GB2575232A - Turbofan engine - Google Patents

Turbofan engine Download PDF

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Publication number
GB2575232A
GB2575232A GB1806427.9A GB201806427A GB2575232A GB 2575232 A GB2575232 A GB 2575232A GB 201806427 A GB201806427 A GB 201806427A GB 2575232 A GB2575232 A GB 2575232A
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United Kingdom
Prior art keywords
engine
fixed structure
outer fixed
plane
terminal plane
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB1806427.9A
Other versions
GB201806427D0 (en
Inventor
Grech Nicholas
A Mosley Christopher
R Wells John
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Rolls Royce PLC
Original Assignee
Rolls Royce PLC
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Filing date
Publication date
Application filed by Rolls Royce PLC filed Critical Rolls Royce PLC
Priority to GB1806427.9A priority Critical patent/GB2575232A/en
Publication of GB201806427D0 publication Critical patent/GB201806427D0/en
Publication of GB2575232A publication Critical patent/GB2575232A/en
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64D—EQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENTS OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT
    • B64D29/00—Power-plant nacelles, fairings, or cowlings
    • B64D29/02—Power-plant nacelles, fairings, or cowlings associated with wings
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02K—JET-PROPULSION PLANTS
    • F02K3/00—Plants including a gas turbine driving a compressor or a ducted fan
    • F02K3/02—Plants including a gas turbine driving a compressor or a ducted fan in which part of the working fluid by-passes the turbine and combustion chamber
    • F02K3/04—Plants including a gas turbine driving a compressor or a ducted fan in which part of the working fluid by-passes the turbine and combustion chamber the plant including ducted fans, i.e. fans with high volume, low pressure outputs, for augmenting the jet thrust, e.g. of double-flow type
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64C—AEROPLANES; HELICOPTERS
    • B64C7/00—Structures or fairings not otherwise provided for
    • B64C7/02—Nacelles
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02K—JET-PROPULSION PLANTS
    • F02K1/00—Plants characterised by the form or arrangement of the jet pipe or nozzle; Jet pipes or nozzles peculiar thereto
    • F02K1/78—Other construction of jet pipes
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2250/00—Geometry
    • F05D2250/10—Two-dimensional
    • F05D2250/14—Two-dimensional elliptical
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T50/00—Aeronautics or air transport
    • Y02T50/60—Efficient propulsion technologies, e.g. for aircraft

Abstract

A turbofan engine 200 comprises an engine core having an outer surface 226 positioned radially inwardly of an outer fixed structure (fan nacelle) with respect to the longitudinal axis X of the engine, the aft or downstream end of the outer fixed structure having a downstream terminal plane 223 which is substantially normal to the longitudinal axis of the engine. The radius R of the internal surface 220 of the outer fixed structure from the axis X in the terminal plane is a function of azimuthal position such that R defines an elliptical path. The internal surface 220 may have a discontinuity at the top to allow for the insertion of a pylon. The discontinuity may be symmetrical about and aligned with a semi-major axis of the elliptical path. The engine may be a mixed-jets or separate-jets engine. The engine may be mounted closer to the wing of an aircraft than a turbofan engine which is axisymmetric in its downstream terminal plane, thus allowing a larger diameter fan to be employed.

