Patent Publication Number: US-2023160337-A1

Title: Geared turbofan engine with a high ratio of thrust to turbine volume

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 17/192,039 filed on Mar. 4, 2021, which is continuation of U.S. application Ser. No. 16/158,545 filed on Oct. 12, 2018, now U.S. Pat. No. 11,053,843 granted on Jul. 6, 2021, which is continuation of U.S. application Ser. No. 14/592,991 filed on Jan. 9, 2015, now U.S. Pat. No. 10,138,809 granted on Nov. 27, 2018, which is a continuation-in-part of U.S. application Ser. No. 13/445,095, filed Apr. 12, 2012, which claims the benefit of U.S. Provisional Ser. No. 61/619,133, which was filed Apr. 2, 2012. 
    
    
     BACKGROUND OF THE INVENTION 
     This application relates to a geared turbofan gas turbine engine, wherein the low and high pressure spools rotate in the same direction relative to each other. 
     Gas turbine engines are known, and typically include a fan delivering air into a compressor section, and outwardly as bypass air to provide propulsion. The air in the compressor is delivered into a combustion section where it is mixed with fuel and burned. Products of this combustion pass downstream over turbine rotors, driving them to rotate. Typically there are low and high pressure compressors, and low and high pressure turbines. 
     The high pressure turbine typically drives the high pressure compressor as a high spool, and the low pressure turbine drives the low pressure compressor and the fan. Historically, the fan and low pressure compressor were driven at a common speed. 
     More recently, a gear reduction has been provided on the low pressure spool such that the fan and low pressure compressor can rotate at different speeds. It desirable to have more efficient engines that have more compact turbines to limit efficiency loses. 
     SUMMARY 
     In a featured embodiment, a gas turbine engine turbine comprises a high pressure turbine configured to rotate with a high pressure compressor as a high pressure spool in a first direction about a central axis. A low pressure turbine is configured to rotate in the first direction about the central axis. A fan is connected to the low pressure turbine via a gear reduction and will rotate in the first direction. The engine is configured to have a ratio of a thrust provided by the engine, to a volume of a turbine section including both the high pressure turbine and the low pressure turbine, that is greater than or equal to about 1.5 and less than or equal to about 5.5 lbf/in 3 . The thrust is sea level take-off, flat-rated static thrust. 
     In another embodiment according to the previous embodiment, guide vanes are positioned upstream of a first stage in the low pressure turbine to direct gases downstream of the high pressure turbine as the gases approach the low pressure turbine. 
     In another embodiment according to any of the previous embodiments, a mid-turbine frame supports the high pressure turbine. 
     In another embodiment according to any of the previous embodiments, the guide vanes are positioned intermediate the mid-turbine frame and the low pressure turbine. 
     In another embodiment according to any of the previous embodiments, there is an intermediate section, and the intermediate turbine section drives a compressor rotor. 
     In another embodiment according to any of the previous embodiments, the gear reduction is positioned intermediate the fan and a compressor rotor driven by the low pressure turbine. 
     In another embodiment according to any of the previous embodiments, the gear reduction is positioned intermediate the low pressure turbine and a compressor rotor driven by the low pressure turbine. 
     These and other features may be best understood from the following drawings and specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    schematically shows a gas turbine engine. 
         FIG.  2    schematically shows rotational features of one type of such an engine. 
         FIG.  3    is a detail of the turbine section volume. 
         FIG.  4    shows another embodiment. 
         FIG.  5    shows yet another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    schematically illustrates a gas turbine engine  20 . 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, for example, three-spools, an augmentor section, or a different arrangement of sections, among other systems or features. The fan section  22  drives air along a bypass flowpath B while the compressor section  24  drives air along a core flowpath C for compression and communication into the combustor section  26  then expansion through the turbine section  28 . The bypass flowpath is defined between a fan housing outward of fan section  22  and a core housing. The core flowpath is within the core housing. Although depicted as a 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 turbofans as the teachings may be applied to other types of turbine engines. For purposes of this application, the terms “low” and “high” as applied to speed or pressure are relative terms. The “high” speed and pressure would be higher than that associated with the “low” spools, compressors or turbines, however, the “low” speed and/or pressure may actually be “high.” 
     The 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. 
     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 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 . The terms “high” and “low” in relation to both the speed and pressure of the components are relative to each other, and not to an absolute value. A combustor  56  is arranged between the high pressure compressor  52  and the high pressure turbine  54 . A mid-turbine frame  57  of the engine static structure  36  is arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The mid-turbine frame  57  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 C 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 mid-turbine frame  57  includes airfoils  59  which are in the core airflow path and act as inlet stator vanes to turn the flow to properly feed the first blades of the low pressure turbine. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. 
     The engine  20  has bypass airflow B, and in one example is a high-bypass geared aircraft engine. The bypass ratio may be defined as the amount of air delivered into the bypass duct divided by the amount delivered into the core flow. In a further example, the engine  20  bypass ratio is greater than about six (6), with an example embodiment being greater than 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 5. 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  and the low pressure turbine has a pressure ratio that is greater than about 5:1. Low pressure turbine  46  pressure ratio is the total 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 a planet gear arrangement such that the fan will rotate in the same direction as the low spool. 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 greatest 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. The flight condition of 0.8 Mach and 35,000 ft, with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of lbm of fuel being burned per hour divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, before the 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 deg R)/518.7){circumflex over ( )}0.5]. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second at the same cruise point. 
