Geared turbofan arrangement with core split power ratio

Abstract

A gas turbine engine according to an example of the present disclosure includes, among other things, a fan section including a fan having a plurality of fan blades, and a nacelle surrounding the plurality of fan blades, a compressor section including a low pressure compressor and a high pressure compressor, the low pressure compressor including a plurality of stages, and the high pressure compressor including 6 or more stages. A turbine section includes a fan drive turbine that drives the fan section through a gear arrangement, and including a second turbine that drives the high pressure compressor. A power ratio is provided by the combination of a first power input of the low pressure compressor and a second power input of the high pressure compressor, the power ratio defined by the second power input divided by the first power input, and the power ratio is less than or equal to 1.0.

Claims

1. A turbofan engine comprising: a fan section including a fan having a plurality of fan blades, and a fan case surrounding the plurality of fan blades to define a bypass duct; a compressor section including a low pressure compressor and a high pressure compressor, the low pressure compressor including a plurality of stages, and the high pressure compressor including 6 or more stages; wherein the fan section delivers a first portion of air into the compressor section, and a second portion of air into the bypass duct, and a bypass ratio, which is defined as a first volume of air passing to the bypass duct compared to a second volume of air passing into the compressor section, is equal to or greater than 12; a turbine section including a fan drive turbine that drives the fan section through a gear arrangement, and including a second turbine that drives the high pressure compressor; and a core split power ratio provided by a second power input to the high pressure compressor measured in horsepower divided by a first power input to the low pressure compressor measured in horsepower, and the core split power ratio being less than or equal to 1.0.

2. The turbofan engine as set forth in claim 1, wherein the second turbine is a two-stage turbine.

3. The turbofan engine as set forth in claim 2, wherein an overall pressure ratio is provided by the combination of the low pressure compressor, the high pressure compressor and a fan root pressure rise of the fan section, and the overall pressure ratio is equal to or greater than 36.

4. The turbofan engine as set forth in claim 3, wherein the fan has a low fan pressure ratio of less than 1.50 across the plurality of fan blades alone.

5. The turbofan engine as set forth in claim 4, wherein the core split power ratio is greater than or equal to 0.71.

6. The turbofan engine as set forth in claim 5, wherein the plurality of stages of the low pressure compressor includes 4 or more stages.

7. The turbofan engine as set forth in claim 5, wherein the low fan pressure ratio is less than 1.45 across the plurality of fan blades alone.

8. The turbofan engine as set forth in claim 7, wherein the gear arrangement is a planetary gear system having a gear ratio greater than 2.3.

9. The turbofan engine as set forth in claim 8, wherein the low fan pressure ratio is less than 1.40 across the plurality of fan blades alone.

10. The turbofan engine as set forth in claim 9, wherein a low corrected fan tip speed of the plurality of fan blades is less than 1150 feet per second, and the low corrected fan tip speed is an actual fan tip speed divided by [(Tram °R)/(518.7°R)]{circumflex over ( )}0.5.

11. The turbofan engine as set forth in claim 10, wherein the core split power ratio is greater than or equal to 0.77.

12. The turbofan engine as set forth in claim 11, wherein the plurality of stages of the low pressure compressor includes 4 or more stages.

13. The turbofan engine as set forth in claim 12, wherein the high pressure compressor includes 8 stages.

14. A turbofan engine comprising: a fan section including a fan having a plurality of fan blades rotatable about an engine longitudinal axis, and a fan case surrounding the plurality of fan blades to define a bypass duct; a compressor section including a low pressure compressor and a high pressure compressor, the low pressure compressor including a plurality of stages, and the high pressure compressor including 6 or more stages; wherein the fan section delivers a first portion of air into the compressor section, and a second portion of air into the bypass duct, and a bypass ratio, which is defined as a first volume of air passing to the bypass duct compared to a second volume of air passing into the compressor section, is equal to or greater than 12; a turbine section including a fan drive turbine that drives the fan section through a gear arrangement, and including a second turbine that drives the high pressure compressor; and a core split power ratio provided by a second power input to the high pressure compressor measured in horsepower divided by a first power input to the low pressure compressor measured in horsepower, the core split power ratio being greater than or equal to 1.0.