Description

TURBOFAN ENGINE
BACKGROUND
Examples of turbofan engines are described.
In a turbofan engine, an engine core bounded by a core cowling is positioned radially inwardly of outer fixed structure or nacelle with respect to the longitudinal axis of the engine, defining a bypass duct between the outer surface of the engine core’s cowling and the internal surface of the outer fixed structure over an axial portion of the engine where both the core cowling and the outer fixed structure are present. Over this axial portion, the internal surface of the outer fixed structure provides an outer wall of the bypass duct and the core cowling provides the internal wall of the bypass duct. In the case of a separate-jets turbofan engine, the downstream terminal end of the outer fixed structure defines a bypass duct exit plane which is fore (upstream) of the exit plane of the engine core, both the bypass duct exit plane and the engine core exit plane being substantially normal to the longitudinal axis of the engine. In the case of a mixed-jets turbofan engine, the downstream terminal end of the outer fixed structure is located downstream of the engine core exit plane, both the engine core exit plane and the downstream terminal end of the outer fixed structure being substantially normal to the longitudinal axis of the engine.
In operation of a separate-jets turbofan engine, exhaust from the engine core is expelled through the engine core exit plane. Bypass air passes through the bypass duct, and is expelled through the bypass duct exit plane as bypass exhaust flow which provides the majority of the engine’s thrust. In the case of a mixed-jets engine, the bypass air and exhaust from the engine core are mixed in the region between the engine core exit plane and the downstream terminal end of the outer fixed structure.
There is an ongoing desire to improve engine exhaust performance to reduce both specific fuel consumption and fuel burn.
BRIEF SUMMARY
According to an example, a turbofan engine comprises an engine core positioned radially inwardly of an outer fixed structure with respect to the longitudinal axis of the engine, the outer fixed structure terminating in a downstream terminal plane which is substantially normal to the longitudinal axis of the engine, and wherein the radius R of the internal surface of the outer fixed structure in the terminal plane is a function R = R((|)) of azimuthal position φ in the terminal plane such that R^) defines an elliptical path in the downstream terminal plane, the radius R being measured with respect to the longitudinal axis of the engine.
The engine may be a separate-jets engine, the engine core having a core cowling the outer surface of which is axisymmetric with respect to the longitudinal axis of the engine. The internal surface of the outer fixed structure may have a discontinuity in the downstream terminal plane thereof. The discontinuity may extend over an azimuthal interval which includes an azimuthal position corresponding to a semiminor axis of the elliptical path. The azimuthal interval of the discontinuity may be symmetric about the azimuthal position corresponding to the semi-minor axis.
Alternatively, the engine may be a mixed-jets engine.
The radii of the internal and external surfaces of the outer fixed structure in the downstream terminal plane may be substantially equal for all azimuthal positions where the internal and external surfaces exist. Alternatively, the radius of the outer surface of the outer fixed structure in the downstream terminal plane may exceed the radius of the internal surface of the outer fixed structure in the downstream terminal plane, for all azimuthal positions where the internal and outer surfaces exist, by an amount which is independent of azimuthal position.
Except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore except where mutually exclusive any feature described herein may be applied to any aspect and/or combined with any other feature described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
Examples are described with reference to the accompanying drawings in which:
Figure 1 is a longitudinal section through a known, separate-jets, turbofan engine, the section including the longitudinal axis (rotation axis) of the engine;
Figure 2 is a side view of a rear portion of the Figure 1 engine;
Figure 3 is a longitudinal section through a known, mixed-jets, turbofan engine, the section including the longitudinal axis (rotation axis) of the engine;
Figure 4 is a side view of a rear portion of the Figure 3 engine; and
Figures 5, 6 & 7 are transverse sections through first, second and third example turbofan engines respectively at the downstream terminal ends of the outer fixed structures of the engines.
DETAILED DESCRIPTION
Referring to Figures 1 and 2, a known three-spool, separate-jets, turbofan engine 10 having a longitudinal (rotational) axis X comprises an engine core 24 having a core cowling 25 located radially inwardly of an outer fixed structure 21 with respect to the axis X. The outer fixed structure 21 terminates at its downstream end in a downstream terminal plane 23 which is substantially normal to the axis X. The portion of the core cowling 25 fore of the terminal plane 23, and the internal surface of the outer fixed structure 21 which longitudinally coincides with that portion respectively define inner 26 and outer 20 walls of a bypass duct 22 which terminates at a bypass duct exit plane coincident with the downstream terminal plane 23 of the outer fixed structure 21. The engine core 24 extends downstream of the bypass duct exit plane 23 so that the engine core 24 has an afterbody portion. The engine core 24 terminates at a core exit plane 19 which is also substantially normal to the axis X. The outer fixed structure 21 may not form complete annulus around the longitudinal axis X because it may be interrupted over a limited azimuthal range by a pylon (indicated by P in Figure 2) for attaching the engine to an aircraft, or by a space for accommodating such a pylon, depending on how the engine 10 is, or is to be, attached to an aircraft. The engine 10 has a propulsive fan 12, intermediate 13 and high 14 pressure compressors, combustion equipment 15, and high 16, intermediate 17 and low 18 pressure turbines. A centre-body 27 extends through the core exit plane 19. The outer fixed structure has an intake 11 having an intake highlight 28.
