FAN MOTOR WITH LOW PRESSURE RATIO AND A DIMENSIONAL RELATIONSHIP BETWEEN INLET AND FAN SIZE

Description

BACKGROUND

[0001] A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustor section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section typically includes low and high pressure compressors and the turbine section includes low and high pressure turbines.

[0002] A nacelle surrounds the engine. An inlet section of the nacelle is that portion of the nacelle that is forward of the fan section of the engine. One function of the inlet is to reduce noise. A minimum length of the inlet is typically required for noise reduction with high bypass ratio engines.

[0003] While longer inlets tend to improve noise reduction, that feature does not come without cost. A longer inlet is associated with increased weight and external drag. Additionally, the airflow at the inlet during takeoff typically creates a bending moment that is proportional to the length of the inlet. Longer inlets, therefore, tend to introduce additional load on the engine structure under such conditions.

[0004] A prior art gas turbine engine assembly having the features of the preamble to claim 1 is disclosed in EP 1,340,903. Other prior art gas turbine engine assemblies including inlet portions of different L / D ratios are disclosed in US 5,915,403, XP055277347, XP000136188 and XP055621717.SUMMARY

[0005] According to the present invention, a gas turbine engine according to claim 1 is provided.

[0006] Features of embodiments are recited in the dependent claims.

[0007] The various features and advantages of at least one disclosed example embodiment will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a schematic view of an example gas turbine engine. Figure 2 schematically illustrates selected portions of the example gas turbine engine and demonstrates an example dimensional relationship designed according to an embodiment of this invention. DETAILED DESCRIPTION

[0009] Figure 1 schematically illustrates an example gas turbine engine 20 that includes a fan section 22, a compressor section 24, a combustor section 26 and a turbine section 28. Alternative engines might include an augmenter section (not shown) among other systems or features. The fan section 22 drives air along a bypass flow path B while the compressor section 24 draws air in along a core flow path C where air is compressed and communicated to a combustor section 26. In the combustor section 26, air is mixed with fuel and ignited to generate a high pressure exhaust gas stream that expands through the turbine section 28 where energy is extracted and utilized to drive the fan section 22 and the compressor section 24.

[0010] Although the disclosed non-limiting embodiment depicts a turbofan gas turbine engine, 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 example a turbine engine including a three-spool architecture in which three spools concentrically rotate about a common axis and where a low spool enables a low pressure turbine to drive a fan via a gearbox, an intermediate spool that enables an intermediate pressure turbine to drive a first compressor of the compressor section, and a high spool that enables a high pressure turbine to drive a high pressure compressor of the compressor section.

[0011] 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 additionally be provided.

[0012] The low speed spool 30 generally includes an inner shaft 40 that connects a fan 42 and a low pressure (or first) compressor section 44 to a low pressure (or first) turbine section 46. The inner shaft 40 drives 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 (or second) compressor section 52 and a high pressure (or second) turbine section 54. The inner shaft 40 and the outer shaft 50 are concentric and rotate via the bearing systems 38 about the engine central longitudinal axis A.

[0013] A combustor 56 is arranged between the high pressure compressor 52 and the high pressure turbine 54. In one example, the high pressure turbine 54 includes at least two stages to provide a double stage high pressure turbine 54. In another example, the high pressure turbine 54 includes only a single stage. As used herein, a "high pressure" compressor or turbine experiences a higher pressure than a corresponding "low pressure" compressor or turbine.

[0014] The example low pressure turbine 46 has a pressure ratio that is greater than about 5. The pressure ratio of the example low pressure turbine 46 is measured prior to an inlet of the low pressure turbine 46 as related to the pressure measured at the outlet of the low pressure turbine 46 prior to an exhaust nozzle.

[0015] 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 as well as setting airflow entering the low pressure turbine 46.