15. The turbofan engine as set forth in claim 14, wherein an overall pressure ratio is provided by the combination of the low pressure compressor, the high pressure compressor and a fan root pressure rise of the fan section, and the overall pressure ratio is equal to or greater than 36.

16. The turbofan engine as set forth in claim 15, wherein the fan has a low fan pressure ratio of less than 1.40 across the plurality of fan blades alone.

17. The turbofan engine as set forth in claim 16, wherein the second turbine is a two-stage turbine.

18. The turbofan engine as set forth in claim 16, wherein the core split power ratio is greater than 1.1.

19. The turbofan engine as set forth in claim 18, wherein the low pressure compressor includes a greater number of turbine stages than the second turbine.

20. The turbofan engine as set forth in claim 19, wherein the core split power ratio is greater than 1.26.

21. The turbofan engine as set forth in claim 20, wherein the second turbine is a two-stage turbine.

22. The turbofan engine as set forth in claim 21, wherein the gear arrangement is a planetary gear system.

23. The turbofan engine as set forth in claim 21, wherein a gear ratio of the gear arrangement is greater than 2.3.

24. The turbofan engine as set forth in claim 23, wherein a low corrected fan tip speed of the plurality of fan blades is less than 1150 feet per second, and the low corrected fan tip speed is an actual fan tip speed divided by [(Tram °R)/(518.7°R)]{circumflex over ( )}0.5.

25. The turbofan engine as set forth in claim 24, wherein the fan is rotatable in the same direction as the fan drive turbine.

26. The turbofan engine as set forth in claim 25, wherein the core split power ratio is less than or equal to 1.4.

27. The turbofan engine as set forth in claim 25, wherein the core split power ratio is greater than 1.3.

28. The turbofan engine as set forth in claim 27, wherein the turbine section includes a mid-turbine frame between the second turbine and the fan drive turbine, wherein the mid-turbine frame supports bearing systems in the turbine section and includes airfoils in a core flow path.

29. The turbofan engine as set forth in claim 19, wherein the core split power ratio is less than or equal to 1.4, and wherein the fan drive turbine includes a greater number of turbine stages than the second turbine.

30. The turbofan engine as set forth in claim 28, wherein the fan drive turbine includes a greater number of turbine stages than the second turbine.

31. The turbofan engine as set forth in claim 30, wherein the core split power ratio is less than or equal to 1.4.

32. The turbofan engine as set forth in claim 30, wherein the low pressure compressor includes 4 stages.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a gas turbine engine.

(2) FIG. 2 schematically shows the arrangement of the low and high spool, along with the fan drive of FIG. 1.

(3) FIG. 3 schematically shows an alternative drive arrangement of FIG. 1.

(4) FIG. 4 schematically shows a gas turbine engine including a three-spool architecture.

(5) FIG. 5 graphically shows the relationship of propulsive efficiency, thermal efficiency, and overall efficiency for a gas turbine engine embodiment.

(6) FIG. 6 illustrates a perspective view of a turbine blade.

(7) FIG. 6A illustrates a cross-sectional view of a portion of the turbine blade of FIG. 6 having a directionally solidified microstructure.

(8) FIG. 7 illustrates a cross-sectional view of a portion of a fan case.

DETAILED DESCRIPTION

(9) 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 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.

(10) 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.

(11) 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.

(12) 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.

(13) 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.

(14) 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)].sup.0.5. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second.

(15) FIGS. 2 and 3 schematically illustrate engines 220 and 320, each which may generally have the features of engine 20 in FIG. 1. As shown in FIG. 2, the engine 220 may be counter-rotating. This means that the low speed spool 30, including the low pressure turbine 46 and low pressure compressor 44, rotates in one direction (“−”), while the high speed spool 32, including high pressure turbine 54 and high pressure compressor 52, rotates in an opposed direction (“+”). The gear reduction 48, which may be, for example, an epicyclic transmission (e.g., with a sun, ring, and star gears), is selected such that the fan 42 rotates in the same direction (“+”) as the high spool 32. In FIG. 3, the fan 42 of engine 320 rotates in the same direction as the low speed spool 30. To achieve this rotation, the gear reduction 48 may be a planetary gear reduction which would cause the fan 42 to rotate in the same direction. Of course, this application extends to engines where the two spools rotate in the same direction.