In operation of the engine 10, air and combustion products pass through the engine 10 in a general direction indicated by 29. Air entering the outer fixed structure 21 at the front of the engine is accelerated by the fan 12. Aft (downstream) of the fan 12 this air becomes divided into two air flows: a first air flow A into the intermediate pressure compressor 13 and a second airflow B which passes through the bypass duct 22. The intermediate pressure compressor 13 compresses the air flow directed into it before delivering that air to the high pressure compressor 14 where further compression takes place. Air flow B is output from the bypass duct 22 at the bypass duct exit plane 23 and provides the majority of the engine’s thrust.
Compressed air output from the high-pressure compressor 14 is directed into the combustion equipment 15 where it is mixed with fuel and the resulting mixture combusted. The resulting hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 16, 17, 18 before being exhausted through the exit plane 19 of the engine core 29 to provide further thrust. The high, intermediate and low pressure turbines 16, 17, 18 drive respectively the high pressure compressor 14, intermediate pressure compressor 13 and fan 12, each by means of a respective interconnecting shaft which has a rotation axis coincident with the longitudinal axis X of the engine 10.
In the engine 10, the outer wall 20 of the bypass duct 22, the core cowling 25 and the centre-body 27 of the engine 10 are each axisymmetric, i.e. they each have circular cross-sections at all positions along the axis X at which they exist. For example, the bypass duct outer wall 20 is circular at the bypass duct exit plane 23 and at longitudinal positions fore (upstream) of the bypass duct exit plane 23. The core cowling 25 is circular at the core exit plane 19 and at longitudinal positions upstream of the core exit plane 19. As shown in Figure 2, a pylon P may interrupt the outer fixed structure 21 over a limited angular range in azimuth around the axis X. The pylon P extends through the bypass duct exit plane 23 so that the bypass duct outer wall 20 (equivalently the internal surface of the outer fixed structure 21) does not describe a closed path in the bypass duct exit plane 23 (equivalently the downstream terminal plane of the outer fixed structure 21).
Figure 3 shows a longitudinal section through a known, mixed-jets turbofan engine indicated generally by 50. Figure 4 shows a side view of a rear portion of the engine 50 with a pylon P fitted. Parts of the engine 50 are labelled using reference numerals differing by 40 from those labelling corresponding parts in Figures 1 and 2. The engine 50 is similar to the engine 10 of Figures 1 and 2 except that it is a mixed-jets engine rather than a separate-jets engine. The outer fixed structure 61 of the engine 50 extends downstream of core exit plane 59 so that engine core 64 does not have an afterbody. The outer fixed structure 61 terminates at its aft (downstream) end in a downstream terminal plane 63. Planes 59, 63 are each substantially normal to the longitudinal axis X of the engine 50. Bypass duct 62 terminates at the longitudinal position of core exit plane 59. During operation of the engine 50, bypass air exiting bypass duct 62 and exhaust from engine core 64 are mixed between planes 59 and 63 prior to being expelled through the downstream terminal plane 63 of the outer fixed structure 61.
In the engine 50, the outer wall 60 of the bypass duct 62, the core cowling 65 and centre-body 67 of the engine 10 are each axisymmetric, i.e. they each have circular cross-sections at all positions along the axis X at which they exist. For example, the bypass duct outer wall 60 is circular at the downstream terminal plane 63 of the outer fixed structure 61 and at longitudinal positions fore (upstream) of the plane 23. The core cowling 65 is circular at core exit plane 59 and at longitudinal positions upstream of the core exit plane 59. In Figure 4, a pylon P interrupts the outer fixed structure 61 over a limited angular range in azimuth around the axis X, however the pylon P does not extend through the downstream terminal plane 63 of the outer fixed structure 61. The internal surface of the outer fixed structure 61 therefore describes a closed path in the downstream terminal plane 63 thereof.
Other turbofan engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of interconnecting shafts (e.g. two) and/or an alternative number of compressors and/or turbines. Further, an engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan.
Figure 5 shows a transverse section through a first example turbofan engine 100 in the downstream terminal plane 123 of the outer fixed structure of the engine 100. The downstream terminal plane 123 is substantially normal to the longitudinal axis X of the engine 100. The engine 100 is a separate-jets engine as defined above so that the plane 123 is also the exit plane of the bypass duct 122 of the engine 100, the bypass duct 122 being defined by the internal surface 120 of the outer fixed structure of the engine 100 and the outer surface 126 of the engine’s core cowling. The general direction of airflow through the engine 100 during its operation is indicated at 129. In the downstream terminal plane 123 of the outer fixed structure (equivalently the bypass duct exit plane), the radius R of the internal surface of the outer fixed structure measured with respect to the longitudinal axis X of the engine 100 is a function R = R((|)) of azimuthal position φ, such that R^) defines an ellipse with minimum and maximum radii R^ R2. In Figure 5 R(0°) = R(180°) = R> and R(90°) = R(270°) = R2 although the origin of φ is arbitrary. Upstream of the bypass duct exit plane 123 the internal surface 120 of the outer fixed structure becomes progressively more axisymmetric so that a certain position upstream of the bypass duct exit plane 123 the internal surface 120 of the outer fixed structure in a plane at that position normal to the axis X is substantially or approximately circular. The outer surface 126 of the core cowling is axisymmetric (substantially circular) in a plane transverse to the longitudinal axis X of the engine at any longitudinal position where the core cowling exists. The φ = 0° and φ = 180° positions may correspond to vertically upward and vertically downward directions respectively when the engine 100 is mounted on an aircraft. Alternatively, the major and minor axes of the ellipse may be inclined to the horizontal and vertical directions respectively when the engine 100 is mounted on an aircraft.
