IMPROVED GAS TURBINE ENGINE

Abstract

A gas turbine engine for an aircraft comprises, in axial flow sequence, a compressor module, a combustor module, and a turbine module. The gas turbine engine further comprises a first electric machine that is rotationally connected to the turbine module, and an electrical energy storage unit. The gas turbine engine is configured to generate a maximum dry thrust T (N). The first electric machine is configured to generate a maximum electrical power P.sub.EM1 (W). The electrical energy storage unit has an energy storage capacity E (Wh), a maximum charge rate C (h.sup.−1), and a maximum discharge rate D (h.sup.−1). The electrical energy storage unit is configured to store electrical energy that may be generated by the first electric machine.

Claims

1. A gas turbine engine for an aircraft, the gas turbine engine comprising, in axial flow sequence, a compressor module, a combustor module, and a turbine module, the gas turbine engine further comprising a first electric machine being rotationally connected to the turbine module, and an electrical energy storage unit, and wherein the gas turbine engine is configured to generate a maximum dry thrust T (N), the first electric machine is configured to generate a maximum electrical power P.sub.EM1 (W), the electrical energy storage unit has an energy storage capacity E (Wh), the electrical energy storage unit has a maximum charge rate C (h.sup.−1), the electrical energy storage unit has a maximum discharge rate D (h.sup.−1), and the electrical energy storage unit is configured to store electrical energy that may be generated by the first electrical machine.

2. The gas turbine engine as claimed in claim 1, wherein the maximum electrical power is the maximum power output of the first electric machine, P.sub.EM1, and a ratio L is defined as: $L=\frac{\left(\mathrm{Energy}\mathrm{storage}\mathrm{capacity}\right)*\left(\mathrm{Maximum}\mathrm{electrical}\mathrm{power}\mathrm{generated}\right)}{\left(\mathrm{Maximum}\mathrm{Dry}\mathrm{Thrust}\right)}$ where L is in a range of between 20,000 and 300,000.

3. The gas turbine engine as claimed in claim 1, wherein the maximum electrical power is the maximum power output of the first electric machine, P.sub.EM1, and a ratio M is defined as: $M=\frac{\left(\mathrm{Maximum}\mathrm{charge}\mathrm{rate}\right)*\left(\mathrm{Maximum}\mathrm{electrical}\mathrm{power}\mathrm{generated}\right)}{\left(\mathrm{Maximum}\mathrm{Dry}\mathrm{Thrust}\right)}$ where M is in a range of between 20 and 400.

4. The gas turbine engine as claimed in claim 1, wherein the maximum electrical power is the maximum power output of the first electric machine, P.sub.EM1, and a ratio N is defined as: $N=\frac{\begin{array}{c}\left(\mathrm{Maximum}\mathrm{Discharge}\mathrm{rate}\right)*\\ \left(\mathrm{Maximum}\mathrm{electrical}\mathrm{power}\mathrm{generated}\right)\end{array}}{\left(\mathrm{Maximum}\mathrm{Dry}\mathrm{Thrust}\right)}$ where N is in a range of between 40 and 400.

5. The gas turbine engine as claimed in claim 1, wherein the gas turbine engine is a turbofan engine comprising, in axial flow sequence, a fan assembly, a compressor module, a combustor module, and a turbine module.

6. The gas turbine engine as claimed in claim 5, the gas turbine engine further comprises a second electric machine rotationally connected to the fan assembly, the second electric machine being configured to generate a maximum electrical power P.sub.EM2 (W).

7. The gas turbine engine as claimed in claim 6, wherein the maximum electrical power is the combined maximum power output of the first electric machine, P.sub.EM1, and the second electric machine, P.sub.EM2, and the ratio L is in a range of between 30,000 and 600,000.

8. The gas turbine engine as claimed in claim 6, wherein the maximum electrical power is the combined maximum power output of the first electric machine, P.sub.EM1, and the second electric machine, P.sub.EM2, and the ratio M is in a range of between 30 and 800.

9. The gas turbine engine as claimed in claim 6, wherein the maximum electrical power is the combined maximum power output of the first electric machine, P.sub.EM1, and the second electric machine, P.sub.EM2, and the ratio N is in a range of between 70 and 800.

10. The gas turbine engine as claimed in claim 2, wherein the fan diameter D.sub.FAN is within a range of between 0.3 m and 2.0 m, preferably within a range of between 0.4 m and 1.5 m, and more preferably in a range of between 0.7 m and 1.0 m.

