Abstract:
A gas turbine engine according to an example of the present disclosure includes, among other things, a fan situated at an inlet of a bypass passage, and a core engine configured to drive the fan. The core engine includes a low pressure compressor section driven by a low pressure turbine section, and a high pressure compressor section driven by a high pressure turbine section. The fan has a fan diameter, Dfan, and the high pressure compressor section has a compressor diameter, Dcomp. The fan diameter Dfan and the compressor diameter Dcomp have an interdependence represented by a scalable ratio Dfan/Dcomp that is greater than about 4.5.

Description:
RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. application Ser. No. 14/188,733, filed Feb. 25, 2014, which claims the benefit of U.S. Provisional Application 61/884,230, filed Sep. 30, 2013. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This application relates to a geared turbofan engine which may be particularly beneficial for application on regional jet aircraft. 
         [0003]    Gas turbine engines are known and, typically, include a fan delivering air into a compressor and into a bypass duct as propulsion air. Air in the compressor is compressed and delivered into a combustion section where it is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors driving them to rotate. 
         [0004]    Historically, a turbine rotor drove an upstream compressor rotor and a fan rotor at a single speed. 
         [0005]    More recently, it has been proposed to include a gear reduction between the fan rotor and the upstream compressor rotor such that the fan can rotate at slower speeds. This has provided a great deal of freedom to the designer of gas turbine engines. 
         [0006]    To date, there has been little activity in tailoring of geared gas turbine engines to the particular application and aircraft which will utilize the gas turbine engine. 
       SUMMARY OF THE INVENTION 
       [0007]    A gas turbine engine according to an example of the present disclosure includes a fan situated at an inlet of a bypass passage, and a core engine configured to drive the fan. The core engine includes a low pressure compressor section driven by a low pressure turbine section, and a high pressure compressor section driven by a high pressure turbine section. The gas turbine engine has a bypass ratio greater than about 10. The fan has a fan diameter, Dfan. The high pressure compressor section has a compressor diameter, Dcomp, and the fan diameter Dfan and the compressor diameter Dcomp have an interdependence represented by a scalable ratio Dfan/Dcomp that is greater than about 4.5. 
         [0008]    In a further embodiment of any of the foregoing embodiments, the fan has fewer than 26 fan blades. 
         [0009]    In a further embodiment of any of the foregoing embodiments, the fan diameter Dfan is greater than, or equal to, about 73 inches. 
         [0010]    In a further embodiment of any of the foregoing embodiments, the high pressure turbine section includes two turbine stages. 
         [0011]    In a further embodiment of any of the foregoing embodiments, a first ratio of a number of stages of the low pressure compressor section to a number of stages of the high pressure compressor section is greater than, or equal to, about 1.6. 
         [0012]    In a further embodiment of any of the foregoing embodiments, the low pressure turbine section has a greater number of stages than the low pressure compressor section. 
         [0013]    In a further embodiment of any of the foregoing embodiments, the first ratio is less than, or equal to, about 3.4. 
         [0014]    In a further embodiment of any of the foregoing embodiments, the low pressure turbine has a pressure ratio that is greater than about 5. 
         [0015]    In a further embodiment of any of the foregoing embodiments, the fan has a pressure ratio of less than, or equal to, about 1.45. 
         [0016]    A gas turbine engine according to an example of the present disclosure includes a fan having 26 or fewer fan blades situated at a bypass passage and having a fan diameter, Dfan, and a core engine configured to rotate the fan. The core engine includes a low pressure compressor section upstream of a high pressure compressor section. The high pressure compressor section has a compressor diameter, Dcomp, and the fan diameter Dfan and the compressor diameter Dcomp have an interdependence represented by a scalable ratio Dfan/Dcomp that is greater than about 4.5. A low pressure turbine section is configured to drive the fan and the low pressure compressor section. The low pressure turbine section has a greater number of stages than the low pressure compressor section. 
         [0017]    In a further embodiment of any of the foregoing embodiments, the gas turbine engine has a bypass ratio that is greater than about 10. 
         [0018]    In a further embodiment of any of the foregoing embodiments, the low pressure turbine has a pressure ratio that is greater than about 5. 
         [0019]    In a further embodiment of any of the foregoing embodiments, the fan diameter Dfan is greater than, or equal to, about 73 inches. 
         [0020]    A further embodiment of any of the foregoing embodiments includes a high pressure turbine section configured to drive the high pressure compressor section, the high pressure turbine section including two stages. 
         [0021]    In a further embodiment of any of the foregoing embodiments, a first ratio of a number of stages of the low pressure compressor section to a number of stages of the high pressure compressor section is greater than, or equal to, about 1.6 and is less than, or equal to, about 3.4. 
         [0022]    In a further embodiment of any of the foregoing embodiments, the low pressure compressor section includes three stages. 
         [0023]    A method of designing a gas turbine engine according to an example of the present disclosure includes providing a fan configured to deliver airflow to a bypass passage, providing a core engine configured to rotate the fan, the core engine including a low pressure compressor section driven by a low pressure turbine section, and a high pressure compressor section driven by a high pressure turbine section. A ratio of stages of the high pressure compressor section and stages of the low pressure compressor section are greater than, or equal to, about 1.6 and are less than, or equal to, about 3.4. The fan has a fan diameter, Dfan, the high pressure compressor section has a compressor diameter, Dcomp, and the fan diameter Dfan and the compressor diameter Dcomp have an interdependence represented by a scalable ratio Dfan/Dcomp that is greater than about 4.5. 
