cone  102  creates airflow  108  around the nose cone  102  that travels adjacent to the contour of the nose cone  102  approximately the entire length of the nose cone  102 . The airflow  108  creates a small pocket of stagnant airflow  100  upstream from the nose cone  102 . Smaller stagnant airflow  100  causes ice crystals to form on the nose cone  102 . 
       FIG. 3  is a schematic of stagnant airflow  200  formed upstream from a nose cone  202  having a blunt forward end  204 . In the embodiment illustrated of  FIG. 3 , the blunt forward end  204  of the nose cone  202  creates streamlines  208  that are more distant from the contour of a leading edge  206  of the nose cone  202  than from the contour of the nose cone  202  further downstream, such as the more aerodynamic contour of a transition section  518  discussed hereinbelow with respect to  FIG. 6 . The airflow  208  forms in a bow wave that creates a larger pocket of stagnant airflow  200  upstream from the nose cone  202 . Larger stagnant airflow  200  causes super cooled droplets to nucleate and form ice crystals prior to contact with the nose cone  202 . The ice crystals deflect into the airflow  208  without accreting on the nose cone  202 . Accordingly, the larger area of stagnant airflow  200  for the blunt shape minimizes an opportunity for icing on the nose cone  202 . 
       FIG. 4  is a graph  300  showing ice formation  302  along a nose cone  304  having a pointed forward end  306 . Specifically,  FIG. 4  shows the ice formation  302  after operating an engine containing the nose cone  304  for thirty minutes. A portion  308  of the ice formation  302  occurs directly upstream from the leading edge  310  of the nose cone  304 . The remainder of the ice formation occurs along the contour of the nose cone  304 . The ice formation  302  directly upstream from the leading edge  310  results in ice crystals forming on the nose cone  304 . 
       FIG. 5  is a graph  400  showing ice formation  402  along a nose cone  404  having a blunt forward end  406  after operating an engine containing the nose cone  404  for nine minutes, and ice formation  408  along the nose cone  404  after operating the engine for thirty minutes. After nine minutes of engine operation, the ice formation  402  occurs upstream from the contour of the nose cone  404 . As the engine continues to operate, stagnant airflow continues to form causing the ice formation  408  after thirty minutes to occur further upstream from the nose cone  404 . The larger stagnant airflow causes super cooled droplets to nucleate and form ice crystals prior to contact with the nose cone  404 . The ice crystals deflect into the airflow around the nose cone  404  without accreting on the nose cone  404 . Accordingly, the blunt profile of the nose cone  404  minimizes an opportunity for icing on the nose cone  404 . 
       FIG. 6  is a graph  500  illustrating the dimensions of various nose cones. A first nose cone  502  has a pointed profile. As set forth above, the pointed profile increases the likelihood of ice formation on the nose cone  502 . However, the pointed profile also increases the aerodynamics of the nose cone  502 . A second nose cone  504  utilizes a Von Karman profile that has minimum drag for a given length and width of nose cone. In general, a Von Karman profile is formed by the equation: 
     
       
         
           
             
               R 
               = 
               
                 
                   
                     R 
                     0 
                   
                   
                     π 
                   
                 
                  
                 
                   
                     θ 
                     - 
                     
                       
                         sin 
                          
                         
                           ( 
                           
                             2 
                              
                             θ 
                           
                           ) 
                         
                       
                       2 
                     
                   
                 
               
             
             , 
           
         
       
     
     wherein 
     
       
         
           
             
               θ 
               = 
               
                 
                   cos 
                   
                     - 
                     1 
                   
                 
                  
                 
                   ( 
                   
                     1 
                     - 
                     
                       
                         2 
                          
                         
                           x 
                           * 
                         
                       
                       L 
                     
                   
                   ) 
                 
               
             