11. The gas turbine engine as claimed in claim 10, wherein the fan assembly has two or more fan stages, at least one of the fan stages comprising a plurality of fan blades defining the fan diameter D.sub.FAN.

12. The gas turbine engine as claimed in claim 2, wherein the turbofan gas turbine engine further comprises an outer casing, the outer casing enclosing the sequential arrangement of fan assembly, compressor module, and turbine module, an annular bypass duct being defined between the outer casing and the sequential arrangement of compressor module and turbine module, a bypass ratio being defined as a ratio of a mass air flow rate through the bypass duct to a mass air flow rate through the sequential arrangement of compressor module and turbine module, and wherein the bypass ratio is less than 4.0.

13. The gas turbine engine as claimed in claim 1, the gas turbine engine further comprising a heat exchanger module, the heat exchanger module being in fluid communication with the gas turbine engine by an inlet duct, and the heat exchanger module comprising a central hub and a plurality of heat transfer elements extending radially outwardly from the central hub and spaced in a circumferential array, for transfer of heat energy from a first fluid contained within the heat transfer elements to an inlet airflow passing over a surface of the heat transfer elements prior to entry of the airflow into an inlet to the gas turbine engine.

14. The gas turbine engine as claimed in claim 1, wherein the electrical energy storage unit is a battery.

15. The gas turbine engine as claimed in claim 1, wherein the electrical energy storage unit is a capacitor.

16. An aircraft comprising a gas turbine engine according to claim 1.

17. A method of operating a gas turbine engine for an aircraft, the method comprising the steps of: (i) providing a gas turbine engine, the gas turbine engine comprising, in axial flow sequence, a compressor module, a combustor module, and a turbine module; (ii) providing a first electric machine rotationally connected to the turbine module; (iii) providing an electrical energy storage unit, the electrical energy storage unit being configured to store electrical energy that is generated by the first electric machine, the electrical energy storage unit has an energy storage capacity E (Wh), the electrical energy storage unit has a maximum charge rate C (h.sup.−1), the electrical energy storage unit has a maximum discharge rate D (h.sup.−1); and (iv) operating the gas turbine engine at a full power condition in which the gas turbine engine generates a maximum dry thrust T (N), the first electric machine generates a maximum electrical power P.sub.EM1 (W), and wherein a ratio L of: $L=\frac{\left(\mathrm{Energy}\mathrm{storage}\mathrm{capacity}\right)*\left(\mathrm{Maximum}\mathrm{electrical}\mathrm{power}\mathrm{generated}\right)}{\left(\mathrm{Maximum}\mathrm{Dry}\mathrm{Thrust}\right)}$ is in a range of between 20,000 and 300,000.

18. The method of operating a gas turbine engine as claimed in claim 17, wherein step (iv) comprises the step of: (iv)″ operating the gas turbine engine at a full power condition in which the gas turbine engine generates a maximum dry thrust T (N), the first electric machine generates a maximum electrical power P.sub.EM1 (W), and wherein a ratio M of: $M=\frac{\left(\mathrm{Maximum}\mathrm{charge}\mathrm{rate}\right)*\left(\mathrm{Maximum}\mathrm{electrical}\mathrm{power}\mathrm{generated}\right)}{\left(\mathrm{Maximum}\mathrm{Dry}\mathrm{Thrust}\right)}$ is in a range of between 20 and 400.

19. The method of operating a gas turbine engine as claimed in claim 17 wherein step (iv) comprises the step of: (iv)′″ operating the gas turbine engine at a full power condition in which the gas turbine engine generates a maximum dry thrust T (N), the first electric machine generates a maximum electrical power P.sub.EM1 (W), and wherein a ratio N of: $N=\frac{\begin{array}{c}\left(\mathrm{Maximum}\mathrm{Discharge}\mathrm{rate}\right)*\\ \left(\mathrm{Maximum}\mathrm{electrical}\mathrm{power}\mathrm{generated}\right)\end{array}}{\left(\mathrm{Maximum}\mathrm{Dry}\mathrm{Thrust}\right)}$ is in a range of between 40 and 400.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0125] There now follows a description of an embodiment of the disclosure, by way of non-limiting example, with reference being made to the accompanying drawings in which:

[0126] FIG. 1 shows a schematic part-sectional view of a turbofan gas turbine engine according to the prior art;

[0127] FIG. 2 shows a schematic sectional view of a turbofan gas turbine engine according to a first embodiment of the disclosure;

[0128] FIG. 3 shows a schematic sectional view of a turbofan gas turbine engine according to a second embodiment of the disclosure;

[0129] FIG. 4 shows a schematic sectional view of a turbofan gas turbine engine according to a third embodiment of the disclosure;

[0130] FIG. 5 shows a schematic perspective view of an aircraft according to a further embodiment of the disclosure; and

[0131] FIG. 6 shows the relationship between electrical power generated by the electric machine(s) and electrical energy storage capability for the gas turbine engine of any of FIGS. 2 to 4.