[0016] The core airflow C is compressed by the low pressure compressor 44 then by the high pressure compressor 52 mixed with fuel and ignited in the combustor 56 to produce high speed exhaust gases that are then expanded through the high pressure turbine 54 and low pressure turbine 46. The mid-turbine frame 57 includes vanes 59, which are in the core airflow path and function as an inlet guide vane for the low pressure turbine 46. Utilizing the vane 59 of the mid-turbine frame 57 as the inlet guide vane for low pressure turbine 46 decreases the length of the low pressure turbine 46 without increasing the axial length of the mid-turbine frame 57. Reducing or eliminating the number of vanes in the low pressure turbine 46 shortens the axial length of the turbine section 28. Thus, the compactness of the gas turbine engine 20 is increased and a higher power density may be achieved.

[0017] The disclosed gas turbine engine 20 in one example is a high-bypass geared aircraft engine. In a further example, the gas turbine engine 20 includes a bypass ratio greater than about six (6), with an example embodiment being greater than about ten (10). The example geared architecture 48 is an epicyclical gear train, such as a planetary gear system, star gear system or other known gear system, with a gear reduction ratio of greater than about 2.3.

[0018] In one disclosed embodiment, the gas turbine engine 20 includes a bypass ratio greater than about ten (10:1) and the fan diameter is significantly larger than an outer diameter of the low pressure compressor 44. It should be understood, however, that the above parameters are only exemplary of one embodiment of a gas turbine engine including a geared architecture and that the present disclosure is applicable to other gas turbine engines.

[0019] 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 10.7 km (35,000 feet). The flight condition of 0.8 Mach and 10.7 km (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 pound-mass (lbm) of fuel per hour being burned divided by pound-force (lbf) of thrust the engine produces at that minimum point.

[0020] "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 1.50. In another non-limiting embodiment the low fan pressure ratio is less than about 1.45.

[0021] "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< (where °R = K x 9 / 5). The "Low corrected fan tip speed", as disclosed herein according to one non-limiting embodiment, is less than about 351 m / s (1150 ft / second).

[0022] Figure 2 illustrates an embodiment of the engine 20 with a nacelle or cowling 80, that surrounds the entire engine. An inlet portion 82 is situated forward of the fan 42. The inlet portion 82 has a leading edge 84, which may be defined by the inlet side cut on the cowling 80. The leading edge 84 is within a first reference plane 86.

[0023] The nacelle 80 in some examples includes a flange 87 that is received against a leading edge on a fan case 88. The inlet portion 82 has a length L between a selected location corresponding to the leading edge 84, such as a location within the reference plane 86, and a forward most portion 90 on leading edges on the fan blades 92 of the fan 42. In this example, the length L may be considered an axial length of the inlet portion 82 because the length L is taken along a direction parallel to the central longitudinal axis A of the engine 20. In the illustrated example, the inlet section of the nacelle 80 and the section of the fan case 88 that is forward of the blades 92 collectively establish the overall effective length L. In other words, in this example the length L of the inlet portion 82 includes the length of the inlet section of the nacelle 80 and some of the fan case 88.

[0024] The fan blades 92 establish a diameter between circumferentially outermost edges 94. The fan diameter D is shown in Figure 2 as a dimension extending between the edges 94 of two of the fan blades 92 that are parallel to each other and extending in opposite directions away from the central axis A. The forward most portions 90 on the fan blades 92 are within a second reference plane 96. The second reference plane 96 is oriented generally perpendicular to the central axis A of the engine 20. The first reference plane 86 is oriented at an oblique angle relative to the second reference plane 96 and the central axis A. In the illustrated example the oblique angle of orientation of the first reference plane 86 is approximately 5°.

[0025] The length L is selected to establish a desired dimensional relationship between L and D. L / D is between about 0.30 and about 0.40. In some example embodiments, the dimensional relationship of L / D is about 0.35.

[0026] As can be appreciated from Figure 2, the length L of the inlet portion 82 (i.e., the combined length of the nacelle inlet and the forward section of the fan case) is different at different locations along a perimeter of the fan case 80. The leading edge 84 is further from the second reference plane 96 near the top (according to the drawing) of the engine assembly than it is near the bottom (according to the drawing) of the engine assembly. The greatest length L in this example corresponds to a value for L / D that is no more than 0.45. The smallest length L in the illustrated example corresponds to a value for L / D that is at least 0.20. The value of L / D may vary between those two limits at different locations on the leading edge 84.