(16) FIG. 4 schematically illustrates an engine 420 arranged as a three-spool architecture. The engine includes similar features as the engine 20 and also has an intermediate spool 31. The intermediate spool 31 generally includes a low pressure compressor 44 and an intermediate pressure turbine 47 interconnected by a shaft extending along the engine central longitudinal axis A. The low speed spool 30 includes a low pressure or fan drive turbine 46 interconnected with a fan 42. In some embodiments, the engine 420 includes a gear reduction 48 positioned between the low pressure turbine 46 and the fan 42. The gear reduction 48 can be located adjacent to the fan 42 (shown) or adjacent to the low pressure turbine 46 as is known in the art. The fan 42 can be configured to rotate in the same direction or in the opposite direction as the low pressure turbine 46 via the gear reduction 48. In other embodiments, the gear reduction 48 is omitted. With the arrangement of any of the engines 20, 220, 320, 420, and with the other structure as set forth below, including the various quantities and operational ranges, the overall efficiency of the gas turbine engine is greatly increased.

(17) Specific thrust can be used to evaluate the relative bulk of the engine. Specific thrust can be defined in one of two ways as:
SpecificThrust=(F.sub.Net)/(W.sub.Atotal)  Equation 1:
SpecificThrust=(1/g.sub.c)/(V.sub.Jet−V.sub.o)  Equation 2:
where (F.sub.Net) is the net thrust of the engine measured in (lbf), (W.sub.Atotal) is the total inlet air mass flow of the engine measured in (lbm per second), (g.sub.c) is the gravity constant (32.174 feet×lbm per lbf per second per second), (V.sub.Jet) is the exhaust velocity measured in (feet per second) at the exit of the engine exhaust nozzle, (V.sub.o) is the flight velocity of the aircraft, and specific thrust (SpecificThrust) is measured in lbf/(lb/s). If an aircraft includes more than one engine exhaust nozzle, then (V.sub.Jet) can be defined as the average of the exhaust velocities of the nozzles. Engines with a low specific thrust are relatively larger in size but have relatively better jet noise and fuel consumption characteristics as compared to engines with a high specific thrust.

(18) The overall efficiency (“η.sub.overall”) of a gas turbine engine can be evaluated in terms of its fuel economy or TSFC defined as follows:
TSFC=(V.sub.o/η.sub.overall)×((3600 seconds/hr)/(J×LHV))  Equation 3:
where (J) is Joule's derived energy conversion (778 ft×lbf per Btu), (η.sub.overall) is the overall efficiency of the engine, and (LHV) is the fuel lower heating value measured in (Btu divided by lbm). As shown, TSFC increases as flight velocity (V.sub.o) of the aircraft increases, and improvements in the overall efficiency of the engine (η.sub.overall) decrease TSFC. Thus, it is desirable to improve the overall efficiency (η.sub.overall) of the engine.

(19) In this disclosure, the overall efficiency of the engine (η.sub.overall) is defined as:
η.sub.overall=(η.sub.propulsive×η.sub.thermal)  Equation 4:
where (η.sub.propulsive) is the propulsive efficiency of the engine, and where (η.sub.thermal) is the thermal efficiency of the engine. In turn, thermal efficiency (η.sub.thermal) and propulsive efficiency (η.sub.propulsive) can be defined as:
η.sub.thermal=(CorePower/FuelPower)  Equation 5:
η.sub.propulsive=(ThrustPower/CorePower)  Equation 6:
where thrust power (ThrustPower) is the net thrust of the engine (F.sub.NET) measured in (lbf multiplied by the flight velocity (V.sub.o) measured in ft. per second of the aircraft), fuel power (FuelPower) is the fuel flow rate measured in (lbm/hr multiplied by the fuel lower heating value (LHV) divided by 3600 seconds per hr), and core power (CorePower) is the total power provided by the combination of the spools.