[0132] It is noted that the drawings may not be to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION

[0133] An axial direction is defined as being in the direction of the axis of rotation of the gas turbine engine. A lateral direction is defined as being perpendicular to the axis of rotation of the gas turbine engine and as extending in the direction of the left and right sides of the gas turbine engine. A vertical direction is defined as being perpendicular to the axis of rotation of the gas turbine engine and also perpendicular to the lateral direction of the gas turbine engine.

[0134] FIG. 1 illustrates a conventional turbofan gas turbine engine 10 having a principal rotational axis 9. The engine 10 comprises an air intake 12 and a two-stage propulsive fan 13 that generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 comprises a core 11 that receives the core airflow A. The engine core 11 comprises, in axial flow series, a low-pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, an intermediate-pressure turbine 18, a low-pressure turbine 19 and a core exhaust nozzle 20. A nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass exhaust nozzle 18. The bypass airflow B flows through the bypass duct 22. The fan 13 is attached to and driven by the low-pressure turbine 19 via a shaft 26.

[0135] In use, the core airflow A is accelerated and compressed by the low-pressure compressor 14 and directed into the high-pressure compressor 15 where further compression takes place. The compressed air exhausted from the high-pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel and the mixture is combusted. The resultant hot combustion products then expand through, and thereby drive, the high-pressure, intermediate-pressure, and low-pressure turbines 17, 18, 19 before being exhausted through the nozzle 20 to provide some propulsive thrust. The high-pressure turbine 17 drives the high-pressure compressor 15 by a suitable interconnecting shaft 27. The low-pressure compressor 14 drives the intermediate-pressure turbine 18 via a shaft 28.

[0136] Note that the terms “low-pressure turbine” and “low-pressure compressor” as used herein may be taken to mean the lowest pressure turbine stages and lowest pressure compressor stages (i.e. not including the fan 13) respectively and/or the turbine and compressor stages that are connected together by the interconnecting shaft 26 with the lowest rotational speed in the engine. In some literature, the “low-pressure turbine” and “low-pressure compressor” referred to herein may alternatively be known as the “intermediate-pressure turbine” and “intermediate-pressure compressor”. Where such alternative nomenclature is used, the fan 13 may be referred to as a first, or lowest pressure, compression stage.

[0137] Other turbofan gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of fans and/or compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in FIG. 1 has a split flow nozzle 20, 23 meaning that the flow through the bypass duct 22 has its own nozzle 23 that is separate to and radially outside the core engine nozzle 20. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct 22 and the flow through the core engine 11 are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example.

[0138] The geometry of the turbofan gas turbine engine 10, and components thereof, is defined by a conventional axis system, comprising an axial direction (which is aligned with the rotational axis 9), a radial direction (in the bottom-to-top direction in FIG. 1), and a circumferential direction (perpendicular to the page in the FIG. 1 view). The axial, radial and circumferential directions are mutually perpendicular.

[0139] Referring to FIG. 2, a turbofan gas turbine engine according to a first embodiment of the disclosure is designated generally by the reference numeral 100. The turbofan gas turbine engine 100 comprises in axial flow sequence, a heat exchanger module 120, a fan assembly 130, a compressor module 160, a combustor module 170, a turbine module 180, and an exhaust module 190. The gas turbine engine 100 has an axial length L 104 between an inlet face 116 of the engine 100 to an exhaust face 194 of the engine.

[0140] The gas turbine engine 100 has a longitudinal axis 102 being the rotational axis 102 of the compressor and turbine assemblies 160,180. The gas turbine engine 100 has a first side 105 and a second side 106 defined as opposing sides of the rotational axis 102 in a direction extending from an exhaust face 194 of the gas turbine engine 100 to an inlet face 116 of the gas turbine engine 100. The first side 105 is the left side of the engine 100 in a direction from the exhaust face 194 to the inlet face 116. Likewise the second side 106 is the right side of the engine 100 in a direction from the exhaust face 194 to the inlet face 116.