[0027] The dimension L is measured between a first location where the central longitudinal axis A of the engine intersects the first reference plane 86 and a second location where the axis A intersects the second reference plane 96.

[0028] The dimensional relationship of L / D is smaller than that found on typical gas turbine engines. The corresponding dimensional relationship on most gas turbine engines is greater than .5. Providing a shorter inlet portion length L facilitates reducing the weight of the engine assembly. A shorter inlet portion length also reduces the overall length of the nacelle and reduces external drag. Additionally, having a shorter inlet portion 82 reduces the bending moment and corresponding load on the engine structure during flight conditions, such as takeoff. A shorter inlet portion 82 also can contribute to providing more clearance with respect to cargo doors and other mechanical components in the vicinity of the engine.

[0029] The example engine 20 is a high bypass ratio engine having a larger fan with respect to the engine core components and lower exhaust stream velocities compared to engines with lower bypass ratios. Higher bypass ratio engines tend to have fan noise as a more significant source of noise compared to other sources. The illustrated example includes a shorter inlet yet does not have an associated effective perceived noise level that is noticeably greater than other configurations with longer inlets. One reason for this is that the example engine 20 includes a low pressure ratio fan that operates at a slower fan speed, which is associated with less fan noise. In one example, the fan 42 has a pressure ratio between about 1.20 and about 1.50. A pressure ratio within that range corresponds to the engine operating at a cruise design point in some example implementations. The shorter length L of the inlet portion 82 combined with the low pressure ratio of the fan 42, which has a slower fan speed enabled by the geared architecture of the engine 20, results in an acceptable perceived engine noise level.

[0030] Utilizing a dimensional relationship as described above allows for realizing a relatively shorter inlet on a gas turbine engine while maintaining sufficient noise attenuation control. Additionally, the short inlet portion 82 combined with the low pressure ratio fan 42 provides improved propulsive efficiency and lower installed fuel burn compared to conventional gas turbine engine propulsion systems.

[0031] The foregoing description shall be interpreted as illustrative and not in any limiting sense. A worker of ordinary skill in the art would understand that certain modifications could come within the scope of this disclosure. For these reasons, the following claims should be studied to determine the true scope and content of this disclosure.

Claims

1. A gas turbine engine (20), comprising: a fan (42) including a plurality of fan blades (92) and having a diameter D between circumferentially outermost edges (94) of the fan blades (92), each fan blade (92) having a leading edge (94); 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), the low speed spool (30) including an inner shaft (40) that connects the fan (42) and a low pressure compressor section (44) to a low pressure turbine section (46), and the high speed spool (32) including an outer shaft (50) that interconnects a high pressure compressor section (52) and a high pressure turbine section (54), the inner shaft (40) and outer shaft (50) being concentric and configured to rotate via the bearing systems (38) about the central longitudinal axis (A); a geared architecture (48), wherein the inner shaft (40) drives the fan (42) through the geared architecture (48) at a lower speed than the low speed spool (30); a nacelle or cowling (80) that surrounds the engine (20); and an inlet portion (82) forward of the fan (42), wherein the inlet portion (82) has a leading edge (84) within a first plane (86), the forward-most portions (90) of the fan blades (92) are within a second plane (96), the second plane (96) is oriented perpendicular to the central longitudinal axis (A) of the engine (20), the first plane (86) is oriented at an oblique angle relative to the second plane (96) and the central longitudinal axis (A), and the inlet portion (82) has a dimension L measured between a first location where the central longitudinal axis (A) of the engine (20) intersects the first plane (86) and a second location where the central longitudinal axis (A) intersects the second plane (96), characterised in that: a dimensional relationship of L / D is between 0.30 and 0.40.

2. The engine (20) of claim 1, wherein the dimensional relationship of L / D is 0.35.

3. The engine (20) of claim 1 or 2, wherein: the engine (20) has a high bypass ratio; and the fan (42) is a low pressure ratio fan (42) having a pressure ratio between 1.20 and 1.50.