(20) More specifically, thermal efficiency (η.sub.thermal) and propulsive efficiency (η.sub.propulsive) can be defined as:
η.sub.thermal=(CorePower/J)/({dot over (m)}.sub.fuel×LHV/(3600 seconds/hr))  Equation 7:
η.sub.propulsive=(V.sub.o)/[(g.sub.c/2)×(F.sub.Net/W.sub.Atotal)+V.sub.o)]  Equation 8:
where ({dot over (m)}fuel) is the fuel flow rate to the combustor 56 measured in lbm (pounds mass) per hour.

(21) FIG. 5 graphically shows the relationship between propulsive efficiency (x-axis), thermal efficiency (y-axis), and the resultant overall efficiency (z-axis) in a gas turbine engine embodiment applying the techniques described herein as compared to prior engines. Engine designers have used various techniques to improve the fuel efficiency. Some approaches to improving fuel efficiency have included increasing the operating pressures and temperatures of the compressor section 24 and high pressure turbine 54 upstream of the fan drive turbine 46, precipitating the need for advanced materials in the turbine and compressor sections.

(22) Vector 62 illustrates efficiency improvements typical of these approaches. Vector 62 has a slope of about 75 to 90 degrees, with an improvement in overall efficiency (η.sub.overall) of about 10%, and about 3% to 0% higher propulsive efficiency (η.sub.propulsive), respectively. Accordingly, these approaches have generally resulted in improvements to the thermal efficiency (η.sub.thermal) but with marginal improvements to propulsive efficiency (η.sub.propulsive) of the engine as a byproduct. Rather, vector 62 demonstrates that prior designers have not been concerned with selecting techniques that consider improvements in thermal efficiency (η.sub.thermal) and propulsive efficiency (η.sub.propulsive) simultaneously. Approaches to improving propulsive efficiency (η.sub.propulsive) have included increasing the bypass ratio (BPR) of the fan section 22, which increases the size and weight of the engine.

(23) Similarly, these approaches to improving propulsive efficiency (η.sub.propulsive) have resulted in marginal improvements to overall efficiency (η.sub.overall). However, the overall efficiency (η.sub.overall) or thrust specific fuel consumption (TSFC) of the engine can be improved by defining an engine architecture that affects propulsive efficiency (η.sub.propulsive) and thermal efficiency (η.sub.thermal) simultaneously, via core power (CorePower).

(24) One embodiment of the engine disclosed herein is illustrated as vector 64. As shown, vector 64 has a slope of about 30 to 60 degrees, which results in an improvement in the overall efficiency (η.sub.overall) of the engine of about 20%, and about 14% to 8% higher propulsive efficiency (η.sub.propulsive), respectively, than prior engines illustrated by vector 62.

(25) The core power (CorePower) of a gas turbine engine can be defined as:
CorePower=(2×P.sub.High)/(1+(P.sub.High/P.sub.Low))  Equation 9:
where (P.sub.High) is the horsepower provided by the high speed spool 32 in a two-spool architecture, or the power provided by the high spool 32 and the intermediate spool 31 in a three-spool architecture; and where (P.sub.Low) is the horsepower provided by the low spool 30.

(26) A core split power ratio of the high spool (P.sub.High) (and intermediate spool in a three-spool architecture) and the low spool (P.sub.Low) can be defined as:
(P.sub.High/P.sub.Low)=[((2×HP.sub.HPC×η.sub.propulsive)/(F.sub.Net×V.sub.o))−1]  Equation 10:
where (HP.sub.HPC) is the horsepower at the (second) high pressure compressor 52 (and intermediate spool in a three-spool architecture). The core split power ratio is greater than 1.0 except when concurrently: 1) the number of stages of the high pressure compressor 52 is less than the number of stages of the low pressure compressor 44; and 2) the number of stages of the high pressure compressor 52 is less than the sum of the number of stages of the high pressure turbine 54 and the number of stages of the low pressure turbine 46. As illustrated by equation 10, the overall efficiency (η.sub.overall) of the engine can be improved by transferring power output from the high spool 32 to the low spool 30. However, prior engine designs have avoided this approach because it imposes undesirable thermal and mechanical stresses on the fan drive turbine 46 based on an increase in power output to drive the fan 42.