[0141] An axial direction is defined as being in the direction of the axis of rotation 102 of the gas turbine engine 100. Axial constraint 264 is provided in the axial direction. A lateral direction is defined as being perpendicular to the axis of rotation 102 of the gas turbine engine 100 and as extending in the direction of the left and right sides 105,106 of the gas turbine engine 100. Lateral constraint 262 is provided in the lateral direction. A vertical direction is defined as being perpendicular to the axis of rotation 102 of the gas turbine engine 100 and also perpendicular to the lateral direction of the gas turbine engine 100. Vertical constraint 260 is provided in the vertical direction.

[0142] The fan assembly 130 (also termed a low-pressure compressor) is rotationally connected to the low-pressure turbine 181 by an LP shaft 140. The compressor assembly 160 is rotationally connected to the high-pressure turbine 183 by an HP shaft 162.

[0143] In the present arrangement, the fan assembly 130 comprises two fan stages 131, with each fan stage 131 comprising a plurality of fan blades 132. In the present arrangement each fan stage 131 has the same fan diameter 138, with the respective plurality of fan blades defining a fan diameter of 0.9 m. Each fan blade 132 has a leading edge 133 and a corresponding trailing edge 134. The fan assembly 130 comprises, in axial flow sequence, a lowest pressure fan stage and a highest pressure fan stage.

[0144] In an alternative arrangement, the two fan stages 131 may have different fan diameters 136 each defined by the corresponding plurality of fan blades 132. As previously mentioned, the fan diameter (D.sub.FAN) 136 is defined by a circle circumscribed by the leading edges of the respective plurality of fan blades 132.

[0145] The turbine module 180 comprises, in axial flow sequence, a low-pressure turbine 181 and a high-pressure turbine 183. Each of the low pressure turbine 181 and high pressure turbine 183 has a turbine stage comprising a row of turbine blades 184, with each of the turbine blades 184 extending radially outwardly and having a leading edge 185 and a corresponding trailing edge 186.

[0146] A fan tip axis 146 is defined as extending from a radially outer tip 135 of the leading edge 133 of one of the plurality of fan blades 132 of the highest pressure fan stage 131, to a radially outer tip 187 of the trailing edge 186 of one of the turbine blades 184 of the lowest pressure turbine stage 181. The fan tip axis 146 extends in a longitudinal plane which contains a centreline of the gas turbine engine 102, and a fan axis angle 148 is defined as the angle between the fan tip axis 146 and the centreline 102. In the present embodiment, the fan axis angle has a value of 18 degrees.

[0147] The heat exchanger module 120 comprises a plurality of heat transfer elements 124 extending radially outwardly from a central hub 122. The heat exchanger module 120 is in fluid communication with the fan assembly 130 by an inlet duct 126. The heat exchange module 120 has an axial length of 0.4 m, this being 0.4 times the fan diameter of 0.9 m.

[0148] The inlet duct 126 extends between a downstream-most face of the heat transfer elements and an upstream-most face of the fan assembly. In the present arrangement, the inlet duct 126 is linear. However, in other arrangements the inlet duct 126 may be curved or convoluted.

[0149] The inlet duct 126 has a fluid path length of 3.6 m, this being 4.0 times the fan diameter of 0.9 m. The fluid path length extends along a central axis 102 of the inlet duct 126.

[0150] The heat exchanger module 120 has a flow area (A.sub.HEX). The heat exchanger module flow area is the cross-sectional area of the heat exchanger module 120 through which an air flow 112 passes before being ingested by the fan assembly 130. In the present arrangement, the heat exchanger module flow area has an annular cross-section and corresponds directly to the shape of the air flow passing through the heat exchanger module 120.

[0151] The fan assembly 130 has a corresponding flow area (A.sub.FAN). The fan assembly flow area is the cross-sectional area of the fan assembly 130 through which an air flow 112 passes before separating into a core engine flow and a bypass flow. The fan assembly flow area has an annular shape since it corresponds to the annular area swept by the fan blades 132.

[0152] The fan assembly 130 is fluidly connected to the compressor module 160 by an intermediate duct 150. The intermediate duct 150 directs a proportion of the inlet air flow 112 into the core engine 110. The intermediate duct 150 extends axially rearwards and radially inwards.