The values Rb R2 may be selected such that Rt < Ro < R2 where Ro is the radius of the internal surface of the outer fixed structure of an equivalent engine in its bypass duct exit plane, the outer fixed structure of the equivalent engine being axisymmetric (circular) in its bypass duct exit plane but the equivalent engine otherwise being identical to the engine 100. R> and R2 may be selected such that the areas enclosed by the outer fixed structures of the engine 100 and of the equivalent engine in their respective bypass duct exit planes are the same, i.e. Ro = V(RiR2). The engine 100 may thus be designed by reference to an equivalent engine having an outer fixed structure the internal surface of which is axisymmetric but which is otherwise identical to the engine 100.
Figure 6 shows a transverse section through a second example turbofan engine 200 in the terminal plane 223 of the outer fixed structure of the engine 200. The engine 200 is similar to the engine 100 of Figure 5; parts of the engine 200 are labelled with reference signs differing by 100 from those labelling equivalent parts in Figure 5. The outer fixed structure of the engine 200 has a discontinuity extending through bypass duct exit plane 223 and having an azimuthal extent a + β in that plane. The discontinuity is asymmetric about the φ = 0° position i.e. α # β and Ra # Rb (Ra, Rb > Rt). In variants of the engine 200 the discontinuity may be symmetric about the φ = 0° position, i.e. a = β with Ra = Rb.
Figure 7 shows a transverse section through a third example turbofan engine 300 in the downstream terminal plane 363 of the outer fixed structure of the engine 300.
The engine 300 is a mixed-jets engine. The internal surface 320 of the outer fixed structure has a radius R = R^) which defines an ellipse in the plane 363 with minimum and maximum radii Rb R2 coinciding with the φ = 0°, 180° and φ» = 90°, 270° positions respectively. The engine’s core exit plane 359 and core cowling outer surface 365 in that plane are indicated by a dotted circular line, however the core exit plane 359 is located upstream of the downstream terminal plane 363 as indicated in Figure 3.
The φ = 0° and φ = 180° positions may correspond to vertically upward and vertically downward directions respectively when the engine 300 is mounted on an aircraft.
Referring again to the first, second and third example engines 100, 200, 300 of Figures 5, 6 and 7, if the vertically upward direction corresponds exactly or approximately to the φ = 0° position when such an engine is mounted under the wing of an aircraft, then the engine may be mounted closer to the wing of an aircraft than is the case for a conventional engine having an outer fixed structure which is substantially axisymmetric or circular in its downstream terminal plane.
Consequently, such the engine may have a fan of increased diameter compared to that of a conventional engine, providing lower specific thrust and greater specific fuel consumption than is the case for a turbofan engine with a smaller fan. Additionally, in the case of a separate-jets engine in which a pylon interrupts the internal surface of the outer fixed structure the engine’s bypass duct exit plane, such as the engine 200 of Figure 6, the wetted area of the pylon in that plane is reduced compared to the case of a conventional engine, lowering drag on the bypass exhaust flow and improving engine performance.
Furthermore, in operation of such an engine, the speed of bypass air in the region of the ‘hump’ of the core cowling around the positions φ = 0° and φ = 180° is reduced compared to the case of an engine having an outer fixed structure which is axisymmetric in its downstream terminal plane, reducing nozzle loss and improving nozzle performance compared to an axisymmetric engine. Additionally, the total length of the outer fixed structure of such an engine may be shorter than that of an equivalent engine which is axisymmetric in its downstream terminal end plane, thus reducing weight and specific fuel consumption and allowing the engine to be mounted closer to a wing in the axial direction.
In other example engines, the outer fixed structure may terminate at a downstream axial position which depends on azimuthal position with respect to the longitudinal (rotation) axis of the engine. An example of an engine having such an outer fixed structure is the Rolls-Royce® Trent® 1000. In such an example, for the purposes of the present disclosure, the downstream terminal plane of the outer fixed structure is that plane, normal to the axis of the engine, furthest downstream at which the internal surface of the outer fixed structure is unbroken in azimuth apart from one or more discontinuities such as that shown in Figure 6 suitable for accommodating an element such as a pylon.
In the downstream terminal plane of the outer fixed structure of any of the engines 100, 200, 300, the radii of the internal and external surfaces of the outer fixed structure at a given azimuthal position may be equal or substantially equal. Alternatively the radius of the external surface may exceed that of the internal surface by a fixed amount which is independent of azimuthal position.
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.