(27) In one embodiment made according to the above design, the net thrust (F.sub.Net) of the engine is 4,650 lbs, the flight velocity (V.sub.o) is 779 ft/sec, the propulsive efficiency (η.sub.propulsive) is 0.71, and the power of the high pressure compressor 52 (HP.sub.HPC) is 10,500 hp. Thus, using Equation 10 above, the core power ratio is:
Ratio=(P.sub.High/P.sub.Low)=[((2×HP.sub.HPC×η.sub.propulsive)/(F.sub.Net×V.sub.o))−1]=[((2×10500×550×0.71)/(4650×779))−1]=1.26
where 1 unit of horsepower is equivalent to 550 ft-lbf/sec. In another embodiment, the ratio was about 1.2. In a further embodiment, the ratio was about 0.8. With ratios in the 0.5 to 1.4 range, and with a propulsive efficiency equal to or greater than about 0.65, a very efficient overall gas turbine engine is achieved. More narrowly, ratios equal to or greater than about 0.71 are more efficient. Ratios in the 0.77 to 1.3 range are even more efficient. Even more narrowly, ratios in the 0.9 to 1.1 range are more efficient. In a further embodiment, the ratio was about 1.0, with the horsepower at the each of the low and high spools 30, 32 being approximately equivalent. As a result of these ratios, in particular, the compressor section and turbine section can be made much smaller than in the prior art, both in diameter and axial length. In addition, the efficiency of the overall engine is greatly increased.

(28) The overall efficiency of the disclosed gas turbine engine is much higher than in the prior art. The exemplary gas turbine engine A (described above) and exemplary gas turbine engine B are compared to a direct-drive comparison engine C and a direct-drive base comparison engine D, and can be found in Table 1 as follows:

(29) TABLE-US-00001 TABLE 1 Comp. Base Engine A Engine B Engine C Engine D Net Thrust (FNet) (lbs) 4650 3925 4880 14158     Flight Velocity (Vo) (ft/sec) 779 779 779 828    Propulsive Efficiency (η.sub.propulsive) 0.71 0.71 0.67 0.65 Power, High Pressure Compressor 10500 8950 12730 39838*     (HP.sub.HPC) Core Split Power Ratio (P.sub.High/P.sub.Low) 1.26 1.29 1.48 1.44 Relative Improvement Propulsive 8.6% 9.0% 3.1% Base (0%) Efficiency (η.sub.propulsive) Thermal Efficiency (η.sub.thermal) 0.54 0.53 0.55 0.56 Relative Improvement Thermal −2.7% −5.0% −2.1% Base (0%) Efficiency (η.sub.thermal) Overall Efficiency (η.sub.overall) 0.38 0.38 0.37 0.36 Relative Improvement Overall 5.6% 3.6% 0.8% Base (0%) Efficiency (η.sub.overall) TSFC 0.51 0.52 0.53 0.57 Relative Improvement TSFC −10.9% −9.2% −6.7% Base (0%) *includes HP for a high pressure compressor and an intermediate pressure compressor

(30) Thus, as shown in Table 1, while comparison engine C has a core power ratio of 1.48, comparison engine C has a lower relative improvement in propulsive efficiency (η.sub.propulsive) and overall efficiency (η.sub.overall) than the exemplary gas turbine engines A and B. The exemplary gas turbine engines A and B also have more favorable relative improvements of TSFC than comparison engine C.