[0153] In the present arrangement, the heat exchanger module flow area is equal to the fan assembly flow area, and the corresponding ratio of A.sub.HEX/A.sub.FAN is equal to 1.0.

[0154] The heat exchanger module 120 has a flow diameter (E) 121, which is the diameter of the air flow passing through the heat exchanger module 120. In the present arrangement, the heat exchanger module flow diameter 121 is equal to the fan diameter 136.

[0155] The heat exchanger module 120 comprises a plurality of heat transfer elements 124 for the transfer of heat energy from a first fluid 275 contained within the heat transfer elements 124 to an airflow 112 passing over a surface of the heat transfer elements 124 prior to entry of the airflow 112 into the fan assembly 130. In the present embodiment, the first fluid 275 is a mineral oil. In other arrangements, the first fluid 275 may be an alternative heat transfer fluid such as, for example, a water-based fluid, or the fuel used by the turbofan gas turbine engine.

[0156] The heat transfer elements 124 have a conventional tube and fin construction and will not be described further. In an alternative arrangement, the heat transfer elements 124 may have a different construction such as, for example, plate and shell.

[0157] The turbofan gas turbine engine 100 further comprises an outer housing 200. The outer housing 200 fully encloses the sequential arrangement of the heat exchanger module 120, inlet duct 126, fan assembly 130, compressor module 160, combustor module 170, and turbine module 180. The outer housing 200 defines a bypass duct 202 between the outer housing 200 and the core engine components (comprising inter alia the compressor module 160 and the turbine module 180). In the present arrangement, the bypass duct 202 has a generally axi-symmetrical annular cross-section extending over the core engine components. In other arrangements, the bypass duct 202 may have a non-symmetric annular cross-section or may not extend around a complete circumference of the core engine components.

[0158] A first electric machine 210 is rotationally connected to the HP shaft 162 axially upstream of the compressor assembly 160. The first electric machine 210 does not extend axially beyond an inlet plane 161 of the compressor module 160. The first electric machine 210 has an axial length 212 L.sub.EM and a diameter 214 D.sub.EM. A ratio of the axial length 212 to the diameter 214 (L.sub.EM/D.sub.EM) for the first electric machine 210 is 1.2.

[0159] The first electric machine 210 may operate as an electric motor and rotationally drive the HP shaft 162. Alternatively, the first electric machine 210 may operate as an electric generator, in which arrangement it is rotationally driven by the HP shaft 162.

[0160] The first electric machine 210 is electrically connected to an electrical energy storage unit 230 by an electrical connection 232. In the present arrangement, the electrical energy storage unit 230 takes the form of a battery pack 230. The battery pack 230 has an electrical energy storage capacity of 20 kWh. In the present arrangement, the battery pack 230 is formed from lithium manganese oxide cells. In alternative arrangements the battery pack 230 may be formed with, for example, an alternative lithium ion architecture or other energy storage architecture.

[0161] When the first electric machine 210 is operating as an electric generator, electrical energy 236 is routed via the electrical connection 232 to the electrical energy storage unit 230. Likewise, electrical energy 234 may be directed from the electrical energy storage unit 230 to the first electric machine 210 when the first electric machine is operating as an electric motor.

[0162] A second electric machine 220 is positioned upstream of the fan assembly 130 and accommodated within the central hub 122 of the heat exchanger module 120. The second electric machine 220 is rotationally connected to the fan assembly 130. As outlined above for the first electric machine 210, the second electric machine 220 is electrically connected to the electrical energy storage unit 230 by an electrical connection 232. Likewise, the second electric machine 20 may be operated as an electric generator with electrical energy routed to the electrical energy storage unit 230 via the electrical connection 232. Alternatively, the second electric machine 220 may be operated as an electric motor with electrical energy routed from the electrical energy storage unit 230 via the electrical connection 232.

[0163] In the arrangement of FIG. 2, the energy storage unit 230 has a maximum charge rate of 25 (h.sup.−1). The energy storage unit 230 also has a maximum discharge rate of 35 (h.sup.−1). FIG. 6 shows a schematic relationship between the electrical power supplied by either or both of the first electric machine 210 and the second electric machine 220 to the electrical energy storage unit 230 during a charging cycle, and the electrical energy storage capacity of the electrical energy storage unit 230 for a range of maximum charge rates C.