       FIG.  2    shows detail of an engine  120 , which may generally have the features of engine  20  of  FIG.  1   . A fan  122  is positioned upstream of a low pressure compressor  124 , which is upstream of a high pressure compressor  126 . A combustor  128  is positioned downstream of the high pressure compressor  126 . A mid-turbine frame  142  may be positioned at a downstream end of the high pressure turbine  130 , and supports a bearing  138 , shown schematically, to support the aft end of the high pressure turbine  130 , and a high pressure spool  132 . A low pressure turbine  134  is positioned downstream of a mid-turbine frame  142 . A low spool  136 , driven by the low pressure turbine  134 , drives the low pressure compressor  124 . The speed change mechanism  48  causes the fan  122  to rotate at a different speed than the low pressure compressor  134 . In embodiments of this invention, the speed input to output ratio for the speed change mechanism is above or equal to 2.3:1, and up to less than or equal to 13:1. The gear also causes fan  122  to rotate in the same direction relative to the low pressure compressor  124 . As mentioned above, a planet gear arrangement may be utilized to cause the fan  122  to rotate in the same direction (“-”) relative to the low pressure compressor  124 . In this embodiment the fan generally has less than 26 blades, and the low pressure turbine has at least three stages, and up to six stages. The high pressure turbine generally has one or two stages as shown. 
     In this particular embodiment, the low pressure compressor  124  and the low pressure turbine  134  rotate in one direction (“-”) and the high pressure turbine  130 , the high pressure compressor  126 , rotate in the same direction (“-”) as does fan  122 . 
     A strut  140  is shown between the low pressure compressor  124  and the high pressure compressor  126 . The strut  140  spans the gas path, and has an airfoil shape, or at least a streamline shape. The combination of a blade at the exit of the low pressure compressor  124 , the strut  140 , and a variable vane, and then the first blade of the high pressure compressor  126  is generally encompassed within the structure illustrated as the strut  140 . 
     Since the compressor sections  124  and  126  rotate in the same direction, the several airfoils illustrated as the element  140  are required to do less turning of the air flow. 
     As will be explained below, since the turbine section is provided with a highly cambered vane, there is less turning required between the two turbine sections. Since the compressor is forcing flow with an adverse pressure gradient, and whereas the turbine has a favorable pressure gradient, this overall engine architecture is benefited by the illustrated combination. 
     Highly cambered inlet guide vanes  143  are positioned in a location intermediate the mid-turbine frame  142  and the most upstream rotor in the low pressure turbine  134 . The vanes  143  must properly direct the products of combustion downstream of the high pressure turbine  130  as they approach the first rotor of the low pressure turbine  134 . It is desirable for reducing the overall size of the low pressure turbine that the flow be properly directed when it initially encounters the first stage of the low pressure turbine section. 
     The above features achieve a more compact turbine section volume relative to the prior art, including both the high and low pressure turbines. A range of materials can be selected. As one example, by varying the materials for forming the low pressure turbine, the volume can be reduced through the use of more expensive and more exotic engineered materials, or alternatively, lower priced materials can be utilized. In three exemplary embodiments the first rotating blade of the Low Pressure Turbine can be a directionally solidified cast blade, a single crystal cast blade or a hollow, internally cooled blade. All three embodiments will change the turbine volume to be dramatically smaller than the prior art by increasing low pressure turbine speed. In addition, high efficiency blade cooling may be utilized to further result in a more compact turbine section. 
     Due to the compact turbine section, a power density, which may be defined as thrust in pounds force produced divided by the volume of the entire turbine section, may be optimized. The volume of the turbine section may be defined by an inlet of a first turbine vane in the high pressure turbine to the exit of the last rotating airfoil in the low pressure turbine, and may be expressed in cubic inches. The static thrust at the engine&#39;s flat rated Sea Level Takeoff condition divided by a turbine section volume is defined as power density. The sea level take-off flat-rated static thrust may be defined in lbs force, while the volume may be the volume from the annular inlet of the first turbine vane in the high pressure turbine to the annular exit of the downstream end of the last rotor section in the low pressure turbine. The maximum thrust may be Sea Level Takeoff Thrust “SLTO thrust” which is commonly defined as the flat-rated static thrust produced by the turbofan at sea-level. 
     The volume V of the turbine section may be best understood from  FIG.  3   . As shown, the frame  142  and vane  143  are intermediate the high pressure turbine section  130 , and the low pressure turbine section  134 . The volume V is illustrated by dashed line, and extends from an inner periphery I to an outer periphery O. The inner periphery is somewhat defined by the flowpath of the rotors, but also by the inner platform flow paths of vanes. The outer periphery is defined by the stator vanes and outer air seal structures along the flowpath. The volume extends from a most upstream end of the vane  400  at the beginning of the high pressure turbine  130 , typically its leading edge, and to the most downstream edge  401  of the last rotating airfoil in the low pressure turbine section  134 . Typically this will be the trailing edge of that airfoil. 
     The power density in the disclosed gas turbine engine is much higher than in the prior art. Eight exemplary engines are shown below which incorporate turbine sections and overall engine drive systems and architectures as set forth in this application, and can be found in Table I as follows: 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Thrust 
                 Turbine section 
                 Thrust/turbine 
               