(31) Similar benefits to the overall efficiency (η.sub.overall) can be achieved by selecting an arrangement of the high pressure compressor 52 and low compressor 44 with respect to each other. The delta enthalpy rises across the high pressure compressor 52 and the low pressure compressor 44 can be expressed as:
(dh.sub.HPC)=T.sub.2.5×c.sub.p×[(PR.sub.HPC{circumflex over ( )}((γ−1)/(η.sub.polytropic×γ)))−1]  Equation 11:
(dh.sub.LPC)=T.sub.2.0×c.sub.p×[(PR.sub.LPC{circumflex over ( )}((γ−1)/(η.sub.polytropic×γ)))−1]  Equation 12:

(32) where (T.sub.2.5) is the temperature at the inlet of the high pressure compressor 52 in a two-spool architecture (or approximately T.sub.2.2 in a three-spool arrangement, measured at the inlet to the intermediate pressure compressor 45), (PR.sub.HPC) is the pressure ratio across the high pressure compressor 52 (and from the inlet of the intermediate pressure compressor 45 to the exit of the high pressure compressor 52 in a three-spool arrangement), (T.sub.2.0) is the temperature at the inlet of the low pressure compressor 44 in a two-spool architecture (or approximately T.sub.1 in a three-spool arrangement, measured at the inlet to fan 42), (PR.sub.LPC) is the pressure ratio across the low pressure compressor 44 (or the pressure ratio across the fan 42 in a three-spool arrangement), (γ) is the ratio of (c.sub.p) to (c.sub.v), with (c.sub.p) being the specific heat capacity measured for a constant pressure process in Btu per lbm per degree Rankine (°R), and being (c.sub.v) is the specific heat capacity measured for a constant volume process in Btu per lbm per degree Rankine (°R). Temperatures (T.sub.2.0), (T.sub.2.2), and (T.sub.2.5) are measured in degree Rankine (°R).

(33) The core split power ratio (P.sub.High/P.sub.Low) can be approximated by a ratio of the delta enthalpy rises across the compressors as:
(P.sub.High/P.sub.Low)=(dh.sub.HPC)/(dh.sub.LPC)  Equation 13:
where (dh.sub.HPC) is the delta enthalpy rise across the high pressure compressor 52 measured as exit minus inlet per lb. of airflow through the high pressure compressor 52, and where (dh.sub.LPC) is the delta enthalpy rise across the low pressure compressor 44 measured as exit minus inlet per lb. of airflow through the low pressure compressor 44. With ratios of the delta enthalpy rises similar to the core split power ratios disclosed herein, a very efficient overall gas turbine engine is achieved. In some embodiments, the low pressure compressor 44 includes 4 or more stages and the high pressure compressor 52 includes 6 or more stages. In further embodiments, the turbine section 28 includes at least 2 turbine stages upstream of the fan drive turbine 46.

(34) The core split power ratios disclosed herein can be combined with one or more features to further improve the propulsive efficiency (η.sub.propulsive) of the engine. As shown in FIG. 6, the turbine section 28, more particularly the low pressure turbine 46, for example, can include one or more turbine blades 29 with features permitting higher inlet temperatures, higher rotational speeds and gear reduction ratios than conventional turbines. The turbine blade 29 includes an airfoil 33 extending radially outward from a root 35. The blade 29 can include one or more cooling features 37 configured to receive coolant from a coolant source 43 (shown schematically) for cooling the blades 29, as is known in the art. In some embodiments, the coolant source 43 is the compressor section 24. The cooling features 37 can be one or more plenums and/or passages formed in the turbine blade 29 to provide impingement or convection cooling. In some embodiments, the cooling features 37 provide coolant to one or more cooling holes 39 for providing film cooling. Each turbine blade 29 can be made of a directionally solidified material (shown schematically in FIG. 6A) or a single-crystal material. Directionally solidified materials include a microstructure having a plurality of elongated grains 66 that are parallel to the major stress axes of the component as is known in the art. Each of the elongated grains 66 can extend the along the airfoil 33 between the root 35 and blade tip 51. Single crystal materials are formed as a single, homogenous crystal of material that includes no grain boundaries in the material, or rather, consist of only one grain. Single crystal materials can include nickel-based super alloys such as Nickel aluminide (NiAl). In further embodiments, the turbine section 28 includes at least two turbine stages upstream of the fan drive turbine 46. Modification of the low pressure turbine 46 with these features enables redistribution of horsepower from the high spool 32 to the low spool 30, which can further result in a reduction of the number of stage counts in the high pressure compressor 52 and a more compact engine arrangement.