[0164] As shown in FIG. 6 the gas turbine engine 100 of the present invention is capable of transferring electrical energy from either or both of the first electric machine 210 and the second electric machine 220, to the electrical energy storage unit 230 at a considerably higher charging rate than prior art arrangements. In other words, the gas turbine engine 100 of the present invention is capable of recharging the electrical energy storage unit 230 at a considerably higher charging rate than prior art arrangements.

[0165] A similar relationship (not illustrated) exists between the electrical power supplied by the electrical energy storage unit 230 during a discharging cycle and the electrical energy storage capacity of the electrical energy storage unit 230 for a range of maximum discharge rates D. In this configuration, the electrical power supplied by the electrical energy storage unit 230 may be directed to either or both of the first electric machine 210 and the second electric machine 220, to an airframe function such as an aerodynamic control surface movement actuator, or alternatively to an ancillary system such as, for example, an atmospheric sensing apparatus.

[0166] The HP shaft 162 is supported on a first bearing assembly 142 and second bearing assembly 144. The first bearing assembly 142 is positioned axially between the fan assembly 130 and the first electric machine 210. In the present arrangement, the lowest-pressure fan stage 131 extends axially partially over the first bearing assembly 142.

[0167] FIG. 3 shows a turbofan gas turbine engine according to a second embodiment of the disclosure. The gas turbine engine of FIG. 3 broadly corresponds to that of the first embodiment shown in FIG. 2 and described above.

[0168] However, in the arrangement of FIG. 3, the second electric machine 220 is positioned in a tail cone 192 of the core engine 110. As described above, the second electric machine 220 is rotationally connected to the LP shaft 140, connecting the fan assembly 130 to the turbine module 180.

[0169] FIG. 4 a turbofan gas turbine engine according to a third embodiment of the disclosure. The embodiment of FIG. 4 differs from the earlier embodiments of FIGS. 2 and 3 in that the gas turbine engine of FIG. 4 comprises only a first electric machine 210, and not the first and second electric machines 210,220 forming part of the FIGS. 2 and 3 arrangements.

[0170] The embodiment of FIG. 4 is therefore simpler than those of FIGS. 2 and 3, while retaining the advantages of an embedded electric machine of power generation, core engine working line optimisation, and autonomous ground and in-flight starting.

[0171] shows a further view of the embodiment of FIG. 3 with the addition of the first engine mount plane 240 and the second engine mount plane 250. The first engine mount plane 240 is positioned at a distance of 0.3*L from the inlet face 116 of the engine 100. The second engine mount plane 250 is positioned at a distance of 0.9*L from the inlet face 116 of the engine 100.

[0172] The intermediate duct 150 extends between the fan assembly 130 and the compressor module 160. An intermediate flow axis 157 is defined extending from a radially outer tip 135 of a trailing edge 134 of one of the plurality of fan blades 132 of the highest pressure fan stage 131, to a radially outer tip 167 of a leading edge 165 of one of the plurality of compressor blades 164 of the lowest-pressure compressor stage 163. The intermediate flow axis 157 lies in a longitudinal plane containing the centreline of the gas turbine engine 102. An intermediate flow axis angle 158 is defined as the angle between the intermediate flow axis 157 and the centreline 102.

[0173] The intermediate flow axis angle 158 has a value of −30 degrees. In other words, in the direction extending from the inlet face 116 of the turbofan engine 100 to the exhaust face 194 of the turbofan engine, the intermediate flow axis angle 158 is inclined in a radially inwardly direction.

[0174] The intermediate duct 150 comprises a radially outer wall 154 and an opposite radially inner wall 156. A radially inwardly facing surface 155 of the radially outer wall 154 has an outer intermediate duct wall angle 153 of −30 degrees. The intermediate duct 150 may have a partially serpentine geometry. In such an instance, for example where the intermediate duct 150 is not linear, the outer intermediate duct wall angle 153 is defined as the corresponding angle of a tangent to the radially inwardly facing surface 155 of the radially outer wall 154 at a mid-point along the intermediate duct 150.

[0175] In this arrangement, the highest-pressure fan stage 131 extends axially completely over the first bearing assembly 142. In other words, the first bearing assembly 142 is axially enclosed by the fan assembly 130.

[0176] Referring to FIG. 5, an aircraft according to an embodiment of the disclosure is designated by the reference numeral 280. The aircraft 280 comprises a machine body 282 in the form of a fuselage with wings and a tail plane. The machine body 282 encloses a turbofan gas turbine engine 100, together with a plurality of ancillary apparatus 274.