             , 
           
         
       
     
     wherein R 0  is a radius of a base  506  of the nose cone  504 , L is a length of the nose cone  504  defined between a leading edge and a base of the nose cone, x* is a position along the length of the nose cone  504 , and R is a radius of the nose cone  504  at the position x*. 
       FIG. 6  also illustrates a nose cone  510  having a leading edge  512 , a base  514 , and a length  516  defined between the leading edge  512  and the base  514 . The nose cone is symmetrically disposed about an axis. The nose cone  510  includes a transition section  518  defined between the leading edge  512  and the base  514 . In one embodiment, the transition section  518  is defined at an intermediate position between the leading edge  512  and the base  514 . The nose cone  510  also includes a forward section  520  defined between the leading edge  512  and the transition section  518 . 
     In one embodiment, the forward section  520  has a radius at any axial location defined by a first equation. In one embodiment, the forward section has an icephobic profile. For example, in one embodiment, the forward section  520  has a blunt profile. In one embodiment, the forward section  520  has a spherical profile. In one embodiment, the transition section  518  has a radius at any axial location defined by a second equation that is different from the first equation. In one embodiment, the transition section  518  is formed with an aerodynamic profile. In one embodiment, the transition section  518  is defined by a Von Karman profile defined by the equation: 
     
       
         
           
             
               R 
               = 
               
                 
                   
                     R 
                     0 
                   
                   
                     π 
                   
                 
                  
                 
                   
                     θ 
                     - 
                     
                       
                         sin 
                          
                         
                           ( 
                           
                             2 
                              
                             θ 
                           
                           ) 
                         
                       
                       2 
                     
                   
                 
               
             
             , 
           
         
       
     
     wherein 
     
       
         
           
             
               θ 
               = 
               
                 
                   cos 
                   
                     - 
                     1 
                   
                 
                  
                 
                   ( 
                   
                     1 
                     - 
                     
                       
                         2 
                          
                         
                           x 
                           * 
                         
                       
                       L 
                     
                   
                   ) 
                 
               
             
             , 
           
         
       
     
     wherein R 0  is a radius of the base  514  of the nose cone  510 , L is the length  516  of the nose cone  510 , x* is a position along the length  516  of the nose cone  510 , and R is a radius of the nose cone  510  at the position x*. In one embodiment, the nose cone  510  is coated with an icephobic material to further reduce ice formation thereon. In one embodiment, the nose cone  510  may be formed from any material, for example a metallic material or a non-metallic material. 
     The modified profile of the nose cone  510  causes increased stagnant airflow upstream from the nose cone  510 . Accordingly, ice crystals form upstream from the nose cone  510 , rather than forming on the nose cone  510  itself. The nose cone  510  reduces ice formation in comparison to nose cones having a complete Von Karman profile, while also providing increased aerodynamic efficiency in comparison to a nose cone having a completely spherical profile. 
     The profile of the nose cone  510  includes two aspects: 1. the blunt (defined herein as spherical or near spherical) shape of the forward section  520  for the reduction of ice accretion; and 2. the transition section  518  connecting the forward section  520  of the nose cone  510  to a downstream portion of an engine inlet hub flowpath to provide a relatively low total pressure (Pt) loss. It should be noted that the ice rejection property of the spherical shape of can be realized without the transition section  518  (i.e. if the entire nose cone were defined as a simple hemisphere). However, when defining the entire nose cone as a hemisphere, a region of high Mach number develops in the air flow over the spherical surface near the junction of the spherical shape and the base. This results in a relatively high total pressure loss. The high total pressure loss causes a loss of efficiency of an engine compression system, thereby leading to an increase in engine specific fuel consumption. Accordingly, the aerodynamic shape of the transition section  518  is provided to reduce the peak Mach number over the surface of the nose cone and reduce the total pressure (Pt) loss. It should be noted that the Von Karman shape of the transition section  518  is only one embodiment of the nose cone  510 . In general, the transition section  518  of the nose cone  510  can be defined as any shape which reduces Pt loss by reducing regions of high Mach number over the length  516  of the nose cone  510  as compared to a hemispherical nose cone. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.