(35) In another embodiment, the fan section 22 includes a hardwall containment system 70 (shown schematically in FIG. 1) arranged about the engine axis A and spaced radially from the fan blades 42. The hardwall containment system 70 is configured to contain, and absorb the impact of, a fan blade 42 separating from a fan hub 41 (shown schematically in FIG. 1) or a fragment thereof. In some embodiments, the hardwall containment system 70 is a hard ballistic liner applied to the nacelle or fan case 15 as is known in the art. The hard ballistic liner can include a rigid material such as a resin impregnated fiber structure, metallic structures, or ceramic structures. However, other materials and structures of the hardwall containment system 70 are contemplated. In yet another embodiment, the fan section 22 includes a fan case 15 made of an organic matrix composite (shown schematically in FIG. 7). The organic matrix composite can include a matrix material 72 and reinforcement fibers 74 distributed through the matrix material 72. The reinforcement fibers 74 may be discontinuous or continuous, depending upon the desired properties of the organic matrix composite, for example. The matrix material 72 may be a thermoset polymer or a thermoplastic polymer. The reinforcement fibers 74 may include carbon graphite, silica glass, silicon carbide, or ceramic. Given this description, one of ordinary skill in the art will recognize that other types of matrix materials and reinforcement fibers may be used. In further embodiments, the fan section 22 includes a fan blade and a disk with a characteristic density of less than about 13.1 pounds per in{circumflex over ( )}2 of frontal area with respect to the engine. In some embodiments, the fan section 22 has a fan blade efficiency greater than about 94.5%, being defined as the amount of thrust generated by the fan blade 42 compared to the work provided to the fan blade 42 by the gear reduction 48 or low speed spool 30. In further embodiments, the bypass ratio (BPR) which is defined as a volume of air passing to the bypass duct compared to a volume of air passing into the compressor section 24 is greater than about 12:1.

(36) The core power ratios disclosed herein can be combined with one or more features to further improve the thermal efficiency (η.sub.thermal) of the engine, expressed below in quantities at a flight condition of 0.8 Mach and 35,000 feet. In some embodiments, the low pressure turbine 46 is configured to rotate at least about 2.6 times faster than the fan section 22 and preferably at least about 2.9 times faster than the fan section 22. In further embodiments, an overall pressure ratio (OPR) of the engine provided by a combination of the low pressure compressor 44 and the high pressure compressor 52 and the pressure rise at the root of the fan section 22 is equal to or greater than about 36. In another embodiment, the fan section 22 defines a fan pressure ratio less than about 1.50 and preferably less than about 1.40, the low pressure turbine 46 is configured to rotate at least about 2.6 times faster than the fan section 22 and preferably at least 2.9 times faster than the fan section 22, the overall pressure ratio is equal to or greater than about 36, and the turbine section 28 includes at least two turbine stages upstream of the low pressure turbine 46. In some embodiments, the fan section 22 has a fan blade efficiency greater than about 94.5%, the fan drive turbine 46 has a thermal efficiency greater than about 90.9%, and the low pressure compressor 44 has a thermal efficiency of at least about 87% and is configured to deliver air to the high pressure compressor 52 having a thermal efficiency of at least about 85.1%. With respect to the compressor section 24, thermal efficiency can be defined as the pressure rise versus the temperature rise between an inlet and an outlet of one of the low pressure and high pressure compressors 44, 52. Thermal efficiency with respect to the fan drive turbine 46 is defined as the pressure decrease between the inlet and the outlet as compared to the work transferred to the low speed spool 30. In further embodiments, the cooling air flow to the turbine section 28 is less than or equal to about 36% of the core airflow along the core airflow path C, which increases the amount of compressed air provided to the combustor section 26. In other embodiments, the gear arrangement 48 has a thermal efficiency at sea-level takeoff and at stationary conditions of greater than about 98.7% as measured by the oil temperature rise between an inlet and an outlet of the gear arrangement 48.

(37) Engines made with the disclosed architecture, and including spool arrangements 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, have increased fuel efficiency, and are compact and lightweight relative to their thrust capability. Two-spool and three-spool direct drive engine architectures can also benefit from the teachings herein.

(38) It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting.

(39) While this invention has been disclosed with reference to one embodiment, it should be understood 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.