[0177] When operating at a full power condition, the gas turbine engine 100 of any of the described embodiments will have a corrected core engine mass flow rate of approximately 20 kg/sec. The term Corrected Mass Flow Rate is the mass flow rate that would pass through the core engine 110 if the inlet pressure and temperature corresponded to ambient conditions at Sea Level Static (SLS) for the International Standard Atmosphere (ISA). These pressure and temperature conditions are 1,013.25 mb (29.92 in) and 15° C. (59° F.).

[0178] In one arrangement of the turbofan gas turbine engine 100, for example that shown in FIG. 4, the engine provides a maximum dry thrust at SLS.sup.2 conditions of 50 kN. It is known from experimental testing that this arrangement of the gas turbine engine produces approximately 10 MW of shaft power from the low-pressure shaft, and approximately 12.5 MW from the high-pressure shaft; i.e. a total maximum shaft power output of 22.5 MW. These shaft power figures correspond to operation of the gas turbine engine at a full-power condition at Sea Level Static (SLS) conditions and in an International Standard Atmosphere (15° C./1,013.25 mb), .sup.2In the present example, the SLS (Sea Level Static) conditions are considered to also be at ISA Standard Atmosphere conditions (1,013.25 mb/15° C.).

[0179] The first electric machine 210, when configured as a generator can produce a maximum electrical power output of 300 kW. Consequently, a ratio R of:

[00007]$R=\frac{\left(\mathrm{Maximum}\mathrm{Electrical}\mathrm{Power}\mathrm{Generated}=P_{EM1}\right)}{\left(\mathrm{Maximum}\mathrm{Shaft}\mathrm{Power}=P_{SHAFT}\right)}$

has a value of 0.013.

[0180] In this arrangement the electrical energy storage unit 230 has an electrical energy storage capacity E of 20 kWh. Consequently, the ratio L of:

[00008]$L=\frac{\left(\mathrm{Energy}\mathrm{storage}\mathrm{capacity}\right)*\left(\mathrm{Maximum}\mathrm{electrical}\mathrm{power}\mathrm{generated}\right)}{\left(\mathrm{Maximum}\mathrm{Dry}\mathrm{Thrust}\right)}$

has a value of 120,000.

[0181] Furthermore, the electrical energy storage unit 230 has a maximum charge rate C of 25 h.sup.−1 and a maximum discharge rate D of 35 h.sup.−1. This in turn results in the ratio M of:

[00009]$M=\frac{\left(\mathrm{Maximum}\mathrm{charge}\mathrm{rate}\right)*\left(\mathrm{Maximum}\mathrm{electrical}\mathrm{power}\mathrm{generated}\right)}{\left(\mathrm{Maximum}\mathrm{Dry}\mathrm{Thrust}\right)}$

taking a value of 150, while the ratio N of:

[00010]$N=\frac{\begin{array}{c}\left(\mathrm{Maximum}\mathrm{Discharge}\mathrm{rate}\right)*\\ \left(\mathrm{Maximum}\mathrm{electrical}\mathrm{power}\mathrm{generated}\right)\end{array}}{\left(\mathrm{Maximum}\mathrm{Dry}\mathrm{Thrust}\right)}$

has a value of 210.

[0182] Taking the example of the alternative arrangement of the turbofan gas turbine engine 100 of, say, FIG. 2, having both a first electric machine 210 and a second electric machine 220, again with both electric machines 210,220 configured as electric generators, the maximum electrical power output is approximately 500 kW. In this arrangement, the gas turbine engine provides a maximum dry thrust at SLS.sup.3 conditions of 50 kN. In this alternative arrangement, the ratio R takes a value of 0.022. .sup.3 In the present example, the SLS (Sea Level Static) conditions are considered to also be at ISA Standard Atmosphere conditions (1,013.25 mb/15° C.).

[0183] In this alternative arrangement having both first electric machine 210 and second electric machine 220, the electrical energy storage unit 230 has an electrical energy storage capacity E of 20 kWh. Consequently, the ratio L of:

[00011]$L=\frac{\left(\mathrm{Energy}\mathrm{storage}\mathrm{capacity}\right)*\left(\mathrm{Maximum}\mathrm{electrical}\mathrm{power}\mathrm{generated}\right)}{\left(\mathrm{Maximum}\mathrm{Dry}\mathrm{Thrust}\right)}$

has a value of 200,000.