               
                   
                   
                 SLTO 
                 volume from 
                 section volume 
               
               
                   
                 Engine 
                 (lbf) 
                 the Inlet 
                 (lbf/in 3 ) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 1 
                 17,000 
                 3,859 
                 4.41 
               
               
                   
                 2 
                 23,300 
                 5,330 
                 4.37 
               
               
                   
                 3 
                 29,500 
                 6,745 
                 4.37 
               
               
                   
                 4 
                 33,000 
                 6,745 
                 4.84 
               
               
                   
                 5 
                 96,500 
                 31,086 
                 3.10 
               
               
                   
                 6 
                 96,500 
                 62,172 
                 1.55 
               
               
                   
                 7 
                 96,500 
                 46,629 
                 2.07 
               
               
                   
                 8 
                 37,098 
                 6,745 
                 5.50 
               
               
                   
                   
               
            
           
         
       
     
     Thus, in embodiments, the power density would be greater than or equal to about 1.5 lbf/in 3 . More narrowly, the power density would be greater than or equal to about 2.0 lbf/in 3 . 
     Even more narrowly, the power density would be greater than or equal to about 3.0 lbf/in 3 . 
     More narrowly, the power density is greater than or equal to about 4.0 lbf/in 3 . More narrowly, the power density is greater than or equal to about 4.5 lbf/in 3 . Even more narrowly, the power density is greater than or equal to about 4.75 lbf/in 3 . Even more narrowly, the power density is greater than or equal to about 5.0 lbf/in 3 . 
     Also, in embodiments, the power density is less than or equal to about 5.5 lbf/in 3 . 
     While certain prior engines have had power densities greater than 1.5, and even greater than 3.2, such engines have been direct drive engines and not associated with a gear reduction. In particular, the power density of an engine known as PW4090 was about 1.92 lbf/in 3 , while the power density of an engine known as V2500 had a power density of 3.27 lbf/in 3 . 
     Engines made with the disclosed architecture, and including turbine sections as set forth in this application, and with modifications coming from the scope of the claims in this application, thus provide very high efficient operation, and increased fuel efficiency and lightweight relative to their trust capability. 
       FIG.  4    shows an embodiment  200 , wherein there is a fan drive turbine  208  driving a shaft  206  to in turn drive a fan rotor  202 . A gear reduction  204  may be positioned between the fan drive turbine  208  and the fan rotor  202 . This gear reduction  204  may be structured and operate like the gear reduction disclosed above. A compressor rotor  210  is driven by an intermediate pressure turbine  212 , and a second stage compressor rotor  214  is driven by a turbine rotor  216 . A combustion section  218  is positioned intermediate the compressor rotor  214  and the turbine section  216 . 
       FIG.  5    shows yet another embodiment  300  wherein a fan rotor  302  and a first stage compressor  304  rotate at a common speed. The gear reduction  306  (which may be structured as disclosed above) is intermediate the compressor rotor  304  and a shaft  308  which is driven by a low pressure turbine section. 
     The  FIG.  4  or  5    engines may be utilized with the density features disclosed above. 
     Although an embodiment of this invention has been disclosed, a person of ordinary skill in this art would recognize that certain modifications would come within the scope of this application. For that reason, the following claims should be studied to determine the true scope and content of this invention.