Claims (8)

1. A turbofan engine (100; 200; 300) comprising an engine core positioned radially inwardly of an outer fixed structure with respect to the longitudinal axis (X) of the engine, the outer fixed structure terminating in a downstream terminal plane (133; 223; 323) which is substantially normal to the longitudinal axis of the engine, and wherein the radius R of the internal surface (120; 220; 320) of the outer fixed structure in the terminal plane is a function R = Ρ(φ) of azimuthal position φ in the terminal plane such that Ρ(φ) defines an elliptical path in the downstream terminal plane, the radius R being measured with respect to the longitudinal axis of the engine.
2. A turbofan engine according to claim 1 wherein the engine is a separate-jets engine (100; 200) and the engine core has a core cowling having an outer surface (126; 226) which is axisymmetric with respect to the longitudinal axis of the engine.
3. A turbofan engine (200) according to claim 2 wherein the internal surface (220) of the outer fixed structure has a discontinuity in the downstream terminal plane (223) thereof.
4. A turbofan engine according to claim 3 wherein the discontinuity extends over an azimuthal interval which includes an azimuthal position corresponding to a semi-minor axis of the elliptical path.
5. A turbofan engine according to claim 4 wherein the azimuthal interval of the discontinuity is symmetric about the azimuthal position corresponding to the semi-minor axis.
6. A turbofan engine according to claim 1 wherein the engine is a mixed-jets engine (300).
7. A turbofan engine according to any preceding claim wherein the radii of the internal and external surfaces of the outer fixed structure in the downstream terminal plane are substantially equal for all azimuthal positions where the internal and external surfaces exist.
8. A turbofan engine according to any of claims 1 to 6 wherein the radius of the
5 outer surface of the outer fixed structure in the downstream terminal plane exceeds the radius of the internal surface of the outer fixed structure in the downstream terminal plane, for all azimuthal positions where the internal and outer surfaces exist, by an amount which is independent of azimuthal position.
GB1806427.9A 2018-04-20 2018-04-20 Turbofan engine Withdrawn GB2575232A (en)

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Application Number Priority Date Filing Date Title
GB1806427.9A GB2575232A (en) 2018-04-20 2018-04-20 Turbofan engine

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GB1806427.9A GB2575232A (en) 2018-04-20 2018-04-20 Turbofan engine

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GB201806427D0 GB201806427D0 (en) 2018-06-06
GB2575232A true GB2575232A (en) 2020-01-08

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090226297A1 (en) * 2008-03-07 2009-09-10 Japan Aerospace Exploration Agency High bypass-ratio turbofan jet engine
US20100050651A1 (en) * 2008-08-27 2010-03-04 Mustafa Dindar Variable Slope Exhaust Nozzle
US20170166318A1 (en) * 2015-12-10 2017-06-15 General Electric Company Exhaust nozzle for gas turbine engine
EP3348820A1 (en) * 2017-01-17 2018-07-18 Rolls-Royce plc Fan exhaust for a gas turbine engine

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090226297A1 (en) * 2008-03-07 2009-09-10 Japan Aerospace Exploration Agency High bypass-ratio turbofan jet engine
US20100050651A1 (en) * 2008-08-27 2010-03-04 Mustafa Dindar Variable Slope Exhaust Nozzle
US20170166318A1 (en) * 2015-12-10 2017-06-15 General Electric Company Exhaust nozzle for gas turbine engine
EP3348820A1 (en) * 2017-01-17 2018-07-18 Rolls-Royce plc Fan exhaust for a gas turbine engine

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