         [0024]    In a further embodiment of any of the foregoing embodiments, the low pressure turbine section has a greater number of stages than the low pressure compressor section. 
         [0025]    In a further embodiment of any of the foregoing embodiments, the high pressure turbine section includes two stages. 
         [0026]    In a further embodiment of any of the foregoing embodiments, the fan diameter is greater than about 73 inches and the fan has fewer than 26 fan blades. 
         [0027]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of an embodiment. The drawings that accompany the detailed description can be briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1A  schematically shows a gas turbine engine. 
           [0029]      FIG. 1B  schematically shows a regional jet aircraft. 
           [0030]      FIG. 2  shows parameters of one example engine. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]      FIG. 1A  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 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 defined within a nacelle  15 , 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. 
         [0032]    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. 
         [0033]    The low speed spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a first (or low) pressure compressor  44  and a first (or 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 second (or high) pressure compressor  52  and a second (or 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 . 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. 
         [0034]    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 mid-turbine frame  57  includes airfoils  59  which are in the core airflow path C. 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 . 
         [0035]    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. 
         [0036]    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. 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 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, 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)] 5 . The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second. 
         [0037]      FIG. 1B  schematically shows what may be called a regional jet aircraft  10  that mounts engines  20 . A regional aircraft may be defined in a number of ways, however, one way is that they typically have a single aisle  12  between passenger sections  11 . Another way may be a total flight length of less than 3000 nautical miles. 
         [0038]    The engines utilized in such an aircraft have a particularly high percentage of time in take-off and climb relative to cruise. That is, compared to jet engines utilized on longer range aircraft, the engines  20  mounted on aircraft  10  will be spending more time at take-off and cruise conditions which are particularly challenging on components within the engine. Thus, there are elevated temperatures adjacent a last stage of the downstream or high pressure compressor  32  and elevated turbine cooling air temperatures utilized to cool components in the turbine sections. This disclosure tailors the gas turbine engine  20  such that it is uniquely structured to address the challenges faced by such an engine. 
         [0039]    In such an engine, there may be a lower overall pressure ratio and a lower temperature at a downstream end of the downstream compressor rotor  52 . The overall pressure ratio across the upstream compressor rotor  44  and the downstream compressor rotor  52  may, in some embodiments, be greater than or equal to  38 , and may, in some embodiments, be less than or equal to  55 . Turbine cooling airflow is typically taken from the downstream compressor rotor, and may be at a lower temperature, consistent with a moderate temperature at a downstream end of the downstream compressor rotor. The turbine cooling air temperature will still be high given the frequent occurrence of take-off and climb temperature exposure on turbine airfoils. 
         [0040]    A greater portion of the total compression work is shifted to the downstream compressor rotor  52  relative to the upstream compressor rotor  44 . Although, the lower pressure spool  30  may be more efficient than the higher pressure spool  32  doing more work with the downstream compressor rotor  52  reduces the temperature of the gas at the exit of the high pressure turbine section  54 , thus, reducing the temperature reaching the low pressure turbine  46 . The first blade of the low pressure turbine may be cast with a directionally solidified material or even a single crystal material. 
         [0041]    Since there is more work done with the downstream compressor rotor  52 , a ratio of compressor stages for the downstream compressor rotor  52  compared to the number of stages in the upstream compressor rotor  44  may be greater than or equal to about 1.6 and less than or equal to about 3.4. In one embodiment a ratio of the stages in the downstream compressor rotor  52  to those in the upstream compressor rotor was 2.7. The speed of the low pressure turbine  46  and the fan  42  may be closer than in other engines. Thus, a gear ratio of the gear reduction  48  may be greater than or equal to about 2.6 and less than or equal to about 3.3. 
         [0042]    The low pressure turbine  46  may have only three or four stages since it is doing less work. 
         [0043]    The gear reduction  48  may be a planet-type epicyclic gearbox where a sun and ring gear revolve around an engine centerline, whereas the intermediate planet gears rotate on stationary axes but do not revolve around the sun. 
         [0044]    The downstream compressor rotor  52  speed is higher relative to the upstream compressor  44  speed since there is a greater amount of work performed at the downstream compressor rotor  52 . Again, this reduces the temperature reaching the low pressure turbine  46 . As an example, a redline tip speed of a first stage rotor in the downstream compressor rotor  52  to the redline tip speed of a first stage rotor in the upstream compressor rotor  44  is greater than or equal to about 1.18 and less than or equal to about 1.43 with the speeds measured in feet/second. 
         [0045]    The higher pressure turbine rotor  54  may have two or three turbine sections. 
         [0046]    The fan may be greater than about 73 inches in diameter and have fewer than about 26 blades. A pressure ratio across the fan may be less than about 1.45 and in some embodiments may be greater than or equal to about 1.35 and less than or equal to about 1.45. 
         [0047]      FIG. 2  tabulates several variables, on one example engine, made according to the teachings of this disclosure. In the illustrated embodiment, the fan diameter is 72.876 inches and a diameter of the high pressure compressor is 16.239 inches, such that a ratio of the fan diameter to the high pressure compressor diameter is 4.488. In embodiments, the fan diameter may be greater than about 73 inches, such that the ratio of fan diameter to high pressure compressor diameter is greater than about 4.5. 
         [0048]    Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.