[0184] Furthermore, in this alternative arrangement, the electrical energy storage unit 230 has a maximum charge rate C of 25 h.sup.−1 and a maximum discharge rate D of 35 h.sup.−1. This in turn results in the ratio M of:

[00012]$M=\frac{\left(\mathrm{Maximum}\mathrm{charge}\mathrm{rate}\right)*\left(\mathrm{Maximum}\mathrm{electrical}\mathrm{power}\mathrm{generated}\right)}{\left(\mathrm{Maximum}\mathrm{Dry}\mathrm{Thrust}\right)}$

taking a value of 150, while the ratio N of:

[00013]$N=\frac{\begin{array}{c}\left(\mathrm{Maximum}\mathrm{Discharge}\mathrm{rate}\right)*\\ \left(\mathrm{Maximum}\mathrm{electrical}\mathrm{power}\mathrm{generated}\right)\end{array}}{\left(\mathrm{Maximum}\mathrm{Dry}\mathrm{Thrust}\right)}$

has a value of 350.

[0185] In the present example, at the full power engine condition, the maximum electrical power output (500 kW) from an engine arrangement having both a first electric machine 210 and a second electric machine 220 as a proportion of the total maximum shaft power is approximately 2.2%.sup.4. .sup.4 (500,000/22,500,000)=0.022

[0186] In an alternative operating condition of the turbofan gas turbine engine 100, the engine may be installed in an aircraft that in a cruise condition, such as an airspeed of, for example, Mn0.6, generates approximately 5 MW of total shaft power (i.e. sum of the low pressure shaft power and the high pressure shaft power). In such an operating condition, the maximum electrical power output (500 kW) from an engine arrangement having both a first electric machine 210 and a second electric machine 220 as a proportion of the total maximum shaft power is approximately 10.0%.sup.5. It is clear that in such an alternative operating condition, the total electrical generating capacity of the turbofan gas turbine engine 100 is a significantly higher proportion of the engine′ power output than in the case for turbofan gas turbine engines. .sup.5 (500,000/5,000,000)=0.10

[0187] The heat exchanger module 120 is configured to dissipate a total waste heat energy to the inlet air flow 112 of approximately 300 kW. A measure of the capability of the gas turbine engine to dissipate heat energy for a given electrical power generation capacity is provided by the ratio S of:

[00014]$S=\frac{\left(\mathrm{Maximum}\mathrm{Electrical}\mathrm{Power}\mathrm{Generated}=P_{EM1}\right)}{\left(\mathrm{Total}\mathrm{Heat}\mathrm{Energy}\mathrm{Rejected}\mathrm{to}\mathrm{Airflow}=Q\right)}$

having a value of 1.00.

[0188] In the alternative arrangement of, say, FIG. 2 in which the turbofan gas turbine engine 100 has both a first electric machine 210 and a second electric machine 220, the ratio S takes a value of 1.67.

[0189] Note that the terms “low-pressure turbine” and “low-pressure compressor” as used herein may be taken to mean the lowest pressure turbine stages and lowest pressure compressor stages (i.e. not including the fan 23) respectively and/or the turbine and compressor stages that are connected together by the interconnecting shaft 26 with the lowest rotational speed in the engine. In some literature, the “low-pressure turbine” and “low-pressure compressor” referred to herein may alternatively be known as the “intermediate-pressure turbine” and “intermediate-pressure compressor”. Where such alternative nomenclature is used, the fan 23 may be referred to as a first, or lowest pressure, compression stage.

[0190] Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example.

[0191] The geometry of the gas turbine engine 10, and components thereof, is defined by a conventional axis system, comprising an axial direction (which is aligned with the rotational axis 9), a radial direction (in the bottom-to-top direction in FIG. 1), and a circumferential direction (perpendicular to the page in the FIG. 1 view). The axial, radial and circumferential directions are mutually perpendicular.

[0192] It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

[0193] The invention includes methods that may be performed using the subject devices. The methods may comprise the act of providing such a suitable device. Such provision may be performed by the end user. In other words, the “providing” act merely requires the end user obtain, access, approach, position, set-up, activate, power-up or otherwise act to provide the requisite device in the subject method. Methods recited herein may be carried out in any order of the recited events which is logically possible, as well as in the recited order of events.

[0194] In addition, where a range of values is provided, it is understood that every intervening value, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention.

[0195] Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.